tahoedon

lightweight flywheel causing problems?

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I recently rebuilt my engine and converted to a getrag 245 5 speed. I used a light weight flywheel and 228 mm clutch. Immediately noticed rattling coming from the transmission when decelerating and a vibration above 3500 rpms. You can also hear a slight rattle at idle with the clutch out once the car is warmed up. The rattle goes away when the clutch pedal is pushed down. I assumed that the transmission had a bad input shaft bearing so I replaced that. It made no difference. I have been doing some research and it seems as though adding a light weight flywheel can cause oscillations at lower rpms causing the "getrag rattle" . Some people recommend adding redline 75w140NS to redline mtl for the transmission oil. Has anyone had this problem? Comments? Thanks 1968 BMW 1600

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How light is "light" ?  My "lightened" FW gives me zero problems...can't remember the weight after machining, but it's not an aluminum one, either.  

 

hmmm...

 

Ed

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Yeppers, the Getrag rattle.  Most people live with it, it's a feature, not a bug?

 

A 'lightened' flywheel by itself saves a few pounds, but at 228mm and with a stock or heavy duty cover, is going to be well over 30 lbs...

 

t

 

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I bought the flywheel from JB Racing. It is made from aluminum and weighs 8 lbs. According to their site the oem flywheel is 16.5 lbs. I also thought that the increase in rotational mass by going up to a 228mm clutch would make up for some of the lighter weight of the flywheel.

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Totally normal noise, it's the backlash between the gears (there HAS TO BE SOME) and when it is warm and the oil gets a bit thinner the rough idle (made worse by the light flywheel) causes them to rattle.  In 1982 BMW came up with a "fix" for the 320i when people complained of the rattle,  it was a new flywheel 6lbs HEAVIER!!!

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2 hours ago, Preyupy said:

Totally normal noise, it's the backlash between the gears (there HAS TO BE SOME) and when it is warm and the oil gets a bit thinner the rough idle (made worse by the light flywheel) causes them to rattle.  In 1982 BMW came up with a "fix" for the 320i when people complained of the rattle,  it was a new flywheel 6lbs HEAVIER!!!

 

Haha, I wasn't aware of that "fix"!

 

My tii (still has the original 4-speed trans) has the same JB flywheel as mentioned above, and I had no idea of this until I tore the engine down for a rebuild. I work on Porsches and BMWs for a living, with a much heavier bias towards the Porsche side. Porsche 911s have a much lighter rotating assembly than that of a BMW M10, so a lightweight flywheel in a 911 tends to make for tricky starts off the line, and gear chatter in G50 and later transaxles. With the heavier M10 rotating assembly, I can literally idle my car off the line with no issues. The throttle response is noticeably better than that of a tii with standard flywheel, so it is a worthwhile upgrade in my opinion.

 

The only problem was that most of the threaded inserts pulled out when I removed the clutch pressure plate and the threads were damaged (the JB flywheel is aluminum). I did not want to spend $500+ for a new one, so I drilled out the holes and installed "Big-Sert" oversized thread inserts and all was well!

 

And yes, a 50/50 mix of your normal gear oil and Swepco 201 or similar will help to cut down the gear chatter somewhat. My shop does this sometimes when a "modern" BMW (E36 and up) is converted from dual-mass to single-mass flywheel . . . .

 

Chris

Edited by cda951

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Are you using a solid or sprung clutch disk?

 

UUC has an article here that goes into some detail - http://www.uucmotorwerks.com/flywheel/gear_rattle.htm

 

Along with a "fix" by changing the fluid with a special mix (WARNING:  Says to use GL-5 which may not be compatible with our trans) http://www.uucmotorwerks.com/html_techtip/techtips/tranny_rattle.htm

 

FWIW, the "fix" did not help my E39 M5 with a twin disk clutch, but it might help your noise.

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Tahoedon, I've got the same problem ... the PO had a lightened flywheel installed, which was fine with the 4-speed. When I recently converted to a 5-speed, the rattles started. Did the fix" solve your transmission/clutch rattle problem, and if so, what mix of fluids did you use? R

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I got rid of a rattle by going to a stock friction disc.  The aftermarket one did not have as comprehensive spring setup as the stock one.  The bummer disc was from Clutch.net, a popular supplier and came as a package with the S14.

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11 minutes ago, jimk said:

I got rid of a rattle by going to a stock friction disc.  The aftermarket one did not have as comprehensive spring setup as the stock one.  The bummer disc was from Clutch.net, a popular supplier and came as a package with the S14.

 

 

But...

 

you may still have a screw loose!

 

HAHAHA!

 

:D

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I used 1 qt. of redline 75w140 mtl and filled the remainder (about 1/2 qt) with redline 75w80 mtl. It seems to have helped a little, but the chatter is still definitely there. I think I am just getting used to it and driving it so as to minimize the noise somewhat, like depressing the clutch earlier when I come to a stop. I'm still not sure that some of the noise isn't coming from the front layshaft bearing. It looked fine when I had it apart though. When I drive in 4th gear the noise is less which some people say indicates a bad front layshaft bearing since there is no load on the layshaft bearings in 4th gear. For right now I'm just trying to drive it as much as possible, its been sitting too long.

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Thank you TahoeDon, Ray and JimK - It looks like changing transmission fluids may not be magic-solution.

 

I continue to have embarrasing / inconsistent squeals and/or chitter noises (not really rattles) noises under a variety of engine startup, clutching, de-clutching, decelerating in gear, reversing, etc. It wakes up the neighborhood on startups and the first few miles, then subsides (but never fully disappears) over the course of the first 2~3 miles. The whole sequence starts again after simply turning off the car, and re-starting.  

 

It's a 1973 2002. I'm currently running a used OD 5-speed (made no noise when run off a high-speed drill, in any gear) with new input/output/selector seals and 4-bolt output flange, all installed c/w lubed input splines; new 323 TO bearing (Ireland/Sachs), new Ireland brass pivot pin, the original 5-speed TO bearing fork and dual-loop holder spring; new clutch master / slave cylinders and new Ireland SST clutch hose, new sealed pilot-bearing (BavAuto, with the original felt & cap re-installed); Massive Brakes tranny mounts c/w shortened cross-member / updated tranny rubber mount; a shortened driveshaft with new center-bearing all properly aligned and pre-loaded; a shortened shifter platform/fork; and using Redline MTL 75W80 oil. As noted previously, I've got a 228 mm clutch setup (which still all looked new & fresh, thus was not replaced) on a Previous Owner lightened flywheel. The tranny bottom cover plate (re-used from the original 4-speed) was originally a noise issue until I shimmed it forward with 4~5 washers.

 

I am mystified ... when I went and re-installed the 4-speed setup back in, none of the noises were there. Put the 5-speed setup back in and here we go again with the inconsistent noises. 

 

Is it possible that the PO's lightened flywheel is causing this (either due to it's reduced mass, or the possibility that with the machining, the FW surface is too far from the TO bearing letting it bounce around somehow)? Is it possible that the new TO bearing is itself bad (it rolled stiffer than the old 4-speed one)? Any other thoughts other than tranny internal bearings? Do I possibly have an engine/crankshaft end-float problem? 

 

The car goes up on stands on Halloween Day, and I'm willing to replace FW, 228 mm clutch package, and TO bearing. Thanks in advance. 

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Squeals?  Like, something is hitting something else?

 

That's odd...

 

t

 

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