Seat Shim Kits - Again- C3

[Edward J.]

Re: Seat Shim Kits - Again- C3

Lynn or dave, one more question, do the washers have a 5/16 hole for the bolt or 3/8 hole ,the holes appear bigger than the longer shim hole.

[Dave S.]

Re: Seat Shim Kits - Again- C3

Lynn or dave, one more question, do the washers have a 5/16 hole for the bolt or 3/8 hole ,the holes appear bigger than the longer shim hole.

Ed,
I should have realized that I left one size off my sketch.
The circular hole in the washer and the circular hole in the shim are both 3/8" diameter.

[Edward J.]

Re: Seat Shim Kits - Again- C3

Dave, thanks.

[Lynn H.]

Re: Seat Shim Kits - Again- C3

Ed (and Dave),
I do not know if the hole sizes are maybe different in different years (mine are from a 1971). There are NO 3/8" holes in any of my pieces. I just checked them with plug gages (pins) and in the rectangular shims the hole size in my parts area nice slip fit with a 5/16" (.3125) pin. The holes in my washers are a standard clearance hole for a 5/16" diameter bolt, which is 11/32" (.34375). Again this was a nice slip fit with a pin, or plug gage.
Lynn

[Dave S.]

Re: Seat Shim Kits - Again- C3

Ed (and Dave),
I do not know if the hole sizes are maybe different in different years (mine are from a 1971). There are NO 3/8" holes in any of my pieces. I just checked them with plug gages (pins) and in the rectangular shims the hole size in my parts area nice slip fit with a 5/16" (.3125) pin. The holes in my washers are a standard clearance hole for a 5/16" diameter bolt, which is 11/32" (.34375). Again this was a nice slip fit with a pin, or plug gage.
Lynn

Lynn,
I believe all 69-72 shim kits were the same. I have 3 original sets (one from a 70 and 2 from 71's) here and was able to double check 2 of them. In both cases the holes in the washers are 3/8" diameter plus meaning there is very slight play when a 3/8" bolt is inserted. The shims have a slightly smaller hole and a 3/8" bolt will not slide through the hole cleanly meaning it is slightly smaller than 3/8".

[Edward J.]

Re: Seat Shim Kits - Again- C3

Dave & Lynn just another delimma, as I was saying earlier in this post, there was likely more than one suppiler,It seems that a washer is really just a washer, sizes do vary from suppliers,although the 5/16 and 3/8 dia. hole either would work with the the seat bumpers,it seems that the archives posts there are some differences with the washers, but the longer shim seems to be pretty direct,not much difference.

[Dave S.]

Re: Seat Shim Kits - Again- C3

Dave & Lynn just another delimma, as I was saying earlier in this post, there was likely more than one suppiler,It seems that a washer is really just a washer, sizes do vary from suppliers,although the 5/16 and 3/8 dia. hole either would work with the the seat bumpers,it seems that the archives posts there are some differences with the washers, but the longer shim seems to be pretty direct,not much difference.

Ed/Lynn,
The washers were most likely a standard 3/8" washer specified to be 1/8" thick and were not made specifically for these shim kits. The shims are another story and were made especially for this application. As I recall the bolts that hold the shims in place are 5/16" so Chevrolet wanted a hole smaller than 3/8" in the shim.

[Lynn H.]

Re: Seat Shim Kits - Again- C3

Guys,
I just double checked my pieces again, just to make sure I did not make a mistake or use the wrong pin, and like I stated earlier, NONE of mine have holes anywhere near 3/8" (.375). They are right at the sizes I listed above. I am certain this is an original seat shim kit, and I also thought they were all the same. Tomorrow, I am going to check some of the seats I have and check the washers and spacers installed on them (if they have them). Aren't the stop bolts, and the screws for these shims and washers 5/16" thread? If so 3/8" would be a pretty loose fit, as standard bolt clearance holes are 1/32" over the bolt size (no matter the diameter). In no way am I insinuating I am right and someone else wrong, but this has my curiosity up now. I would be interested in hearing from anyone else with original parts.
Lynn

[Edward J.]

Re: Seat Shim Kits - Again- C3

Lynn, I would say that since they were just a plain old flat washer, that someone decided that either washer size would work .although I believe that 5/16 inside dia. would make the perfect fit .my thought was that when they went to eight washers the sizes and thickness changed, the 68/69 shims seem to be alittle smaller in dia. and thickness was 1/8 .but its only my thought.

[Lynn H.]

Re: Seat Shim Kits - Again- C3

A "standard" 5/16" washer, would have a "standard" 5/16" clearance hole, which would be 11/32". A "standard" 3/8" washer would have a "standard" 13/32" clearance hole. The 1/32" clearance for standard fasteners is the "standard" regardless of the diameter. Also, I do not believe a "standard" washer for either of these sizes would be 1/8" (nominal) thickness, although thicker washers are available they would NOT be considered "standard". I will pull out the Machinery's Handbook, and check what "standard" would be for the thickness of the washers, but I would think these items were manufactured for this application and NOT just "standard" washers. I was in the automotive fastener business (screw machine and cold heading) for 30 years, and am very comfortable with my assessments.
Back to the rectangular shims, the holes in the ones I have (pictured earlier) are NOT "standard" clearance holes, they are EXACTLY 5/16" (.3125). They would have had to been manufactured like this as they could be made bigger, but you can't put material back in.
I am actually VERY curious about this now and will be investigating further for verification. Would be interested in hearing from others with original seat shims.
Lynn

[Edward J.]

Re: Seat Shim Kits - Again- C3

Lynn, im not a machinist but would the 11/32 be possaiblly big enough for a 3/8 bolt given that there are + or- with the washers dia.maybe this is where the difference is that Daves washers will fit the 3/8 bolt through the washer.

[Lynn H.]

Re: Seat Shim Kits - Again- C3

Ed,
In NO WAY do I want to be interpreted as being argumentative about this, I am honestly curious and interesed knowing what they should be. And, I am a machinest (almost 35 years). The key here I believe is the size of the stops and screws in the seats themselves, which I believe (I would have to go out in the cold garage and check) are 5/16" thread. A 3/8"bolt (.375), will not go into a standard 5/16" clearance hole (.34375). The large (rectangular) shims I have do NOT have standard clearance holes, which tells me they were designed to have a closer fit on the screws than standard clearance (less slop). I will certainly be doing some in house reasearch on this, as I know I have a bin full of seat shims and washers that were removed off of disassembled seats. All the ones pictured, came in the bag in the rear compartment of an orignal one owner car. I will let you know what I come up with on this tomorrow.
Lynn

[Lynn H.]

Re: Seat Shim Kits - Again- C3

Lynn, im not a machinist but would the 11/32 be possaiblly big enough for a 3/8 bolt given that there are + or- with the washers dia.maybe this is where the difference is that Daves washers will fit the 3/8 bolt through the washer.

Ed,
A 3/8" bolt will not go into a 11/32" hole no matter how hard you try, the hole would have to be at least 3/8" (nominal). The washers I would bet were manufactured by a process known as "cold heading". This is the fastest and most productive method of producing "washers", and most all the bolts you will ever run across for just about any application that uses "standard" thread dimensions. Threads are added to nuts and bolts in what they call "secondary" operations, such as thread rolling and tapping. The standard for threads is considered to be what they call 75% engagement. For this reason if you check most bolts with a micrometer they will check lightly smaller than the nominal size. For example a 3/8" bolt (.375 dia) will check around .370. Threads on bolts such as most that we encounter are "rolled', not "cut", like internal threads would be with a tap. As a matter of fact most high volume production internal thread are made with what they call a "roll" tap. These make VERY consistent parts compared to thread cutting, or chasing (as it is called when you machine threads on the lathe) or cut with a tap or die. The holes in the washers would have been "pierced" in the cold heading operation and been very consistent. A nominal 11/32" hole may have a tolerance of +/- .005, which at the high side would be .348. A Standard 3/8" bolt at approximately .370 would still NOT fit in this hole.
Like I stated, I am very curious about this in regard to these shims. As mentioned earlier, there was certainly more than one supplier for these parts, but they should have all been working to the same print, which would make the parts only inconsistent to the extent of the tolerance provided. I doubt very seriously that the tolerance on the holes in these parts would have been 1/32". Which it would have to be for the 3/8 bolt to fit in a hole that was 11/32 (nominal size with a tolerance of plus 1/32"). That would be a HUGE tolerance when it comes to the manufacturing of fasteners in general.
I would bet the larger rectangular shims were "stamped" by a large press, that pierced the holes at the same time the outer dimensions were "cut out". Most likely making more than one with a single hit, and again pretty consistent. I am definitely going to be doing some more investigating on this subject.
Lynn

[Lynn H.]

Re: Seat Shim Kits - Again- C3

Ed,
I should have realized that I left one size off my sketch.
The circular hole in the washer and the circular hole in the shim are both 3/8" diameter.

I hate to be re hashing old news, but I did get a chance here to go out and check through a fairly large sampling of shims and washers, that I have removed from seats over the years. As we know, not all seats had the washers and shims installed. Most of the ones I just examined were in small parts bags that were marked with the year they were removed from, if I knew at the time I disassembled them. I did not go through ALL of the parts I had, but within 5 minutes I was able to come up with three of the large rectangular shims and seven washers that I am convinced are correct. I also found quite a few washers in the bunch that were obviously different and not correct (thinner,plated,etc.).
All of the pieces I have were exactly as the pieces I listed earlier in the thread as far as the holes are concerned. The holes in the large shims are EXACTLY .312 (5/16"), and the holes in the washers .343 (11/32"). While this certainly does not in any way "prove" that only washers and shims with this size of hole are original, I would seriously have to question the use of either of these items with a .375 (3/8") hole in them, in something other than some sort of extenuating circumstances. This being based on the fact that the fasteners are 5/16" diameter. I think if anyone were to take a 5/16" bolt, and a washer with a hole that actual size is 3/8" (.375), and put them together, the fit would be loose to the extent that you would have to question the use of it in this application with that type of fit. Not personally being a GM engineer, but knowing more than a few (retired and current), I would say that everyone of them would agree if I asked them.
I would be curious as to the actual size of the washers and shims in the kits that are KNOWN to be reproductions, as well as hearing from anyone who has KNOWN original parts with 3/8" holes in them (like David's). Most people would have to be able to check this with something other than a scale or tape measure. I used ground gage pins and realize not everyone has access to items like this. a vernier caliper would most likely work well enough. You may want to contact me by PM if you are inclined to, so as to NOT get the thread out of control. This is not, in anyway, any type of intent to make anyone else appear to be "wrong" about this. My interest in this is for the following reasons, as these items qualify in my opinion as something I can include.
While some may think BS (and it may be), I have spent quite a bit of time researching fasteners and small components on these cars, and have collected hundreds of pages of original examples of fasteners and other components. I hope to one day put it all together with the hopes of it being of interest to the hobby. This is something that I have actually been putting a fair amount of time on in the last couple of months. I even have one of those out of work GM engineers drawing me pictures with UG. They look really nice. I hoping to do it in a way that references part numbers from the AIM's, and cross references to typical known examples (size, length, special features), and incorporating head markings. If and as this gets farther along, I will be attempting to solicit help and information from the membership in some way if I can, and folks are willing.
Thank you,
Lynn Houk

[David S.]

Re: Seat Shim Kits - Again- C3

Dave, great pictures with descriptions....I'm still on the look out for an original set & these pics will come in handy.

I have dismanteled alot of these cars . I have a box full of shims and some bags.