Rear spring mounting plate
Thread Starter
Melting Slicks
Joined: Oct 2006
Posts: 2,193
Likes: 156
From: Navarre FL
Rear spring mounting plate
What size are the rear spring mounting plate bolts on 78? I ordered a set from a vendor and they are too small, dont even come close. I tried some 5/8 bolts, but threads seem to fit loose for the first three or four threads. The thread pitch is right, as they will turn all the way into the hole. But when under pressure they do not grab very well. Im thinking i just have some damaged threads, but want to verify the correct bolt and thread pitch.
Team Owner
Joined: Sep 2006
Posts: 31,274
Likes: 4,366
From: Westminster Maryland
Hi V-k,
I believe originally the four bolts that mount the spring to the carrier were 9/16"-12 x 3 1/4".
Perhaps your carrier was drilled out and re-tapped?
Regards,
Alan
I believe originally the four bolts that mount the spring to the carrier were 9/16"-12 x 3 1/4".
Perhaps your carrier was drilled out and re-tapped?
Regards,
Alan
Last edited by Alan 71; Nov 4, 2012 at 09:59 AM.
Thread Starter
Melting Slicks
Joined: Oct 2006
Posts: 2,193
Likes: 156
From: Navarre FL
Alan, thanks for the reply. I suppose that would be possible. I am pretty sure the bolt I used was a 5/8 though. Your scenario would make a lot ore sence to me if I were using a 9/16 and he had tapped it out to a 5/8 same pitch. Either way, I dont feel like its taking a full bite on the threads. Its pretty difficult to get a pitch guage in there without taking the diff cover off. I believe some years use 1/2 bolts? I think 1/2 would be plenty to hold it. Ill catch crap for this, but I may explore the helicoil option for these. But I have never had to use those before, so Im not too sure how that will work out. Its either that or just replace the cover and add another $140 to the ever growing spreadsheet!
Le Mans Master
Joined: Dec 2007
Posts: 6,422
Likes: 591
From: McHenry Illinois
Vette Kid, many poeple confuse the bolt size with the size wrench used to fit the bolt head, the bolt size is determined by the size of the shank or threaded area. A 7/16 bolt usually uses a 5/8 wrench, and a 9/16 bolt will usually take a 13/16 wrench.
Thread Starter
Melting Slicks
Joined: Oct 2006
Posts: 2,193
Likes: 156
From: Navarre FL
Hey guys, thanks for the info. I apologize, I had different bolt sizes floating around in my head and think I mispoke as to what size is in the hole now. I believe it is actually a half. I suppose thats just close enough to 9/16 in pitch to thread in and just feel loose. I just wasnt able to get a pitch guage in there to verify, and the manuals dont give bolt sizes (grrr). So I believe at some point they swapped the diff, or at least cover. Ill try and dig up some 9/16 bolts tomorrow and verify it. Oddly, the only bolt I dont have in my stock right now is a 9/16! I probably would have found the right size with trial and error if I had one around to try! hudrend of bolts in the bin, just not the right ones, ha!
