Torque Converter Issues? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Matador · 03-30-2015, 06:55 PM

I just bought a 2000 K3500 Crew Cab/Long bed. I put it in here, because it's a GMT 400 truck. If it belongs in the 99+ section, please feel free to move it.

Anyways, the truck had rod knock, so I had the guy I bought it from put in a new Goodwrench 350. The transmission is the automatic, and it has the floor-shifting 4x4. The truck drives nicely, but it has an odd shifting problem:

You're driving along normally, doing 65 at about 2200RPM. The torque converter locks up as you climb a hill, and the RPMs rise to 3000. So far, so good. The problem is that the torque converter never unlocks. You'll stay there until you stop the truck and shut it off for a minute.

I have it going into the shop on Thursday, but didn't know if you had any idea. The mechanic (different guy than I bought the truck from) knows a lot about these trucks, but has never heard of this happening.

Any ideas?

Tom · 03-30-2015, 08:14 PM

Im confused, you mean the convertor UNlocks and the rpm's rise, and after that point it never locks back up? If so then it sounds like a servo or the torque convertor itself going bad. I had the lockup clutch in my 200mile old built 200-4R go bad on me once. If instead you mean the convertor locks and thats when the rpm's rise, then sir you are properly screwed as thats not how it supposed to work lol.

Matador · 03-30-2015, 08:42 PM

My terminology isn't the best.

The truck will drive down the road normally at 65 at 2200 RPM, like it should. Then, as soon as I get to a hill, the torque converter does something (Unlocking- my phrasing was backwards), and the RPMs increase to 3000-3100 (Same RPM as if I shift into third). Then, it stays there until I stop and turn off the truck. If I go down a hill with cruise control on, the RPMs will fall to 1000 (Idle), and will pick right back up at 3000 at the bottom of the hill.

I'm basically driving in third gear and not overdrive after I encounter a hill.

HeavyChevy81 · 03-30-2015, 09:49 PM

Doesnt sound like a Converter problem to me. I'm thinking more along a transmission sprag not holding.
Normal lockup decreases revs approx 150-200.
the increase you are seeing is more like downshifting a gear, therefore a possible sprag.
Could also be a solenoid issue, not allowing upshift at high pump pressures.
Will it upshift if you manually pull down to direct, then manually go to OD?
Just my 2 cents.

Lane

Matador · 03-30-2015, 09:59 PM

Moving the lever from Overdrive to 3rd on the column doesn't change the RPMs at all. If I go back to OD from 3rd, the RPMs stay the same (As they are in 3rd gear). So, I'm basically in 3rd then, right?

If it's a sprag or solenoid, what does that mean I'm in for?

HeavyChevy81 · 03-30-2015, 10:09 PM

Trans is probably a 4L80E, I'm assuming.
OD is an additional reverse rotation sprag added to the extreme rear of case.
The sprag is simply a mechanical one-way clutch to hold when a planetary unit is engaged for gear reduction.
This being said, if sprag is bad, or planetary failure, means the tranny is coming out to be rebuilt. Automatic tranny failures usually require a complete rebuild for cleanup of debris. I would continue testing, every piece of info you can give to you mechanic of choice is valuble in determining course of action.
Hate to sound so negative, but prepare for the worst, hope for the best.

Again, just my 2 cents.

Lane.

HeavyChevy81 · 03-30-2015, 10:14 PM

also, you stated going downhill rpms's drop to approx 1000. This is another indication of a sprag not holding. (no engine braking).

Matador · 03-30-2015, 11:08 PM

Yeah- the engine is idling when I go down a hill. It's the 4L80E. Is there anything I need to be aware of? I don't want to make matters worse.

If it's overdrive causing the issue, would it be best to use 3rd gear when taking the truck in for repairs?

It sounds like I may be getting a second transmission swap done in 12 months! I was trying to avoid this!

HeavyChevy81 · 03-30-2015, 11:12 PM

Honestly, damage already done.
Just get to repair shop as easily as possible.

Lane

Matador · 04-12-2015, 06:47 PM

Sadly, everyone was right. The transmission was slipping big time.

We're having a reman one put in. Any tips to make it last the longest?

So, the man we bought the truck from put a new engine in there for us and drove it around. I'm assuming that he would have known about these issues, right?

At least we'll have everything replaced and in good order when it's finally usable!

03-30-2015, 06:55 PM	#1
Matador Registered User Join Date: Sep 2013 Location: Big Wonderful Wyoming Posts: 40	Torque Converter Issues? I just bought a 2000 K3500 Crew Cab/Long bed. I put it in here, because it's a GMT 400 truck. If it belongs in the 99+ section, please feel free to move it. Anyways, the truck had rod knock, so I had the guy I bought it from put in a new Goodwrench 350. The transmission is the automatic, and it has the floor-shifting 4x4. The truck drives nicely, but it has an odd shifting problem: You're driving along normally, doing 65 at about 2200RPM. The torque converter locks up as you climb a hill, and the RPMs rise to 3000. So far, so good. The problem is that the torque converter never unlocks. You'll stay there until you stop the truck and shut it off for a minute. I have it going into the shop on Thursday, but didn't know if you had any idea. The mechanic (different guy than I bought the truck from) knows a lot about these trucks, but has never heard of this happening. Any ideas?

03-30-2015, 08:14 PM	#2
Tom driving is in my blood Join Date: Dec 1999 Location: Mesa AZ Posts: 5,763	Re: Torque Converter Issues? Im confused, you mean the convertor UNlocks and the rpm's rise, and after that point it never locks back up? If so then it sounds like a servo or the torque convertor itself going bad. I had the lockup clutch in my 200mile old built 200-4R go bad on me once. If instead you mean the convertor locks and thats when the rpm's rise, then sir you are properly screwed as thats not how it supposed to work lol. __________________ -78 c10 short/step: 388cid, M20, 5/5 drop, lots more. Playtoy and first vehicle. -98 c1500 x-cab: 5.7L, 17" rims, 5/6 drop, flowmaster, helper bags,NBS rear disk brakes. -02 Suburban 4x4: leveled front -CBR600F4i, CBR600RR, CBR1000RR, and standup skis DISCLAIMER: I cant spell for the life of me.

03-30-2015, 08:42 PM	#3
Matador Registered User Join Date: Sep 2013 Location: Big Wonderful Wyoming Posts: 40	Re: Torque Converter Issues? My terminology isn't the best. The truck will drive down the road normally at 65 at 2200 RPM, like it should. Then, as soon as I get to a hill, the torque converter does something (Unlocking- my phrasing was backwards), and the RPMs increase to 3000-3100 (Same RPM as if I shift into third). Then, it stays there until I stop and turn off the truck. If I go down a hill with cruise control on, the RPMs will fall to 1000 (Idle), and will pick right back up at 3000 at the bottom of the hill. I'm basically driving in third gear and not overdrive after I encounter a hill.

03-30-2015, 09:49 PM	#4
HeavyChevy81 Registered User Join Date: Nov 2014 Location: West Texas Posts: 30	Re: Torque Converter Issues? Doesnt sound like a Converter problem to me. I'm thinking more along a transmission sprag not holding. Normal lockup decreases revs approx 150-200. the increase you are seeing is more like downshifting a gear, therefore a possible sprag. Could also be a solenoid issue, not allowing upshift at high pump pressures. Will it upshift if you manually pull down to direct, then manually go to OD? Just my 2 cents. Lane

03-30-2015, 09:59 PM	#5
Matador Registered User Join Date: Sep 2013 Location: Big Wonderful Wyoming Posts: 40	Re: Torque Converter Issues? Moving the lever from Overdrive to 3rd on the column doesn't change the RPMs at all. If I go back to OD from 3rd, the RPMs stay the same (As they are in 3rd gear). So, I'm basically in 3rd then, right? If it's a sprag or solenoid, what does that mean I'm in for?

03-30-2015, 10:09 PM	#6
HeavyChevy81 Registered User Join Date: Nov 2014 Location: West Texas Posts: 30	Re: Torque Converter Issues? Trans is probably a 4L80E, I'm assuming. OD is an additional reverse rotation sprag added to the extreme rear of case. The sprag is simply a mechanical one-way clutch to hold when a planetary unit is engaged for gear reduction. This being said, if sprag is bad, or planetary failure, means the tranny is coming out to be rebuilt. Automatic tranny failures usually require a complete rebuild for cleanup of debris. I would continue testing, every piece of info you can give to you mechanic of choice is valuble in determining course of action. Hate to sound so negative, but prepare for the worst, hope for the best. Again, just my 2 cents. Lane.

03-30-2015, 10:14 PM	#7
HeavyChevy81 Registered User Join Date: Nov 2014 Location: West Texas Posts: 30	Re: Torque Converter Issues? also, you stated going downhill rpms's drop to approx 1000. This is another indication of a sprag not holding. (no engine braking).

03-30-2015, 11:08 PM	#8
Matador Registered User Join Date: Sep 2013 Location: Big Wonderful Wyoming Posts: 40	Re: Torque Converter Issues? Yeah- the engine is idling when I go down a hill. It's the 4L80E. Is there anything I need to be aware of? I don't want to make matters worse. If it's overdrive causing the issue, would it be best to use 3rd gear when taking the truck in for repairs? It sounds like I may be getting a second transmission swap done in 12 months! I was trying to avoid this!

03-30-2015, 11:12 PM	#9
HeavyChevy81 Registered User Join Date: Nov 2014 Location: West Texas Posts: 30	Re: Torque Converter Issues? Honestly, damage already done. Just get to repair shop as easily as possible. Lane

04-12-2015, 06:47 PM	#10
Matador Registered User Join Date: Sep 2013 Location: Big Wonderful Wyoming Posts: 40	Re: Torque Converter Issues? Sadly, everyone was right. The transmission was slipping big time. We're having a reman one put in. Any tips to make it last the longest? So, the man we bought the truck from put a new engine in there for us and drove it around. I'm assuming that he would have known about these issues, right? At least we'll have everything replaced and in good order when it's finally usable!



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