: Wierd shudder - torque converter?

02-22-10, 07:09 PM
My car shudders cruising in fourth gear under light acceleration

I have a 99 SLS with 218,000 miles. Its had the P0741 for about three years. Last year I changed the tcc solenoid in an effort to pass emissions, it did nothing. later found out I needed to have another code, P18something for it to mean a solenoid. My car has never shown this code.

From what I understand, this indicates a bad seal in the torque converter not allowing enough pressure to engage the lockup clutch.

Since I was lucky enough to find a loophole to avoid emissions, it didn't seem worth it to drop the cradle again. The SES light just became a part of the background after a little while.

Fast-forward one year:
During the winter (Boston), the car started exhibiting a strange problem. After sitting all night, it would act like a stall converter and need some revs before it would move. I just attributed this to the same seals allowing a leakdown. Which, combined with the viscosity of the oil at that temperature, would create a delay before the converter filled up and started to work. No big deal, just let the car run for 10-20 seconds before you put it in gear.

This brings us to present day.

The car just started exhibiting a shudder at cruising speed. Let me try and describe the problem as well as I can:
It feels like a misfire. It happens when I'm in fourth gear around 35-45mph, 1600-1800rpm under light load, like going up a hill or just speeding up a few mph. The tach bounces a bit, maybe up an down 100-200rpm when this happens.

This is the ONLY time this happens, and it doesn't even happen all the time. In fact, I haven't been able to reproduce it in the last two days. Otherwise the car runs and drives great, idles smooth, pulls hard, no shudder under any other conditions.

Plugs and wires are confirmed good, and there are no misfire codes, so I think we can eliminate a misfire. The tranny fluid level is fine, but its a little brown and maybe a little burnt, but i'm not really sure what burnt ATF is supposed to smell like (I've never lost a tranny in any of the old-ass GM vehicles I've owned over the years), and it was never particularly red.

A friend with moderate mechanical experience said that maybe it was a wobble in the torque converter bearings, and he said the fluid was burnt.
This makes sense, since the converter obviously isn't right.

First of all, what do you guys think this is? Am I on the right track here?

If so, does this mean the end for my 4t80 or can I save this thing? I'm especially worried about the burnt fluid. I know if you change fluid in a desperate attempt to fix a worn out tranny, it usually expedites the process. This thing doesn't slip or anything, and I don't see any metal in the fluid on the dipstick. I want to flush this shit out immediately, but I don't want to kill the thing even faster. Did it burn because of the slipping converter, or something deeper inside the autobox?

I'm willing to change the converter if that's all that's wrong, and I can expect to get more service out of what seems to still be a solidly running trans. I dropped the cradle for the TCC solenoid, and I've done a motor swap and a head gasket job on a couple of Eldos, so I'm not sweating the job.

I don't want to bother if the tranny is terminal. Is this something anyone has seen before and successfully repaired?

Sorry about the novel! Thanks for reading and your feedback

02-22-10, 09:08 PM
How do you know that the wires are good?

See if this sounds familiar.

02-22-10, 09:37 PM
.............and go ahead, change the transmission fluid to the new DEXRON-VI synthetic, used as standard fill since the 2006 model year began, and is 100% backwards-compatible with the old DEXRON-III.

If the fluid is now brownish and even remotely smells burnt you will hurt NOTHING by changing it - changing it, not flushing it. Have a GM dealer do it and don't obsess over how or why they do what they do.

Also, follow Ranger's advice and try to track down a possible plug/wire/coil fault.

02-23-10, 04:55 PM
How do you know that the wires are good?

I guess I don't. I had a valve cover leaking oil into the spark plug tubes about 6 months ago, so I repaired that and changed plugs/wires. I pulled the #8 plug and it was fine, and a visual inspection of the wires showed no damage.

If the fluid is now brownish and even remotely smells burnt you will hurt NOTHING by changing it - changing it, not flushing it. Have a GM dealer do it and don't obsess over how or why they do what they do.

I definitely want to get this fluid out ASAP. the car will not be going to a GM dealer for anything. I've never brought a car to another mechanic in my life, and I'm not about to start now. Is there a reason not to flush it? If I drain the pan and refill, I'm not really accomplishing much, just mixing a couple quarts of fresh stuff in, that doesn't seem very productive to me. Wouldn't it be best to pump it out the cooler line as I refill? Or am I mixing up the terminology here?

02-23-10, 05:49 PM
So the wires are 6 months old? I guess we can assume they are good then.

02-23-10, 06:36 PM
are you sure you replaced the tcc solonoid??

rock auto lists 3 solonoids under tcc, i bought the wrong one, found out after it showed up.

The pressure solonoid is the one i got, but it was listed under tcc

02-24-10, 06:12 PM
Hi, I posted about the same thing, and was given this response by carnut.

At the speed and RPM you describe is when the torque converter just locks up. The reason Ranger asked about plugs and wires is because once the torque converter locks up secondary ignition misfires can be felt. You can confirm this by keeping the RPM steady with your right foot and gently depressing the brake pedal with your left. The brake switch disengages the TC lock up and the RPM should increase maybe 500 RPM. The term studder is fairly accurate, tehnicians call it a "CHUGGLE" The new DEXTRON MERCON TYPE IV fluid was designed to lessen chuggle because its synthetic and has more lubricitity. You might be just feeling a normal TC engagement.

02-25-10, 08:23 AM
DEXRON-VI. TCC engagement drops engine rpm by about 300 and is usually a very smooth, imperceptible operation. Even the test sequence (steady speed, flat road, hold the gas steady, touch the brake pedal with left foot, watch for 300 rpm increase, no speed change) is a smooth operation with NO shift clunks or bumps.

Does the 4T80E have a torque converter drainback check valve like the -65E ? If it does, then the drainback valve might have a chip under the ball, allowing the converter fluid to partially drain overnight.

02-25-10, 11:58 AM
I will eventually exchange my fluid with DEXRON VI.

02-25-10, 04:07 PM
I will eventually exchange my fluid with DEXRON VI.

At 218,000 miles, if it were me, I would save my money on the Dexron VI fluid change, drop that cradle again (only partly), and apply that money toward a rebuilt transaxle and torque converter. If you are willing and able to do the R and R yourself, that would be a big part of the expense - here's a link I found for a rebuilt for $1,300.00 - probably you could find one locally and for even less:


02-25-10, 08:29 PM
Keep in mind that I am not the OP. Mine has 103,000 miles :P