Stock 8.5 rear end

[john87442]

So I’m flipping through the posts today as I’m on duty at the fire station and thinking about the work I have for my restoration of my 87 442 and the differential comes to mind. I’m going to make it rear disk brakes but besides that it works fine no problems but it’s all original 170k miles and since I’m doing everything else should I just rebuild it also? G80 option 3:73. Besides taking it off the frame I haven’t opened it up. Should I think about axel replacement? Going to be about 400 hp with 200r4 rebuild. Thoughts and opinions welcome.

 

[Built6spdMCSS]

Somehow you double posted so I'll reply to this one and the other one can get nixed.

Does the Posi unit still work? 400hp is nothing on an 8.5, they can take more than that especially with an auto. It's the manual setups with power that beat the crap out of the drivetrain.

 

[john87442]

Yeah everything seems to work fine with it. No sign of problems.

 

[Built6spdMCSS]

If it's not broke...don't fix it.

 

[john87442]

Ok so finally have had the time to get this opened up, there seems to be to much gear lash between the ring gear and pinion. My dial gauge magnetic base hasn’t been delivered yet for me to get an actual measurement but as stated it has a lot of miles on it and although I’m not just trying to throw money away I would like to know how to confirm a new gear set is warranted. I’m sure bearings and pinion nut etc is needed, but a new Richmond set is over four hundred bucks and not sure if it’s just piece of mind or throwing money away. I know I could use the yellow indicator grease to check the pattern but that’s more for shimming. Any suggestions are appreciated.

 

[69hurstolds]

IMO, they're not that hard to redo, just take your time and measure everything for the correct clearances/preloads. IIRC, I think you already got a new clutch pack, so that's a win right there. Hopefully you watched that video link and it gives a great insight as to what to expect getting in there and working on the rear end. If you buy crush sleeves, I suggest buying a few to have on hand. Just in case. Luckily they're fairly cheap.

If the gears aren't severely worn and the pinion bearing/seal area is in good shape, you should be able to just re-use them. Check for cracks in the teeth, etc. Check the wear on the cross shaft as well. I think you can still get those new, I think. If the wear on the gears is enough to actually see or feel material worn away, then you may have to bite the bullet and get some new gears.

Check your axle splines, too. Just make sure they're ok. Some wear to be expected, but if splines are barber poling or getting chewed, you will need to find out why. Recall if you want to increase splines to like 30 instead of 28, you'll need to replace the case as well.

 

[john87442]

I did watch that video and you’re right it was very informative and gave me the confidence to do the project, probably should watch it again. I wasn’t sure how to determine too much wear on the gears because they look good still with no diffinative wear pattern or markings just a little too much gear lash. I was thinking about replacing the bearings and seals and yes clutch pack and hopefully that would work. If I didn’t have to remove the pinion gear then I wouldn’t need a pinion depth gauge to verify the spacing was ok because that thing is hard to find to rent and expensive to buy for just one time, but I also don’t want to go half a$$ at this either… and the video clearly shows the importance of having it correctly aligned……. I just answered my own question. Ok good talk. Thanks

 

[olds307 and 403]

You can inspect and rebuild as necessary. You can replace the posi clutches and just shim the carrier to achieve the proper backlash, if the bearings look good. I plan on doing the gear upgrade and posi in the 8.5" Type O for my 70S next fall. I found a set of nice used 3.08 gears and paid another $1100 CAD for the modified 8.8 ferd Yukon 28 spline posi. Still need another $350 US for all the bearing and seals. The 71-72 axle still retains the bolt in axles but uses the same gears as your 8.5", which cheap in comparison.