May I ask for advice on Beam's 140" WSCH300 seat belts?

[robroy]

Good morning!

In Fall 2008 I bought a pair of 140" Beam's (WSCH300) retractable seat belts from SeatBeltPros.com for #50. As seems to be the rule with car projects, months became years--nearly two years later I'm just now ready to install them!

Although I may remove them again before #50 is fully on-the-road, I wanted to install the belts now to reduce the chances of getting a ticket (or at least a bad ticket) during one of my upcoming test drives.

Note that I already asked two questions regarding these belts, yet I wanted to start a new thread to document the complete installation in a fashion that's easy to find for other members in the future. Here are my previous, related threads:

Must the shoulder belt mount holes be tapped?
How long should a center position seat belt be?

I have some questions that I'll list at the end of this post! All of these images may be clicked upon to yield much higher definition and resolution versions.

Here's my receipt:



And here's the current state of my cab. Although my present wood-based seating is both luxurious and high-fashion, I'll swap the blocks out for something even better soon!



Here's the kit:



Two of these hardware sacks were included with my order. I may not wind up using most of what's in these kits; I ordered them just be sure I'd be fully equipped for installation.



Here's the contents of one of the hardware sacks.



I was a little surprised that the fine-thread bolts included in the kits are grade five; I might use grade eight bolts instead.



The hardware kit included this simple warning sheet. I think I get it!



Here's the short portion of the belt. I think these are installed in the middle of the bench seat.



One of the belt portions contained this tag--I ripped it off.



This additional tag was hiding under the previous one. You may wish to click on these images to make them legible.



And here's the retractable shoulder portion, from every angle. The retracting action feels fantastic!





A plastic cover lifts up to reveal the visible portion of the retracting mechanism.



Inside the cab, I found the inner seat belt bolt-down hardware where I placed it nearly two years ago. I believe part or all of this hardware came with the after market belts previously installed in #50--yet perhaps the bolt and heavy washer are OEM?



Here's a close look at that funny bracket; is this an OEM part? It doesn't look like one to me.



And here's the bolt and washer; these look more OEM, yet I can't be sure.



Here's another look at the inner seat belt portion laying on the cab floor with assorted brackets. Note that the terminal piece on the end of this belt portion is perfectly flat.



And here's where I'd like to bolt it down (the OEM location).



Here's the L-shaped bracket that was included in the hardware kit--should this be used here, as shown in this photo?



Questions, Round 1:

• How should this inner seat belt segment be fastened to the cab floor? Should it be fastened flat against the floor (using no brackets), fastened using the old, probably non-OEM bracket, or fastened using the L-shaped bracket that came in its hardware kit?
• Do y'all think the slightly bent, silver bracket is left over from my previously installed universal belt kit?
• Do y'all think the heavy bolt and washer is left over from the universal kit, or are those Ford parts?
• Is it true that I should poke the skinny end of the middle belt segment through the crack in the bench seat from the front, then set the seat in the cab, then bolt the inner segments down?

Thanks very much for the superb guidance!
Robroy

[robroy]

Good afternoon!

I decided that the brackets could probably be figured out with the seat sitting in the cab, so I cleared a path to it and tried to dust it off. I neglected to cover it very well and have had it in storage since 2008, so it was pretty nasty!

Here's the under-side (left) and back (right). I took these photos while de-spidering.



Here's the driver's side track area. In the photo on the right, you can see a bit of upholstery wire that came loose during storage. For the time being, I just pulled it snug and wrapped it around one of the upper rails.



Here I am poking one of the inner belt segments through the seat.



And here they're both poked through.



That's when I made a telling discovery, which may provide an answer to my initial question about which bracket(s) to use! The terminal pieces on the two inner belt segments aren't identical! "A" is straight while "B" has a bend in it. I'm guessing that I was supposed to receive the belts with two "B" style terminals on them!




Kasie helped me to set the seat in the cab. I forgot how space in the cab the seat occupies!



And here's a shot of the passenger side rail (left), and I'm sitting in the driver's seat on the right. This was the first time I'd ever sat in this seat, and I must say, it feels superb! It has a firm yet cushioned feel, similar to what's found in some newer cars. It's perfect!



I just started a couple of bolts to hold it in place for the moment--I was eager to try it out!



Based on my discovery regarding different inner belt terminals, I might write and/or call SealBeltPros.com to see what they have to say. Since I bought the belts in 2008 they'll probably not be fond of the idea of a return of one of the parts, yet I'll try to get their advice regardless.

That said, I'm guessing that I can use the L-shaped bracket on the "A" style belt terminal without problems! What do y'all think?

Thanks for the most excellent guidance!
Robroy

[robroy]

Good afternoon!

As it turns out, a physical attempt to fasten these belts down is answering most of my questions! First, it doesn't appear to be a problem that the inner belts have dissimilar terminals.

Based on the angle of the belt as it fastens down, it seems that the L-shaped brackets are the things to use!

Here's a photo of one installed. After tightening it down lightly, I slid the seat back to check for clearance--there's plenty on both sides.



I consulted the 1972 Ford Truck Shop Manual, page 41-50-2, and found this diagram. It seems that I want the torque value for "B."



And here's the chart on page 41-50-6; it looks like 25 ft/lbs is the right torque.



I cleaned the threads on these peculiar bolts and coated them with anti-seize before the final installation; I torqued them to 25 ft/lbs.



With that complete, the next step was to determine how to attach the inner belt terminals to the L-shaped brackets.



The hardware kit I ordered with these belts came with grade five bolts and unknown grade nuts (left). I dug around in my ever-growing bolt/washer/nut stash and came up with a superior replacement (right).

The replacement bolt's USA-made, grade eight, and has the armor-coat finish. The replacement nut's a grade eight center-lock distorted thread lock-nut; I think it's also USA-made but I forget (some of the center-locks I ordered weren't). This hardware's from McMaster-Carr.



As you can see, the grade five bolt supplied with the belts (left) has fine threads, while the grade eight bolt I'm using (right) has coarse threads. I'm guessing that this is not a problem--what do y'all think?



Since these fasteners live inside the cab, and since the bolt threads are mostly exposed to the air, I used no grease of any kind here. The nuts are waxed and the bolts are coated, so they went together smoothly.



Here are the belts fastened to the L-brackets (but not yet torqued)!



Questions of the Hour:

• What torque setting do y'all think is appropriate for the bolts that hold the belt terminals to the L-brackets? 25 ft/lbs, like the others?
• Should the belt terminals be fastened down while they're sticking straight up, or would a slight angle towards the seat they service make them stronger?

Thanks very much for the most excellent guidance!
Robroy

[Happy_Camper]

Hey Robroy,
Nice pictures and thread on these belts! Looks great with the seat.

My thoughts are 25lbs/ft will be sufficient. Although you may want to get lock nuts (or use lock-tite), so that you wont have to worry about them coming loose over time.
I agree with you that the straighter the pull on the belt, the better it is on the webbing. So you may want to set a slight angle.
Great job amigo!
BTW: You NEED a crew cab!

[robroy]

Good evening Scott, thanks for your fantastic reply!

Nice pictures and thread on these belts! Looks great with the seat.

Thanks very much! I had a sample of the yellow seat belt material that I took with me to the upholstery shop, so that's how they got the decent color match.

My thoughts are 25lbs/ft will be sufficient. Although you may want to get lock nuts (or use lock-tite), so that you wont have to worry about them coming loose over time.

Okay, thanks! Those nuts are distorted thread "Center-Lock" lock-nuts, so I think I'm OK there. They're fairly difficult to thread both on and off!

I agree with you that the straighter the pull on the belt, the better it is on the webbing. So you may want to set a slight angle.

Great! My current idea's to loosen the anchors slightly, then set the seat back in place and sit in there and yank on that part of the belt. I'll try to yank on it in the most natural way, in the same direction as it would be yanked during a panic stop!

Then when I pull the seat back out, hopefully it will stay put and I can lock it down at that attitude.

While visualizing the webbing being stressed during a panic stop, I keep imagining what it's like to tear a paper from a yellow legal pad. If you try to pull it straight out, at a perfect right angle to the perforations, it won't budge! Yet pulling at an angle concentrates the force on a much smaller area of the perforated line, and the paper's readily yielded.

Great job amigo!

Thanks Scott!

BTW: You NEED a crew cab!

While I don't doubt this and have honestly dreamed of having a crew cab, what's your reason for mentioning this? Is your intuition high-powered? How did you know?

I'm obviously extremely fond of and committed to #50, so please don't tell him. But if I WERE to find myself Bumpside-less and start over, I would be looking for an ultra heavy duty 1967 crew cab!

Scott, thank you again for your superb reply!
Robroy

[Happy_Camper]

I like your idea on settng the anchor angles. Your explanation on the paper is excellent. If it doesn't work out by "pulling" on the webbing, you can mark where the belts ride while wearing them, and then visually extend the angle back to the anchor.

I was just thinking, when you pick up a nice camp trailer to pull behind #50, it may get a bit crowded with dogs, cats, fish, etc...
I mean, 534lbs/ft of torque at 2,500 rpm just begs for family camping trips.

[robroy]

Good afternoon Scott, thanks for your excellent reply!

I like your idea on settng the anchor angles. Your explanation on the paper is excellent.

Thanks Scott! The idea for setting the anchor angles worked out well (photos below)!

If it doesn't work out by "pulling" on the webbing, you can mark where the belts ride while wearing them, and then visually extend the angle back to the anchor.

That's a great idea Scott!

I was just thinking, when you pick up a nice camp trailer to pull behind #50, it may get a bit crowded with dogs, cats, fish, etc...

You could be right here! The idea of #50 taking us on a camping trip is indeed a happy one.

I mean, 534lbs/ft of torque at 2,500 rpm just begs for family camping trips.

I'd been thinking that the exuberant lack of fuel economy would prohibit extensive camping with #50, yet I suppose there are plenty of nice areas nearby Salinas to camp; I don't have to drive a thousand miles to find a good spot!

This afternoon I got the fasteners that hold the belt terminals to the L-shaped brackets just barely snug, so it was still possible to rotate the terminals (with some effort), then moved the seat back in place and put a couple of bolts in to hold it there.

Then I climbed in on each side, pretended to buckle up, and gave the belt some sudden, hard pulls. I could hear the terminals rotating against the L-shaped brackets!

With the seat moved forward again, the natural terminal angles were revealed (left). The finished product's on the right--this is out of order but the photo fit nicely there.



This photo does a better job of illustrating the natural terminal angles. They turned out just like we might have imagined they would! I locked the terminals down to the L-shaped brackets at 30 ft/lbs, which was a guess based upon the 25 ft/lbs spec for the OEM bolts.



This photos just for fun, showing off the finish on the lever and the nice upholstery work!



I got to looking at the 3/8-16 x 1" (3/4" threaded) seat hold-down bolts. Several of them had imperfect threads! I also remember reading Td's story about wrecking his first Bumpside, and how the bolts that held the seat in sheared off! Since reading that I've figured that it wouldn't be a bad idea to install grade eight replacements.

The flange built in to the head of these bolts is about 3/4" wide.




I'm thinking of replacing these OEM bolts with McMaster-Carr 92316A624; it seems like a good upgrade! Here's the McMaster diagram:



With the inner belt anchors finalized, I turned my attention to the area which may be of greatest interest: tapping the shoulder anchor holes!

Here's the right-hand (passenger's side) hole. Its inner diameter appears to be about 5/16". Below this initial photo, there are two more of that side--I used the camera's aggressive flash to illustrate the depth of those holes.




And here are the same types of photos for the left-hand side (driver's side):




According to the 1972 Ford Truck Shop Manual pages 41-50-2 and 41-50-6, the bolt I want in these spots is a "7/16-20, 2 and 1/4" long, pan head tapping, 0.88 shoulder." Luckily a nearly identical specification's given for the center belt anchor bolts, which I have samples of!

Today's Questions:

1. Should I buy a 7/16-20 hand tap for these shoulder anchor bolt holes? Or, given that the tap would be removing as much as 1/8" of metal from the hole, should I begin with an intermediate tap size?
2. I've never before used a hand tap to put threads where none previously existed. Is it difficult to get a hand tap to cut threads in a perfectly straight fashion? Do they tend to "fight," trying to cut the threads at an improper angle, or do they tend to be easily guided by the direction of the existing hole?

Scott, thanks again for your superb reply!
Robroy

[70_F100]

Robroy, if you definitely have a 5/16 hole, the proper tap size would be 3/8-16. You DEFINITELY don't want to try to enlarge the hole by using successive taps, as you would with drill bits.

So, my suggestion is to first verify exactly what the diameter of the hole is. It may be slightly smaller or larger. You'll need to use a dial caliper or other similar device, or you could, alternatively, use the solid end of a drill bit as a gauge.

To go to 7/16-20, the hole will have to be enlarged to 0.3860", which is a "W" drill bit. You could also use a 25/64" bit, which would reduce the % of thread from 79% to 72%. To go to 3/8-24, the diameter of the hole should be 21/64" to provide 87% thread.

Here's a good tap drill size chart for your reference: http://www.widell.com/drillsiz.html

The issue of going larger is whether or not the steel backing plate is substantial enough to provide the same support with the larger bolt. There appears to be a "sleeve", if you will, around the hole. This sleeve provides additional strength for the installed bolt by providing additional thread length. If you drill to the larger diameter to enable you to use a 7/16 bolt, will there be enough of this shoulder left to provide the holding power you need? Or, would the steel plate itself be thick enough to provide the necessary strength? In other words, will a 3/8-16 or 3/8-24 bolt provide the same holding power as the 7/16-20, given the strength of the anchor? Another way to look at it would be will a 3/8 bolt with, say, 10 threads engaged give the same holding power as a 7/16 bolt with 8 or so threads engaged? That's something that would require some calculations to determine. It may be that you'll be fine with a 3/8 bolt, and that would be much simpler to install.

As for tapping the hole with a hand-held tap, you'll need to make sure you have the proper hole diameter, a good quality "starter" tap, and I suggest a good quality tap handle. Just make sure you hold the tap perpendicular to the hole, start the tap slowly, and after each 1/4 turn or so, unscrew the tap a little more than you just turned it in to remove the residual metal in the threads. Continue to do this until you have the full length of the hole threaded. Unscrew the tap, and you'll be ready to insert the bolt.

[robroy]

Good afternoon 70_F100, thanks for your superb reply!

Robroy, if you definitely have a 5/16 hole, the proper tap size would be 3/8-16. You DEFINITELY don't want to try to enlarge the hole by using successive taps, as you would with drill bits.

Understood!

So, my suggestion is to first verify exactly what the diameter of the hole is. It may be slightly smaller or larger. You'll need to use a dial caliper or other similar device, or you could, alternatively, use the solid end of a drill bit as a gauge.

Thanks so much for this great suggestion! I poked a 5/16" solid drill bit end in both the LH and RH holes, and the bit was slightly loose in there. Also, a 3/8" solid drill bit end (the next size up that I had on hand) wouldn't go in at all; it seemed too wide.

To go to 7/16-20, the hole will have to be enlarged to 0.3860", which is a "W" drill bit. You could also use a 25/64" bit, which would reduce the % of thread from 79% to 72%. To go to 3/8-24, the diameter of the hole should be 21/64" to provide 87% thread.

I see!

Here's a good tap drill size chart for your reference: http://www.widell.com/drillsiz.html

Thanks so much for that! That chart unlocks a whole new understanding of hole sizes and thread-making that I've been sincerely (yet nebulously) wondering about for some time.

The issue of going larger is whether or not the steel backing plate is substantial enough to provide the same support with the larger bolt. There appears to be a "sleeve", if you will, around the hole. This sleeve provides additional strength for the installed bolt by providing additional thread length. If you drill to the larger diameter to enable you to use a 7/16 bolt, will there be enough of this shoulder left to provide the holding power you need? Or, would the steel plate itself be thick enough to provide the necessary strength?

I see exactly what you mean--these are great points!

In other words, will a 3/8-16 or 3/8-24 bolt provide the same holding power as the 7/16-20, given the strength of the anchor? Another way to look at it would be will a 3/8 bolt with, say, 10 threads engaged give the same holding power as a 7/16 bolt with 8 or so threads engaged? That's something that would require some calculations to determine. It may be that you'll be fine with a 3/8 bolt, and that would be much simpler to install.

Thought-provoking points again--thank you!!!

I had a mind-expanding thinking session on this (a joke about how mystified I am by the concept of threads), with these results. Please forgive me if one or more of these points merely describe the same conclusions you've already shared with me--my brain had to synthesize the new concepts and reach conclusions in its own oddball fashion.

• The size of the holes is between 5/16 and 6/16 (3/8). Their size could be closest to any of 21/64 [0.3281"], 22/64 (11/32) [0.3438"], or 23/64 [0.3594"]. I'd need a better measuring system/tool to know for sure.
• Considering that range of possible hole sizes, the only two taps that would stand a chance at making threads with a favorable mesh % are 7/16-14 and 3/8-24. At the low end of the range of possible hole sizes, using a 3/8-16" tap would yield a ~59% thread mesh, which seems like a loose mesh compared to the other options.
• I happen to already own a 7/16-14 tap! I gently tried to get it started in both holes, and it did not want to go in there. It's a tap wherein the first ~5 threads are tapered, and yet it still would not start in the holes. It nearly would, but it's really too wide.

Based on these three points, I've arrived at this: if I wish to avoid drilling the holes to a larger size, a 3/8-24 tap seems to be the best/only option!

Does my thinking make sense?

As for tapping the hole with a hand-held tap, you'll need to make sure you have the proper hole diameter, a good quality "starter" tap, and I suggest a good quality tap handle. Just make sure you hold the tap perpendicular to the hole, start the tap slowly, and after each 1/4 turn or so, unscrew the tap a little more than you just turned it in to remove the residual metal in the threads. Continue to do this until you have the full length of the hole threaded. Unscrew the tap, and you'll be ready to insert the bolt.

Thanks very much for this fantastic guidance 70_F100!

This Afternoon's Questions:

1. Based upon my finding that the hole sizes are between (non-inclusive) 5/16" and 3/8", does using a 3/8-24 tap seem like a sensible move (considering my probably-naive rationale above)?
2. Is it true that after taping with a 3/8-24 tap, I'll be able to FEEL the % of thread mesh by screwing a suitable bolt in and wiggling it around? Or is this something that cannot be felt, and must be measured first (before tapping)?
3. If I installed 3/8-24 threads and a suitable bolt did not feel secure enough, once screwed in, to be confidence-inspiring, would it be feasible to run a suitable drill bit through the holes, then try again with a 7/16-20 tap?
4. Is it true that in theory, a 100% thread mesh is strongest? Or is it impossible to screw a fastener together that has threads 100% meshed?
5. Speaking generally, if that's possible in this context, what's a good thread mesh % to aim for?

70_F100, thank you again for your patient, generous and highly instructional reply!
Robroy

[robroy]

Good evening!

I've gathered supplies to make some progress! Meanwhile, the weather has been absolutely perfect both yesterday and today.



I picked out this General model 166 plain tap wrench; it's USA-made and was $16.04. It feels like a truly decent tool!





I also grabbed a DeWalt 21/64" drill bit, to use as a simple gauge in the yet untapped shoulder belt anchor holes. It's from Germany and was around $8.



And here's the USA-made, 3/8-24, Vermont-American 20073 tap. It was $6. I hope it's hard enough to be effective for this!




Since the Beam's kit seemed to come with grade five hardware, and bolts aren't particularly expensive, I grabbed a variety of USA-made, grade eight 7/16-20 and 3/8-24 bolts. I wasn't sure exactly which lengths I'd need and didn't feel like burning $10 in gas to cruise back to the hardware store for the right ones! Of course that's mostly a rationalization, since I know I'll be back there soon enough anyways--I just like bolts.




I tried the end of the 21/64" drill bit in the holes and it's nearly a fit; it's just slightly loose in there. It seems to me that if Ford intended for those bungs to be threaded without needing to be drilled first, they must have intended for folks to use 3/8-24 threads. That's rather curious considering that the Ford Truck Shop Manual seems to say that 7/16-20 bolts are found there!

I also held the 3/8-24 tap against the anchor bung and it seems like a natural fit. The tap has a total of four or five tapered threads, and it goes in up to about the third one (as you can see form the photo, the first two threads are nearly non-existent).

Unless I receive additional advice indicating that I should avoid using the 3/8-24 tap in favor of a better strategy, I'll go ahead with this next time I'm out in the garage!

Thanks for all the outstanding replies and fantastic guidance!
Robroy

[70_F100]

Robroy, I tried to find some information on bolt strength, and what I found was pretty much the same everywhere I looked.

The tensile strength of bolts such as the ones you're using is detailed in the chart located at http://shopswarf.orconhosting.net.nz/boltid.htm

Now, since you can see from the chart that the bolt strength is approximately the same for 3/8 vs. 7/16 bolts, the limiting factor will be the anchor point.

IMHO, it's pretty much like I stated previously. You have to look at the steel backing plate to determine which would work best.

The ability of a threaded fastener to provide full holding strength is determined by several factors, but in this case, the single most determining factor will be the thickness of the backing plate. For discussion purposes, I'll call that plate the "nut".

The generally-accepted rule of thumb is that for bolts and nuts of the same strength, the thickness of the nut is approximately the same as the diameter of the bolt. In other words, a 3/8 nut should be 3/8" thick, and a grade 8, 3/8 bolt should be used with a grade 8 nut to provide maximum holding strength.

In the case of these "nuts", Ford probably used mild steel for the plate. The "shoulder" you see is probably a slightly harder material. That being said, since the hole is approximately the correct diameter for a 3/8-24 bolt, the thickness of that insert is probably close to 3/8". The thickness of the backing plate itself is obviously less than that of the insert.

Since drilling out the insert to accept a 7/16 bolt will remove a substantial amount of the insert, and tapping the hole to 7/16 will remove even more, the ultimate holding power will be reduced significantly. With that in mind, I think I would go with the 3/8-24 bolts.

The best solution, in my opinion, would be to find a 3/8 bolt similar to the original seat belt bolts (a bolt with a larger-diameter shoulder and head). That would center the bolt in the bracket and, in the event of an accident, would distribute the load evenly across the head of the bolt. Otherwise, if the hole in the bracket is not centered, the shear force applied to the bolt would not be equal, and could, potentially, cause the bolt to fail. The use of a flanged metal bushing would probably produce the same results as a bolt with a shoulder.

You may find that due to the curvature of the cab, the bracket may hit the cab wall before the bolt is completely tightened. To compensate for this, a spacer could be placed between the mount and the bracket to allow the bolt to be fully tightened (which provides maximum strength). This would also allow the bracket to swivel somewhat to compensate for differences in height of the persons using the belts.

All of this is just my , and there may be others that have different opinions, so I'll shut up and open the floor for dissention!!

[robroy]

Good afternoon 70_F100, thanks so much for your superb, detailed reply!

Robroy, I tried to find some information on bolt strength, and what I found was pretty much the same everywhere I looked.

The tensile strength of bolts such as the ones you're using is detailed in the chart located at http://shopswarf.orconhosting.net.nz/boltid.htm

That's an excellent chart! I'm definitely going to save this one--along with the other one you already posted--for future reference.

Now, since you can see from the chart that the bolt strength is approximately the same for 3/8 vs. 7/16 bolts, the limiting factor will be the anchor point.

I see your logic here!

IMHO, it's pretty much like I stated previously. You have to look at the steel backing plate to determine which would work best.

The ability of a threaded fastener to provide full holding strength is determined by several factors, but in this case, the single most determining factor will be the thickness of the backing plate. For discussion purposes, I'll call that plate the "nut".

The generally-accepted rule of thumb is that for bolts and nuts of the same strength, the thickness of the nut is approximately the same as the diameter of the bolt. In other words, a 3/8 nut should be 3/8" thick, and a grade 8, 3/8 bolt should be used with a grade 8 nut to provide maximum holding strength.

In the case of these "nuts", Ford probably used mild steel for the plate. The "shoulder" you see is probably a slightly harder material. That being said, since the hole is approximately the correct diameter for a 3/8-24 bolt, the thickness of that insert is probably close to 3/8". The thickness of the backing plate itself is obviously less than that of the insert.

Since drilling out the insert to accept a 7/16 bolt will remove a substantial amount of the insert, and tapping the hole to 7/16 will remove even more, the ultimate holding power will be reduced significantly. With that in mind, I think I would go with the 3/8-24 bolts.

I understand what you're saying and think this makes perfect sense!

I poked a machinist's pick in there and measured the insert's deepness; it seems to be around 5/16" or 3/8" deep, as predicted!

The best solution, in my opinion, would be to find a 3/8 bolt similar to the original seat belt bolts (a bolt with a larger-diameter shoulder and head). That would center the bolt in the bracket and, in the event of an accident, would distribute the load evenly across the head of the bolt. Otherwise, if the hole in the bracket is not centered, the shear force applied to the bolt would not be equal, and could, potentially, cause the bolt to fail. The use of a flanged metal bushing would probably produce the same results as a bolt with a shoulder.

I think you're right about this! I'll try to come up with something, and suppose I'll get a better idea of what the best parts will be by trying to put it together.

You may find that due to the curvature of the cab, the bracket may hit the cab wall before the bolt is completely tightened. To compensate for this, a spacer could be placed between the mount and the bracket to allow the bolt to be fully tightened (which provides maximum strength). This would also allow the bracket to swivel somewhat to compensate for differences in height of the persons using the belts.

Excellent thinking!!! I can visualize what you're saying here and think it's a great idea.

All of this is just my , and there may be others that have different opinions, so I'll shut up and open the floor for dissention!!

Well thanks so much for your super generous help with this 70_F100!

Update: the threads are complete on the RH side!

Here's the tap stuck in the insert. I dipped the end of the tap in motor oil first, and it started in the insert very easily; it also tended to stay straight, once started--it didn't fight. And gosh, 70_F100, I can see from this experience how right you were about it being nice to have a tap T-handle. It really made short work of this!



Here's how the tap came out after its first run through the insert.




After the initial time, I blew compressed air in the insert and ran the tap through a second time, just to get the threads as clean as possible (left). And my best photo of the tapped insert is on the right; you'll probably want to click on it to see the detail.



This photo doesn't show the threads very well, but it's the best photo of the insert I've managed to get to date--trying to use the tripod in the cab is pretty awkward!



Then came The Moment of Truth: I tried a 3/4-24 bolt in there! It went in just fine and felt smooth, yet even when the bolt was threaded in quite a ways, it had a noticeable wobble to it; it's not a tight fit.

The bolt's certainly not going to pull out by hand or anything--it's not that loose, yet I'm not sure if it's a problem or not. I'm in need of an experienced eye!

The following video clip illustrates the amount of play in the threads. As y'all know, the H.264 video will play only on up-to-date computers while the WMV video will play anywhere.

H.264 (8MB) WMV (4.5MB)


Am I ready to move on to the next stage, or are these threads too loose?

70_F100, it's very kind of you to have invested the time to think about my scenario and offer your fantastic guidance--thank you!

Robroy

[70_F100]

Robroy, I'll try to measure the holes in my truck today. Hopefully they will be the same size in a 70 as in a 72. Then, maybe I can better evaluate what you've got going on.

My first project at hand today is to get my lawnmower back up and running so I can mow my "hay field". The transmission came out of it a couple of weeks ago, and the parts just arrived Friday to fix it.

If I don't get the grass at least knocked down a little bit, they're going to kick me out of the neighborhood!!!

[robroy]

Good afternoon 70_F100, thanks for your superb reply!

Robroy, I'll try to measure the holes in my truck today. Hopefully they will be the same size in a 70 as in a 72. Then, maybe I can better evaluate what you've got going on.

That sounds marvelous--thanks so much for this!

My first project at hand today is to get my lawnmower back up and running so I can mow my "hay field". The transmission came out of it a couple of weeks ago, and the parts just arrived Friday to fix it.

If I don't get the grass at least knocked down a little bit, they're going to kick me out of the neighborhood!!!

That sounds like a good project! I can relate to the weeds. At the moment I'm living in a place with a landscaper who comes, but I grew up on ten rural acres that turned in to a wild jungle every Spring!

I've also exchanged a couple of e-mails with VernF110; Vern just finished installing the shoulder belts in his truck, and his truck came with the inserts pre-tapped! I asked him if he happened to remember what thread size was used. I'll probably hear back about that soon--it could be another interesting data point.

Since the 1972 Ford Truck Shop Manual seems to indicate that 7/16-20 bolts are used on the shoulder anchors, perhaps they intended for those inserts to be enlarged slightly prior to tapping?

70_F100, thanks for all of your extremely generous guidance!
Robroy

[speed bump]

The torx head bolt and large washer I believe are OEM. Ford used them forever for seat belts and you can still buy them from Ford.

Personally I tapped the shoulder belt holes for 3/8 or 7/16 coarse thread (I can't remember which right now but i'm almost certain the head is a 5/8" which is either a small headed 7/16 or a normal 3/8") and it seem to be fine.