Noisy transmission

[yale]

My 1970 901 limited slip trans is fairly noisy. I am somewhat aware of noise as I work with music plus I had a 1980's diesel Mercedes that every different little noise foretold of something. So i learned to pay attention to anything sounding differently. Since the trans was rebuilt before I got the car but not installed for a couple of years I assume the metal parts are not at their happiest hanging out together. Mechanics have put in red line trans fluid, then Amsoil, and now Swepco. It has been noisy woth all three. The Swepco seems the noisiest. We used the Amsoil limited slip additive with the Swepco and the Amsoil already had that so the limited slip is now silent. Other then the noise the trans works well.

Any suggestions? Or is this something I should not try to make an issue of.

[Mr9146]

My 1970 901 limited slip trans is fairly noisy. I am somewhat aware of noise as I work with music plus I had a 1980's diesel Mercedes that every different little noise foretold of something. So i learned to pay attention to anything sounding differently. Since the trans was rebuilt before I got the car but not installed for a couple of years I assume the metal parts are not at their happiest hanging out together. Mechanics have put in red line trans fluid, then Amsoil, and now Swepco. It has been noisy woth all three. The Swepco seems the noisiest. We used the Amsoil limited slip additive with the Swepco and the Amsoil already had that so the limited slip is now silent. Other then the noise the trans works well.

Any suggestions? Or is this something I should not try to make an issue of.

Steel synchromesh transmissions are old dinosaurs and should be kept lubricated with old dinosaurs. Switch to a proper 80/90 GL5 from your favorite manufacturer and that should help.

[M_deJong]

Describe the noise you are hearing.

[sithot]

Marco; I sure as heck don't want to pull the pin on a gear oil grenade thread!!!

There have been too many discussions about GL5's compatiblilty with the old "stuff" (brass/bronze). I know BMW guys that are using "Morris Lubricants" (me too) in our dinosaurs because they actually make a GL4 gear oil. They also make a very low detergent engine oil for these bikes that don't have a "true" filtration system. The "traps" or "slingers" rotate and the oil is dripped into them from the mighty (NOT) oil pump. Since they are roller bearing engines they don't require a ton of oil so this works pretty well. Under normal circumstances you pull the engine down about 25-30K and clean the slingers although I know for a fact that a gentleman put 100,000 miles on an R68 without touching the bottom end. He used Harley Davidson oil!

Just curious, that's all.

Best,

Tom

[911quest]

The only good thing about swepco products is its easy to figure out whats leaking.... now onto the noise does it do it during accleration, deceleration or certain gear selections? Dont throw out the idea of faulty rear wheel bearings will the noise go away on turns?

[chris_seven]

I agree with Mike that some description of the noise would help.

Plate type LSDs generally only make a noise when there is stick/slip between the plates and this normally occurs at low speed and on tight curves where there is maximum speed difference across the diff.

Friction Modifers are a concern as I have always believed that they may have an adverse effect on the synchromesh making gear shifts slower.

I agree about oils but there are some simple basics that could help.

Porsche recommended GL4 oils for the 901 and the 915 up to around 79/79 when they changed to GL5.

I am not sure that GL4 or GL5 ratings have much to do with lubricity - I think that it is more concerned with pressure rating and temperatures but would like to know more.

I am sure that early GL5 oils did attack yellow metals but I don't think this is any longer the case.

The G50 for example uses yellow metal synchroniser parts and GL5 is recommended.



I agree with comments about Swepco and have used Redline products for the last few years.

[yale]

Damn, I thought Swepco was a religion in the vintage Porsche world. Anyway, as to what the noise sounds like. It is not a limited slip noise, as I have said that was eradicated by the Amsoil limited slip additive. It is a meshing of metal sound on acceleration, much worse at lower revs then higher but I have heard that some of that is normal for low rev situations and it's possible that at high rev's the engine is louder and covers up the sound of the transmission. At any rate it is only upon the acceleration. If you want a meshing of metal descriptor that will be difficult. It is a mid level (not high pitched) whine I guess.

[304065]

Yale,

Who rebuilt the gearbox? Why did it sit for two years? Why was it rebuilt? How many miles/hours since this happened?

So you have noise on acceleration but not on coast. Sounds like improper meshing of ring and pinion, right? Hence the question about who did the work. If you said it was Gary Fairbanks, that's one answer-- but if the answer is "unknown" then that raises the eyebrows.

It is a one day job to drop the engine, de-mate motor and gearbox, pop the nose cone, pull the gear stack and have a look inside. A gasket set and some fluid gets you back. One long, intensely focused day, with all the little things like seals, etc., on hand to change while the engine is out. Not for the faint of heart however.

If you REALLY want to go to town, perhaps we should organize a visit from Dr. Evil, who puts on trans rebuild school. I had Peter Dawe do mine, but I have a spare box that could use it.

[frankmar]

I thougth it was normal for the LSD to sound a bit at low speed and a tight corner.

[yale]

Speaking to 304065 - Looking through my notes I don't have names for the engine and trans rebuild from Curt. Perhaps "master shop foreman from rusnak"?