Trans. Vacuum Modulator Adjustment

[dbmoylan]

Would anyone happen to know how to measure the pressure when setting a 722.502 transmission vacuum modulator(1993 Benz 300SE / W140)? I understand it is suppose to be about 30 bar trans. pressure and measured when the car is moving. Needed to understand which parts of the transmission the gauge & hose are suppose to be hooked into & procedure for measuring.

Also understand that counterclockwise adjustment on the modulator "T" reduces harshness of shifts, and clockwise makes engage faster. Thanks.

 

[television]

Try this young man

http://www.peachparts.com/Wikka/Trans722VacMod

 

[dbmoylan]

Malcolm . . . you're the guardian angel!

Can you please confirm where's a banjo bolt gotten from - what is "ALDA" as mentioned in that thread?

Thanks again.

 

[television]

We also have one very good thread on here from a while back, just one, I will try and find it

 

[Number_Cruncher]

ALDA is Mercedes speak for the boost control diaphragm on the injector pump - only applicable to pre 1996 turbo diesel models.

What problem are you having?

 

[roofless]

some info here that might help http://www.mercedesdismantlers.com/AutomaticTransmissionInformation.html

 

[dbmoylan]

Thanks guys. I'm now trying to track down the proper modulator pressure for my 722.502 transmission. I've seen readings for different earlier models at about 3 bar (27psi), and mine may be 4 bar (58 psi). I understand the values are in a TDM, but don't have access to that manual. Was able to locate a banjo bolt kit on Ebay. Any help is appreciated.

 

[Number_Cruncher]

It's quite a difficult/odd test to do;

The vacuum needs to be disconnected from the modulator valve, and you need to run the car at 31 mph with full throttle - using the brakes to keep to 31mph.

It might be safer to do on a rolling road rather than on the road itself.

The closest I can find in my info - for 722.507 and 722.508, the modulating pressure should be 58 psi

Are you having a specific problem, or, have you just overhauled the gearbox?

 

[dbmoylan]

Number Cruncher, thanks for your email. I had the trans./gearbox overhauled a few months ago & had a new modulator (updated version) installed during the rebuild. The trans. shop did not do the reinstall & was not responsible for the adjustment of the modulator.

I did not like the harshness of the shifts (but realize the harsher the better for less pad wearing). I also read Benz factory materials that recommend the calibration of the modulator w/ the pressure values and not doing it by "feel." Malcolm's link/help seems to indicate that calibrating it in park w/ engine on is acceptable & I want to make sure I'm in the ballpark vs. having a modulator that is way out of specs. Doing the test when the car is running and using the brake to keep at 31 seems a bit intense (but yes, that is what the procedure calls for).

At a min., if the modulator is calibrated properly, then I know any harsh shift symptoms would likely be another issue (like possibly the valve body). Shifting harshness is not that bad though, only really noticeable at slow speeds (city driving) vs. at high speeds where it seems for the most part OK. My 1993 722.502 trans. only had about 60K miles before the reverse gear started to fail & had very bad flaring in forward shifts. Even had the valve body sent to Silver Star Trans. in OK, USA to make sure I got a good rebuild as they don't have a dynotester locally.

Thank you.

 

[Number_Cruncher]

>>Malcolm's link/help seems to indicate that calibrating it in park w/ engine on is acceptable

I would tend not to agree with that part of the link.

If you consult the hydraulic diagram for these gearboxes, you'll see there's an interplay between working pressure and modulating pressure, and governor pressure and modulating pressure, and kickdown pressue and working pressure. Phrased another way, engine load, engine speed and vehicle speed have an input to determining what modulaotr pressure is. I suspect it's the difference between getting the setting somewhere near, and getting it right.

 

[dbmoylan]

I can't disagree w/ you Number Cruncher. I'm a by the book type person myself. At the same time, I see some mechanics do some time honored tricks that get things going w/ much less pain. On this subject I just don't know & would like to try the harder procedure if I can get my act together & then compare it to parking pressure as the web article suggests.

An update to my post is that I tested the modulator (relatively new) and was surprised to see it leaking down the vacuum applied. I removed it & replaced the Benz updated modulator w/ an Efebe brand (original equipped unit w/ my car) and the car worked remarkably better (no harsh shifting). Still have to get/make the proper test gauge for the modulator pressure though (still working on that). The fitting for my 722.502 modulator pressure bolt - that the web article didn't clarify is actually 8mm x 1. Need to get a banjo fitting in this size (not 12 x 1.25).

 

[television]

Number cruncher is a wonderful guy and by the book in great detail, and is the first guy that I have met on a forum that goes into the detail that he does, I have had to amend some post thanks to him, and that cant be a bad thing.

Some things can be done a little easier, and other ways found on doing jobs,,at least he points out the correct way, so thank you for that.

 

[Number_Cruncher]

Thank Malcolm.

I know that I am a bit of an extremeist, and that sometimes that isn't what people might want to hear - and I apologise if sometimes that's problematic!

However, I take the view that part of what you're buying with a MB is the time and money that has been spent by MB in developing the cars. Nearly everything I've seen so far, with very few exceptions makes me think that the engineers at MB are thinking carefully and deeply when they design the cars, and write the service procedures. I simply don't know anywhere near enough to know when it's OK to deviate from the procedures or from original replacement parts.

>>then compare it to parking pressure as the web article suggests.

That would be a really interesting result. My bet (virtual pint?) would be that performing the test when parked gets you close, but, not bang on. Whether that's close enough is another matter!

>>the car worked remarkably better (no harsh shifting).

That's a good result already. Other vacuum leaks in the same circuit will also make the gearbox tend towards harshness. I don't know the layout on your car, but, I would imagine the vacuum circuit for the modulator should be separated from the rest of the circuit by a restrictor or two.

 

[television]

At least number cruncher you give us the correct way to do these jobs, and no one can argue with that

 

[dbmoylan]

Thanks guys for spending your time to even share your experiences. My 722.502 trans. w/ a M104.990 works off of the intake manifold vacuum to regulate the trans. vacuum modulator.

Since the rebuild, obviously I've been keen to monitor the transmission's performance since it was pretty traumatic & a real learning experience getting into the most complicated part of this "beast." My approach is to put everything back to factory spec. & move on to next system to evaluate whether that was the cause. The harsh shifting was the symptom of a problem & the most likely culprit (if you're lucky) is the vacuum modulator & its performance & adjustment.

I understand that that module can actually even bleed trans. fluid into the intake manifold when failing and/or fail to move in or out (1st sign is colored exhaust indicating engine burning the trans. fluid). Worse case would be that you don't catch it and the fluid gets so low that the trans. wears due to low fluid (most people don't check their trans. fluid regularly, esp. if they don't see a leak under the car).

In this case Benz's redesigned modulator (which was practically new) apparently is no longer maintaining a vacuum, though it is still moving when a vacuum is applied. Still observing but my test so far showed an elimination of the harsh shift and now adjustments are needed to put into a factory-spec. type shift (don't like flaring of gear shifts vs. harsh shifts which I know are better on the pads).

Anyhow, am hunting down a 8mm x 1 fitting or banjo connection to build my tester for this model trans.

If anyone has the psi/bar specs. I should calibrate the modulator to for a 722.502 trans. I'd appreciate them. I am suspecting it's a 4 bar / 58 psi reading I will be calibrating the modulator to.

 

[television]

Can I have the cars first 6 vin numbers its easier to find with them

 

[dbmoylan]

Thanks Malcolm - WDBGA3.

 

[television]

Is not it a 140 ??? the next 3

 

[television]

I have found the info that you require

It is 4.2 on the 502 box

Just for reference its 3.8 on the 500/501 and 3.6 on the 504/505 and 506. On the 503/507and 508and 509 it 4

All in bars.

 

[dbmoylan]

Thanks Malcolm. The VIN is WDBGA32E9PA107945 & is a W140. The chassis is 140.032 12. Is that modulator pressure the same as what you just posted?