'92 Sport issue with 4th gear overdrive.

[Good Sport]

Hey , it's been awhile! I'm approaching 30 years ownership of my '92 Chevrolet Sport (reg cab/swb) that I purchased new in 1992. It just turned 158,000 miles.

Unfortunately, it has developed a problem during highway speeds around 50-60 mph. It begins to shudder or buck while the overdrive has engaged (shifts fine into overdrive though). If I let off the gas it will smooth out and return to normal. There is no issue driving in 3rd, or other gears. All my sensors etc on top of the engine are new or recent.

With the above description, does anyone here have a clue what I need to check? Thanks.

[Boog]

V8 ?

SES light on? Check for codes.
#1 fuel pressure. Should be 9-13 psi.

[Good Sport]

Originally Posted by Boog

V8 ?

SES light on? Check for codes.
#1 fuel pressure. Should be 9-13 psi.

It's a 5.7 V8. No SE/Light or codes. I'm now wondering if this is might be engine/fuel related, and not the trans. Going through my records, I see the fuel filter was replaced in 2004, and it has 44,000 miles on it. I just removed it and will install a new one tomorrow. In any case, the filter is long overdue to be replaced. Will update tomorrow. Thanks.

[special-K]

How about the transmission? Has it been flushed, new filter, new fluid any time lately?

[Palf70Step]

My old 94 acted that way when my friend Ed owned it and it was the torgue convertor. We replaced it and no issues. This was around 220K.

[Good Sport]

Originally Posted by special-K

How about the transmission? Has it been flushed, new filter, new fluid any time lately?

I put new fluid & filter in around 12 years ago @ 130K. Still looks good on stick, not dark or burnt.

[Good Sport]

Maybe this is the problem. I had the truck inspected two weeks ago, and also had them balance the wheels. Drove it today and around 50+ mph the vibration issue returned, and I can feel it through the steering wheel. My wife could see my arm shake. So this may not evenbe engine/trans related at all! I'm going to take it back to Firestone and have them check the balancing. This was not happening prior to the inspection and wheel balancing.

[Good Sport]

Update: it's not the wheels. Took it back and had the front tires/wheels rebalanced. Once it got up to highway speeds on the way home, the shaking returned. In fact, it seems to be getting worse. It's intermittent, you're going along no problem, then out of the blue, the shaking/vibration rears it's ugly head, and then goes away. Looks like I'm going to have it checked out with diagnostic equipment. I'm a decent mechanic, but this seems over my head. Thanks.

[special-K]

Intermittent even at a particular speed where it does happen, hmmm.....

[Good Sport]

There is nothing much in my area (rural) in the way of good repair shops. I'm going to check my local Chevy dealership service center later this morning and have them look at it next week. I really can't complain, the truck has been the most trouble free vehicle I've ever owned. Bought it brand new in September 1992. My wife and I have debated about selling it at some point, we're kinda elderly and have to have a dependable pickup. Funny thing is, even though this is a full size truck (regular cab, shortbed), it looks like a compact compared to most modern trucks.

[Just call me Sean]

Sounds like it could be a misfire, or the torque converter locking and unlocking quickly.

[Good Sport]

Well, the big city Chevy dealership said: "We don't work on anything that old!"

Went to the small town dealer and they said: "Sure, we can check it out."

Closest appointment is 2 weeks. So, hopefully they can diagnose the problem.

[chevmn]

Have you checked ignition (distributor)? Could it be a misfire? I had a 92 and recall having some odd misfire issue and the distributor and rotor had a lot of corrosion and simply replacement of those fixed. My truck was a Sport 4x4 with 350 but had the 5 speed (hated that transmission). Bought it new as well. Great truck except for that transmission.

[Good Sport]

Originally Posted by chevmn

Have you checked ignition (distributor)? Could it be a misfire? I had a 92 and recall having some odd misfire issue and the distributor and rotor had a lot of corrosion and simply replacement of those fixed. My truck was a Sport 4x4 with 350 but had the 5 speed (hated that transmission). Bought it new as well. Great truck except for that transmission.

Yeah, I had that happen a few years ago. It was the ignition module in the distributor. Installed a MDS/Holley distributor with new module etc, and as far as I know, that is all working fine. There is a possibility that I'm having an ignition/fuel related problem. I'd rather deal with that than the tranny.

[hatzie]

This is only happening in OD or does it happen at the same speed with the shifter set in D or 3 to lock out OD?

[Good Sport]

Originally Posted by hatzie

This is only happening in OD or does it happen at the same speed with the shifter set in D or 3 to lock out OD?

So far, it has only happened when vehicle is at highway speeds, in the 47-60 mph range after overdrive/4th has kicked in. It's somewhat random, usually after driving 5-10 or so miles. It has not occurred in 3rd gear.

[hatzie]

Torque converter clutch malfunction?

[Boog]

Probably not your issue but I had an 88 with similar symptoms and it was the egr valve but it always set the CEL also.

[Good Sport]

MAP sensor, EGR valve & EGR sensor were replaced 2-years ago.

I'm sure this issue is not driveshaft/u-joint related, but since the original u-joints were still in it, I pulled the d-shaft today and will be putting in a new set I had on hand (Moogs w/grease fitting).

[Good Sport]

Waiting on a transmission shop to check it out (cancelled local dealership diagnosis). Drove the truck to the shop 40+ miles in 3rd, and it had a few rough shifts on the way. So it looks like its 3rd and 4th now. Could be a week or so before they can get to it, which seems the new normal these days.

[Just call me Sean]

Might want to check the TV cable adjustment.

[special-K]

On the transmission flush. The fluid can still be good and have flow issues. Was it flushed when filter and fluid were replaced?

[jjzepplin]

Kinda sounds like the lock up clutch in the converter may be going out.

[Accelo]

Originally Posted by jjzepplin

Kinda sounds like the lock up clutch in the converter may be going out.

jjzepplin wins the prize! At least that's what I think it is. The proof is to use your left foot to activate the brake light but not not enough to apply the brakes while keeping your right foot steady on the gas. It the shuttering quits it's the torque converter or the converter system.
Cheers.

[Good Sport]

Originally Posted by special-K

On the transmission flush. The fluid can still be good and have flow issues. Was it flushed when filter and fluid were replaced?

No, I didn't do a complete flush at the time (12 yrs. ago). I replaced equal amount (around 7-qts?) after taking pan off. Then, over a month or two, I used a syphon pump through the fill tube to remove a few more qts and replaced what was removed.

Sean: I checked the TV cable and it seemed ok. Will wait and hear from the trans shop on whether it is causing the problem. In any case, I'll probably have a new one installed.