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Old 01-28-2009, 14:08   #1 (permalink)
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91 auto transmission slipping

We just bought my 16yr old a 91 T-bird 3.8 with auto tranny. It drove fine driving it the 50 or so miles home, shifted good and sounded good. When we got it home we did a full service on it, changed all of the fluids and filters. We removed the tranny pan and filter and let it drain a couple hours, I cranked the engine and shifted through the gears and turned it back off to help pump out any extra fluid, total run time about 30 seconds. We then put new filter and fluid in and test drove. As expected she slipped some when we first drove it. Only problem is it still slips after a few days driving. Seems to only happen taking off, it takes off good and strong for a couple seconds then immediately slips and revs up for about 3 seconds then catches hard and goes. Never seems to slip anytime accept first taking off and it shifts very firm between all the gears with no feel of slip at all.
The fluid level is full idling hot in park or neutral. I added some Lucas transmission additive to it and it seems to have helped. There were no signs of metal of shrapnel in the pan and the old fluid looked okay.

Any ideas why servicing would cause this to happen?
Any idea what it is and/or how to fix it?
Does this thing have anything that needs periodic adjustment?
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Old 01-28-2009, 18:44   #2 (permalink)
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Re: 91 auto transmission slipping

After you drained the fluid and restarting the motor you probably burned the pump or burned the clutch of the converter. You have an A.X.O.D. transmission. There is a change up in the front piston. It probably cracked. Send it out and have it put on the scan tool. No one will tell you on the internet what is wrong with your transmission let alone fix it.
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Old 01-29-2009, 07:23   #3 (permalink)
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Re: 91 auto transmission slipping

Although new to this site I’ve been a member of powerstroke forums and tractor forums for some time now and so far I have gotten and given help and answers with almost every question asked so I have great confidence in the nice and helpful folks on the net. I’ve also been a mechanic for many years and work on lots of different equipment. I find it hard to believe that running the engine for less than 30 seconds would burn up a transmission but I admit I’m not a transmission man, the most I have ever done with them is service them, change them out and put shift kits and valve bodies in them. An old fart years ago taught me the crank it and shift through the gears and shut it right back off trick to remove more of the fluid, so what your saying is this particular tranny can’t tolerate that or the old fart was crazy and I’ve been lucky all these years until now?
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Old 01-29-2009, 10:03   #4 (permalink)
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Re: 91 auto transmission slipping

Two totally different technologes. The old oil pumps were gear pumps. as in gear to
gear like an old brass gear pump. If they are in good shape they will pump air for a
few mins. transmission pumps are gear pumps but not the same as an old gear pump. if you changed the filter and then everything went funny after that i'd check to see if the
filter is set properly on the pick up. doesn't take much for that filter to move and suck
air. sounds like your problem. If you have drained the transmission of oil and start the
motor nothing will come out. The oil has already been drained. Very strange things can
happen to a transmission to make it act up. My wife ran the trans in her car 1 qt. low
for a week. burned out the lock up clutch in the converter. Same transmission you have.
also caused havoc with the over drive shift. Her transmission shifts to O.D. very late
and the lock up might happen once or twice a month, maybe. It costs only $500.00
with converter to rebuild that transmission but i'm tired of pulling them out. Put your's
on the scan tool. Her bad converter and bad 4th gear show a code on the scanner.
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Old 01-29-2009, 11:43   #5 (permalink)
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Re: 91 auto transmission slipping

Thanks for the help, I got an OBDII code reader I can try on it but I’d have to take it somewhere and pay to have it scanned by a real scanner. Thing is the darn thing shifts and acts great all the time except when first taking off from a stop. This is my boys “new” car so we haven’t had much time with it yet and I haven’t driven it much at all. I guess I can’t expect too much out of a good looking $700 car.

I do feel better now about it if it only costs $500 for a rebuild, my other recent auto tranny experiences have been with my powerstroke and the tranny in that thing costs over 2G.

The boy says it seems to be getting better, either that or he’s getting used to it, I hoped it was either air in the system or maybe the Lucas would help it. I also feared that it may have been the fluid, I don’t have a book for it and the O’riely parts store said it took dexron/mercon and sold him their store brand universal fluid and said it was the right thing for it. I run nothing but Mercon V from the Ford place in my truck. I guess I need to stop with my brief startup during fluid changes routine. I just wish the torque converters all had drain plugs like my original truck tranny did.
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Old 01-30-2009, 12:39   #6 (permalink)
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Re: 91 auto transmission slipping

You have a 0BD1 system. You can buy those readers for $50.00 and they will give you
transmission codes. I have one. Your code reader will not work. Your trans takes marcon 3. Marcon 4 will work. same crap. You are describing the exact problem my 91 Taurus
had. Drove great for the first 5 months i had it. stopped at the first light after a hyway
run of 60 miles. Light changed green and a slipping and a sliding i went. After cokesing
it for the first 20 feet it drove fine. It finaly got worse and quit. The front clutch pack
was burned out. I might have miss lead you about the cost of a rebuild. I buy from the
suppliers. the same place transmission shops buy from. My parts cost was approx $578.00 with converter. Then add oil and filter. Make sure you check the planatary
set very closely on that trans. They are prone to go bad. If that is the case your
transmission is now a core. Also the bushing on the pump drive is a bad apple. If it leaks bad enough it will flood the converter or starve the pump. I R and R the trans. myself and also do the rebuild myself. After you changed the oil you probably cleaned out any " sealing " grease or dirt and now it slips. I'll bet my last beer on a sunday your front clutch pack is bad. Hay, don't worry. I've been wrong before. In all seriousness though you have to put your transmission on a scan tool or we will be playing guessing games forever. It could be as simple as a bad connection on the wiring harness on the
valve body. If you do the transmission youself it could take approx 2 1/2 days to r and r
it and 4 hours to rebuilt. One bit of advice. Don't even think of not replacing the converter. You will get no warranty from a trans shop if the converter is not replaced.
Good luck.
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