TC lock/unlock rapidly, delayed overdrive shift

kas83

kas83

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Oct 18, 2007
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Got my 95 back last night. This truck always had an issue or two in the tranny, but seems to have gotten much worse. When I say delayed shift into overdrive, we're talking 30 full minutes of driving, with the truck being warmed up in neutral for approx 10 minutes. With the motor fully up to temp, air temp at 0*, I can run the truck up to 85mph in drive, torque converter unlocked, 3200 rpm, and hold it. However, after driving the truck for awhile, it will shift into overdrive. Then, it will lock and unlock the torque converter numerous times per minute. It's not slipping, simply unlocks and locks repeatedly. Fluid is dull red, filter was changed two weeks ago. As far as I know, the tranny is stock. These problems are happening at crusing speed(60-70 mph), with cruise set, truck empty.

I've contacted Dave G about a tranny, will see if I can swing one with tax rebate. Just wondering what to do in the meantime. With heading out on the road, the truck will be sitting for awhile, am looking for ideas on what to look into.
 
your TPS may bo bad. mine had some problems so i replaced it with a potentiometer (from radioshack), but then the overdrive piston seal got ripped so i lost overdrive, and when replacing that discovered all the clutches were smoked. so i went with a billet goerend unit. I am very satisfied with it so far. he does very good work, and was also very negotiable and quick service.
 
I was leaning towards possibly a torn piston on the OD unit. The initial apply could take some time as your filling the cavity that is leaking. Maybe this is causing you to lose line pressure also? Or you have a sticky relay/bad connection. If you have a corroded connection, the two relays applying at the same time will have a larger voltage drop across the bad connection, possibly causing the voltage at the relay to drop enough that it could drop in and out.
 
Ok, should I look into wiring, or should I just not worry about it until spring time and throw a different tranny in? If this is electrical, I'd like to get it sorted out before throwing a $4000 trans in and still have the same stuff. Won't see the truck for 2 weeks, just trying to get a list of ideas together to look into when I get home.
 
the delayed overdrive shift is most likely the torn od piston seal, the rapid lock unlock i would say is something electrical like a bad relay.
 
Check your voltage on your TPS. If you lower the voltage from your TPS your O.D. shift will happen sooner. I just dealt with a customers that would not shift into O.D. unless it had very light throttle input or full throttle at about 70mph. I replace the TPS and it still had the problem at .5 volts where it was suppose to be set, knocked the bushings out of the TPS and got it down to .4 and it fixed it. Tranny now is perfect. You could also throw a psi guage on the port on the drivers side back by the O.D. unit and see what kind of psi its sending to your O.D. It will only show psi while in O.D.
 
Also if your temp. sender is bad it won't shift into O.D. It has to read over 100* to alow a O.D. shift.
 
Ok, will check TPS and temp sensor.

Any schematics/diagrams as to relays for the tranny?

If everything checks out with the electrical side, I will just let the tranny be until I can afford the replacement. Just want to rule out any other issues beforehand.

Thanks for the replies.
 
try a lock-up switch....when it starts acting up flip the switch and see if it goes away...I have a 95 also but the tps has a bad spot in it when it acts up i just flip the switch and its gone...make sure you turn it off when coming to a stop...
 
gmcz71502 said:
try a lock-up switch....when it starts acting up flip the switch and see if it goes away...I have a 95 also but the tps has a bad spot in it when it acts up i just flip the switch and its gone...make sure you turn it off when coming to a stop...
Click to expand...

If you'll do the TPS mod with the pot in it's place it will eliminate all that crap, this has to be the best mod I have done to date......and the cheapest.

Jim
 
how exactly does the TPS elimination hook up and work I'm tired of my truck doing the same thing and don't want to spend another $200 and some change on a TPS.
 
Middle wire is your 5V wire, the other two either way as all they change is in you increase/decrease clockwise or counter clockwise. I've had mine done for a while now and I have yet to see a down side. You control the 3-4 by how much you give it voltage then lockup happens later depending on acceleration, then when you are slowing down the converter is locked in O/D till you get to said MPH, once your there(again depending on were you set it initially) it will unlock the converter and down shift 4-3 and will remain unlocked unless you de-select the O/D. Example mine makes 3-4 at say 52-55 and down shifts at 43-47.

Jim
 
Thanks for the link to pot mod, Jim.

Also, I wired up a lockup switch lastnight. It will lock in 2nd gear and up, and if I leave it locked in O/D, it will lug it right down to almost stall. When I give it about half throttle with the switch flipped to lock it, it will momentarily unlock, then relock, and hold fine. Cruising is locked, no back and forth. WOT slips the torque converter bad.

I'm picking up a new temp sensor today. Lately it's been warmer, only takes 10 minutes or so to get O/D. I've been talking to Dave G, and he still feels that's too long. I'm getting closer it seems, he suggests replacing the TPS for good measure. And I will be picking up one of this trannys when my return comes in, should take care of everything else.
 
I fought that TPS for a long time, changed, adjusted ect and the POT mod fixed it, the others are a waist of money.

Jim
 
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