On Sat, 18 Dec 2004 14:59:10 +0000 (UTC), Jonathan Grobe
> wrote:

>On 2004-12-17, frank-in-toronto > wrote:
>> On Fri, 17 Dec 2004 00:24:02 +0000 (UTC), Jonathan Grobe
> wrote:
>>
>>>The transmission seems to slip when going in reverse in
>>>my 1980 Chevrolet Caprice (OK going forward). Transmission
>>>fluid is OK.
>>>
>>>Is there anything one can adjust--or does the transmission
>>>have to be torn apart or replaced to fix? (I assume replacement
>>>from the junk yard would be cheaper?)
>> i wouldn't care about it. i have a 1987 caprice and i'm
>> afraid it qualify as a "beater car". your's sounds
>> like one too. unless you can backup on a little hill,
>> let it go. stop backing up.
>
>I talked to my mechanic and he said that slipping in
>reverse in Chevrolets is an early warning signal that
>the transmission is going bad (higher pressures in
>reverse or something...) Anyone agree or disagree?
>Is it going to start slipping in forward?

Depends on why it's slipping in reverse but yes, most likely it's not
going to last a whole lot longer. The deal with the higher pressure
is that due to design issues, the reverse band had to have VERY high
pressure applied to keep it from slipping, something like 150 psi.
Normal pressure for the bands and clutches is usually significantly
lower. As the tranny wears and the pump clearances increase the pump
can't generate as high a pressure, plus all the internal seals are
getting worn and leaking more and more which requires the pump to pump
a higher volume to maintain whatever pressure is needed. So even if
nothing is actually broken but it's all just getting worn out, the
high pressure for reverse may become impossible for the pump to
supply.

If it were my car and I wanted to avoid spending more then $15 on
repairs, here's what I would do....

1 - buy a can of "STP" or other brand of oil viscosity improver, the
stuff that's like pouring honey into your engine and that makes the
oil "thicker". Except instead of putting it into the engine, put it
in the tranny. Make sure the tranny if fully warmed up before you
start adding it and it will take a while to pour it down the dipstick
tube because it's so thick.

This will raise the viscosity of the AT Fluid when it's hot and the
higher viscosity will allow the pump to generate more pressure and
will also reduce the leakage at the various internal seals.

2 - buy a can of Trans-X or some other "transmission seal conditioner
and rejuvenator". To avoid overfilling the tranny look for one that's
pint sized rather then quart sized. Pour that down the dipstick tube.
This stuff will soften and swell the internal rubber seals which will
also reduce leakage internally which will give the pump a better
chance of building up the high pressure it needs to keep reverse from
slipping.


It will take several days to perhaps a couple weeks for this to do
it's magic, if it works at all. Since we don't really know why it's
slipping, this may or may not help. It will not hurt anything in the
transmission. I have done this routine in several transmissions and
sometimes it helps. It has never caused a problem. You can even dump
in two cans of the "STP" type stuff if you want or feel it might help.
The only thing "bad" about the higher viscosity is that it takes a
little more power to pump it around which means theoretically your gas
mileage could go down one or two percent. You have bigger issues to
worry about then that.

If this does stop the slipping in reverse, then you may get quite a
few more miles out of the transmission. The other thing you can do,
but it's more work, is drop the tranny pan (before doing any of the
above) and change the filter just in case the filter is dirty enough
to be reducing oil flow to the pump which would lower the pressure.
My guess is that won't help, I've never seen a AT filter that had much
stuff on it nor have I ever had a filter change affect how the tranny
shifts felt or how it otherwise performed. Unless the tranny is
actually starting to come apart, there just isn't much to filter in
them. That's why new cars now go 100K on the original fluid and
filter (if nothing goes wrong).
--
Elbridge Gerry, of Massachusetts:

"What, sir, is the use of militia? It is to prevent the
establishment of a standing army, the bane of liberty. . .
Whenever Government means to invade the rights and liberties of
the people, they always attempt to destroy the militia, in order
to raise a standing army upon its ruins." -- Debate, U.S. House
of Representatives, August 17, 1789