It's CRITICAL... how you set your transmission's vacuum system on your diesel MBZ... - PeachParts Mercedes-Benz Forum

dieseldan44 · #1 12-16-2006, 01:15 PM

the saga contnues...

i swapped out my modulator last night and went for a test drive today. i am very sorry to say it made no appreaciable difference. here's what i did:

-replaced modulator
-put modulator pin in a 'midway' setting
-tested vacuum - modulator held vacuum in car, -vacuum looked good, went down from 10 to 0 at full throttle smoothly like it should
-went for a drive. no big difference. doh. i was hoping for some flaring or smoother shifting or something different now that theres some vac present.

i would have expected to at least have some difference, no matter what the setting of the modulator was as long as it was something.

so what do I do now? i have replaced every vacuum component, finding a problem at every stage. is there anything else i can do at this point? can i more directly test whats going on with whatever recieves the vac signal in the trans?

here's some more info for troubleshooting:
-i drained the trans pan last night. fluid was perfectly red. no metal, burning or otherwise bad signs.
-FWIW my transmission looks new.
-im pretty sure i have bad engine mounts and engine shocks. vibrations at idle, engine throbs a lot went shut off. could this affect anything?
- i definitely have bad rear axles, PO drove on them for a while. they creak when car is being driven at low speeds. dont know if this makes a difference. could this make all of the shifts seem poor?
- is there something else that would make the shifts seems poor?

i have a sinking feeling that i am starting to get into painful territory.

please advise....
dd

Brian Carlton · #2 12-16-2006, 03:36 PM

Quote:

Originally Posted by dieseldan44

so what do I do now? i have replaced every vacuum component, finding a problem at every stage. is there anything else i can do at this point? can i more directly test whats going on with whatever recieves the vac signal in the trans?

Getting the modulator to hold vacuum is only the first step. Now that it does, you can tune the VCV. Don't give up the ghost now. Hopefully, additional vacuum to the modulator will soften the shifts.

Adjust the VCV so that it puts out 15-16" to the trans at idle. Then drive it and observe any differences.

If the modulator is working properly, the change in vacuum must affect the shifts.

Samuel M. Ross · #3 12-16-2006, 04:01 PM

Quote:

Originally Posted by dieseldan44

the saga contnues...
-went for a drive. no big difference. doh. i was hoping for some flaring or smoother shifting or something different now that theres some vac present.... please advise....
dd

DD - Don't give up after coming so far.

Clarify how the tranny is shifting when you drive... is it shifting quickly from 1-to-2-to-3... and 4th gears?

IF YES to the above, then take a healthy 3 full turn to the right on the modulator "T" key adjuster.

Regards,

Brian Carlton · #4 12-16-2006, 04:04 PM

Quote:

Originally Posted by Samuel M. Ross

IF YES to the above, then take a healthy 3 full turn to the right on the modulator "T" key adjuster. [/B]

Adjusting the modulator to the right (clockwise) will increase modulator pressure.........AFAIK.

Samuel M. Ross · #5 12-16-2006, 05:46 PM

Quote:

Originally Posted by Samuel M. Ross

DD - Don't give up after coming so far.
Clarify how the tranny is shifting when you drive... is it shifting quickly from 1-to-2-to-3... and 4th gears?
IF YES to the above, then take a healthy 3 full turn[s] to the right on the modulator "T" key adjuster.
Regards,

Above is the full text of what I said... maybe I should have said "softly" AND quickly.
What the heck does "AFAIK" mean anyway Brian ?
Keep talking to us " DD " so we will know for sure what's happening!
Regards,

Brian Carlton · #6 12-16-2006, 06:23 PM

Quote:

Originally Posted by Samuel M. Ross

Above is the full text of what I said... maybe I should have said "softly" AND quickly.
What the heck does "AFAIK" mean anyway Brian ?
Keep talking to us " DD " so we will know for sure what's happening!
Regards,

AFAIK: "as far as I know"

If the modulator is turned clockwise, the pressure will increase, as far as I know..........this would cause the shifts to get intolerably harsh.

Samuel M. Ross · #7 12-16-2006, 07:16 PM

Quote:

Originally Posted by dieseldan44

the saga contnues...
i swapped out my modulator last night and went for a test drive today. i am very sorry to say it made no appreaciable difference...
Please advise... dd

... yes, I made a concerted effort to find what your shifting symptoms were DD... so would your repeat them so I can advise how you might want to adjust the mid-range setting on your modulator!
Regards,

dieseldan44 · #8 12-17-2006, 12:41 AM

Here's a detailed description of whats going on:

-all shifts are somewhat late. they seem to be inconsistent, somewhere between 2500-4000. i know i need to make a bowdern cable adjustment here.
-1/2 is the harshest. shifts strongly into gear, car pops forward.
-2/3 is harh, less harsh than 1/2
-3/4 is harsh, but a little better than 2/3. maybe its better just because the car is moving faster.
-downshifts are similar to the upshifts of the same gears
-shifting into gear while stopped car noticeable hard shifts into gear. going into reverse the car 'snaps' to attention, the back end lifts up a couple inches noticeably. could this be due to slop somewhere else in the drive train?
-all of these symptoms seem a little inconsistent. because the car needs other work i have been relucant to cruise around anymore than necessary in fear of making something else work. therefore, i dont have a ton of time behind the wheel wiith the problems happening.

The part of this that's troubling to me is that these symptoms haven't changed through all of the vacuum fixes. especially now that I *know* that at least some vacuum system signal is being correctly delivered to the vavle body.

My next step is to adjust the bowden cable and modulator again and just seem if theres a difference. should I adjust the modulator or VCV first?

what task am i looking at if the vacuum signal reciever in the valve body is not working? i'd imagine that since the transmission is shifting strongly that I am not in rebuild territory....but first things first, i havent given up on this.

Brian and Sam, thanks again for all of your help. what kind of data can I give you guys that would be helpful? would a movie of driving and looking at the tach be helpful?

thanks again,
dd

Samuel M. Ross · #9 12-17-2006, 01:12 AM

nursing a bad back so let me get back to ya tomorrow a.m. I thought your car had the more traditional soft/early shifts... but there are some ideas roaming around in my head that MIGHT help. Just a thought... a GOOD dealer man can take the tranny's S/N and compare it to the VIN and tell you IF it is original to the car! How many miles to you think the car has?
Regards,

dieseldan44 · #10 12-17-2006, 09:48 AM

the car has a legit 206k miles. the trans does look newer. in fact it looks downright new sitting under there. ill find out from my dealer Monday. where's the serial # under there? i havent seen it yet in my undercar travels...

Sam, sorry to hear about your back...

dd

Samuel M. Ross · #11 12-17-2006, 10:51 AM

Quote:

Originally Posted by dieseldan44

the car has a legit 206k miles. the trans does look newer. in fact it looks downright new sitting under there. ill find out from my dealer Monday. where's the serial # under there? i havent seen it yet in my undercar travels... dd

On our 1980(s) models the # are on the right side [looking forward]... just above the tranny pan... along the edge of the case of the transmission.
There are typically two #(s) E.g. - 1232703201... & 722.118.02.098161. I think the last of these includes a S/N where the 1st is the MBz P/N.
I still intend to go over your previous POST and get back to ya. I'm thinking that you need to turn the modulator adjuster " key " to the left but wait until I can examine you POST.
Regards,

Samuel M. Ross · #12 12-17-2006, 01:46 PM

WELL……….. you sure have a lot running through your mind about this project!!!... maybe too much? Let’s see if we can sort things out a bit… one thing at a time !

You had a lot in the POST below so I have edited it and put my comments [in RED] inside the quote box so it’s easier for you and others to follow along with my thoughts without going back-and-forth!

Quote:

Originally Posted by dieseldan44

Here's a detailed description of what’s going on:

[a] - all shifts are somewhat late. they seem to be inconsistent, somewhere between 2500-4000. [I’m taking this to mean hard shifting ]
[b] i know i need to make a bowden cable adjustment here.
[I have absolutely NO experience with Bowden cables… but IF we trust what is said in this POST: 1992 w124 Vacuum Control Valve Operation “The Bowden cable only controls shift points (speed/RPM), not shift firmness.” ... maybe this does need to be done. Let’s see IF Brian will make comment on this.
[c] - 1/2 is the harshest. shifts strongly into gear, car pops forward.
[ Well my first inclination is to ask you to make sure you have a functioning green “ dashpot ” chamber installed on the top of the VCV to reduce “surge” which is typically worst for the ½ shift. I have added these to both of our 1980 models for this reason. Vacuum test the chamber to make sure it does not have a crack. If you do find a crack somewhere airplane glue should fix it. ]
…. -2/3 is harsh, less harsh than 1/2
…..-3/4 is harsh, but a little better than 2/3.
……maybe its better just because the car is moving faster.
[d] - downshifts are similar to the up-shifts of the same gears
[e] -shifting into gear while stopped car noticeable hard shifts into gear. going into reverse the car 'snaps' to attention, the back end lifts up a couple inches noticeably. could this be due to slop somewhere else in the drive train?
[f] -all of these symptoms seem a little inconsistent. because the car needs other work i have been reluctant to cruise around anymore than necessary in fear of making something else work. therefore, i dont have a ton of time behind the wheel with the problems happening.
[ In response to ALL the above, I would take a healthy 3 to 5 full turns TO THE LEFT on the vacuum modulator “ T / Key ” adjuster and see if this makes any noticeable difference. This is a good time to suggest a diagnostic step that I used that is somewhat similar to what Brian has related… namely after make a 5-turn to left adjustment you drive the car with all the vacuum control system hooked up… note how the tranny shifts… and immediately disconnect the vacuum line to the modulator (in engine compartment) and note how the tranny shifts again – report back the results) ]

The part of this that's troubling to me is that these symptoms haven't changed through all of the vacuum fixes. especially now that I *know* that at least some vacuum system signal is being correctly delivered to the vavle body. My next step is to adjust the bowden cable and modulator again and just see if there’s a difference.
[ I canNOT help you with this but I know there are tons of POSTs on the FORUM to help you and IF my back allows will do some research to see what I can come up with !]
[g] should I adjust the modulator or VCV first?
[ I think it is safe to say the VCV is at least close to the proper setting… so lets work with your new modulator for now ]
[h] what task am i looking at if the vacuum signal receiver in the valve body is not working? [ not sure what that component is… let’s not go there yet ]

[i] i'd imagine that since the transmission is shifting strongly that I am not in rebuild territory [ I agree ] … but first things first, i havent given up on this.

Brian and Sam, thanks again for all of your help. what kind of data can I give you guys that would be helpful? would a movie of driving and looking at the tach be helpful?
thanks again,
dd

Merry Christmas Dan !,