TR4/4A Differential setup question

[Sarastro]

I've encountered a problem setting up my solid-axle TR4A's differential. I think I know what's going on, but I thought it best to pass it by you guys, in the hope that you might have more insight.

I clearly got the setup wrong first time I did it. This week I pulled the axle and checked the mesh with gear-marking compound, and it clearly wasn't right. The marks indicated that I should move the ring gear out of mesh, but the backlash was already at the spec maximum (0.006 inches). Anyway, by time I moved the ring gear enough to get a reasonable pattern, the backlash was 0.020 inches. That strikes me as way too much. I'm using a used ring and pinion set, so I'm prepared to go outside the specs a little, if necessary, but not that much.

My guess is that the gears are just worn. Do any of you agree, or have other ideas?

 

[Madflyer]

In a IDEAL WORLD with new gears you would have full face contact but 80 % is a good fit. and seating would be in the middle of ring face. As for lash .004 to .006 would also be ideal so placing pinion gear shim in the right order will get you into spec. I would not go under .004 and .010 max. Now depending on oil weight 90 to 140 ( this is a factor for the type of driving and weather ) Any time ring and pinion gears are moved some seating will happen IE. noise at HY speed, Look for any surface pits or color change on gears. Just changing bearings can cause a thing to change also.

 

[bobhustead]

If using a used ring and pinion, the set-up should be exactly like that in which the gears previously operated. Even if it is wrong.

Bob

 

[Sarastro]

Thanks for the responses. I could have been clearer.

This is a used gear set, which I bought to replace the original one. The original was actually rusted, so it was trash, and the bearings also were shot. I bought the used gear set, new bearings, the whole shebang.

I realized (or, at least, realize now) that it probably wouldn't be perfect, that I probably would have to settle for more backlash, and I expected some noise. But what I got was way too much of both. So, the basic question, I guess, is this: does this mean that the gears are too worn to use, or am I missing something?

 

[bobhustead]

Are the wear marks from the prior use at all visible on the gears? If you have the correct pinion depth and you can't get the lash/pinion to ring gap in spec, the gears will not be satisfactory.
Bob

 

[Sarastro]

Yes, I can see some wear marks, but they are fairly light, I think. In the past, I have seen ring gears and pinions with obvious wear, striations and such, but there is nothing like that.

 

[bobhustead]

Doesn't look too good, but hard to assess from a picture. Bottom line is you have evidence that the gears are not right.

Bob

 

[titanic]

To me, it looks like the contact is near the outside of the ring gear and the pinion should be moved deeper into mesh by putting shims under the pinion head. Then the backlash should be adjusted by moving the ring gear.
Berry

 

[bobhustead]

To me, it looks like the contact is near the outside of the ring gear and the pinion should be moved deeper into mesh by putting shims under the pinion head. Then the backlash should be adjusted by moving the ring gear.
Berry

Problem is that the gear has obviously been run a long time in one position and you can't, without engendering a racket and likely premature (and sometimes very quick) gear failure, put the old gears in a new position.

Bob

 

[Sarastro]

It's starting to sound more and more like I should just bite the proverbial bullet and get new gears. They aren't cheap, but fortunately they are available.

The upside of this experience is that it has really been an education. I don't mean that cynically; I think I've learned quite a lot, and that has real value.

 

[titanic]

Steve-Looks like the only options are new gears, take a chance on used gears, or take a chance and install your present gears after resetting to the correct contact.
Berry

 

[CJD]

Can we get a pic of the pattern? The pic above looks like it was after you wiped the grease off...or you need a bit more grease across the face to better highlight the contact patch. I doubt you need a new gear...

 

[Sarastro]

Sure. Here are the last two iterations. The first two pictures (1344.jpg and 1345.jpg) are with 14 mils of backlash. The pattern is still pretty well toward the toe. My references say that this is still too far into mesh, and that I had to move the ring gear farther from the pinion. I tried that, and got the second set of pictures. the pattern is a little more centered but still not there, the backlash is now 20 mils (!). It also seems too close to the edge of the tooth.

So, that's the problem. My info says that the ring gear should be moved even further out of mesh, but that's clearly not possible. That's why I concluded that the gears are probably worn.