Rebuilding differential

[Weber Sarge]

There are several different thickness shims available , I prefer to use a very thick one first and then a thin one to make up the tolerance . I do remember something in the manual about that 4 shim limit thing - shouldn't be a problem . You could just use some Sch80 pipe and machine it to length for a spacer...
Sarge

 

[RustyNailJustin]

Like sarge said.
Also I have been building diffs for over 20 years and had to use more than the 4 shims on a several occasions and it's not an issue.

 

[JAFO2014]

Thank you guys very much for sharing your knowledge. Feel much better. Then for sure I can set my pinion pre-load exact tonight.

 

[cruiseroutfit]

There are several different thickness shims available , I prefer to use a very thick one first and then a thin one to make up the tolerance . I do remember something in the manual about that 4 shim limit thing - shouldn't be a problem . You could just use some Sch80 pipe and machine it to length for a spacer...
Sarge

How do you address the taper difference with Sch40?



I wouldn't get hung up on more than 4 shims. A 1/4" of shims would be one thing but 5 shims is another

 

[Pin_Head]

The reason that the older FJ40 FSM says to use no more than 4 pinion preload shims is because there were only 5 sizes of pinion depth shims. After you set the pinion preload with one of 20 different preload washers, you then adjusted the pinion depth and then compensated for the pinion depth by adding the proper number of shims (0-4) depending on the thickness of the pinion depth shims. This is for the differentials that used the pinion depth shims under the outer race, which ended in '78 to '79. Sounds strange, but that is the way they did it: pinion preload first and then pinion depth. Later diffs use the pinion depth shims under the inner bearing race.

 

[Weber Sarge]

Great point , Pin head - I had forgot about the shim placement difference between early and late versions of this 9.5" diff .
We used sch.80 several times to make solid spacers for different builds - the shaft taper differences in the Toy 9.5" would not allow that - you'd have to use some really heavy-walled dom tubing and a fair amount of machine work . I had bought two sets of depth shims from one of the vendors - maybe it was Kurt? , but it was a nice selection...

Sarge

 

[JAFO2014]

I will share some various things I discovered during this process.

1. .005" feels like a lot of movement. Meaning, during setting the pre-load I had the pinion spacer in place with shims and pinion nut torqued. There was still slop. I laid the diff over so I could push and pull and then measure the movement with my dial indicator. It was only .005" movement, but it felt like a lot when I moved the pinion.

2. Removing .010" of shim got the slop out, but I had 0 inches of pre-load.

3. I then removed another .010" of shim. Too tight. So I took the solid spacer and rubbed it back on forth on a piece of emery cloth laying on a solid surface and basically took .003" off the spacer length. Put all back, with the .010" shim back in place (the first one I removed still out of the picture) and then torqued the nut down. Seemed to get about 16 inches of pre-load resistance. So a couple thousandths an inch can make a very big difference in how things fit.

4. 16 inches of pre-load doesn't feel like a lot of resistance. You can turn the pinion flange by hand fairly easy, feeling a slight resistance to begin turning. So when you are torquing the pinion nut, use caution and tighten in small amounts once the flange starts to squeeze the bearings together (flange is pushing against the top bearing which causes the pinion to pull the inner bearing into its race). A few thousandths makes a big difference regarding how tight the bearings are.

5. When setting the ring gear backlash, .008" feels like a lot of ring gear movement actually. You can definitely feel it move back and forth as it touches the pinion teeth. It is not a lot of movement, but you can feel the ring gear move.

 

[JAFO2014]

Well the diff is ready to go back in. I did some work very early this morning before heading to the office. Got the carrier caps torqued and also removed the axles so I can get the diff out this evening and do the swap.
So others won't make the same mistakes I did.
1. The 2.170" spacer I had would have worked as is (with a couple of spacers). I goofed when I torqued down the pinion flange the first time (I guess worried I was over torquing) and guess I had not pulled things together. And still had slop and thought I was firm against the spacer. Thinking the spacer was too long I turned down the spacer, then ended up adding shims making it longer than 2.170". Felt stupid, but it was a lesson.
2. Then later I over torqued things, not paying attention to how tight I was getting the bearings. The inner bearing looked fine, but I didn't feel good about the outer bearing, so bought another new one. Might not have needed to, but don't want to take any chances. So lesson here is torque things down very slowly, in stages, constantly stopping to check if the pinion flange still turns freely.
3. Not a mistake, but a note. Checking the pre-load: I used a beam type inch pound torque wrench. The inch pound reading should be while you are constantly turning the pinion flange. You will get a higher reading until the flange overcomes the force needed to start the flange moving, then the reading will settle out to a lower number as you turn the flange. Make sure to get the pinion pre-load set correct and record that number. Then when you are doing the carrier pre-load you are just making the inch pound reading while turning the pinion about 4 inch pounds higher once you are also turning the ring gear. My pre-load when all done is around 20 to 21 inch pounds turning the flange.

 

[JAFO2014]

Well just drove the first 22 miles and all seems good. Wife and I are eating lunch so the diff does the break in cool down. Fingers crossed I did this correctly.

 

[JAFO2014]

120 miles and still rolling. Been doing short 20'ish mile drives with diff cool down between. I figure the initial break in is done. Now will drive it 500 total miles, making sure to drive easy. Then pull the cover to check the diff and replace with fresh gear oil. Then drive it. Also, now that I really have the 3.70 in the rear I can see the slight difference on the highway. It really is not that much different, but.....I more easily drive 60 mph without the engine screaming. So it really is a positive change for people driving on the highway. I'm not sure someone that mostly uses their FJ40 trail driving would like the 3.70 gearing at all. For me it is fine. I have a steep hill behind the house and took the FJ40 down that dirt road over the weekend. In 4 wheel low range I can creep down the hill fine without using the brakes. The hill is pretty steep, at least 15% grade, maybe a little more at times.