722.3xx Transmission... today's job - Page 2 - PeachParts Mercedes-Benz Forum

dennislarock · #1 03-03-2017, 05:25 PM

Quote:

Originally Posted by MBCAJUN

My son and I put a 1984 trans into a 1985 car with no big problems. We did bypass the "blue flying saucer" in an attempt to correct shifting problems but it might not have been the problem. Car was still running and shifting great when he sold it recently. Only problem was a mile or two difference in the speedometer.

Hey Ed! I'm a big fan of the Vacuum Amplifier (Blue Flying Saucer) I will probably put the whole unit in. I did get the engine & tranny ready to pull today... I have a mini excavator @ the ready to lift it out if the *new* *properly* adjusted modulator fails tomorrow.

I've been out of this car thingy for about a year or so... and, my memory ain't what it used to be but we are dealing with 722.315 and 3:07 for both years. Wonder how a 2:88 would be in a D?

Ed... did I tell you I bought five Lionel Locomotives in December (Christmas present to myself)? We have to get some train time in... you will crap your pants when you see them!

dennislarock · #2 03-04-2017, 07:24 AM

Headed out to install new modulator and pressure test/adjust.

Here's a little diddy on the *Blue Flying Saucer* of the '85 (and why I like it) should I go that route....

The vacuum modulator with high vacuum softens the shifts at a low throttle response and a modulator with lower vacuum firms up the shifts with more throttle. This is predicated only on throttle position and no other variables.

On the 1985 models, Mercedes engineered a transmission vacuum system that didn’t just rely on throttle position to control the softness or firmness of shifting. It also relies on turbo boost pressure which becomes dependent on engine load and temperature.

The vacuum transducer/amplifier (blue flying saucer) works in relation to turbo boost pressure and engine temperature. Unlike the prior years, the system now starts off at a high vacuum of 12-17 Hg to the modulator. It now leaks down five inches when full throttle travel is given. When the turbo boost pressure goes up, the boost applies an input to the vacuum transducer. This produces an upward deflection of the transducer diaphragm, lowering the amount of full vacuum applied to the modulator valve to zero. The hydraulic modulating pressure in the transmission is increased which firms up the shifting.

MBCAJUN · #3 03-04-2017, 12:05 PM

Quote:

Originally Posted by dennislarock

Headed out to install new modulator and pressure test/adjust.

Here's a little diddy on the *Blue Flying Saucer* of the '85 (and why I like it) should I go that route....

The vacuum modulator with high vacuum softens the shifts at a low throttle response and a modulator with lower vacuum firms up the shifts with more throttle. This is predicated only on throttle position and no other variables.

On the 1985 models, Mercedes engineered a transmission vacuum system that didn’t just rely on throttle position to control the softness or firmness of shifting. It also relies on turbo boost pressure which becomes dependent on engine load and temperature.

The vacuum transducer/amplifier (blue flying saucer) works in relation to turbo boost pressure and engine temperature. Unlike the prior years, the system now starts off at a high vacuum of 12-17 Hg to the modulator. It now leaks down five inches when full throttle travel is given. When the turbo boost pressure goes up, the boost applies an input to the vacuum transducer. This produces an upward deflection of the transducer diaphragm, lowering the amount of full vacuum applied to the modulator valve to zero. The hydraulic modulating pressure in the transmission is increased which firms up the shifting.

Good post! Probably the problems we experienced when replacing our trans were not related to the actual transducer. More than likely we fixed ours by bypassing a hose leak. Hope your new modulator solves your problem and you can avoid replacing the trans. Good luck, keep us posted.

dennislarock · #4 03-04-2017, 01:13 PM

NOPE!!!! DANG IT!!!! Should have went with my gut. New tranny time. 5 fracking hours... I could *not* get the *new* *improved* MB Modulator in. Try as I might... *very* clean, patiently, methodically, very straight, very square, lubricated O-Ring ...I could not get it in. I did not *tap* it as I never was able to get the modulator & O-ring even started. Put the old one back in... in ten minutes.

Moving on... I'm pizzed!

kuene · #5 03-04-2017, 01:30 PM

ugh, that sucks to hear. I hope I have better luck as I'm just about to try putting my new one it. It was a pain in the ass getting the old one out - that is for sure. If you are taking your transmission out - then you are disconnecting the driveshaft entirely, seems like you'd then have then more room to push the tranny to side and attempt to get the new modulator in, no?

If i can't get it in there by hand, I'm thinking about trying my caliper piston spreading tool, as a way to maybe use it between the modulator and side of transmission tunnel to press the new one in. Kinda like an inverse c-clamp that can spread out in some very tight areas.

dennislarock · #6 03-04-2017, 01:42 PM

After I take the one out of the '85 I will go ahead and put new springs, piston, modulator, seals in *before* I install it. With the tranny completely out and sitting on a bench it will be a piece of cake.

I dropped the rear of the tranny and had no problems getting the old one out and back in... I did pressure test it and set it to 2.9 bar ...but, it could still be bad.

It was impossible (for me) to see or feel the entirety of the o-ring and whether or not it was seating properly... I could have winged it and tapped/levered/pressed but I was not comfortable that it would have *fallen* into place ...I've not that sort of luck.

kuene · #7 03-05-2017, 06:01 PM

I wish I had read of your struggles before I took mine out earlier this week. I spent like 3-4 hours today trying to get the new one in. I don't think it is possible while the tranny is in the car. There is just NO way to get it seated, and I think I may have broken it in the process. It's easy to get the old one back in because the o-ring is pretty flattened out.

I just don't know what to do now. With my experiences so far (several attempts just to get old one out, now stumped getting new one in) I think it's ridiculous that anyone would say its a reasonable idea to do this with the transmission installed. I want to roll my car off a cliff after today!