Good day folks, I am upgrading my 72' 8.5 rear to 3.42s and a yukon unit. I reused the shim (stamped 43) from the stock gear and pressed on the new bearing, here is what the pattern looks like. My inexperienced impression is that it need a smaller shim as it look deep into the gear, but this is my first go around. Let me know what you think. If I need to change it, ill use a bearing separator and a little heat before pressing it. Ring Gear 2 by gnx423 posted Aug 28, 2020 at 10:19 PM Ring Gear 1 by gnx423 posted Aug 28, 2020 at 10:18 PM Thanks, Mike
Something that I find that helps is with the checking compound...add a few drops of oil.....stir it up paint 3 or 4 teeth.....then use a drill to turn the set both direction and you will get a copy pattern on all the other teeth......sample pics from a 12 bolt I was doing just this week. The oil helps the compound flow better Ps when you pull that bearing off unless you have a clam shell type puller you will more than likely destroy that bearing. You either need to make a checking bearing by having the inside honed out so it slips over the pinion to allow easy adjustment to be made......and that bearing will then be able to be used on 12 bolt car, 8.5, and 8.8...............or use a shim kit from ratech that allows you to put a smaller shim...but close...say like .022 under the pinion bearing.......and then add te rest in shims that go under the rear pinion race...... The bad to this is every time you drive the race out you basiclly destroy the shims that are there so you can run out f shins real fast.
Ok, so the backlash here was set to 6 thousandths. And I am concerned on ruining the bearing if I pull it. I did read on the checking bearing, but took the gamble as it was not easy to order another koyo separately from the kit. It does spin freely, and stock shim is .043
Just a follow up here. Light heat from a propane torch and the bearing separator worked without too much force. I took 5 thousands out and reset the backlash to .006. Pattern looks better. Thanks for the help! Mike
YEP, i agree too deep. dump that .043 those work for GM gears not go for the Yukon . .035-.038 is where most of the ones I do end up. .022 will never work for any 8.5 guaranteed. I have done 30 years of 8.5s and never have gone below .030 ever. .035 is even pushing to shallow. .043 is just about .005 -.007 off and open the backlash to about .008 You do not need to go .006 for a street driver. You are risking noise the tighter you make the backlash. Jim JD
Jim I didn't say only put .022 in...i said he could put a shim thst close.....the .022 was a number just pulled from.mid air.....then make up the rest behind the rear pinion race as a way to not have to keep pulling the bearing off if no checking bearing
Its not my favorite way to do it, but for someone who only sets a setup only a few times.....it is a way to fet around making a checking bearing or destroying a couple pinion bearing
Based on the recent picture,a .035” should do it. See how the pattern has improved? You are going the right direction.
You have to remember...THIS is what Brian and I have to do also. We have to take it apart change the pinion depth and reinstall. There is no other way to get it correct. Sometimes you have to go past the point over the other side to know you have the correct shim and go back to what it was also. LABOR....it is what we get paid to do. The PATTERN is KING it tells you whether your in the sweet spot or not. Good luck... As stated all my Yukon gears set up at .035 to .038 had a few even go to .034 .033 in some cases. (10 bolt 8.5 GM housing 1971 - 1977 era. remember different eras could change like a 2004 chevy rear could be totally different with maybe .040 shim or the other way at shallower??? You the installer have to find the correct depth no matter what it is. Jim JD Race
there is no doubt it can be a pain chasing that last thou......i don't do anywhete near as much as you two do.......i do 5-10 a year. Enough to ve very familiar with the process, but still doubting of my results. The last rear just did was a 12 bolt, yukon stuff, it only took a .030 shim.........my 8.5 with motive gears took either .040 or .042 Its crazy how even a minor backlash change can really effect the pattern Pics 1 and 2 that 12 bolt .030 pinion shim with .005 backlash, pics 3and4 same .030 shim, but .009 backlash. Then love how sometimes there is a couple teeth in a row where contact is slightly different than most of the others. Red circle. If i did it more I would take the time to organize my shims better
how often do you find jim and Brian that even if you gets a very close of spot on pinion depth measurement that the pattern looks like poo and you just end up reading what the pattern wants and totally forget about the depth measurement
The last thing I would ever do is try and get the depth measurement that is scribed on the pinion. It is simply a starting point. The pattern tells you if it is correct or not. I have done numerous repairs on rearends that had the gears installed incorrectly,and they tell me “we put them right on the numbers”.