Hey ya’ll,

I was hoping to get some input on my contact pattern for my new 4.11 ring and pinion. It’s a new Tom’s US Gear ring and pinion that’s replacing my stock 3.55 after a T56 swap. I’m currently at 0.021” on the pinion shim with 0.007” backlash. How’s it look? Thanks in advance.

 

If it were mine, I’d be bolting on the cover and grabbing a cold one.

 

Thanks for the input, there were definitely some cold ones involved in the many trials before getting to this. I still have the mock up bearings on the pinion so hopefully there’s not too much change when the actual ones get pressed on.

 

Looks like a nice, wide pattern that does not get down into the root of the gear teeth. It shouldn't 'sing' to you.

 

I hope not! Thanks, now I am just waiting on a drain plug to get delivered before final assembly.

 

Pattern appears to be equal between the root and crown, center to slight toe. If you thin the paste with gear oil and apply more drag the pattern will sharpen up. 021 is low for a US gear set but I have used them in the past. typically 24-26 is where they dial in with 5-7 lash, the lash will open up a little once broken in. remember to follow proper break in on heat cycling.

 

Thanks for weighing in Gary. I thought .021 seemed a little low with the stock shim (for stock 3.55’s) being .026 but I wasn’t getting a good read from the paste but I wasn’t as thinned down with it as I am now. How much do you usually thin it down I’m probably at a 1:3 paste to oil ratio? It’s still mocked up so I can play with it some more. Here’s what I had at .026 with .005 BL

 

Here is with .024 pinion shim and .005 BL. Looks a little better on both coast and drive side to me. I thinned the compound even more and made a tool to add more drag but can’t seem to get it any better.

 

Looks like .021 to .023 would work well. Gary is the expert on what pattern position (drive and coast) would be best for you. I would opt for .022 from the pics you have shown.

 

Your 024 pictures do show low, the pattern is longer in the root so you have been on top of it. If you are using the common kit shims then they come in 002 increments, which you may start to see a change with. Pattern setup is different with every housing due to machining dimensions, posi case, and the gear set. US Gear has been pretty consistent right up till they stopped making gears recently. I have not had to use a thinner shim then 024 in a long time but that doesn't rule it out, your pattern indicates it. Did you go to 018-019 to compare? the pattern should then be too long at the crown or top of the tooth. You pretty much have it under control and know how tedious the process is. I sometimes will grind shims 001 to get the dial in where I want but you need a surface grinder for that.

If 021 is the best pattern then that's it. The mesh should be smooth, no clunking. I made a spin tool out of an axle so I can rotate the gears and listen to the mesh. I also radius the edge of the teeth on both the R&P.

Keep in mind that paragraph in the setup sheet relating to noise. It is there because they must be aware of the machining process now used has a higher chance of a gear whine. Usually it will show up about 50 mph letting off the gas and will be heard in the car but it should not be a loud whine. Even thought the gears are lapped that has been the case for a few years now, where as 8+ years ago it never was.

I would have blended the posi case to remove those sharp edges as well but rebuilders don't take the time to do that these days. As you may know I also don't use the spring pack.

Here is a case I just finished polishing, again your choice but this helps stops cracks from forming and all Eaton cases can crack, some more then others. You never know it either.

 

A thing of beauty!!!

 

Thanks guys, for some reason the responses didn’t show up the last few times I logged on. Anyways here is with a .019” pinion shim and .006” BL. Also referring to case machining I think I may have gotten the end of the day after a liquid lunch guy on mine in ‘78 based on the LF side cap. Would you use this or go with a steel one and fit it? Also I was trying to do this gear swap on a “budget” since I had it rebuilt a few years back and have probably less than 1k miles on it since. It’s all Timken bearings with the koyo (non caged) side bearings. The end play was also .004” on each axle after the posi was done so I didn’t want to tear it apart to polish it unless you think it would be a good idea while I’m in there? I don’t need it back together for a few months as I’m in MI so saving up and doing it right one time is cool with me. I’m using the grizzly shim kits for both pinion and carrier.

 

And a sanity check with the .021 again. THANK YOU for all of the help with this!

 

19 showing high so the 21 is good.

The caps are fit both factory and steel caps. I doubt you will break out on that cap so if it has 001" rock it is good. A steel cap has to be machine fit as well and really is only for launching and only needed on the LH side, not the RH side as some say. To correctly fit a cap you will need a surface grinder and mill to do it right. The caps come all over the place, every housing is different so each one has to be fit.

Polishing the case is done to prevent cracks from forming and involves more then just cleaning up the windows as some do and call it polished. Is it worth while for you to do it? that is up to you. How many common rebuild diff's are polished by rebuilders? none. Would I use one like that, no. Your picture shows the cross shaft bolt. Remove it and lay it outside the case to see how much of it extends into the case, not much. I machine the pads for better engagement, again do you need to do that? Do rebuilders do that? no. If this was rebuilt 1000 miles ago and you have 004 endplay the posi has been worked on but what type of clutches used? 004 is too tight, should be 005-007 maybe 010 max but I stick with 5-7.

If you're not in a rush and want to do it better then what you got 1000 miles ago, give it a shot, Use ARP RG bolts and clean it up.

I just setup a set of 355 US Gear here is the final pattern, mesh is very quiet.

 

Excellent work. Thanks again for all of your help with this. I read through almost all of your post regarding diff builds and replies to other post so I did follow most of your cheap upgrades like the ARP bolts and knocking the edge off of them, socket head bolts, stoning the gear and posi mating surfaces and I measured ~.0015” rock on the left and about ~2 on the left. I checked the cross pin bolt already and like you said it has a little but not much. I think you talked me into polishing the case just to check the previous work anyways and to see what’s in there. I have access to a Bridgeport up at my grandparents so I might take the pin screw pad down a little further like I saw in one of your posts. As far as cleaning up the posi would you take down the excess material I have around the windows down to flush before polishing just to rid a possible stress riser there? Also if I decide to redo the posi clutches and tune it where is the best source to get new clutches and shims, Tom’s?

 

002 rock is too much. That will be 001 parallel. The larger the cap the more clamp load on the race and too much will burn it up, too little and they will spin. 001 rock is perfect. The shim kits come in 005 increments, Toms or any Eaton dealer will have the clutch kit which come with shims. If the diff was rebuilt were new clutches installed? If so they will still be good. Who did the work?

 

Ok thanks. I should be able to dial that in and get them to .001”. I had Van Steel do the previous work and new clutches were supposed to be included with the build. I wasn’t sure if I would be able to tune it with used clutches or with that few miles and never really hammering on it (hammered once and trans grenaded) would the amount worn from them be negligible and still be fine as long as I put them all back in the same order I removed?

 

If they were new, then they should be good. They should be solids not snowflakes or fiber. I wouldn't use either but you won't know until you take it apart. Be sure to witness mark the spider orientation so they go back in the same. Mic the clutches they should be 069. Now if you blew up the stock trans you may need to address other areas depending on power level. Power and abuse will find the weak links every time.

 

Thanks for the .069 spec. As far as indexing, just make sure they are on the same end of the cross shaft with the same thrust washer or is there more that that to keep in mind? I’d estimate I’m only around 375 hp and maybe slightly more torque on a good day. Pretty sure using the “race” spring in the TH350 shift kit is what did the sprag in.