Adjusting backlash.

[2017RoushStage3]

Let me preface with saying, I have little experience in rebuilding differentials...
I have two 8.8 rear differentials with excessive backlash and would like to attempt on adjusting. From my research I have found adjusting back lash is accomplished by moving the shims from the passengerside and moving to the driverside. However some sites show i need to spread the carrier and other don't. Can't find exact directions for this rear differential with the torsen.

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[WD Pro]

PM me your email - have the rebuild instructions and I can send them to you on Monday (they are on my work pc)

WD

 

[GT-DM]

Factory shims are rarely thin enough, & located on the correct side, (pass side in your case) to just move one or two shims over to the other side, & achieve the new measured backlash clearance you desire.

I would find it extremely rare, unless someone has already been inside it, & put aftermarket shims in it, that this plan, using stop OEM shims, will work out.
Possible? Yes.
Likely? No.

You didn't mention how much backlash your measuring in it right now? If it's only a few thousands more than a factory recommended amt, or even 0.005" / 0.010" more than OEM recommended...
& the patterns on both the Drive side & Coast Side of the ring gear look good?
& the carrier itself isn't loose between the shims in it now?
Than moving the B/L a small amount could be both a waste of time, & cause more problems, than what you believe is going on now, w/to much backlash.

If you haven't measured it yet, than that task is imperative. Especially before you move forward & start buying parts, & materials to do this job. Like an aftermarket shim set.

It's very rare to see to much backlash, unless someone's been in it before you... & messed it up....
(& yeah, that is very possible) if you see aftermarket shims inside it, than you do need to be concerned before going forward.

It's usually a rather high mileage veh. Or a very poorly maintained diff, ran low on gear lube, to see this phenomenon of to much B/L from general use.

In that is the case,
(Like poor maintainence, or a bad previous setup by someone after the factory set it)
your problem now likely bigger than excessive B/L itself. Running a diff with a bad setup can cause problems in the gear pattern on 1 or both sides of the ring gear tooth. Move it now, & it could get noisy.

It takes a little detective work at times,, on your part, & some evaluation of what your working with, to know what your up against. 1 thing OEM car manufacturers do really well is rear gear setups. This goes back over half a century. As they didn't want warranty problems from people complaining about annoying noise from the rear-end. So they have always done a good job of cutting & lapping hypoid gear teeth pressure angles, & setting them up, so they don't have a bunch of warranty work to deal with after sale.

Depending on your definition of excessive is, it may be quite acceptable.
No way to say without measuring it.
If it's been ran w/excessive BL for 10s of thousands of miles like this, already...?? Tightening it up will possibly make it more annoying to the ear when ran. Just because it "feels" or "sound" like it's got a lot of B/L, may not mean that once it's measured, it infact does have to much.

When measuring, make sure your dial indicator is perpendicular to the tooth you have it on, so that your getting an accurate measurement of tooth movement. Be sure to hold the pinion side flange with the other hand. Or have someone else hold it for you. This can otherwise give you a false reading of clearance. This is a bit common for rookie setup techs.

I have rarely seen a rear end fail because it had to much backlash, as long as it's not more than about 0.025". On the contrary, they work better with more BL than factory settings. Not enough B/L is what gets a person in trouble when setting up a differential.

Our racecar program has done hundreds of rear end setups, & although some written materials say to use a case spreaders, it is unnecessary, & in many cases a bad idea in the hands if the inexperienced. You run a greater risk of damaging the diff using 1 than not using 1, if not careful.

I would not trust everything you read, like using case spreader.

What you will likely need though is a package of aftermarket shims. Factory shims are generally to thick to move the backlash the amount you would be needing to.

Measure it. If it is to much, I'd be concerned there are other issues going on, that need to be uncovered. How did it get to this point?

On the end it's your rear-end. Do what you feel is best for you.
We will listen to the numbers your measuring, & help you evaluate it if you like.

 

[Crackerjack17]

Not sure what the guy above is talking about, but if you don't use a case spreader your going to have one hell of a time getting the diff out. The Ford manual explains how to use the case spreader. You place a dial gauge on the pumpkin and only spread within a certain spec and then you can lift the diff out. It's not real complicated. I rebuilt mine, changed all the bearings and seals and put in 3:31 gears. I reused the factory shims and everything was within spec.

Also, mine only had two thick shims. One on each side. You can see them in the picture laying on the jack crosbeam.

I have all the shims that came in the Ford rebuild kit if you want them.

My simple "case spreader"

 

[Crackerjack17]

This is how I checked the backlash.

 

[2017RoushStage3]

PM me your email - have the rebuild instructions and I can send them to you on Monday (they are on my work pc)

WD

Thank you. You actually already sent me it. I will review again. Life got in the way and just haven't had the time to dig into it and also completely forgot that I have already asked this question....thanks again!

 

[2017RoushStage3]

Factory shims are rarely thin enough, & located on the correct side, (pass side in your case) to just move one or two shims over to the other side, & achieve the new measured backlash clearance you desire.

I would find it extremely rare, unless someone has already been inside it, & put aftermarket shims in it, that this plan, using stop OEM shims, will work out.
Possible? Yes.
Likely? No.

You didn't mention how much backlash your measuring in it right now? If it's only a few thousands more than a factory recommended amt, or even 0.005" / 0.010" more than OEM recommended...
& the patterns on both the Drive side & Coast Side of the ring gear look good?
& the carrier itself isn't loose between the shims in it now?
Than moving the B/L a small amount could be both a waste of time, & cause more problems, than what you believe is going on now, w/to much backlash.

If you haven't measured it yet, than that task is imperative. Especially before you move forward & start buying parts, & materials to do this job. Like an aftermarket shim set.

It's very rare to see to much backlash, unless someone's been in it before you... & messed it up....
(& yeah, that is very possible) if you see aftermarket shims inside it, than you do need to be concerned before going forward.

It's usually a rather high mileage veh. Or a very poorly maintained diff, ran low on gear lube, to see this phenomenon of to much B/L from general use.

In that is the case,
(Like poor maintainence, or a bad previous setup by someone after the factory set it)
your problem now likely bigger than excessive B/L itself. Running a diff with a bad setup can cause problems in the gear pattern on 1 or both sides of the ring gear tooth. Move it now, & it could get noisy.

It takes a little detective work at times,, on your part, & some evaluation of what your working with, to know what your up against. 1 thing OEM car manufacturers do really well is rear gear setups. This goes back over half a century. As they didn't want warranty problems from people complaining about annoying noise from the rear-end. So they have always done a good job of cutting & lapping hypoid gear teeth pressure angles, & setting them up, so they don't have a bunch of warranty work to deal with after sale.

Depending on your definition of excessive is, it may be quite acceptable.
No way to say without measuring it.
If it's been ran w/excessive BL for 10s of thousands of miles like this, already...?? Tightening it up will possibly make it more annoying to the ear when ran. Just because it "feels" or "sound" like it's got a lot of B/L, may not mean that once it's measured, it infact does have to much.

When measuring, make sure your dial indicator is perpendicular to the tooth you have it on, so that your getting an accurate measurement of tooth movement. Be sure to hold the pinion side flange with the other hand. Or have someone else hold it for you. This can otherwise give you a false reading of clearance. This is a bit common for rookie setup techs.

I have rarely seen a rear end fail because it had to much backlash, as long as it's not more than about 0.025". On the contrary, they work better with more BL than factory settings. Not enough B/L is what gets a person in trouble when setting up a differential.

Our racecar program has done hundreds of rear end setups, & although some written materials say to use a case spreaders, it is unnecessary, & in many cases a bad idea in the hands if the inexperienced. You run a greater risk of damaging the diff using 1 than not using 1, if not careful.

I would not trust everything you read, like using case spreader.

What you will likely need though is a package of aftermarket shims. Factory shims are generally to thick to move the backlash the amount you would be needing to.

Measure it. If it is to much, I'd be concerned there are other issues going on, that need to be uncovered. How did it get to this point?

On the end it's your rear-end. Do what you feel is best for you.
We will listen to the numbers your measuring, & help you evaluate it if you like.

Thank you for the detailed write up. I have yet to actually measure the backlash with a dial indicator my conclusion is based on rotating the driveshaft about 1/4 of a turn before it engages the axles. It is significant enough that causes a thunk while driving while shifting and especially noticable while coasting and then accelerating. I have driven and inspected other s550 Mustangs and none of them have this issue. Inspection of the gears doesn't show any abnormal wear patterns.

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