When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I've stupidly managed to drop my diff while hanging it up to paint. Now the two output shafts are locked together and will only rotate just under one turn. Any ideas where I should start looking for the problem?
John
If a tooth broke, it will stop dif where it hits pinion gear. Turn til it stops. Turn back approx 1/2 turn and look between teeth on ring gear. A ring gear with broken tooth won't stop dif from turning. The tooth itself will.
Oh dear how embarrassing is this! First I drop the diff then I miss the bleeding obvious.
I took off the rear cover and saw nothing wrong, but it still wouldn't rotate more than 1 turn. Then I saw that one of the universal joint clamps was catching on the outside of the case!!!!! Easy fix though.
Whilst I had the cover off I measured the stub axle end float. It's 0.030" on both sides. Is this reasonable for a car that's done at least 75000 miles?
Also, can someone explain why both stub axles will only move together. My limited understanding of a LSD made me think that it would operate like a standard diff until it sensed an imbalance of torque on the output shafts.
Oh dear how embarrassing is this! First I drop the diff then I miss the bleeding obvious.
I've been that guy. Truth be told, every member here has been "that guy" at one time or another! I'd rather feel a little stupid, than find something that costs me huge $$$. Greg
You have the diff and the cover off. check to see if the ring gear bolts are original- they will not have lockwashers under them. These often backed out and will shear, possibly wrecking the diff completely. You can replace them with ARP's but you have to countersink the holes, if you want to save a few bucks, back one out at a time. Wire brush it and wash the holes out with brake clean and air. Reinstall using a drop of Loctite #271 or 272 on the threads. Torque to 60 ft/lb. Replace the hex bolts in the posi case bearing caps with socket heads, pull the axles and check the face hardness and dimension from the face to the snap ring. should be about 50 Rc and 190-200". You can go to a NAPA if you have one near you or order online new axle seals to install- pack grease around the seal spring. If you want to get more involved you can install a new pinion seal and check the yoke OD for wear. 73-79 diff's are known for soft faced axles and loose RG bolts.
You have the diff and the cover off. check to see if the ring gear bolts are original- they will not have lockwashers under them. These often backed out and will shear, possibly wrecking the diff completely. You can replace them with ARP's but you have to countersink the holes, if you want to save a few bucks, back one out at a time. Wire brush it and wash the holes out with brake clean and air. Reinstall using a drop of Loctite #271 or 272 on the threads. Torque to 60 ft/lb. Replace the hex bolts in the posi case bearing caps with socket heads, pull the axles and check the face hardness and dimension from the face to the snap ring. should be about 50 Rc and 190-200". You can go to a NAPA if you have one near you or order online new axle seals to install- pack grease around the seal spring. If you want to get more involved you can install a new pinion seal and check the yoke OD for wear. 73-79 diff's are known for soft faced axles and loose RG bolts.
Garry, thanks for posting about this, it's a little know issue that occurs more often than I think many would suspect.
I first heard about this in the early 90's when a friend mentioned it to me while I was rebuilding the rear suspension on my (new to me) '73 with less than 40k on it. I decide while I was back there tearing into everything I should remove the rear cover and just check to see how mine was. When I removed the cover I immediately noticed that my ring gear bolts had (new looking) lock washers on them and breathed a sigh of relief. Then I examined the rear cover and noticed the strengthening web had a couple of nicks in it. I then concluded that some of the bolts had come loose at one point and someone had already been in there and dealt with it. Fortunately the web was not cracked, just nicked, so it drove home the issue for me.
I didn't take any pictures back then, but I did find this one on the WEB that shows what you might look for when checking out your rear differential.
The problem manifests itself as one (or more) of the ring gear bolts work loose and finally strike the web. You will hear a clicking noise in the rear and wonder what it could possibly be. Then the noise stops (a bolt head has sheared) only to return again and also disappear. Eventually the rest will loosen until one of the bolt heads gets drawn into the gears or the ring gear loosens enough and all heck breaks loose...
I'm sure Garry has dealt with the consequences of this and has many more stories than I can imagine.
Gary,
Thanks that's really useful info. As best as I can measure in situ, I seem to have at least 0.200" from the face to the snap ring. I'm trying hard not fix anything that's not broken, as I've already suffered from a bad case of "while-I'm-at-it-itis" I started off planning to do a mild restoration and 2 years later I've just sandblasted and painted my chassis, so no prospect of actually driving the car any time soon. However I don't want risk serious damage that can be easily fixed now. Do these look like original bolts?
Gusto
Yes sounds like your 73 had some RG bolt issues. This happened from 63-79 but more so when GM got cheap in late 77 and went with a flanged head RG bolt without any thread locker. Now Loctite was around back then because I was using it rebuilding Bridgeport heads during the late 70's. The earlier cars had shoulder bolts with hardened lockwashers and those were better and would last much longer. I recall walking into shop in the early 80's and they had a very low mileage 78 on the lift that the bolts backed out on. Instead of fixing it they went to the local Chevy dealer and bought a new complete diff to install.
UKJohn- if your diff is quiet and not leaking then you do not have to rebuild it but you have it out now so now is the time to do those simple upgrades I mentioned. You can replace the RG bolts one at time with the posi still in the diff. I can not see your pictures on the PC I am using but will check when I get back to my shop later today.
Here is what the backed out bolts will do, just like a fly cutter in a mill.
Here are the common "kit" bolts in place and loctited with the lockwashers. These will work for a street car but I consider it a cheap out and no longer use them. This is from 10+ years ago. Someone slapping a diff together can use them but the ARP bolts are much better and shoulder type, these are fully threaded.
Those are not flanged head bolts, there are lock washers under them. I can see the stock cast shim on the LH side so it might be original but they should be flange head. I would still pull one to check it. If it's fully threaded it is not original. If it wasn't too tight or no Loctite on the threads I would do them all.
diff locked up
