Rear Pinion Slop - Now what?

[Rooster47]

I've searched for a FAQ or thread on rebuilding the rear axle and can't seem to come up with anything helpful related to rear axle rebuilds.

I've got a '76 FJ40 that I took the rear drums off, to evaluate the brakes. I noticed that one of the axle seals was leaking, so I took the rear cover off to get to the C-Clips so that I could remove the axle shafts and replace the seals. When I went to spin the drive line so that I could get the gears in the correct position I noticed some "slop" in the pinion. It is not rotational slop. If I grab the driveline I can move the pinion slightly side to side or up and down, it feels slightly loose in there. I did have a slight driveline vibration that I was going to get around to figuring out, but I think I've now stumbled onto it...

So, I don't know that much about axles and gears, where do I begin on fixing this, and how do I evaluate if damage has been done? Or should I just take the axle in to a shop and have them evaluate it?

I guess I'm asking how many 's this sounds like...

Thanks

 

[Pin_Head]

Asssuming that the nut didn't just back off, the pinion bearings have lost their preload, either due to wear on the bearings or preload shims. Replacing the bearings involves removing them and replacing them and setting the pinion preload, backlash and carrier bearing preload. If you reuse the original preload depth shim, the tooth contact pattern should be fine as the bearing dimensions are precise. This is a 3 bannana job and you will need a dial micrometer to set the backlash.

There is an illustrated tutorial in tech links.

The EZ way to fix it is just get a good used differential assembly. That is a one bannana job.

 

[Rooster47]

Thanks for the feedback Pin_Head.

So my first task is to get the driveline unbolted and see if the Pinion nut is loose? I'll try and check it out tomorrow.

If it is loose, is it possible that I can just tighten it and everything is good? Or is it more likely that if it is loose that it has damaged something?

 

[Pin_Head]

If the nut is lose, take the flange and seal off and check out the outer pinion bearing and the shim pack. If there is evidence of wear, the bearing and/or shim pack will need to be replaced. Fitting the shim pack is trial and error until you get the proper pinion preload of about 5-10 inch pounds.

If there is no evidence of wear, put the seal and flange back on and torque the new nut down to 15o ft lbs and stake the nut and you should be good if the preload check out.

 

[Rooster47]

So I got the drive shaft unbolted this evening...

And good news, the pinion nut was loose!

The bearing and race appear to be in good shape, so I'll reuse them. The shim pack was still on the pinion, I didn't slide it off to look at it, I assume it's fine if it is still there and intact?

Guess I'll get a new seal and nut put it back together.

I was reading in another thread that I should put it back together without the seal first, to check the preload? Then if it was good, I could take the nut back off and put the seal on and tighten it down?

Do I still need to set the backlash?

Thanks!

 

[Pin_Head]

Yes, it looks good. It is your lucky day. To get it back together, put the rear axle on stands, take off the wheels and then put the flange back on with the bearing and shims and tighten the new nut finger tight. Then measure the torque it takes to turn the flange. You can use an inch pound torque wrench or a fish weighing scale on one of the flange holes. Calculate the inch pounds by measuring the distance in inches from the center line of the flange to the center line of the hole. Multiply the inches times the pounds to get inch pounds.

This measurement is the base line preload of the axle without the pinion preload.

Then tighten the nut increasingly tight and measure the preload again. If you can tighten the nut to 150 ft pounds without increasing the total axle preload by more than 10 inch pounds, you are good to go. If it is more than 10, you need thicker shims. If it is less than 5 more inch pounds you need thinner shims. You can get shims at Toyota or gear shops and you can thin the shim pack by sanding the thick washer (not the washer under then nut).

Don't forget to install the seal and stake the new nut so it can't back off. Don't install the seal until you get the preload set. or you won't be able to get the shims in and out.

No need to set backlash, just the pinion preload described above.

 

[Rooster47]

Alright, sounds like I can handle this, thanks for the detailed instructions, it's really helpful!

I'll let you know how it works out

 

[Pin_Head]

It is worth fishing out the shim pack and inspecting it for wear and damage. If there are concentric rings worn into the surface of the shims from them spinning, they may be worn. You will also know the difference between the thick and thin shims. The thickness of the thick shim is used by the factory to set the preload. There can be 0-3 thin shims that the factory used to compensate for the thickness of the pinion depth shim.

 

[DanS HJ-45]

Follow up to this:

The pinon nut on the 40 apparently decided to back off last night. I discovered it because it started making terrible noises whenever the truck would coast. So, I limped it to the garage (about 20 miles) and this morning discovered the loose pinon flange caused by the nut backing off. It's got 1/4-1/2 inch of play--quite a bit.

How much damage should I be expecting in there from that, or should I just tighten the nut again, maybe with some thread locker, and restake it? I did not remove the pinon from the diff, but I did install an ARB carrier, and replaced the pinon seal and flange about 3,000 miles ago, but went wheeling yesterday and did a few miles on a pretty rough road to get there and back. I'm wondering if it got rattled loose.

Dan

 

[Pin_Head]

Torque it down and measure the preload with the wheels and drums off and the nut finger tight. Then torque the nut to 150 and measure the preload again. If it is more than 20 inch pounds more than when it is finger tight, then the pinion preload will need to be reset.

 

[DanS HJ-45]

Torque it down and measure the preload with the wheels and drums off and the nut finger tight. Then torque the nut to 150 and measure the preload again. If it is more than 20 inch pounds more than when it is finger tight, then the pinion preload will need to be reset.

Is that because you suspect damage to the pinon bearing from it working its way loose, or just as a method to tighten it (which I'm comfortable doing).

I'm just worried about what bad stuff may have happened while it was making it's racket and grinding in there. Or are you saying that I should just retorque the nut, check the gear oil for chunks of metal, and go along my way?

Dan

 

[Pin_Head]

There could be wear on the bearings and/or preload shims. Measure the preload both before and after torquing the pinion nut. If the preload increases only by about 20 inch pounds or less after torquing, then it is probably OK. If it is tight, something is worn and the preload needs to be reset.

 

[DanS HJ-45]

There could be wear on the bearings and/or preload shims. Measure the preload both before and after torquing the pinion nut. If the preload increases only by about 20 inch pounds or less after torquing, then it is probably OK. If it is tight, something is worn and the preload needs to be reset.

Cool. Thanks!

Here's hoping I do the easy/short job instead of the big job I don't feel like doing!

Dan