Adjusted Rear Diff Backlash, some hints

[jeff97vr4]

I just got through adjusting the backlash of the ring and pinion of the rear diff. I’ve set up rear diff’s before so this wasn’t new ground for me. There are some tricks I’d like to share in case anybody wants to do this. This isn’t meant to be a primer on setting up a rear end. I won’t repeat the information in the factory service manual and I will be using the same nomenclature for parts that the manual uses. The only specialty tools needed are a dial indicator and a magnetic stand to attach to the carrier so backlash can be measured. You will also need two oil seals for the drive shafts and two quarts of gear oil to refill the rear carrier.

The job can be done with the differential carrier still in the car. It is easiest if the exhaust is removed. I was going to remove just the rear section of the Borla but couldn’t get it separated. I thought it was back far enough but it was still in the way. If here was just one thing to do, it wouldn’t have been worth the time to remove it, but you will be spending time adjusting and measuring and the exhaust pipes got in the way. The drive shafts were easy to remove, though if you live in the rust belt the bolts at the companion flange may require some soaking in PB Blaster or like rust fluid. I didn’t remove the main drive shaft, I probably should have, it would have been easier to rotate the pinion gear but then there wouldn’t be as much drag for measuring the backlash.

Drain the gear oil before you start to minimize the mess, unless you like be coated in smelly gear oil. The carrier needs to be supported by a jack when the rear support bracket is removed. The carrier will rotated about the front support brackets. There will probably be some gear oil draining when you remove the diff cover, so have some paper towels or rags handy.

Since you have already checked the backlash, BL, at the companion flange and determined that there is excessive BL, page 27-14 in the manual, you did do this rather than assuming the total driveline free play is at the rear diff, you can remove the oil seals. The snap rigs can be easily removed with a sharp pick. Measure the BL at 4 or more points around the drive gear and write the values down unless you have a great memory. Make sure the dial indicator shaft is tangential to the ring gear and isn’t binding on the next tooth.

Since you are adjusting because there is too much BL, you will need to loosen the right side, passenger side. I found that 1//4”-28 X 1.25” grade 5 or better machine bolts work as pins in the holes of the side bearing nut. They can be tapped in and the nut is turned with a long screwdriver. Position them as needed. The nut is tightened against the bearing for preload so be prepared for some initial resistance. Loosen the nut and then tighten by hand to zero preload. You may want to mark the position with marker for reference. Loosen the nut a small amount, about one hole diameter and tighten the left side. There will be some resistance because you are moving the case in the bearing bores. Check to see that the case moved by seeing if the right side nut is now tight. This is something you will have to do a few times to develop a good feel. Measure the BL and readjust until you have the desired BL. Be patient because you could ruin the rear gears if they aren’t adjusted properly.

After you have the desired BL, you are ready to set the bearing preload. Bearing preload is important for the proper functioning of the diff. Both nuts needs to be tightened 1/2 of the distance between 2 holes. Check to see if the snap ring can be inserted in one of the two positions. If it can’t, tighten the nut just enough so that it can be installed. THIS IS IMPORTANT, check the BL one more time to be sure it hasn’t changed. If it is the same as the last measurement, you’re done. If not, remove the snap rings and keep adjusting.

Installing the oil seals is easier if a thin coating of grease is smeared on the outer seal wall, oil didn’t work as well.

The BL on my diff was about 0.010” and that was about 0.25” at the companion flange. I set the BL at 0.004” and that was about 0.075” at the flange. The driveline does feel tighter now and I think the improvement was worth the effort. With a new DXD-F clutch and UR lightweight flywheel, the extra play was more noticeable.

If there are any questions I will try to answer them. Please read the manual, there is good information on much of the work.

Jeff

[surgeon83]

Thanks for posting this. I've been wondering about that for a while; it sounds like something I would completely mess up, so how long would it take for a professional to do, to give me some idea of what I'm going to have to pay to have it done? Thanks again.

[Multiades]

Thanks Jeff! I have been meaning to try this for quite a while, as I feel it is one of the more prevalent problems with our cars. Drivetrain backlash pisses me off A LOT, and I hate hearing that thunk out of the rear when I take up the slack quickly.

I need to get a magnetic arm dial indicator and set aside some time to take care of this issue. I bet your writeup will help.

-Chris

[jeff97vr4]

I probably spent about 5 hours doing this. I tend to work slow, this is a hobby and supposed to be fun . If I was more familar with the actual adjustment and didn't spend the time to clean the undercoat of the cover, it would have been about a 2-3 hour job. I would rather take my time with a rear end set-up because it is so critical.

Jeff

[jeff97vr4]

Quick updatre now that I've driven the car for a while under various conditions. This was definitely worth the effort. The "driveline" feels much tighter during all driving conditions.

Jeff

[surgeon83]

Glad to hear it helped you. Thanks for all of the info!

[AdamVR4]

Wow. *subscribe* I'll definately read over this when I get to my house.

That thunk can fuck itself...

[kcaz007]

I wish I knew how to do this... think someone w/okay mechanical inclination can do this? I would looooooooove to get rid of the clunk!!!! I even have a CFDS, it sure helped a LOT but this would complete it.

[jeff97vr4]

Originally Posted by kcaz007

I wish I knew how to do this... think someone w/okay mechanical inclination can do this? I would looooooooove to get rid of the clunk!!!! I even have a CFDS, it sure helped a LOT but this would complete it.

If you have the manual and know how or can learn to use a dial indicator, you should be able to do this. Be patient and don't rush. When you think you have it right, measure it one more time. Make sure you set the preload correctly.

Jeff

[xteekayx]

shit... i wanna do this on my car but never worked on a rear diff before... and don't really know what u talking about there with those bolts and nuts... some pics would help if u have any