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Pontiac Transport Won't OD

Q. I was having a trans problem in my '95 Pontiac Transport van. After about 30 miles of highway driving the trans would drop out of overdrive. The only way it would shift back into o.d. was to turn the van off for about 1/2 hour. I took it to a transmission shop and they rebuilt the trans (reman. torque converter, overhaul kit, 4 solenoids, new TP Sensor), I picked the van back up on a Friday and went on a weekend trip Saturday and about 30 miles into the trip the trans dropped out of o.d. again. Same problem as before. I took it back to the trans shop and they had it for 9 days and can't figure out where the problem is. They even replaced the computer thinking that was the problem. They said they pulled a code out of it but the code wasn't in the book and didn't make sense. I contacted a friend that works for a Pontiac dealership and he talked to their service advisor and he seems to think that it is something mechanical in the trans still (bad spool valve or something). The trans shop told me to go ahead and drive it until they can get some answers from there tech support. Do you have any ideas?

1995 Pontiac Transport van
3.8
automatic 4T60E
163,000

Thanks again,
Chuck

A. I would tend to think the transmission valve body here Chuck. The valve body is a pretty complicated part and it doesn't take a whole lot to gum up the works. Tolerances are so close that the normal gums and varnish that build up could make the OD valve stick. Most transmission shops don't take them apart if they don't have to, not because they are lazy, but because they can be tricky to put back together. They are also quite expensive to replace. If they reused your old valve body, then when they rebuilt your transmission they reinstalled the problem.

I'd wait to hear from the GM Tech Support team before replacing it, there may be a known fault of a confirmation of my feeling.

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