Hi guys, I've been told that my diff is one of those 71-72 8.5 inches 10 bolt. My car is a 1968 convert skylark with stock 350, TH375. I calculated that I have about a 2.7 gear (open). I want to change to posi 3.42 but am afraid to buy the wrong parts. I'm in canada and with the current exchange rates and shipping fees, Amazon.ca is my best friend. I found 1. Yukon Gear #YG GM8.5-342 + 2. Yukon Gear and Axle (#YDGGM8.5-3-28-1) Dura Grip Differential and 3. Yukon Gear and Axle (#YK GM8.5) Rear Master Overhaul Kit Are these the correct part numbers for my diff ? I read that a 2.73 gear is a series 3 and shouldn't be a problem to upgrade to 3.42, right? I also read that the yukon YK GM8.5 has Timeken bearings but are they the SET9 and 712146 I read that fit this diff? Thanks!
Be sure to verify that your information is correct. Unless it has been changed, your car came with a 68-70 Buick only 8.2 rear. It did not originally come with a TH 375 either. If you want the correct the parts buy them from one of the Buick differential suppliers and experts on this board. One is Brian Trick and the other is Jim M. whose Board name is “Monzaz”.
Brian already identified it (see picture) as a 71-72 8.5 10 bolt on another site. Looking to buy from amazon.ca because exchange rate, customs and shipping will cost me a fortune.
That does look like the 8.5 10 bolt (not 12 bolt). So as long as you buy parts for the 8.5, you are good to go. The Posi carrier is correct for 28 spline stock axles, and takes 2.73 and up gears, https://www.yukongear.com/productdetails.aspx?ProdID=1562
My bad, 10 bolt it is, not 12 as I initially wrote. I guess I only need to confirm now that the yukon YK GM8.5 has Timeken bearings that will fit. Are they the SET9 and 712146 I read that fit this diff?
Yes, unless it is a wagon rear, should be SET9 bearings and 71246 seals. I say that because your car did not come with that rear, it came with the 68-70 Buick only 8.2 10 bolt. Someone put that rear in it. It's bolt in axle, why not pull an axle and see what it has? Also be aware that there is a problem with the 71246 seals that are not the correct dimension in thickness. This creates excessive axle end play. You need to measure the seals before you use them. The correct ones are .490" thick. http://www.v8buick.com/index.php?threads/slip-n-slide.355035/
I'm not equipped or knowlegable enough to pull the axle out. Next step will be to find a good mechanic near me to do the job. So do you know if yukon #YK GM8.5 have Timeken SET9 and 712146 ?
The stock axles in a passenger car 71-72 8.5 10 bolt take the SET9 bearing and 712146 seal. You actually don't have to replace them to replace the carrier and gears. I would just buy the Posi carrier, gears, and install kit for the carrier.
I can't find an install kit on Yukon's site. Something like this, https://www.jegs.com/i/Richmond-Gear/836/83-1021-1/10002/-1 I would PM Monzaz here, http://v8buick.com/index.php?members/monzaz.3880/ or call him. This is his site, www.jdrace.com He might be able to cut you a better deal.
