Re: Transmission rattle in neutral. Mechanic says normal.

[Peter du Bois <allegro1@xxxxxxxxxxxxx>]

Neil,

My '87 325is did the same thing until I stopped using Redline MTL. The
transmission also made noise under load with MTL.  The LSD made a lot of
noise during low speed turns with Redline oil . Both the LSD and
transmission are now noise free since changing to Amsoil gear oils. The
Amsoil makes the transmission very slightly stiffer to shift on cold
mornings, I can detect no difference in shifting at operating temp.

I started using Amsoil motor oil at the same time and have since
observed a fuel economy increase of about 7%.  The increase in fuel
economy is consistent with the change I observed when I changed the
conventional gear oil to Amsoil gear oil in my K100 motorcycle.

I used Redline gear oils for 4 years before giving up on them. I suppose
that I did not switch sooner because they are widely thought of as the
ultimate oil. I have concluded that they not appropriate for street use,
at least not in my car.
I have been using Amsoil oils for about a year and have yet to find any
fault with them.

Complete details of my dissatisfaction with Redline oils would not only
be too long for the digest but would also start a religious flame war,
which is not the intent of this posting.

I do not consider a rattling transmission normal or tolerable! A
significant contributing factor to a noisy transmission is engine
roughness at idle.  Is your car chipped? Both Dinan  and AutoThority
(the worst of the two ) have a rougher idle than the stock chip.

I think the stock spec. on the idle speed is 750 +/- 50 RPM. So 600 is
well out of limit.

The transmission gears are going to coast to a stop once the clutch has
been disengaged, thus no rattle.


Peter du Bois

Neil Deshpande wrote:

My 1988 325is makes a rattling sound from the transmission when it is in

neutral.  It is clearly audible at idle at 600 RPM.  Any higher and it
either goes away or is drowned out by the engine noise.

One mechanic I took it to says it is normal backlash noise.  This sounds

reasonable to me.

It never did this before, but I have cured a high idle problem only
recently by cleaning out the idle control valve and put in Redline MTL.
The MTL, being thinner(?), might not damp out the rattle as well.  Any
opinions?

The rattle occurs only when the car is in neutral.  If I disengage the
clutch (push it down) the sounds goes away completely.  Of course, it
might be happening when the car is in some other gear, but it is not as
easy to hear when the car is moving.

Neil Deshpande
88 325 is
89 325 iC

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