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I noticed that my car has what it seems to be significant differential play. I have a 1993 Acura Integra with automatic transmission. What I mean by play is simple: say I jack up only one front wheel and leave the other one on the ground. Then I can turn the wheel that is in the air probably close to 20 degrees without significant resistance. There is no noticeable backlash between the wheel and the axle and also no bearing noise. I can also replicate this by going under the car and turning the axle by hand, with identical results. I am guessing this backlash is coming from the differential, but I really don't know enough about the inside of automatic transmissions to be confident.

My question is twofold: what amount of backlash is normal in an automatic transmission/differential and at what point should I get worried? Second, what are the most likely reasons for too much backlash and are there any (relatively) easy things to try and fix it before opening the transmission up for an overhaul?

I should mention that all the above applies when the transmission is in park. The other symptoms that might be related and make me worry that this is excessive play are a slight clunk when changing into drive/reverse and also a slight readjustment (sliding forward or backward) after putting the car in park, shutting the engine and releasing the brakes.

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Am I correct assuming you're talking about the situation where the transmission is in park? –  R.. Oct 28 '13 at 2:02
    
@R.. yes, definitely talking about when the transmission is in park. A similar thing is noticeable in neutral, but I didn't test is extensively. –  vlsd Oct 29 '13 at 16:18
    
In neutral there should be unlimited motion. –  R.. Oct 29 '13 at 16:45
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In neutral, with an open differential, you should be able to turn one wheel as much as you like without the other wheel turning. This is a natural side-effect of the diff working - it has to allow the two wheels to turn at different speeds. In park however, the gearbox output shaft should be locked, so the movement should be limited to the amount of play available in the diff, plus the amount of play allowed by the parking pawl in the 'box. –  Nick C Nov 4 '13 at 10:01
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They will, if both are free to turn - but if one is still on the ground, it can't, so the propshaft will turn correspondingly slower (though you won't be able to see that with a FWD gearbox). The easiest way to check the play would be to compare it with another Integra, unless book figures are available online. Perhaps an owners club or racing team might have access to such figures? –  Nick C Nov 4 '13 at 16:56
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1 Answer

up vote 5 down vote accepted
+50

What you are describing is a normal condition. The drive axle is connected to the Drive Pinion Gear which is meshed with both Differential pinion gears. As you turn the wheel both of the differential pinion gears rotate around the other drive pinion gear since it's being held by the other wheel on the ground. This turns the Carrier which is attached to the ring gear (AKA Final Drive Gear), which turns the pinion gear attached to the countershaft that's attached to the parking gear that is being stopped by the parking pawl.

What you are seeing is a accumulation of all of the play within all of those parts. You can check the backlash of the differential but it requires disassembly of the transmission. Again what you have is a normal condition.

If you are having symptoms like a clunk when shifting into drive or reverse there may be an issue to troubleshoot.

I have added an image to illustrate the play in the parking pawl alone.

enter image description here

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I understand that backlash in any mechanism is unavoidable but in this particular situation it seems excessive. There indeed is a slight clunk when shifting into drive and reverse and also the car sometimes re-adjusts after setting it into park and releasing the brakes. –  vlsd Nov 4 '13 at 17:18
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@vlsd again that's normal even 40 - 50 degrees would be normal. There is at least 1/4 inch or more of play in just the parking pawl and parking gear alone. Take any car in park with out the brake on and you can rock the car back and forth. There is no way to check it or narrow it down without transmission disassembly. The first place to check for you clunk would be the transmission and engine mounts, it's also possible for it to be internal to the transmission, or to the drive axles. –  Larry Nov 4 '13 at 17:47
    
ok so I can rule out both mounts and axles (both recently replaced). This really points inside the transmission, correct? –  vlsd Nov 4 '13 at 20:26
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@vlsd Yes, but again only for the clunk, and it would have to be significant for me to tear down a transmission over it. –  Larry Nov 4 '13 at 21:30
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