Question regarding the bolt size - Diff carrier cushion
Thread Starter
Pro
Joined: Jul 2004
Posts: 713
Likes: 61
From: Waterford CT
Question regarding the bolt size - Diff carrier cushion
I have been studying my C2 and C3 cars and replacement diff cushions, and am searching for guidance as to the correct size of the bolt that secures the front of the differential carrier, through the cushion. The following "facts" are what I have learned, so far.
1. My very original '71 LT-1 has a 7/16" bolt
2. My recently purchased '66 coupe has a 5/8" bolt
3. I have three new diff cushions on hand, one rubber, one Prothane urethane, and one urethane of unknown manufacture, and all have a 5/8 inch center hole meaning a 7/16 bolt is a very loose fit
4. I looked in my copy of the AIM for 1971 and it calls out GM part 454949 for this bolt, but lists no size. I did a google search on the part number and found one site that calls it out as 7/16 - 14 X 2.75 long.
5. I do not have a copy of the AIM for my '66, yet, so I can't compare.
6. I looked at the Corvette Central catalogs for both C2 and C3 applications and it calls out the SAME part number for both, although it fails to note the size of the bolt.
My question for the forum members is simply, what size should that bolt be? Is it possible that the C2 is supposed to use a larger 5/8" bolt, even though the CC catalog calls for the same bolt in both applications? Based on the hole size in the cushion, the 5/8 bolt would be the better fit. I await your input!
1. My very original '71 LT-1 has a 7/16" bolt
2. My recently purchased '66 coupe has a 5/8" bolt
3. I have three new diff cushions on hand, one rubber, one Prothane urethane, and one urethane of unknown manufacture, and all have a 5/8 inch center hole meaning a 7/16 bolt is a very loose fit
4. I looked in my copy of the AIM for 1971 and it calls out GM part 454949 for this bolt, but lists no size. I did a google search on the part number and found one site that calls it out as 7/16 - 14 X 2.75 long.
5. I do not have a copy of the AIM for my '66, yet, so I can't compare.
6. I looked at the Corvette Central catalogs for both C2 and C3 applications and it calls out the SAME part number for both, although it fails to note the size of the bolt.
My question for the forum members is simply, what size should that bolt be? Is it possible that the C2 is supposed to use a larger 5/8" bolt, even though the CC catalog calls for the same bolt in both applications? Based on the hole size in the cushion, the 5/8 bolt would be the better fit. I await your input!
Le Mans Master
Joined: Aug 2006
Posts: 7,427
Likes: 1,560
From: mount holly NC
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
All the vendors sell the same product with the 7/16th bolt, and list it as fitting all C2s and C3s.
The larger hole in the top cushion doesn't matter because the bottom cushion fits into the top and is held in the frame with the bolt.
The larger hole in the top cushion doesn't matter because the bottom cushion fits into the top and is held in the frame with the bolt.
Thread Starter
Pro
Joined: Jul 2004
Posts: 713
Likes: 61
From: Waterford CT
It does appear that they all supply 7/16th's bolts; however, the hole through the steel sleeve in the middle is still 5/8" as is the hole in the differential carrier bracket on the C2 so it's a loose fit. That may be by design to ensure that the bolt can be easily inserted during assembly. The torque reaction in forward gears applies simple tension on the bolt with no shear loads expected so the fit within the hole really shouldn't matter. I will find a copy of the C2 AIM and check what the factory used for C2's. I'd just like to know if the 5/8 bolt in mine is original and correct, or an "upgrade" that someone put in at some point in the past.
