Transmission slips only on the highway going up an incline

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handogg - 14 Mar 2006 10:25 GMT

Hello. I drive a 98 gs 300 w/ 110k miles. Lately the transmission
would slip/shudder on the highway if I was going about 75 mph and going
up an incline. I changed whatever fluid was in the pan and it reduced
the problem but it still happens every couple of inclines as opposed to
every single one. What would cause this? The fluid was pretty dirty
when I changed it. I plan on a few more fluid changes to switch out as
much of the fluid as I can.

So what would cause this to happen and is this something I should
classify as a warning to a major failure. Thanks Ray J... or whoever
else decides to help. Thanks.

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Ray O - 14 Mar 2006 18:34 GMT

> Hello. I drive a 98 gs 300 w/ 110k miles. Lately the transmission
> would slip/shudder on the highway if I was going about 75 mph and going
[quoted text clipped - 7 lines]
> classify as a warning to a major failure. Thanks Ray J... or whoever
> else decides to help. Thanks.

It is possible that you are feeling the torque converter unlock,
transmission slip, or engine hesitation.

You mentioned that the fluid was pretty dirty when you changed it. Has it
ever been changed before? If the transmission is actually slipping, the
replacement transmission fluid will become dark pretty quickly. Of course,
if you just drained the fluid out of the pan, then there was dirty fluid
still in the torque converter and transmission fluid cooler so you will get
some darkening of the fluid from mixing the old and new.

The best way to properly diagnose the condition is for a technician to hook
up transmission pressure gauges and take the car for a test drive to
duplicate the condition and record pressures.

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Ray O
(correct punctuation to reply)

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handogg - 15 Mar 2006 00:50 GMT

Yes I put in new fluid and Yes it darkened up VERY Quickly. I'm not
wealthy otherwise I wouldn't try to fix the problem myself. Should I
attempt to Flush the fluid somehow or just keep changing it out the way
I am now? Is this a serious matter? If so then I guess I would have
to bite the bullet and take it to lexus. Thanks Ray. Your advice is
always appreciated.

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Ray O - 15 Mar 2006 06:47 GMT

> Yes I put in new fluid and Yes it darkened up VERY Quickly. I'm not
> wealthy otherwise I wouldn't try to fix the problem myself. Should I
> attempt to Flush the fluid somehow or just keep changing it out the way
> I am now? Is this a serious matter? If so then I guess I would have
> to bite the bullet and take it to lexus. Thanks Ray. Your advice is
> always appreciated.

Unfortunately, it does sound like the transmission is slipping. Slipping
occurs when one or more of the friction surfaces is worn or burnt, or the
pump is not developing sufficient pressure, or one of the passageways is
clogged or restricted.

You can take it to a dealer or transmission shop to have the transmission
flushed, although the process occasionally causes problems. I would try 2
or 3 more fluid changes until the automatic transmission fluid (ATF) is
relatively clear and see what happens. It might be worth it to invest in a
transmission pan gasket and drop the pan and check out the screen. If the
screen is clogged, try flushing it with some ATF. Some metal particles in
the screen are OK but a lot of metal particles means that something in the
transmission is broken or badly worn. Dark sludge on the screen is an
accumulation of friction material from the clutches and brakes - there
should not be a lot of it. By the way, make sure you are using the ATF
listed in the owner's manual.

Good luck!

Signature

Ray O
(correct punctuation to reply)

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handogg - 15 Mar 2006 08:14 GMT

Ray that response makes great sense. I have been using the correct ATF
from Lexus. I considered dropping the pan to check the screen and
magnets but like you said I will replace a few more times and see what
happens. Here is what I feel is the key to my problem which can
further narrow down what may be wrong. The transmission only slips
while doing 75 mph AND going up a steep incline. The transmission runs
fine during all other times. It doesn't slip at 80mph and it doesn't
slip and 65mph. It also doesn't slip at 75mph unless going up an
incline. Does this narrow the problem down at all ?? I was hoping to
take a cross country road trip next month but dont know if it's such a
good idea anymore.

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Ray O - 15 Mar 2006 19:25 GMT

> Ray that response makes great sense. I have been using the correct ATF
> from Lexus. I considered dropping the pan to check the screen and
[quoted text clipped - 7 lines]
> take a cross country road trip next month but dont know if it's such a
> good idea anymore.

Without taking the car for a road test, it's hard to say what is happening.
If it is a continuous slip, then you have a problem. If the RPM jumps about
100 to 300 RPM and holds steady, then it sounds like the torque converter is
unlocking, which isn't a problem. Hopefully, this is all that you are
experiencing.

good luck!

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Ray O
(correct punctuation to reply)

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