Mind checking my pattern?

[mplex2000]

Hey guys, haven't been active online in a long time so I feel a bit guilty but this is only my second time to do a full diff and gear swap, and it's my first time by myself and on a Chevy

I'm installing a Yukon posi and 3.73 r&p, all new bearings and what not as well. Vehicle in a 79 Big 10 with a 12 bolt truck axle, of course which had the original open diff and 3.09 gears.

I honed out the original pinion bearing for setting pinion depth. Went with the recommended .026 for a new 3.73 gear set. Installed the pinion with the honed out original and then the new bearing on the outer. I bought a solid spacer kit in lieu of using the crush washer, so I put the spacer in as well with no shims while measring preload. Measure at 10 in lbs of preload.

Installed the carrier with new shims roughly the same thickness as the originals. Pattern looked pretty good (to me). Checked backlash which came up about .018. Tossed a .012 shim on the left side and now backlash looks to be about .075. Re-painted the compound and I feel like it looks good but it seems to good to be true. I was expecting to be in the garage for many hours before getting to this point

If any of you gear pros could take a look and let me know what you think I'd greatly appreciate it. I guess if this is good, I just need to go press on the new pinion bearing and then set preload with the spacer shims, re-install and torque the carrier, re-check the pattern and call it good?

[PGSigns]

I am guessing that you meant .0075 on the backlash. That seems a bit tight. Pattern looks good to me.
Jimmy

[homemade87]

That pattern looks really good . What I mean by that is the drive side looks to be center in both directions with a good smooth ( no hard lines ) all the way around the pattern . This is what you are looking for . The coast side looks to be the same . Both patterns seem to be the same toe to heal as well .

I would run it .

[Ironangel]

Pattern looks good. The ring gear backlash should be from .006" - .010"... The pinion preload should be 13 to 15 in-lbs (new) 6 to 7 in-lbs (reused)
https://www.drivetrainshop.com/GM_12_Bolt_s/105.htm

[mplex2000]

Thanks for all the input!

You're right I was a little zero off

You think the backlash is too tight? I keep seeing between 6-9 and 6-10 depending on where look, either way I figured this one being right in the middle would be cool. If not, I'm all about changing it now and not doing this again for sure.

On the pinion preload, I've seen varying numbers depending on where I look. Add to that the fact that I'm using the old bearing on one side and new bearing on the other side (maybe I should have put on both used bearings?) 10 seemed good. I suppose we'll know for sure if I were to press on the new pinion bearing and re-check the pattern?

[Ironangel]

Originally Posted by mplex2000

Thanks for all the input!

You're right I was a little zero off

You think the backlash is too tight? I keep seeing between 6-9 and 6-10 depending on where look, either way I figured this one being right in the middle would be cool. If not, I'm all about changing it now and not doing this again for sure.

On the pinion preload, I've seen varying numbers depending on where I look. Add to that the fact that I'm using the old bearing on one side and new bearing on the other side (maybe I should have put on both used bearings?) 10 seemed good. I suppose we'll know for sure if I were to press on the new pinion bearing and re-check the pattern?

I think your good to go. Anywhere from six to ten thousandths is good for backlash. The pinion preload should be good as well because your going with one used and one new bearing. If your confident that both pinion bearing races are firmly set, and that there was zero end play when you checked the preload at 10 in lbs, you should be good to go. The preload should increase when the carrier is installed because your reading the combined preloads of the carrier and the pinion. Yukon should have sent a small pamphlet outlining the order of assembly and procedure with their gear set. In the back of the pamphlet is a break-in procedure, do you still have that? Here's the break-in procedure... https://www.ringpinion.com/Technical...r_break-in.inc

[andyh1956]

You can get a more accurate pattern by using a large screwdriver between the housing & the carrier case on the outer diameter where the ring gear bolts. Pry between the two to impart some drag on the carrier as you rotate the pinion.

[mplex2000]

I don't think there was anything included with the Yukon diff. The (to my dismay, made in India) "SVL by Dana" gearset also came with nothing. The nice USA Standard Gear master rebuild kit DID come with a decent doc at least.

Now I'm going to double check, but I don't believe the pinion had any endplay and I'm pretty dang sure those races are fully seated.

As far as drag on the gears when pattern checking, I applied resistance to the yoke while turning the ring gear.

[Ironangel]

Originally Posted by mplex2000

I don't think there was anything included with the Yukon diff. The (to my dismay, made in India) "SVL by Dana" gearset also came with nothing. The nice USA Standard Gear master rebuild kit DID come with a decent doc at least.

Now I'm going to double check, but I don't believe the pinion had any endplay and I'm pretty dang sure those races are fully seated.

As far as drag on the gears when pattern checking, I applied resistance to the yoke while turning the ring gear.

Yeah it's sad that nearly all the foundry's in the United States are closed and moved over seas. I called Yukon and they indicated that all their gear sets are made in other countries. They also said that they undergo testing and lapping as well as packaging here in the US. Richmond, Yukon, Motive, USA Standard are all foreign made. US Gear is one of, if not the last USA made gear set.

[homemade87]

I looked into the us gear for my 8.5 . They do not have one for earlier trucks . They have one listed for a 8.5/8.6 which looks like it will work but the pinion has splines for later models . 32 spline on the pinion . 80's trucks are 30 spline .

Let me know if I am wrong . But I could not find one to fit from us gear on there web site . This leaves me out with them .

[Wrenchbender Ret]

That is a really good pattern & backlash. Lets just hope it doesn't change when you put on the new brg.

George

[mattfranklin]

Looks like a picture from a textbook on how to do it right.

[andyh1956]

Originally Posted by mplex2000

I don't think there was anything included with the Yukon diff. The (to my dismay, made in India) "SVL by Dana" gearset also came with nothing. The nice USA Standard Gear master rebuild kit DID come with a decent doc at least.

Now I'm going to double check, but I don't believe the pinion had any endplay and I'm pretty dang sure those races are fully seated.

As far as drag on the gears when pattern checking, I applied resistance to the yoke while turning the ring gear.

OK then. That's backwards. The proper procedure is to rotate the pinion CW looking at the front AGAINST the ring gear. Same direction as when the pinion is turning when driving the truck. Then you can rotate the ring gear / carrier assy AGAINST the pinion in same direction to check the "Coast" pattern.
I know all of this is kinda complicated & the smaller the gearset the harder it is to set up. The last 12 bolt I set up took me six tries before it suited me. 18 wheeler gearsets are a breeze compared to these.
But it does look like an acceptable pattern you have, good work!

[mplex2000]

Interesting, everything I've read says to turn the ring gear rather than the pinion (which is contrary to what I'd have thought since turning the pinion is how the thing works).

At any rate I pressed on the new bearing. Used the solid spacer and some shims to obtain a 20 in lb preload on the pinion. Had to cram a couple of shims in on the left side to get both a very tight carrier preload and to get the pattern back.

Found out that the new brake lines I bought from Summit actually are the wrong ones despite what they say on their site. I've ordered replacements after already mangling the lines and realizing they're not right at all since one of the tube nuts is the wrong size, but it looks pretty nice regardless!

[homemade87]

Pattern changed . Your to deep now . You did not say what the backlash was . If the same as before you are going to have to remove .002 from the pinion and look at it again .

As for rotating the ring gear . This is how I have done it for years . Takes more pressure between the ring gear and pinion to turn the pinion . Works just fine .

You can turn the pinion instead but you have to hold the ring gear somehow to to get pressure between the gears .

[mplex2000]

The backlash is the same as before (after adding more carrier shims).

Ugh, we thought it looked good so it's all back together and filled with oil. If I have to take it apart again though better now than after it's too late.

[homemade87]

Just so you know what I am talking about . Notice the straight hard line at the bottom of the pattern on both side . Your first pattern did not have that . It had a smooth pattern all the way around which is what you want . I think .002 may get it . Must have changed when you did your pre load on the bearings or there was that much difference between your old honed out bearing and the new one .

[mplex2000]

Thanks again for the information, I love to learn. Tore it back down and unfortunately my bearing splitter killed the pinion bearing. Normally I don't care since I am usually throwing away the bearing I'm pulling.

Koyo is what came in my kit and I couldn't find another at a reasonable price (was hoping using the same brand would give me a better chance that things won't change). Got a new Timken bearing and a OTC splitter as well, let's hope things go smoothly this time around.

Side note, has anybody had issues getting their C clips on and off with a posi? Mine was easy on the open diff but with those plates in there it's tough. One axle is ok, the other I have to really work to get the C clip on or off. I tested the axles on both sides, one axle is ok on both sides, the other is a pain on both sides so it seems the issue is one axle should be about 1/16" longer!

[homemade87]

I always use the big bearing I am going to install on the pinion and press it on ( one benefit is I have a press ) For reasons you have already encountered . I have never damaged a bearing doing it this way . The small bearing does not matter to hone it out . I believe I would start with removing .002 and see what happens . Also duplicate the back lash since we know it has been proven itself for a good pattern . We just need to find where you were before the other new bearing .

On the c clips , Sometimes it is close and can be a bear . If you have someone close have them push in on the alxe just enough to clear . It is usually the seals rubber part holding it out and a little pressure will make it clear . Along with a magnet and you should get it out no problem .

Let us know how it goes .

[mplex2000]

Yeah I have a press as well, just a crappy splitter. It bashed up the cage over the rollers. I got my new one and bearing a while ago, so if I have to remove it again that should not happen.

Anyway, backlash is now .007 instead of .0075. Took .002 out of the pinion shims and I think it actually is worse, but given that this is now a totally different bearing I was somewhat expecting the pattern to be out of whack. I see hard lines everywhere but now I'm doubting my ability to correctly intemperate the damn thing so I can't decide if it's perfect or if it's totally wrong. Good thing I don't do this for a living!

[homemade87]

That actually looks better . Notice how the lower hard line smoothed up . Now all edges are more smooth and uniform all around . I would run that .

[mplex2000]

Thanks for all of the help. I guess we'll close the case on that one. Even though I have a LS swap waiting to go in this one, I'm going to try to get that th350 to stop leaking so much. Probably a waste of time but it drives me nuts.