Ok guys, I'm in the midst of my first rear end rebuild. I've got a 1967 BOP 8.2 with 2.93 posi. Its original to my 1967 GS400. I'm just putting in new bearings/races and reinstalling the original carrier, ring and pinion but I'm having trouble with my pattern. I've increased pinion shim width 4 times now (by a lot!) and think I'm headed in right direction but figured I'd post some pics for confirmation....I didn't think it would be this difficult to reinstall my factory gears in original housing. Here are 4 sets of pics (drive side followed by coast side in each set) for each of the 4 pinion depths. As you will see, I included the backlash and pinion shim width on each pic. Each pattern was obtained with 12-15 in-lbs pinion preload and very snug carrier preload. I oiled all bearings with gear oil but not the ring and pinion teeth. I'm turning ring gear by hand and there's quite a bit of resistance so it should yield an accurate pattern. So I started with the factory .032 pinion shim and barely caught the edges of the teeth. I kept backlash at .007-.008 while adding pinion shim depth to increase gear mesh but I've now added .033 and its getting better but I'm still not there! I thought a few thousandths would be all I needed. Am I on the right track here? Thanks in advance!
Forgot to mention I took a roloc to the inner race of the old pinion bearings so I can slip them on/off and I'm using them for initial set-up here.
Something's not right. If all you're doing is installing new bearings on the original gearset, then the oem shim should be about perfect. Your pattern shows the pinion way too deep. You are moving in the right direction. Double check and find out what changed to make the oem shim insufficient.
I thought something seemed fishy. I did raise a couple burrs on the lip of the inner pinion race seat but I knocked them down w a die grinder before installing new race. And if that were the problem it would require reducing shim, not adding it. I'm at a loss. I'm just gonna hit the pause button for a few days and think more about it. Give a chance for some others to weigh in too.
Yup, original gears that were running just fine. I didn't even replace ring gear bolts, just replaced bearings as I'm about to put much more power to the rear. This is really perplexing.
If the pinion bearing was not seated all the way,or the race not seated fully into the housing,it would put the pinion deeper into the mesh,but your pattern shows that it is too far away. Since those gears are original to the housing,you would normally reuse the existing pinion shim,and place the carrier shims back on the sides that they came from. Jump up to a .042" pinion shim,reset the backlash at .008-.010,and take the pattern again to see what you get.
Only thing I was thinking was the carrier not being seated in the saddles all the way - I have had some 12 bolt rears that if you did not install the bearing caps on every time you seated the carrier it would not draw all the way to the base circle of the saddles...which could cause this depth issue. Only thing else i had ONE TIME where the pinion bearing specs on the thickness of the land was .030 off on a Monza 10 bolt 7.5 rear. IT cause me days of craziness... I would remove the set-up bearing after I had the depth correct and installed the what I thought was correct spec bearing assembled everything and double checked the pattern one final time and NOT CORRECT. went back and forth cleanign doubler checking moving shim around OVER thinking...etc. Went NUTS... finally I depth measure the bearing side by side in the a same race and found out the bearing was totally different back cut depth where the bearing seated against the shim of the pinion. Changed out the bearing and all was good. CRAZY stuff that you would normally think is fairly the same with in .001 difference. UNLESS you ground way too much of the casting in the race pocket?
Given that I'm comfortable that the carrier is fully seated your second scenario is the only possible explanation. Im using the old bearing for set up, so I know it's correct, but it's sitting in the new race. In think logical next step is to drive that race back out and measure it's depth and bearing surface angle exactly. There's no way I ground too much casting out of the race pocket. I literally just knocked a couple burrs down with a die grinder so they were back even with the rest of the surface. I only touched maybe 3% of that surface. Thanks for provoking more thought.
Just trying to brainstorm as much as possible... THERE has to be a reason and I am just as curious as you. Jim
Place the old bearing/race next to the new bearing/race. Run a straight edge across the tops and mic down to the table or whatever surface they are sitting on. See if the numbers are different. If the new one is shorter,or less distance,then it will make a lot more sense.
Well, here's the answer....I disassembled everything again and drove the newly installed inner pinion race back out. As suggested, I then measured overall height of both the old bearing/race combo and the new bearing/race combo. Yup, the new bearing/race combo is .050 shorter! Now remember I was using the old bearing in the new race to set initial pinion depth, so just for grins I measured the depth of the old and new pinion races...the new race was about .012" shorter. Not sure this specific measurement is all that meaningful compared to overall combo height, but the point is this appears to be where the issue lies. Old brand was Hyatt, new brand is Koyo. Bearing numbers are the same except for a -N on the end: Hyatt HM89449 vs Koyo HM89449-N. Anyone have any insight as to the difference here, if any? Does the -N denote anything? Or is this just a case of different brands being that much different? As frustrating as this is I'm glad there does appear to be a sensible explanation. Now to find a solution...probably not ideal but maybe place an appropriately-sized shim under the inner pinion race? Try a different bearing brand? Monzaz (Jim), I'll give you a call tomorrow to discuss best option.
I use Timkens in everything. Yes,they cost more,but I like the finishes on the rollers better,and their specs are more consistent. You can use those Koyos,but you will need more pinion shims,or a thicker one.
Glad you've nailed down the cause! Good thing you checked the pattern, eh? you can add pinion shim to offset the difference between the bearings. At least now the reason why is known.
.As stated.... I only had that ever happen one other time. So as often as it appears I have not had any issues in the umpteen rears I have built.... There is nothing perfect out there. That is the reason for the shims.... Yes this one is way off ... But it does happen sometimes. Still nice to know we can be smart and figure out the troubles... Keep your brains working people. Jim
I was going to buy just one additional koyo bearing as a set up bearing, but for only $10 more I can get two timken bearings and a race. So I ordered those. Perhaps they'll also be closer in size to original bearing. I'll post pics of final pattern, hopefully next weekend. Thanks all for the help.
Alright I got back this today and I'm very close to getting an acceptable pattern, but the thinnest pinion shims in the NitroGear rebuild kit I have are .020". This is way too thick. I think I only need to add .001" or .002" to the factory shim. Anyone know where I can get these shims for a BOP 8.2 pinion?
