diff/gearbox/??? backlash

Hi E30 gurus,
I've got a question about diagnosing drivetrain backlash please. How do I check whether it's a loose diff or gearbox or CVs anything else?

My symptoms are a "clang" kind of sound from the rear end after letting the clutch out on 1-2 and 2-3 shifts. (not a very loud noise though, I only hear it cos I'm becoming an automotive hypochondriac...). And I think it is harder than it should be to achieve a smooth shift.

Also I have a steep driveway so I'm engine braking in 1st gear to get down it. When I put the clutch in near the bottom (to stop before merging into the road), there is a shunting feeling and a noise similar to loose linkages being moved.

Thanks.

Before delving into the differential, I would check my transmission mounts and the guibo. Check the driveshaft joints as well.

alan

Check all the above and the differential backlash. The transmission is probably the least backlash in the whole drive train.

Bob in Lake Havasu

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nomis3613
Hi E30 gurus,
I've got a question about diagnosing drivetrain backlash please. How do I check whether it's a loose diff or gearbox or CVs anything else?

My symptoms are a "clang" kind of sound from the rear end after letting the clutch out on 1-2 and 2-3 shifts. (not a very loud noise though, I only hear it cos I'm becoming an automotive hypochondriac...). And I think it is harder than it should be to achieve a smooth shift.

Also I have a steep driveway so I'm engine braking in 1st gear to get down it. When I put the clutch in near the bottom (to stop before merging into the road), there is a shunting feeling and a noise similar to loose linkages being moved.

Thanks.

Engine braking and then a clunk when giving it gas in 1st and 2nd was the axle U joint for me. At the point when the U joint is clinking, a visual inspection reveals very warn metal. As others stated, also check the transmission mounts.

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1989 - E30 - M20 - Manual. Approximately 270,000 miles
2000 - E46 - M52TUB28 - Manual. Approximately 110,000 miles

Thanks everyone for the suggestions. The universal joint thing may also explain my previous 105km/h vibration problem, so I'll start by checking that. I've read the Bentley procedure, but I don't know what a worn out uni-joint looks/feels like. So if you've got any tips, please share!

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nomis3613
Thanks everyone for the suggestions. The universal joint thing may also explain my previous 105km/h vibration problem, so I'll start by checking that. I've read the Bentley procedure, but I don't know what a worn out uni-joint looks/feels like. So if you've got any tips, please share!

A good way to do this is to roll the two rear wheels up on two 2x10s and center the wheels on the planks, this allows you to get under the car. Have a friend rock the car front to back with it in second gear, while you are under the car and put your hand directly on the U joints, it's usually the rear one that goes first but check all of them. If it's the loose part of the equation, you'll feel it right in your hands, just looking does not really tell you much, if anything; you've got to feel it.

Cheers, Rick

Well, here is what my destroyed U-Joint looked like. Another angle will a little less play.

I do remember that it was important to grab the shaft with both hands () and try and twist it. The drive shaft is heavy, and the metal can wedge itself into a stuck position.
Likely, the damage is being done when the car is accelerating, and this is the way it will get stuck. Try and make the last maneuver you do before checking it out a reverse.

Also, by the time my drive shaft was this bad I was getting a very high frequency vibration at highway speeds. The kind of frequency that blurred the mirrors. As you can see from my video, when the shaft was cockeyed, it would have been pretty out of balance. Also, and potentially because of, my center bearing was SHOT by the time I replaced my drive shaft.

Good luck!

-----------------------------------------------------------------------------------
1989 - E30 - M20 - Manual. Approximately 270,000 miles
2000 - E46 - M52TUB28 - Manual. Approximately 110,000 miles

Quote
Earendil
Well, here is what my destroyed U-Joint looked like. Another angle will a little less play.

I do remember that it was important to grab the shaft with both hands () and try and twist it. The drive shaft is heavy, and the metal can wedge itself into a stuck position.
Likely, the damage is being done when the car is accelerating, and this is the way it will get stuck. Try and make the last maneuver you do before checking it out a reverse.

Also, by the time my drive shaft was this bad I was getting a very high frequency vibration at highway speeds. The kind of frequency that blurred the mirrors. As you can see from my video, when the shaft was cockeyed, it would have been pretty out of balance. Also, and potentially because of, my center bearing was SHOT by the time I replaced my drive shaft.

Good luck!

This is preciously why I tell everybody to check U joints under a load; when you're rocking the car back and forth in gear you Will feel all the play.

Thanks everyone! Your help means I won't be making all of the above mistakes...



Edited 1 time(s). Last edit at 03/17/2011 04:08AM by nomis3613.

Finally, I checked it out.

Rotating the driveshaft at the input flange to the diff gave about 5 degrees of play and then a clunk from within the diff once the slack was taken up. Diff backlash yeah? So I'd better start saving up for a new diff? (mmmm...LSD...).

Just wondering about the tests you mentioned, to test the rear uni properly, did you have to remove any stuff? It seems that the rear crossmember is in the way to be able to grab the shaft properly?

Thanks for all the help,
Simon