Hi, I was under my 91 formula last night trying to replace my leaky pinion yoke seal. Everything was going smoothly, until I decided to remove the differential cover so that all of the gear oil wouldn't get dumped on my head as I remove the pinion yoke. All of the differential cover bolts were very rusty and incredibly tight. Much tighter than the 22 ft-lbs of torque specified by the manual. 9 of them cam out fine. The tenth bolt I have not been able to remove. It is located on the driver side of the cover just below the axle tube. It seems like the previous owner of the car had used some king of a heavy duty silicone / plastic material as a gasket, very different from RTV. He had also filled the bolt holes with it prior to tightening the bolts. I have tried almost everything that I can think of that I have in my disposal in order to remove the bolt. The bolt head was beginning to get rounded, so I got a 1/2" socket bolt extractor. Even with this I had a hard time removing the bolt. I sprayed plenty of WD-40 to try to get the bolt to loosen up. I got the extractor to bite into the bolt head, but the thing seems to be so frozen in place that even with my might I can't get the thing to budge. I have tried tapping on the bolt with a socket and hammer, using pipe as an extension on the driver and no luck. I was able to drain the oil by slightly pulling the diff cover apart, and I suppose I could tighten the rest of the bolts back on, but don't want to risk having a differential cover leak and would like to get this resolved. Has anybody had experience with such situations and what are somethings that I can try to get this bolt out without braking it and having to drill it out. Any help would be greatly appreciated. Thanks in advance.

try heating the case with a torch but not the bolt
also you could try using a spray solvent like break clean to try to break down the silicone
just be careful if you use both brake clean is flammable

Try PB Blaster. WD-40 has its place, which includes spraying bees, stopping rust from happing on an engine block waiting to be installed, spraying your lawnmower deck every season, etc. PB Blaster does an amazing job of loosing up bolts that are hard to get.


About using heat....um no. Im not a big fan of using a torch on cars. I worked at a shop one time and they used a torch on everything and since then im not a big fan of it. Use the torch as a last resort.

I had the same exact problem the other day try hammering on a 1/2 or a 12mm socket depending on how rounded off it is. I used the bolt extractor and cheater bar but I had to go down a size with the extractor cause it kept rounding off.

As someone above said, heat is your friend. Even a propane torch will likely soften whatever is holding it.

Where do I get the PB Blaster? Is this a spray like the WD-40? I tried to use brake fluid and that seemed to take some of the rust off, but I think the problem is with the threads being held by the silicone. As far as heat is concerned, I don't have access to a torch, and I am afraid that I may do some harm with it since I have no experience in using one. I guess I could go to home depot and get a propane torch if all else fails.

Did you use a the 12 mm socket or a smaller extractor to remove the bolt? I suppose I could try to hammer in a 12mm socket.

Thanks

Impact gun. The shock force does a lot more to break a bolt loose than a constant pull. Don't forget about trying to tighten in before you try to loosen it- I use this technique all the time.

No silicone/gasket goo is holding that bolt in under that kind of force unless maybe he used high strength loctite.

use pb blaster or kroil...if no luck then nothing beats a torch

I am not sure what he used. I have opened other differentials before and have seen nothing like it. It looks like white plastic. He put it on the mating surfaces between the differential cover and the carrier and also in the bolt holes. It crumbled off of the bolts that came out.

I used a smaller extractor I have a craftsman set and the #7 one is what eventually worked for me cause the #9 kept rounding it off my set only has the odd #'s so i'm sure the #8 would have worked best.

HAHA i have that same kit...it even has empty spots in the kit for the other sizes right?! I went to the local sears and got the extension kit. So now i have all the sizes id ever need. Guess what tho. They give you some that dont go into the nice case the originals came from! So now i have a few loose ones that float in my (special tools) drawer.

....Yes guys i am organized and have a drawer specifically for special tools...like o2 sensor socket, extractor tools, torque wrench, and blah blah blah lol

Update on the stubborn bolt:
So I got a can of the PB Blaster and soaked the area nicely and tried loosening the bolt by giving it a few whacks with a hammer and an old oil pump drive shaft on the head. Tried tightening it first as much as I could, and then loosening it. No luck. The head was getting pretty rounded off. So I drilled a hole into the center of the head and got one of my bigger screw extractors to fit. I have a good grip on it now but the bolt would not budge. I have used 3/4 of the PB blaster and no luck. The way things stand right now, I am thinking that perhaps the threads are damaged. I think I have two options so far.

1) Some of you have suggested heat. I am a bit reluctant to use a torch, since on the can it says that the PB blast has a high flash point. I don't want to start a fire underneath my gas tank. Does anybody have a suggestion, and perhaps step by step instructions as to how to heat the bolt and get it out that way.

2) I could drill a pilot hole through the bolt. Remove the head of the bolt, and expand the pilot hole all the way out to the outer edges of the bolt, where the threads are. Re-tap the hole and use a new bolt, or expand the whole a little bit and use a helicoil thread insert.

Any advice and suggestions are greatly appreciated.

I'd get that extractor out of there before it snaps off and you're really screwed. I've torched bolts treated with PB many times. It's volatility evaporates pretty fast. Some heat on the case right where the bolt is stuck may work wonders. Even a heat gun if a torch worries you. You just need some expansion.

I know what you are saying. I have had an extractor brake inside a bolt before and know what kind of a pain in the behind that is. The extractor I have in there is in the bolt head. It is large, and if it broke off inside it would be in the head. I only have it in place because I have no way of grabbing hold of the bolt to twist it. I am also careful not to twist things hard. I can try to gently heat up the case around the bolt, but did not know if the heat gun would be hot enough. I suppose it wouldn't hurt to try. I don't have a torch, but perhaps I can purchase a cheep one from home depot and give that a try.

Stubborn differential cover bolt is out! Finally
I tried heating the differential housing and no luck. I was able to get it out by drilling a small pilot hole through the bolt and drilling the head off the bolt. After the head was off, the differential cover cam off. I used a small extractor and the bolt pretty much came out by hand, not much effort at all. I guess that bolt was way too tight on there and it was the clamping force that prevented it from coming out.

I put my pinion yoke back on and tightened the nut to about 1/16" past my marks on the nut and the pinion shaft. It took a great deal of force to get it there, but again it took a great deal of force to get it off. The inside of my differential looked pretty good. No worn out teeth or metal shavings. There is a little bit of a play between the pinion shaft and the ring great with the car off the ground and the wheels hanging. How much play is supposed to be there, if any at all?
I did not pay any attention to how much play was there prior to me taking things apart.

Thanks again for all your help.