Ford 8.8" rear end slop - Hot Rod Forum : Hotrodders Bulletin Board
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Old 07-15-2012, 01:07 PM
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Ford 8.8" rear end slop

I used the search engine but wasn't able to come up with much. Here is a video.

IMG 2572 - YouTube

We are measuring about 5/16" in slop between the flange and the wheels. IOW with the brake on and the car in neutral the flange spins approx. that amount. With the brake also on but with the car in 1st there is only about 1/32" of play. Opinions please. Is this normal?

Ford 8.8" out of a 2006 mustang.

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Old 07-15-2012, 01:25 PM
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There is going to be some free play in the pinion because of backlash settings. Different gear ratios will have different amounts. A 4.56 gear will have more than a 2.73 gear because of the difference in the size of the pinion gear. You are also feeling the slop between the axle and pinion gears and the splines in the axles and axle gears. What you are feeling here is a stack up of several things in the rear end that have some clearance in them. If you were to remove the cover and hold the ring gear completely still you would feel less slop because you would only be feeling the clearance between the pinion gear and the ring gear. If you were to hold the pinion gear completely still and set up a dial indicator on the ring gear you could accruately measure the backlash between these 2 gears. It should be between .008 and .010 inch on a used gear.


While you were turning the drive shaft did you check for any up and down or in and out movement in the pinion? If you have any movement in the pinion other than rotation then you have a pinion bearing problem or you have a loose pinion nut.
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Old 07-15-2012, 01:40 PM
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Current gearset is a 4.10.

I don't have any howling or whining coming out of the rear end. I do get clunking going up into my driveway. It's much worse when out of gear. We did check for wobble and fore/back at the flange and were unable to detect any. The driveshaft was in during these tests. Not sure if that matters.

I am trying to get an idea if the amount of slop I'm seeing here is acceptable or if the cover has to come off for inspection. If it does I will have to take it to someone who knows what they are doing.
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Old 07-15-2012, 01:46 PM
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There is no way to tell by turning the pinion. The only way to accurately measure backlash is by setting up a dial indicator like the one in the picture that I posted. When you check backlash you MUST hold the pinion COMPLETELY still. If the pinion moves the slightest bit then your measurement will be wrong.
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Old 07-15-2012, 01:55 PM
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I appreciate the response. But it does leave me wondering what, if anything, I ought to do next.

This amount of slop is ambiguous if I am understanding you correctly. If that is the case then I'm not sure it's worth cracking the cover if everything else seems normal minus the clunking I hear going into my driveway.
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Old 07-15-2012, 04:41 PM
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Were the gears installed by someone who knows how to set up gears? If the job was done right then there is probably nothing to worry about. If they were installed by someone who doesn't know how to set the pinion depth, bearing preload and backlash then you need to check it out.
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Old 07-15-2012, 06:02 PM
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The shop that did the gear install is experienced. Nobody is beyond making a mistake but if I was their mistake let's just say that was some pretty crap luck.

A friend of mine has a 8.8 with a 3.27 gearset and his has a lot less play in it than mine. Same test conditions with brake set and in neutral. Some or all of the difference could be due to my 4.10. I just don't have the experience to know.

I have had at least one person on another forum tell me his is just like mine. And seen posts from people who said up to 14 degrees of slop at the flange is fine. I just keep reading conflicting stuff. Makes it hard for a newb to decide on a course of action.

I appreciate the responses here. Guess I'll have to think this over a bit. Would be nice if I had another car to compare that had the same rear end and gearset to get an apples-apples.
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