Noticeable 'thump' sound when shifting..

[Ski]

I have had my ride for a year and a half now, '94 325is w/ 61k 5 speed..this has always been my question and I still don't have an exact answer yet..

When I shift into 1st gear ONLY, from a nuetral position like say at a red light, I sometimes get a thump sound coming from the ass end..it hasn't gotten any worse, or better, but every once in a while, i get it..not any other gears, only shifting INTO 1st..

I have had a mechanic look at the 'flex' or guibo disc and it is not cracked..
I have heard that someone put 'redline' tranny fluid in and then it stopped..
I have also heard that this is completely normal and it was only happening in '94 model year..

Thanks in advance!! B)

[fatty]

i used to work with landrovers, and it was a common thing on them..... from memory i think on them it was the syncro rings. i may be wrong!

[GreenDragon]

Also happens in my '98 328is.

Ski - have you shifted into 2nd from neutral, like at a light? I did that today and heard the thump. I haven't tried 3rd and up.

[Ski]

Originally posted by GreenDragon@Aug 6 2003, 10:37 PM
Also happens in my '98 328is.

Ski - have you shifted into 2nd from neutral, like at a light? I did that today and heard the thump. I haven't tried 3rd and up.

No.. when that happens I've been told the flex disc is going..


Edit: what the hell are you shifting into 2nd for??

[EXtech]

Ski, try this: at a light (in neutral), try going to second and from second to first in on motion (without letting off the clutch). This sounds like a synchro issue. I think this might have been what GreenDragon was suggesting. You can try a little heavier weight oil in the trans, might help, might not. The shifting thing I mentioned above can also be done in any other gear ( ie. third to first or fourth to first. sometimes reverse even works). This just slows down the synchros in the tranny allowing them to mesh with ease.

[Ski]

So if I do this EXtech, shifting into 2nd at the light, and noise..or no noise??
What's the scoop..

[EXtech]

usually if there is a synchro issue in the tranny you can shift into second on your way to first (fourth is a good one too since it's down then up to first). If it works, it should eliminate the noise. I'm guessing there may be a little resistance when shifting into first (when the noise happens)? sometimes this is the case. anyway, the thump should not be there if it works. Did that answer your question?

[Ski]

Forgive my ignorance but how is that going to solve my problem??

[GreenDragon]

Originally posted by Ski@Aug 6 2003, 11:43 PM
No.. when that happens I've been told the flex disc is going..


Edit: what the hell are you shifting into 2nd for??

Just messing around, waiting for the light to change.

EXTech - I'm gonna try that tomorrow, see what's what.

[EXtech]

you said

When I shift into 1st gear ONLY, from a nuetral position like say at a red light, I sometimes get a thump sound coming from the ass end

you have two choices:
1) do what I instructed and possibly not hear the noise -or-
2) don't and still hear the noise

Just make a habbit of it. Every time you're at a light, go from neutral to second to first in one continuous motion and you shouldn't feel or hear the thump again. It might work and might not. Usually it does.
This is probably the way it happens:
You pull up to the light, push in the clutch, move into neutral. Then you let off the clutch to give your foot a rest and wait for the light. Then, as the light turns green you mash the clutch, stab it in first and hear the thump. correct?
What happens there is when you let off the clutch at the light to give your foot a rest. Now the clutch is engaged and spinning the input shaft of the trans. Then when you make the move to put it in first, you press the clutch and put the shifter into first position. When you press the clutch in, the input shaft is still spinning from momentum. Now you've got to somehow get the first gear to match the speed of the input shaft. This is the job of the synchro. First gear is the first to do this because of the difference in number of teeth (it's a lower gear). The synchro works the first gear in to mate with the input shaft to then transfer power to the output shaft. What's happening in your situation is the first gear and synchro are not transitioning smoothly and that thump is the sudden engagement and subsequent loading of the driveline instantaneously. If you use another gear to slow and stop the input shaft from spinning, then first will fall right in... usually. Does this explain enough? It's not going to solve or fix your problem, it's just going to keep it from happening. Make sense?

[Ski]

Yes that makes sense to me..I take it that since it hasn't gotten any better or worse then I'm not going to worry about too much..just live w/ it..but that is very good info EXtech, thanks!!

[Furious]

from what ive heard from actuall bmw designers is that bmw purposly left play in the whole drivetrain, especially in the differential. the thump is suppose to be there. ive also heard from reading bimmer magazines that, the E46 M3 has the worst thump and almost sounds like something is gonna drop out, this was during a test drive a few years back. forgive me if im not hitting the proper problem, i only quickly read the thread.

[lwebb12]

My altima does the same thing Ski.

[EXtech]

:wink anytime!

[civilizd]

my 96 328 does the same thing. but i get a thump in 1st and 2nd.