Manual Gearbox(s) - Rattle - Advice Please

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E9KNZ047

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Here's a puzzle - hopefully with a lateral solution. Symptoms as follows.
My 5 speed Getrag has a a real rattle ONLY when warm and at idle in neutral - if I engage the clutch completely it disappears. 3 different experienced people have advised it is the input shaft bearings that are the most likely culprit. OK
So I get the gearbox taken out for a complete bearing overhaul (another story) and had a good friend allow me to use his spare 5 speed in the interim. I pick up the car today low and behold the 'new' box has the absolute exact same symptoms and EXACTLY the same noise I have had to bear for the last few months.
I know the obvious response is that the bearings are knackered in the 'new' box also - however as we all know we get highly tuned to the idiosynchracies (spelling ?) and noises of our own cars - I am struglling to accept that the symptoms in the second box are identical in all respects. Is it more likley that there is another potential cause that we have over looked that still exists in my car outside the gearbox?
 
Depress the clutch, tranny in neutral and the noise goes away in both cases? I would look at the throw out bearing and pivot arm assembly. Possibly the slave cylinder. Something in the bell housing is not right.
 
You failed to mention that whether or not the noise was not present while your friend's 5spd gearbox was intalled and used during the interim. I am assuming that the noise was not present when your/s friend's gearbox was installed...right? No noise present with your friend's gearbox could only point to a problem with your original gearbox and rebuilt gearbox.

The obvious answer seemed to be the gearbox input shaft bearing?

I did an auto to manual swap, new balanced driveshaft, guibo and center bearing and a used (new to me) 5spd CR. A had an immediate rattle like you described. and figured a bad input shaft bearing. I then swapped out the used CR for a used (new to me) OD gearbox and had the same rattle! I took it to a transmission shop and they inspected and drove the car. They said they did not think it was the transmission.

So I pulled the rebuilt/balanced driveshaft and replaced the "new" center bearing.....cheapest way to start. Duh! The "new" center bearing was the source of the rattle! I would have bet money that the rattle source was the transmission input shaft bearing since I had heard that trans noise/rattle in a trans some years previous.
 
Thanks guys - just to clarify my previous post - when I mention 'new' gearbox I am actually referring to the loaner from my friend which is still in the car.
My own gearbox is not yet rebuilt.
Will talk to mechanic today and advise outcome.
 
They all do that... ZFs or Getrags.

It's most likely the clutch fork -- the linkage gets loose over the years and rattles against the bell housing while you sit at lights with the clutch out. Tightening up the linkage might help. Or not. Every BMW I've ever owned does it. I just live with it.
 
MichaelP said:
They all do that... ZFs or Getrags.

It's most likely the clutch fork -- the linkage gets loose over the years and rattles against the bell housing while you sit at lights with the clutch out. Tightening up the linkage might help. Or not. Every BMW I've ever owned does it. I just live with it.
Click to expand...

What Michael said. Or, "that's not a bug, that's a feature..."
 
velocewest said:
MichaelP said:
They all do that... ZFs or Getrags.

It's most likely the clutch fork -- the linkage gets loose over the years and rattles against the bell housing while you sit at lights with the clutch out. Tightening up the linkage might help. Or not. Every BMW I've ever owned does it. I just live with it.
Click to expand...
What Michael said. Or, "that's not a bug, that's a feature..."
Click to expand...

True, when they're worn!

Perhaps these are kludge-y tricks, maybe not
a) teflon cap on the clutch slave shaft head (snaps on)
b) teflon bush that snaps onto the fork pivot ball, and sits under the recessed groove in the pivot ball shoulder (thus held in place by the spring and the pressure of the fork)
c) in lieu of a) and b) some good MOS2-based assembly lube on those pivot points
d) Throwout bearing not properly lubed and/or worn.

--shrug--these things cost just a little bit of money and a little bit of time to ferret out, if that bugs (the time and money) ....don't bother, just turn up the stereo. :lol:
 
There is nothing wrong with the gearbox or the throw out fork or bearing, the problem is caused by the idle speed happening to coincide with with the natrual harmonic fequency of one of the gear sets causing that gear set to chatter when it is not under load i.e. in neutral. Sadly after spending money on having your tranny overhauled you will find that it is still the same.
The answer to your problem is to adjust the idle speed slightly (up or down shouldn't really matter) and the problem will dissapear without spending a dime.
Oh and if it isn't too late ring the transmission "specialist" (who should have been able to tell you this if he knew his stuff) and tell him you don't need the job doing after all.

Let me know how you get on.

Regards gazzol
 
Thanks all - and gazzol you may well be onto something. I read your post just now and as luck would have it last night as part of the visit to my mechanic (who has always admitted he is no transmission specialist - my mistake to give him the job) I asked him to adjust my warm idle speed as a side task - was at 400rpm (now 900rpm)and with a warm cam just a little too lumpy and low and behold the rattle alsmost completely disappears - I ask him, he scratches his head for a minute and then explains the noise reduction exactly as you had. Just prior to this he also indicated that even input shaft bearing wear to whatever degree in any gearbox ( in my case 2 boxes) would contribute to gear rattle and this is likely why the rattle was consistent even when boxes were swapped i.e. the noise is the gears not the bearings - that I can understand and accept.
Bottom line my gearbox is out , likely the bearings are probably worn anyway and 2nd gear syncro was definitely a little notchy and declining so all is not lost - a very worthwhile learning curve for me.
Extremely grateful for all advice from site members
 
Hi,

Gazzol is right. My E34 535i had the same "clatter" and so does my E90, albiet much more muted. I spoke with Getrag at one point about this and it is indeed the resonance of the input shaft and gears that causes this.

On dual-mass flywheels it can be even more pronounced (do E9's have these?). The only way I found to cure it on the E34 was to change gearboxes, which reduced the noise but didn't eliminate it. A combination of the dynamics of the dual-mass wheel and input shaft. I learned to just live with it.

Regards.
 
Interesting. I installed a much-used 5 speed OD trans and there was quite a rattle. Taking my cue from 2002 days, I replaced the trans oil with ATF for several months. Supposedly the ATF had much more "detergent" in it and being less viscous allowed better action from worn synchros, but not long-term good for bearings. Hmmm. Some months later I switched back to Castrol 80/90 GL5.

Nowadays there is no rattle, and I hardly remembered the rattle/whine when I first installed.
 
The original poster has likely fixed or abandoned his project by now; although it might be helpful if an update were provided. :wink:

I suppose there is some validity to the "resonance theory." But I am dubious if the harmonics are loud enough to annoy the passengers - unless the transmission uses straight cut gears (M22 rock crusher) or came from a vehicle with a 5th wheel. (Even the Muncie is relatively quiet at idle (if you could hear it over the exhaust and the blaring 8 track).

If I hear transmission noise at idle with the clutch engaged (pedal up) - with the noise disappearing when the clutch is disengaged (pedal depressed) - I agree with SFDon and others regarding a worn transmission. I would carefully look for metal debris attached to the magnetized drain plug or sitting at the bottom of the transmission or in the drained trans lube. I have personally experienced bearing cage failures for both the main input bearing and the forward layshaft bearing. When one fails, the metallic asteroids have a way of promoting additional wear in other area of the transmission. I am currently nursing such a patient. Changing to a heavier viscosity lube may quiet things down at the expense of additional friction and sluggish operation and is rarely a substitute for worn or missing metal.

http://www.metricmechanic.com/catalog/ultimate-transmission-part-1.php

Hope this helps someone.

00552077_z.jpg
 
MMercury said:
The original poster has likely fixed or abandoned his project by now; although it might be helpful if an update were provided. :wink:

I suppose there is some validity to the "resonance theory." But I am dubious if the harmonics are loud enough to annoy the passengers - unless the transmission uses straight cut gears (M22 rock crusher) or came from a vehicle with a 5th wheel. (Even the Muncie is relatively quiet at idle (if you could hear it over the exhaust and the blaring 8 track).

If I hear transmission noise at idle with the clutch engaged (pedal up) - with the noise disappearing when the clutch is disengaged (pedal depressed) - I agree with SFDon and others regarding a worn transmission.
Click to expand...

Hi,

My two data points suggest a somewhat opposite view. On the E34, because of a gearbox issue, a fresh factory recon unit was installed. It was so loud that other drivers at stop lights would turn their heads, wondering what the noise was. This box was therefore rejected and the next one was better but still had the characteristic noise.

My E90 was purchased brand new and has the noise (as do many other E90's). Not loud enough to annoy anyone but definitely there if you know what to listen for.

In all cases, the noise went away when the clutch pedal was pressed.

Regards.
 
Healey3000 said:
On the E34, because of a gearbox issue, a fresh factory recon unit was installed. It was so loud that other drivers at stop lights would turn their heads, wondering what the noise was. This box was therefore rejected and the next one was better but still had the characteristic noise.
Click to expand...

FWIW, plenty of transmission noise discussion:

http://www.e9coupe.com/forum/showthread.php?t=9555
http://www.e9coupe.com/forum/showthread.php?t=4716
http://www.e9coupe.com/forum/showthread.php?t=1619
http://www.e9coupe.com/forum/showthread.php?t=4734
Hard to say what is normal, any more than what is comfortable or good looking. Perceptions vary as do pain levels. As much as we would hope, very few, if any, mechanical devices are perfect and all the new cars being serviced at the dealers are probably not all there because of hypochondriacal-type customers. Enough problems, including transmission noise that competes with emergency sirens, could negatively impact reputations and values.

I am sure there are exceptions for brand new "tight" transmissions; nevertheless, odds tend to favor a noisy transmission remaining noisy, or getting noisier.
 
not sure if it is an urban legend or not but it was claimed that used car salesmen would put bananas or sawdust in the gearbox if it gave off a rattling sound so remove it temporarily :)
 
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