Jmac

Changed the Rear Diff fluid today and one of the bottom bolts wouldn't tighten down to 30# so I backed it out and it sheared in half. 45 min later after drilling it out and unscrewing it with a small straight blade screwdriver I went to Advanced Discount auto parts and got a replacement (M8-1,25mm x 20mm). I backed out a stock bolt from the top of the diff. and put it in the bottom hole of question (where the bolt sheared off) and it tightened down to 30# fine. I put the new auto parts bolt in the top hole that wasn't even where the problem was and it won't tighten down and I'm afraid to strip out the threads on the diff.

Did the kid give me the right size bolt?

Should I use a washer with the new bolt?

30# cover bolts and 24# fill plug for torque right?

If I stripped out the threads (using a torque wrench set at 30#?????) can that be fixed?

FYI when drilling and working out the broken bolt I noticed the flat axle surface of the diff is fairly soft and will scratch easily????

BTW I use the torque wrench every time to make sure I don't overtighten the bolts to avoid this very problem.

anyone

Jamie

TonyB

This may not help, but I never have to deal with the bolt problem again!

Sidestep the problem: put a mag-hytec cover on the diff! Fill plug, dipstick, drain plug, and temperature sender port.

www.mag-hytec.com

HTH

Tony

MikeyB

When I installed the PML cover I torqued the new bolts to around 15 ft lbs. 30 seems too high.

MikeyB

Jmac

Soooo, what's the correct torque spec. on the bolts and fill plug??

thanks Jamie

nickleinonen

proper torque is as tight as you can turn it by hand using a stubby wrench...

Jmac

?????????

J BODY

Out with my 3/8 impact....In with my 3/8" drive mac air ratchet.....and the torque value is kind of Iffy with all the loc tite they put on those things, unless of course you cleaned all the threads on the bolts, and chased all the holes with a tap.....I didn't think so.

lucey

I just checked the manual and it says the 40NM(30 ft./lbs).

Mikey4X4

Correct torque 30#. Torque wrenches can be outta calibration. But sounds more like the parts hand gave you the wrong sz. bolt. Did you compare it to one of the old ones you took out?

jawmail

There have been a few reports on this forum and the other of guys shearing those bolts. I for one feel like the spec. of 30 lb-ft is al little too high. Oil on the threads can mess up your true reading. Last time I changed the oil it felt like one of my bolts was going to shear so I stopped short.

nickleinonen

i am asuming this is in responce to my post:

by tightening the diff covers like that, unless you are a 400lbs gorilla, there is no way you can snap off the M8 bolt...

torque wrenches have their places, but for diff covers, i couldn't ever even think of doing that...

i know every nut&bolt has a torque value, but doing that can be bad [as in your case with a bolt breaking] a lubed fastiner normally should be torqued with up to 50% less torque than a dry fastiner [according to many torque charts and depending on lube used on the threads] being it was a lower diff cover screw, it could have gotten some diff lube in/on the threads...?

at work when i am working on engines, the lower end gets torqued, the injector gets torqued, the rocker studs get torqued and the cylinder holddown studs/bolts get torqued [by hand or with a hydraulic machine]... everything else is by hand or air ratchet

Jmac

OK, so when I do my diff service next time I should clean off the oil from the threads? So I get a good reading on the torque.

The bolt did twist right in half and I'm not a 400lb gorilla. I could have had a bad bolt by murphy's law.

I think I'm going to go down to 25# on the bolts and clean them with some brake cleaner.

Diff lube does get all over the bolts and in the holes.

thanks for the help.

BTW I ordered 3 stock bolts from local dealer $3.58 a piece!!!

Jamie

MikeyB

For the next time just order the aluminum PML cover and then you can drain the oil via the drain plug. And it even comes with new stainless steel allen head bolts.
Pics are in my photo gallery.

MikeyB

Jmac

MikeyB,

How do you know when you have the right amount of gear lube in the diff?

Jamie

MikeyB

There's a level check plug on the right hand side of the cover, it's at the same level as the stock cover fill hole. I filled up to the hole and held exactly 5 qts.

MikeyB