Engine/Transmission (1994 - 1998) TC clutch briefly unlocking now and then

[Blakers]

Occasionally my torque converter clutch will briefly unlock and lock up again while cruising down the freeway at 70. It may do it every couple of miles for five or ten minutes, then not do it again for a month or so.



The rpms don't go up too much - maybe 150 - 200 when it unlocks since I have the Goerend TC, but it's a little annoying and I am wondering if it's leading up to something going wrong. Road bumps and wind do not seem to be causing it.



Thanks.



Blake

 

[illflem]

easy fix

Blake, sounds like your TPS is dirty. Just spray some electronic cleaner where the shaft enters the TPS while working the throttle back and forth. The TPS is the device with wires going to it where your throttle cable ends. Do this at every oil change for no more problems.

 

[Blakers]

Thanks Bill! I'll give it a shot. I know the guy I bought my truck from had a new TPS installed, but that's been a few years now.



Take care and Merry Christmas!

 

[JerryB]

Mine has done that a couple times already. I just bought a second TPS, and swap it out. That way I can take the time to clean the switch properly at my liesure. The best way is to pop it open, clean up the contacts with electrical cleaner, and then re-seal the cover with hi-temp silicone (just enough to seal, don't get too much in there).

If you shoot cleaner around the shaft, you are also washing the grease off the shaft, losing its lubrication. I also think the grease helps somewhat with water resistance.

 

[shendren]

cleaning the tps' wouldn't fix mine. i had to pull the 3 tps wires out of the harness. pull them out about 2-3 feet and wrap in and put in their own loom..... good luck

 

[dcasselberry]

Blakers:



I had the problem of the TC going in and out of lockup at the 60-60 mph speed range about a year ago. The initial diagnosis looked like TPS, but my mechanic checked it out and it showed normal. We went for a drive with it hooked up to the computer and still, nothing showed up. Then the mechanic felt the drop out of lockup when his foot slightly touched the brake pedal, and said, "I know what the problem is now". Turns out there is some kind of sensor connected with braking that can also get out of adjustment. We got back to the shop, he adjusted it, and no further problems. Just one additional possibility in case cleaning the TPS doesn't solve the problem.



Dan

 

[illflem]

If the brake pedal sensor is the problem it will also drop out of cruise control.

 

[Blakers]

Thanks guys. I know it's not my brake pedal switch as I fixed that the first day I owned the truck. It would drop cruise control everytime I hit a bump. I'm gonna try the contact cleaner and some other posible causes as soon as I get over a cold and have a little daylight time.



Take care and thanks again.

 

[Blakers]

Re: easy fix

Originally posted by illflem

Blake, sounds like your TPS is dirty. Just spray some electronic cleaner where the shaft enters the TPS while working the throttle back and forth. The TPS is the device with wires going to it where your throttle cable ends. Do this at every oil change for no more problems.

Well Bill, I gave it a shot of contact cleaner and the problem has not occured again. I guess that did it!



Anyone know what these TPSs look like inside? Can they be opened up? I have an old one an I was wondering if a small hole could be drilled to allow contact cleaner to be sprayed inside and then tape the hole up to keep dirt out.



Thanks,

Blake

 

[illflem]

Blake, I've asked the same question here a few times and never got an answer. I've looked at the tps and it looks as though it would take some grinding to get it apart and glue to hold it back together. Haven't wanted to experiment on my original stock tps since a shot of cleaner at every oil change has been working for 180k miles, but agree a hole drilled in it would be great.



If anyone has a dead tps they'd like to donate for research PM me.

 

[Ben Rumson]

Re: Re: easy fix

Originally posted by Blakers



Anyone know what these TPSs look like inside? Can they be opened up? I have an old one an I was wondering if a small hole could be drilled to allow contact cleaner to be sprayed inside and then tape the hole up to keep dirt out.



Thanks,

Blake

YES there are pictures of a torn apart TPS in the Reader's Rigs section of the TDR. A guy from Moab Utah posted some pics of his TPS cleaning. I saw them just the other day. Can't remember his name... ?



There is a raised bubble on the back side of the TPS - opposite the side that the throttle pin goes in. He took a very thin dremel bit/cutter and cut through the edge where the "bubble" raises above the main flat surface of the TPS. Once this bubble or "lid" has been removed, you have full access to the internal parts of the TPS.



I'm assuming you could then just glue the bubble back on with some silicone adhesive.



Note: You're only removing the raised bubble portion. This is not splitting the entire TPS in half - just the slightly raised bubble on the fender-side of the TPS.



For cleaning, I've been removing mine from the truck and then squirting brake parts cleaner and starter fluid all over and then work the spring loaded gear by hand with a screw driver. I then dry it out real good with compressed air and re-install. This fix is lasting less and less time. Next go-around, I'm going to remove the bubble and clean it from the back side as well.



Keeping water (car wash) off the TPS is supposed to help them stay running better as well.



Good point with the wire loom. I may try un-looming the 3 wires next time and separating them from the other wires as suggested.

 

[champspa]

It's my understanding that it drops out every time you let the accelerator up all the way and every time you touch the brake.

 

[chrleb1]

If you are having a problem with your TC locking and unlocking, there is a sure fire way of solving it. Install a mystery switch. It is quite simple on the earlier truck (pre 96 i believe). We put one in my brothers and it made it quite fun also. You know how it pulls pretty hard when you hit overdrive, well... ... imagine that at 20 mph.

 

[Ben Rumson]

When my TP switch starts acting up and I'm at highway speed I, as well, use my "mystery" switch to keep it locked.

 

[PHaller]

Yes, I removed my TPS and tore it apart and cleaned it. There is a kidney shaped insert on the back side and you can use a dremel or a knife to remove the plastic that holds it in place. The cover pops off and you can clean and relube then, reseal with silicone. It's a lot of work and dangerous too. The TPS is not that well built inside and it doesn't take much to damage the resistor foil or the contacts. You can damage it just pulling it apart. If you aren't careful you will also have the thing come apart while trying to reinstall it and really destroy it. Ask me how I know!!

Somebody wrote in and said that you can clean them by drilling a hole in the top to squirt in cleaner. After pulling one apart, I can't see how. There is a circular hollow inside the TPS and the resistor foil wraps around the outside of this cavity. The contacts attach to a plastic sleeve over the shaft and contacts the foil. If you drill it you'll go right into the foil unless you know by taking it apart exactly where to drill.

IMHO, it's not worth it. Just clean it every oil change with spray cleaner. If they fail they are real pricy for as cheesy as they are. Last time I bought one, they cost around 150$

The real answer here is to just NEVER buy an auto transmission. After 3 and still trying to get it working right!!! :{ :{

-Paul R. Haller-

 

[Blakers]

Originally posted by champspa

It's my understanding that it drops out every time you let the accelerator up all the way and every time you touch the brake.

Yes. This is what they are supposed to do.

 

[KWIKKURT]

FYI, On a 460Gas engine to 8. 3L / Allison Conversion I am doing in a Motorhome some of the Wiring from the Engine / Trans to the Drivers compartment (wire looms) are over 25ft long. They also contain a couple Hundred wires. I noticed that sensitive wires like the TPS were twisted together. This would help greatly with interference. So splitting them out of the other loom and or twisting them together may help.



L8tr Kurt

 

[jimk]

TPS

I to have a switch that i use only when the ... ... . switch acts up. I think that Paul hit the nail on the head about the auto. JimK

 

[GSnook]

My 96 un locks past 55 all by itself in DD but not in OD took it in and had it flashed also did a diognostic road test the mech told me that the computer was telling it to unlock. The transmission pressure is bumped to 160 psi and I have a resistor installed I think on pin #7 I dont think its the TPS ( but maybe) also the problem seems to migrate from 55 to 62 mph in dd.

 

[shendren]

it is the tps. it needs to be rewired. it will fix the problem immediately. you can buy a kit that will do the job. questions? pm me. scott.