Pinion Preload

[sturmtyger380]

A few months back I found during an internet search a guy who was trying to set his pinion preload and the whole pinion assembly was way too tight. Now I can't find that.

Now I have the same problem on my original differential housing and NOS pinion:

I have all new bearings from a dealer and they are supposed to be correct. I have compared them and they seem to be exactly the same.

I started with the original spacer from the old bearings. I pressed the inside small pinion bearing on and added the spacer on top. I put the front bearing in. Everything has got gear oil on it. I added the threaded retaining ring to the front of the housing. I put the washer on and then the front companion flange. Then I tightened up the flange nut.

I start torquing down the flange nut and I can't even get to 130 foot pounds of torque before the flange gets almost impossible to turn by hand.

I have the full set of spacers so I went to the largest spacer and it is still way too tight to turn.

Any ideas as to what's going on?

[sturmtyger380]

I had a good phone call with Dave out in Oregon where I got my bearings. He has built many of these before.

I started by taking my calipers and measuring the size of the old parts and the new parts. I am finding that the new NOS pinion is .005 shorter and the double bearing race is .008 taller. So this combines to make the pinion bearings .013 tighter.

Dave thinks my set up is really close and that I need to take the double race out and sand it on fine sand paper to remove about a thousandth at a time and keep testing it until I get to the right preload. I will report my work and results.

[sturmtyger380]

As Dave suggested I went and found some fine sandpaper for my belt sander. So took my bronze drift and pounded the double bearing race out of the housing.

Using my old school calipers I measured the double bearing race. It measured 1.564 inches.

(Dave told me that both sides of a new double race are the same size. The reason one side has a Y marked on it was a requirement of Dodge. This was so during maintenance the bearings that had wear or modification could be put back in the same position.)

I held the non Y side of the race on the face of the sander for a few seconds and kept rotating my hold on the race to try and get an even grind. After about a minute of this I measured and came up with:

1st Grind – 1.561

I then pressed the race back in the differential housing. I took the thickest spacer that came with the set the 0.1930 and put it on top of the first small pinion bearing. I figured if I ground too much off the race I could compensate by using one of the thinner spacers. Once everything was assembled I torqued it to 120 ft lbs and the assembly was too tight to turn by hand. I did this process over and over.

2nd Grind – 1.559 - Still locks up.
3rd Grind – 1.555 – Still locks up.
4th Grind – 1.552 – Too tight but now not locking up.
5th Grind – 1.549 – Still a little tight.
6th Grind – 1.546 – Now it has the preload that I like.

So my estimate of how much the new assembly was off was - 0.013.

The total removed from one end of the double bearing race was – 0.018

So a difference of 0.005. It amazes me how close it was but still locked up.

Just for fun, the difference from the original spacer and the one I am using is - 0.004

Now on to the rest of the differential build.

[Kaegi]

thanks for posting this. good job. Dave know volumes if is the same Dave I know in southern Oregon. most likely. Gear shaped head. ;/)

[sturmtyger380]

Same Dave. He was working on a differential for a different vehicle when we chatted. His brain has gears turning inside.