MarcDeSoto Posted January 12, 2015 Report Posted January 12, 2015 I'm trying to put the seat back on the seat frame in my 48 DeSoto business coupe. I looked over my hardware and got what I thought to be the correct special large domed head bolt. 3/8 thick with 16 tpi. It is about 1 1/8" long not counting the domed head. I can get the bolt through the seat back hole, but not through the seat frame. Is a 3/8" bolt too thick? The parts manual says the bolt is rd-hd, S., 3/8 - 16 X 31/64". What does the 31/64" refer to? It can't be length as that would not be long enough. Does anyone know what rd-hd means? and what S means? A 3/8" nut and washer is what the bolt goes into on the other side of the seat frame. Quote
Plymouthy Adams Posted January 12, 2015 Report Posted January 12, 2015 you already denying that what you know... Quote
DJ194950 Posted January 12, 2015 Report Posted January 12, 2015 A quick look look at My 50 Mopar parts book( I know wrong year) page 3 (in this one) is a standard abbreviations list that is used thoughtout the book, Most have them. 3/8" Bolt dia., 16 threads per inch, 31/64 threaded part length, S is steel, rd-hd is round head. Quote
MarcDeSoto Posted January 13, 2015 Author Report Posted January 13, 2015 Thanks DJ! Good info on the bolt abbreviations! I just realized why I was having trouble getting the bolt through the hole. I was using a bumper bolt that is 7/16" thick and I need a 3/8" bolt. That is one of the problems with working with unlabeled coffee cans full of nuts and bolts. Hard to believe that it's only 1/2" long though. Quote
MarcDeSoto Posted January 13, 2015 Author Report Posted January 13, 2015 (edited) I went out to the garage and there really must be something wrong here. I looked at the seat back and the seat frame and there is no way a 31/64" bolt could hold these two big, heavy seat sections together! Anyone out there have any experience with seats? Edited January 13, 2015 by MarcDeSoto Quote
BobT-47P15 Posted January 13, 2015 Report Posted January 13, 2015 Do you have any other bolts in your collection that look like they might fit?......regardless of what you think they may be for. My car is at the upholstery shop so I can't go look at the bolt in that location. Quote
MarcDeSoto Posted January 13, 2015 Author Report Posted January 13, 2015 (edited) I just had an idea. When the parts manual says the length is 31/64" could that mean that the actual bolt could be 1" or 2" and that the 31/64" is just the threaded part at the end of the bolt? thanks, Adams for the pics! I forgot that the bolt has a phillips head. Edited January 13, 2015 by MarcDeSoto Quote
bamfordsgarage Posted January 13, 2015 Report Posted January 13, 2015 ...could that mean that the actual bolt could be 1" or 2" and that the 31/64" is just the threaded part at the end of the bolt?... A quick look look at My 50 Mopar parts book( I know wrong year) page 3 (in this one) is a standard abbreviations list that is used thoughtout the book, Most have them. 3/8" Bolt dia., 16 threads per inch, 31/64 threaded part length, S is steel, rd-hd is round head. Sounds like that's it. Quote
james curl Posted January 13, 2015 Report Posted January 13, 2015 (edited) Structural bolts used through two moving parts have a grip length before the threads start. This is to prevent over-tightening the two parts so that they cannot move freely. In this case the grip length will be a few thousands longer than the thickness of the two parts to be moved. Edited January 13, 2015 by james curl Quote
Dave72dt Posted January 13, 2015 Report Posted January 13, 2015 Is the hole in the seat bottom the same size as the hole in the seat back? I ask because if the seat back needs to pivot forward, it may use a shouldered nut which would give you more threads and the 1/2 length would work fine. Normally the length is from the bottom of the head of the bolt to the end. Quote
DonaldSmith Posted January 14, 2015 Report Posted January 14, 2015 I get it now. The photo in post #7 shows it. My DeSoto Suburban has coupe seatbacks on the first and second seats. You can get to the second seat from the front door, if you want, and to get to the third seat you need to pull the second seat back forward. I've removed and re-installed the seat backs several times. Ah, yes. It's a special philips-head cap screw with a shoulder through the seat back, and threads only about a half-inch long. Quote
Dodgeb4ya Posted January 14, 2015 Report Posted January 14, 2015 That special seat pivot bolt... 1 Quote
MarcDeSoto Posted January 14, 2015 Author Report Posted January 14, 2015 Dodgeb4ya, Thanks for the pics! Now I know what to look for! If I can't find them, I guess I'll have to substitute with a modern bolt. How long is it? I would guess about 1 1/2". I doubt if anyone would sell that bolt today. Does this bolt screw into a nut as the parts manual says? Quote
DonaldSmith Posted January 14, 2015 Report Posted January 14, 2015 Yes, nut and lock washer on the seat cushion side. (It's easier to get at with the seat cushions out.) So, that's a special bolt with two shoulders and a special washer. The washer goes right against the head, between the head and the upholstery of the seatback arm. Quote
MarcDeSoto Posted January 14, 2015 Author Report Posted January 14, 2015 Thanks Donald, those are much needed directions. Thanks! Marc. Quote
MarcDeSoto Posted January 15, 2015 Author Report Posted January 15, 2015 Eureka! I finally found my two coupe seat bolts, but not the washers or nuts. But those should be standard nuts I can buy at any hardware store. the rare items are the special bolts. You can't buy those anywhere today except from a guy with a parts car! thanks to everyone in this thread and especially to Donald and Dodgeb4ya!!! Quote
DonaldSmith Posted January 15, 2015 Report Posted January 15, 2015 I found that a good source for exotic, rare hardware parts is the local Ace Hardware. But seriously folks, a lot of hardware on these old cars was standard stuff. Sometimes the real odd stuff can be bought on-line from McMaster-Carr. Shipping for a two-cent part can seem absurd, but if you really need it... Bundle your orders if you can. 1 Quote
Plymouthy Adams Posted January 15, 2015 Report Posted January 15, 2015 if one was really serious about looking for a shoulder bolt...they would look at the large varied offed on e-bay...by specs... Quote
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