Rear differential cover
Le Mans Master
Joined: Jun 2019
Posts: 7,650
Likes: 2,466
From: Indiana
'79 stock cover is aluminum, correct?
Remember, torque values are less for aluminum than for cast iron..
Likely why you'll find variations listed as generalizations, also, it changes if bolt is galvanized or not, and lubrication or dry, these all present a differnt torque value for the same size bolt. . .
Remember, torque values are less for aluminum than for cast iron..
Likely why you'll find variations listed as generalizations, also, it changes if bolt is galvanized or not, and lubrication or dry, these all present a differnt torque value for the same size bolt. . .
https://www.corvetteforum.com/forums...estions-2.html
Thread Starter
Le Mans Master
Joined: Jun 2019
Posts: 5,453
Likes: 2,168
From: Loveland
Something for those who install a new 9 or 7 leaf steel spring. After about a year I checked the 4 bolts, they were all loose. I think the rubber spacers compress after a while. It would be a good idea to check the torque after a few months to make sure they are still to spec. I got a 79 spring plate to go with the 79 diff cover, and new longer 7/16 inch bolts. I got grade 8,,,, 7/16 x 4 inch bolts. I couldn't find 3 3/4" flange bolts. I cut off about 1/4 inch to fit without breaking the diff. I'm going to use blue loctite during the install.
Even if you are installing a fiberglass aftermarket rear spring, you need to measure the required bolt length very carefully.
Even if you are installing a fiberglass aftermarket rear spring, you need to measure the required bolt length very carefully.
Last edited by kodpkd; Nov 7, 2021 at 11:20 AM.
Thread Starter
Le Mans Master
Joined: Jun 2019
Posts: 5,453
Likes: 2,168
From: Loveland
If it's blue,,,, and if it's Loctite brand, it should be ok.
I installed the bracket with 35 ft/lbs, felt like plenty of torque. Seemed just short of bending the bracket.
I installed the bracket with 35 ft/lbs, felt like plenty of torque. Seemed just short of bending the bracket.
Last edited by kodpkd; Nov 7, 2021 at 02:56 PM.
Racer
Joined: Sep 2024
Posts: 256
Likes: 26
Thank you GTR. I installed a new 9 leaf spring on my 68 last year. All seems good since then, I think. At the time I didn't know about the two different covers. I tried to torque the bolts to 70 ft/lb as per the 68 manual. It became clear that 70 was way to much torque. So researched what cover I actually have. It's the 78 79 cover with the 7/16 in bolts. In doing more research I find the issue about to long of bolts in the front two positions of SPELAB Differential Cover. I also learned about the 2.25 inch vs the 2.50 inch spring width. UGH! THEN,,, there is the issue with how thick the new 9 leaf spring is. At this point I am not sure I have the correct bolt length in the front two positions. I have read about to many people cracking the cover. In the assembly manual, it also shows different washer- lock washer combination front vs rear. The rear two shows just a lock washer, the front two show lock washers and flat washers.
The issue I am going to try to figure out, with the new 9 leaf spring, is how long the front bolts should be. If they are to short, they won't go into the cover far enough, if they are too long, they could be bottoming out. I'm not confident the stock 3.25 inch bolt is correct with the new spring. I'm going to try to measure, bottom of the hole to the plate.
I hope this info helps someone else when they think about replacing their spring or diff cover. Don't go through the trouble to just bust holes in your cover.
The issue I am going to try to figure out, with the new 9 leaf spring, is how long the front bolts should be. If they are to short, they won't go into the cover far enough, if they are too long, they could be bottoming out. I'm not confident the stock 3.25 inch bolt is correct with the new spring. I'm going to try to measure, bottom of the hole to the plate.
I hope this info helps someone else when they think about replacing their spring or diff cover. Don't go through the trouble to just bust holes in your cover.
Thread Starter
Le Mans Master
Joined: Jun 2019
Posts: 5,453
Likes: 2,168
From: Loveland
It's been a long time. I think the later year C3 covers are stronger than the 68. Unless you are going to race your car, I wouldn't worry about any heat build up. I'm sure there are all sorts of options if you are looking to build a race car.
Tech Contributor
Joined: Aug 1999
Posts: 15,166
Likes: 3,967
From: Connecticut, USA
The stock covers were the same from 65-77, the 63-4 and the 78-9 were different. They are fine as long as they are correctly installed, and the spring loaded. The HD covers sold are good, they have thicker lower ears that typically won't break. Installing the wrong size bolts will blow out the inside of any cover.
Aftermarket covers for cooling are not stronger and if gear oil heat is a concern, then external cooling or REM polishing the parts will help. This is really only needed for road race cars, not street cars.
Aftermarket covers for cooling are not stronger and if gear oil heat is a concern, then external cooling or REM polishing the parts will help. This is really only needed for road race cars, not street cars.
Racer
Joined: Sep 2024
Posts: 256
Likes: 26
I have the diff cover that uses 4, 7/16 inch bolts to hold the rear spring on f150 rear differential cover. Do the front two bolt holes dead end or do they extend through the top of the case? I think used on the 78 and 79.
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