Shudder in Driveline

[greg2010]

Hi guys.

I've got a 1994 6.5 Turbo in my C1500 pickup. Brand new Automatic overdive transmission installed by GM about 75,000kms ago & engine rebuilt nearly 50,000kms ago, and since the time of the rebuild I've put in a new injector pump, new injectors, new PMD, new lift pump, new computer, K&N cone intake air filter, and a bunch of new sensors (intake air temp, coolant temp, the three sensors on the left valve cover for boos & egr), and some other little miscellaneous stuff. All preventative maintenance since the engine and transmission replacement has been followed to a "T" according to the owner's manual.

Recently (over the past month or two), I've noticed a vibration/shudder coming from the driveline during acceleration. It's not an intermittant problem though. Essentially, I'll be stopped at a light, then I'll accelerate, and the truck increases speed normally (there's no hesitation to speak of), but there is a shudder coming from the driveline between about 1,000 and 2,200 rpm, but then goes away above 2,200 rpm. Also worth mentioning, the vibration isn't noticible once the tranny shifts into 2nd gear.

Once it gets into second gear, the problem goes away....until I'm cruising. Once the truck is up to speed and I'm cruising at say, 80km/h or 100km/h, I can feel a the truck surging a little bit. It's not something harsh or abrupt, but it is noticible if you concentrate and feel for it... If you know what I mean?

Don't know if this is related to the problem or not, but when the truck has been sitting all night and I start driving in the morning, it seems to lack power and I'll get a harsh 1-2 shift until everything gets a warm, then it drives normally once it's up to temperature. The harsh shifts were noticible with the old transmission as well, so that's why I don't think it's attributed to my vibration. The harsh shifts don't happen if I let the truck idle in the driveway for five minutes before heading out.

I was thinking maybe the harmonic balancer or the torque converter was going, but wouldn't that give me a constant vibration? Also, last time I had a bad balancer was on a gas engine, and I was constantly throwing belts and I had shiny spots on the pulley's. None of this seems to apply to my situation though.

The truck has nearly 430,000kms on it now and the only code showing in the ECM is related to throttle pedal position sensor (Code 14)

Any thoughts? :confused:

[grancito]

here´s a long shot, take a look at your engine mounts, the rubber may be colapsing, they can cause strange vibrations. Just replaced mine.

[greg2010]

I'll check out the motor mounts this weekend, but as a weird twist....if I plug in the block heater to pre-heat everything before I start out in the morning, the shudder won't happen (until I let the engine get stone cold again), and the transmission shifts normally.

I'm going to give the whole truck a once-over this weekend and see what I can find.

[grancito]

my 82 chev changes so hard when cold that it feels like a rear end impact, changing from 1st to second. It is because the oil is thick. Your block heater will also heat to some degree the trans oil. You could at that rate have torque converter shudder.

[Biginch D]

I've had issues with the drive shaft slip yoke. There's actually a bulletin on this. Shudder at 40 mph on acceleration. My fix was to replace the yoke and have it balanced at a driveline shop. All gone now.

[grancito]

thanks for the feed back on that, I´ll note the cure, pleased you had an easy fix

[sixnickel]

The first thing I would check is the "U" joints. You could have a seized joint You have to pull the shaft out to check it for that. Try to move the joints around and any binding is bad. You might not have any play but the joints must move freely.