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I own a 72 SB with a 4 speed. I drive it as much as I can and began to notice a thump coming from the rear as I changed gears, especially 1st and 2nd. Thought it was time for a rear differential lube change, bought all the supplies, took the spare tire and carrier off. I was surprised to find that 2 of the bolts holding the leaf spring to the differential were gone, 1 was completely loose and only 1 was still holding the leaf in place! If I hadn't noticed and continued driving it this way, this could have been very, very bad!
What is the best way to remove the remaining bolt, re-align the bracket, and install the bolts? Should the wheels be on the ground / supported, and then remove the last bolt?
the weight of the car is pushing the spring towards the carrier, you can leave the car on the ground, looks like an easy fix, go get your replacement bolts and don't forget the lock washers LOL
looks good down there, very little rust, maybe that is the reason why they backed out( no rust holding it in LOL)
the weight of the car is pushing the spring towards the carrier, you can leave the car on the ground, looks like an easy fix, go get your replacement bolts and don't forget the lock washers LOL
looks good down there, very little rust, maybe that is the reason why they backed out( no rust holding it in LOL)
CanadaGrant is correct. The weight of the car should be on the spring with the car sitting on the ground. If not you risk breaking the ears off of the rear diff cover.
Thanks for the responses everyone. I put the car back onto the ground, with the rear on ramps, and this took the pressure off the bolts. I removed the loose bolt that is seen dangling in the background (it was being held up by the exhaust!) and bought 2 bolts to install on the front of the pumpkin. Once these are loosely in place, I will remove the last bolt on the rear and buy 2 bolts to install on the rear. I will then torque them all down including lock washers and thread lock on all the bolts too!
The car is almost all original with only 87k miles. The bottom is in good shape, only light surface rust, mostly just dirty. I haven't wanted to get a pressure washer down in there as I have found many of the original factory markings in this area, including above and in front the gas tank. Plus, don't want to get with water up into the half-shafts.
you may want to run a tap through the holes in the differential cover to clean the threads and lessen the chance of stripping or breaking of the cover.
Thanks for the responses everyone. I put the car back onto the ground, with the rear on ramps, and this took the pressure off the bolts. I removed the loose bolt that is seen dangling in the background (it was being held up by the exhaust!) and bought 2 bolts to install on the front of the pumpkin. Once these are loosely in place, I will remove the last bolt on the rear and buy 2 bolts to install on the rear. I will then torque them all down including lock washers and thread lock on all the bolts too!
The car is almost all original with only 87k miles. The bottom is in good shape, only light surface rust, mostly just dirty. I haven't wanted to get a pressure washer down in there as I have found many of the original factory markings in this area, including above and in front the gas tank. Plus, don't want to get with water up into the half-shafts.
Thanks, I'll update the post when Im done.
I would certainly be trying to figure out why these bolts backed out in the first place. Seems unusual if indeed it is mostly original.
Hi Frank,
The four bolts have 1 part number shown in the AIM which means they're all the same length.
The front 2 holes are blind so bolts that are too long CAN damage the rear cover.
Regards,
Alan
you may want to run a tap through the holes in the differential cover to clean the threads and lessen the chance of stripping or breaking of the cover.
I got this kit a few years ago and have used it so often on my old rusty projects, including replacing those same bolts in my diff cover.
Thank you everyone for your great posts. I decided to replace all 4 of the bolts as the one seen in the above picture dangling above the exhaust suffered some damage to the threads. I ordered the bolt kit from one of the vendors and while I waited stripped, primed and painted the bracket satin black.
Also while I waited, I drained the pumpkin with a hand pump / siphon, and put 2 fresh quarts of 85W-140 conventional gear oil with the GM additive.
When I received the bolts, I noted they were a little longer than the originals. No bid deal on the rear bolts as they the bolts pass through the "ears", however the front one are right below the case. After measuring, I used an extra lock washer as insurance to avoid any damage to the case. Torqued all the bolts, took her for a spin, and she drives fantastic. Vibration and "thump" from the rear during gear shifts are gone.
BTW, I don't own a tapping kit, but I did clean out the bolt holes with a 1/2" OD cylindrical wire brush I bought at Home Depot. Cleaned all the holes with compressed air and its incredible the rust and gunk that came out. Holes were nice and clean for the new bolts.
Another way to clean threads that works pretty well: Find a similar bolt that fits the threaded hole you are working on, use a cutoff wheel and cut a groove through the threads plus slightly deeper the length of the bolt. Flip it over 180 degrees and do the same. Wire brush it well to remove burrs. Run it in & out of hole, the debris collects in the grooves you cut. Use good judgment here, you don't want to jam a weakened bolt and have it break off.
Last edited by vette_jim; Oct 16, 2015 at 10:22 PM.
Reason: Mispell
Loose Rear Spring HELP!
