1990 Jeep Wrangler Tranny looses 3rd when warm.

RATYJ

MEMBER
1990 JEEP WRANGLER
6 CYL
4WD
AUTOMATIC
145,000 MILES

The automatic transmission in my 1990 Jeep Wrangler YJ (with a/c, if that matters) shifts nice and smooth in all gears until I've driven for about 20 minutes (i.E. Everything is up to temp) then 3rd doesn't hold, just slips in and out.

I've been told that if first and reverse are ok, then the tranny itself is ok, something else is ammis (wrong fluid type, some sort of control mechanism/circuit)

I've also been told the transmission is toast. But I can drive all day in 2nd (speed limit in town is 25, so it's not a problem) and have been doing so for the past few years (only a few hundred miles a year, though)

Any ideas?

4 Replies

SERVICE WRITER

MECHANIC
9,123 POSTS

If the fluid is pink and clear, and has always been changed on schedule with the proper fluid-ATF+3 or ATF+4, then it isn't the fluid. I know that sounds contrite, but if the wrong fluid has been added, you'll have problems. IF it hasn't been changed as it should, the clutches may be burned out. Leaving a rebuilt situation.

The guy that says the tranny is toast may well be correct. You may see it as, "why can't I just replace the 3rd gear clutches?". But when you go into the transmission, the other parts are almost equally worn meaning "if you go in, do it right". IT may not even go back together without a rebuild situation.

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Tuesday, September 2nd, 2008 AT 7:13 PM

RATYJ

MEMBER
3 POSTS

I wasn't clear. My question regarding third gear being the only no-op gear was that I've been told: if first and reverse work, there's nothing wrong with the gearing/clutches because the way the TF999 is set up, it's the same gears and clutches in different positions, not a separate 3rd gear set. That's the point I'm trying to verify. Guess I should buy myself a teardown guide.

I'm pretty sure the wrong fluid has been added as I found a receipt in the glove compartment when I bought it for some kind of tranny additive and I've read Chrysler trannys don't play well with additives or Dextron.

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Wednesday, September 3rd, 2008 AT 8:40 AM

SERVICE WRITER

MECHANIC
9,123 POSTS

I stand corrected it is Mercon ATF in that year. The info I have on the is sketchy, but this may help.

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Wednesday, September 3rd, 2008 AT 7:01 PM

RATYJ

MEMBER
3 POSTS

Yes, that helps a lot actually. I think my next check will be the radiator and cooling lines from the converter. It's always been suspicious to me that 3rd gear goes out about the time the radiator thermostat opens. I did order the ATSG manual for a little light reading. Thanks fro the info!

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Wednesday, September 3rd, 2008 AT 9:34 PM