I'm going to be changing the fluids in my front & rear diff's this spring and I read a write-up on here where the person painted their rear diff cover and used grade 8 bolts when they put the cover back on. I thought this gave it a real nice look with the painted cover contrasted by the shiny bolts and figured I could do the same thing on both of my diff covers. Question is, what are the bolt specs for the front & rear diffs? Can anyone provide me with thread size, bolt length, etc.?

 

"SCREW AND WASHER, Hex Flange Head, .312-18x.562" that's what the parts manual says.
I searched autozone.com and it gave me this
"Spectre/12 pcs. 5/16 in. - 18 x 3/4 in. grade 5 zinc plated differential cover bolts and washers fits GM 10 and 12 bolt and Dana 44"

The bolt diameter is the same, 5/16 = .3125, but the service manual bolt length is closer to 9/16" (.5625) than 3/4" like what autozone says.
I narrowed it down to 2 choices for ya lol. Maybe send a PM to the guy that did the write up to see if he remembered.

 

I painted my rear differential cover about 2 years ago, stock bolts and all. I did go out and buy a bunch of those cool looking stainless bolts that use an Allen wrench but am waiting for fluid change time to install them. I took a top bolt out and carried it to match up, leaving the truck parked and having rtv it didn't leak, using a top bolt was just insurance. I suppose I could probably install these one at a time and not crack the rtv, but just the same I'm in no hurry and will wait till change time...

 

I thought about removing a top bolt from each diff to check the threads. We have a machine shop here at work so I have access to thread gauges. I might just go that route to be on the safe side.

 

Thanks for your research! At least they both spec'd the thread size as 5/16-18. I've been meaning to download the service manual from weedahoe to see if they spec the bolts in there but I haven't gotten around to it yet.

 

No problem! the parts manual and service manual come in very handy. Although the parts manual can be tricky to decipher all the codes it uses, sometimes it's not very clear.

 

Yeah I just downloaded both manuals from weedahoe the other day. I'm going to be getting a lot of use out of the service manual for sure. So far, I'm not too crazy about the parts manual, but it's nice to have it around.

Weedahoe, if you read this thread, thanks for making all that stuff available for everyone!

 

Ok, I'm gonna bring this thread back real quick. I was at Home Depot the other day and figured I would see if they had any of these bolts in stock. The only 5/16-18 x 3/4" long zinc plated bolts they had were grade 2 so I went ahead and bought some because they were like 17 cents each or something. Will grade 2 bolts be strong enough? Or should I go for a minimum of grade 5?

 

I do not have any research to back this up, however, grade 2 would be more than ample in my opinion. there is no shear stress on these botls at all. To be honest the only stress they would see is with you tightening them. But if it were me I would spend the extra 0.03 $ and get grade 5. lol

 

Believe me, for piece of mind, I would much rather get some grade 5's. But the Depot only had grade 5 in 5/16-24, so that won't work. Looking at the yield strength of the grade 2's, plus the fact that there's 12 of them holding the cover on, makes me think they should be ok. I was just wondering if anyone could produce any evidence that the grade 2's won't hold up.