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Old 07-19-2003, 03:45 PM
Posts: n/a
Geez Steve,

For response shortness, I didn't feel the need to explain that A. I had a financial reversal after buying the car and B. Even though I knew the seller and trusted his opinions and the car's history I had the car checked over before committing by an MB tech you probably know, and C. Not only did I look the car over hard myself, but I pounded it home to Minnesota and it performed perfectly, and D. I had a backup vehicle just in case. At first the car ran so well and I had such confidence, that when the money problem arose and I got an offer for the back up car, I took it....big mistake. But ok, dumbness point taken and 20-20 hindsight doesn't solve the present problem. Back to it, in response to Peter's latest post.

Your tranny problem is the stuck pin -- if it won't move, it cannot transmit pressure to the control valve the modulator operates. Clean it off, clean the bore (no abrasives, please) and see it you can get it to slide freely. If not, get a new one. Also make sure it isn't in backwards -- I've not seen one, so I don't know if you can install incorrectly or not.

This hardened steel pin was stuck into its recess inside the old modulator, but the diaphragm inside seemed to be working as the pin would rock from side to side. When I got it out with vise grips, it looked liked caked ATF had caused it to be stuck. The steel is so hard, the vise grips made no mark and it fit loosly into the new modulator, which I presume is normal. I can't get up between the frame and the modulator hole to peer inside, but I imagine there is something the pin's end fits into inside the tranny.

Does the tranny shift more firmly at wide throttle? If so, the modulator is working.

NO. I have to start from a stop very slowly and then both the 2-3 shift and the 3-4 shift are VERY smooth. The 3-4 shift happens at 30mph, and slips until about 45 when it seems to finally lock in and I can then accelerate normally. If I try to accelerate before then, it slips.

Another thought is to replace the filter in the tranny, but a filter and fluid change on an old transmission can be worse than leaving it alone.....

There was a filter change 8K ago (part of my checking before purchase though all the receipt said was "transmission service- 162K) and with the radiator change and still another change of fluid when replacing the modulator, the fluid is certainly fresh.

That braket is a possible source of the vibration, by the way -- it is supposed to have a clamp on it that holds the exhaust up at the rear of the tranny. No bracket, and it will vibrate badly at resonance speed, and cause the exhaust to drum on the floor pads. Also check the rubber rings that hold the exhaust up at the rear, if they are stretched or broken, the rear muffler will pound on the body pad there making a horrible thunder.

Yup, it does do that. Exhaust is all new. (something else I checked) Doughnuts are all in place, but somewhere near the muffler there is a loud heat shield type rattle when sitting at idle and the compressor running. I haven't tried to hard yet to find it, partly because I have these more pressing problems, partly because the florida plate on the rear was vibrating and loose too, and hoping this was the problem, I waited till the Minnesota plates arrived (2 days ago) before epoxying the loose female license plate bushings tight. And finally, when I get out of the car and my 240 pounds aren't lowering the car, the rattle/vibration disappears, so I need a fat friend to sit in the car while I search.

The rear tranny mount gets soft when it goes bad, so the tranny can move up and down. This causes a drumming on acceleration, otherwise it's usually quiet.

Then the tranny mount rubber is probably bad and so the source of my vibration at speed problem. When I removed it to get wrench access to the modulator, I first took out the two bolts in the center of the mount's support bracket, and then the 4 bolts holding the support bracket. With the bracket off, there is this odd metal part around the rubber that has an allen head bolt which passes thru the rubber and holds the bracket itself in place loosely and the bottom of this odd part is where the bolt holes are that connect the mount to the support bracket. I had to push hard to get the bracket close enough to the frame to get the bolts back in, but lying under the car which was up on ramps, I doubt that I was exerting more than 40-50 pounds of push...far less than I'd guess it would take to adequately support the tranny.

I read Steve's article on modulator adjustment, and while I've been calling friends to see if I can borrow a vac gauge, I haven't had luck yet, so here's what I have tried. I put in a new modulator last night leaving it set just as it came out of the box. Refilled the tranny and went for a drive. No change. Talking to the same tech who blessed the car, he said to turn the key in about 4 turns and try again. No change.

Thinking it possible a leak on the door vacuum was denying vacuum to the modulator, I went to the manifold connection, unscrewed everything, cleaned the residue of ATF off and stuck my head down into the compartment and blew into the hose with the door side blocked, figuring if I could force air through there would be a hose leak. That didn't reveal anything. So before I put the door side hose back on the manifold fitting, I put elec. tape over the nipple and then pushed the hose on on the guess that this would redirect vacuum to the modulator line. Then I went to the store and bought 8 feet of vacuum line. No change on this drive. If anything it might have slipped a bit more. I'm typing this, waiting for the car to cool down enough that I can pull the hose at the modulator, start the car and see if I can feel vacuum with my finger over the hose end. If I do, then I'm guessing that while the old modulator was bad (ATF leak), the real problem is inside the tranny. If I don't feel vacuum, I'll bypass the entire old line with new hose.

Is my plan logical?

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