OT - 94 GMC Suburban Transmission, Any Experts??

I have a '94 GMC half ton Suburban. When sitting at a light with Tran in Drive, it lugs the engine down almost to the point I think it is going to stall. If I shift to neutral engine revs up to idle speed again. Vehicle has also developed a vibration at highway speed that I think might be related.

Any thoughts on where to start looking for problem(s).

Thanks,

Kirk

Aren't you thinking of those old 125Cs (3T40) that would lock 'em up solid and kill the engine at a stop light? Those solenoids were mounted to the valve body as I recall.

The 4L60/4L60E uses a different approach and the electrical solenoid is located at the case/pump mounting area and they "almost" never fail.

Also, there is no "board" in the '94 4L60E transmission that I'm aware of.

A vibration caused from the torque converter/any rotating part in these rascals is just about non existant and the "shudder" that everyone likes to blame on the TQ clutch is (here again) "almost" always engine related.

Sure not saying that it can't happen, but I'm bettin' that Kirk has trouble elsewhere besides his transmission. Would hate to see him drop $2K on a tranny and still have a sick truck. :>(

Dunno,

Allan

It soon started smoking burning oil out from under it and long story short - a U joint had frozen up which caused it to crack the transmission housing in two!

I've changed plenty of U-joints on pickups, but always heard a click or some tell-tale signal beforehand.

Sure wish I would have thought to check them in this case! It might have saved me $1800. But after a rebuilt trannie, we've got about 220,000 miles on it now and it's still running strong.

Howard

Everything else seems normal? Does it upshift okay? Plenty of pep?

Any unfamiliar noises like a squealing sound coming from underneath or up forward?

Allan

No unusual noises other than anything related to the shudder. We have been avoiding driving it unless absolutely necessary so as not to do anything further if we can help it.

A little more info as requested...We have 286k miles on the vehicle, seems to drive OK otherwise. Good engine response. Engine does use more oil than I would like (probably a quart in 3000 miles) but I feel like I have gotten my use from it. At this point I don't want to describe the vehicle as disposable, but if repairs get to dicey, the cash will probably go towards a new/nearly new one. I do like this older style though. I think they are heavier than the new ones and make better tow vehicles. Ours is used pretty regularly for the two horse trailer.

Thanks Again,

Kirk

With those kinds of miles and since you've been using it to tow, that transmission could very well be ready to fall out on the ground, who knows?

All I'm saying is to be careful in your diagonsis. Those darned things can fool a guy, especially those old Chevy trannys. Something fairly simple up in that engine department can make ya think you have major tranny problems.

Have your mechanic check it out, run his scans like you were planning to do/like the other guys say and if he comes up nil on the tranny codes, have him do a cylinder balance test while he is at it.

That "shudder" and a weak idle just "smells" like a weak hole to me. Could be something as simple as a faulty plug wire or a cracked plug.

Heck, I've seen engines locked up tight, truck hanging on a tow hook, the owner just about in tears and come to find out, the only problem was a $2 bearing at the alternator and the 'ol boy was driving out the door in 20 minutes.

Hope ya get 'er figured out and hope it doesn't skin your wallet,

Allan

This one is certainly not held together with spit and baling twine yet, but after 13-14 years and quite a few miles you kind of start to wonder when to let go.

Regarding towing, for us regular probably amounts to twice a month over the summer and monthly over the winter figure 18 times a year and rarely over 50 miles round trip. Often only one hay burner if we are going to one of my daughter's shows.

Thanks again for the insight,

Kirk

You`re ahead of the game if your gonna get it scanned. In 94 most powertrain codes won`t turn on the check engine light, but they will be stored in memory.

Bob is right about there being a range of causes, if you get it scanned and get any codes post them back here and I can hopefully point you in a direction. Be sure to get the code numbers, not the definitions, the def varies from tool to tool.

Also with a scan tool he should be able to enter the datastream(watch all the sensors and peramiters). Depending on the tool there should be one for TCC slip RPM, if when the truck is vibrating that RPM climbs up over 75 or so, more than likely your converter is causing the vibration.

Another not so sure fire way to tell if the converter is causing the vibration is to get up to speed(get it to start vibrating)then while holding your foot steady on the gas, press your other foot lightly on the brake. If the engine RPM jumps up a bit and the shudder stops, more than likely it`s in the converter. I should say that you eliminate the driveline(ujoints,dif).
What you are doing is activating the brake switch and that signal releases the converter lock-up clutch..

Sorry for the long post, these naughty buggers are my life, so I can tend to get long winded.

In my opinion this is a great transmission.
Much better than the 700R4, just don`t tell Allan I said that..SSSSHHHHH H
Good Luck BW

The causes for this range from some simple electrical causes to some "hydraulic" issues in the valve body, to the need to replace the torque converter.

Something gone wrong in the converter COULD cause some vibration issues, as well, or you may simply have a bad "U" joint.

Has the "service engine" light come on? Whether or not it has, a scan tool will likely shed some light on what is going on with the tranny.

So far I have not seen the service engine light come on.

Thanks,

Kirk