Creating more bleed for at transmission

[seth411]

Or I guess I should say creating more restriction.
I replaced my break booster line and the orifices are much bigger. Now I have to much vacuum to my AT. Idles at 22 hg.
I've been searching and reading and I can't seem to find how to create more bleed for my AT. I've followed the petershmit diagram for my 80 300td and still do not get a anything lower than 10hg driving around with awful flaring.
http://peterschmidtransmission.com/vacuum/1980/123_1.jpg

I'm currently reading the book It's CRITICAL... how you set your transmission's vacuum system on your diesel MBZ...

Thanks for any help

[yellit]

If you search the DIY articles under (General) the last one is on vacuum tuning the transmission...
If you have too much vacuum you probably have accidentally removed the orifice that feeds the line to the valve network on top of the valve cover..(this is the vac source to the bleed network)....( the main orifice is located in the side tee on the big vac line )

When I first tried to do this I removed it by mistake and tried to compensate by adjusting the IP linkage bleed valve (which can be done) but I was wasting vacuum and the IP valve sounded like a wounded animal from the excessive air flow......

I used a small brass plumbing valve as an adjustable orifice to set the vacuum presented to the network instead of swapping orifices for first step adjustments....pick one up at any hardware store....I think they use them to control water flow in refrigerator icemakers....post back if more info needed....

[seth411]

Thanks for the help. i think everything is hooked up I'll check that article.

[Brian Carlton]

Originally Posted by seth411

Thanks for the help. i think everything is hooked up I'll check that article.

The problem is not creating "more bleed".

What you need to accomplish is "more restriction". Ahead of the VCV is a restrictor that allows the VCV to function properly without too much flow. This allows the VCV to dump sufficient vacuum to achieve a proper low level.

If the restrictor is missing or if it's too large, you'll get the identical issue that you have.

[yellit]

If you need any more info post back....I went through the wringer fighting this system when I first got my diesel Benz.....

The trick is that it takes very little vacuum flow from the main vacuum source to give the needed amount for the bleed valve to vent to give the changing value at the modulator....

The biggest problem is the cheesy little white pass valves on top of the valve cover....some folks bypass them and live with a little extra vacuum at idle throttle settings....

I have thought of putting an electronic bleed valve in place of that whole mess using a throttle position sensor box controlling needed bleed at the proper load levels.....but I have gone even further & going to put in a 4 speed manual tranny.....still it was a fun learning thing....kevin

[seth411]

I got a small valve and placed right before the trany line. I restricted the flow I think. When I put my mighty vac after the valve it seems the hg is the same but moves slower. As of now it will barley shift with.

I turned the modulator valve clockwise thinking that this would help and but it made it worse.

I've checked my CVC and have my lines set up like the schmit site, but I think I need to find the banjo bolt to get the modulator valve even close, or am I missing something. Could my CVC not be bleeding enough?

I read that really good DIY article and it seems that finding the right spot on the modulator is my problem now. My brain hurts but I need to work until the night. I Should have left it flaring...

Even after turning the modulator valve counter clockwise three rotations it still doesn't want to shift. When I remove all vacuum it doesn't shift at all. Fluid looks good and at the right level.

Thanks for the help, even though there are a million post.


UPDATE
I changed the Modulator Valve and now its back to flaring. But at least I can drive it. Reads a slooow moving 10-18 while driving.

BRIAN I know your the man but the schimt diagram doesn't have a dashpot before the CVC and neither dose mine. Should I get one?

[yellit]

If you want a simple place to start just run the vac line after the orifice to the IP valve by itself (by-passing the valve cover switch)......
Hook your vac gauge to this line so you can see what the range is from idle to heavy throttle...

Do not worry about modulator adjustments until you get the vacuum curve set.....


If you are only descending from 18 to 10 then there is still too much vacuum on the bleeding side of the orifice....or the IP valve is not set to bleed enough but it is probably ok if everything was working before the main hose change....

Sounds like your only problem is still too large of an orifice if all was working ok before....

Begin this by using the very smallest orifice size available or with the adjustable orifice almost completely shut.....then tweak it open while watching the vac gauge during throttle increase...
The right size is when the vac curve follows throttle position up and down smoothly....a too small orifice will cause a slow return to high vacuum when the throttle is closed...

[seth411]

[quote=yellit;

Begin this by using the very smallest orifice size available or with the adjustable orifice almost completely shut.....then tweak it open while watching the vac gauge during throttle increase...
The right size is when the vac curve follows throttle position up and down smoothly....a too small orifice will cause a slow return to high vacuum when the throttle is closed...[/quote]

Should My valve be right after the brake booster orifice? As of now I have it right before the tranny line and only noticed that the vacuum gauge reading slowed its movement, but still went to 18hg. This is after opening it slowly from the closed position.

My vcv also is at max adjustment. Mine has the arm that you adjust. I tried to take it apart and bend the spring but wasn't able to.

Thanks yellit for the help.

[yellit]

Put the VCV back like it was......I made this mistake too...

In the simplest form the modulator vac line should tee onto the same vac line that is attached to the VCV ....

Think of the modulator as just sampling the vacuum level at the line that comes from the orifice....this is the point of vacuum the VCV is changing.....

The VCV is made to bleed small amounts of air ....if a large vacuum source is attached to it ....it cannot accuratly dump that much vacuum...this is why a very small orifice is needed

The modulator does not change or affect the vacuum level.....the modulator is controlled by the vacuum level that the VCV varies....

I think you are speaking of the one way check valve when you refer to the (brake booster orifice)....this thing has nothing to do with the transmission control circuit....

The path....Without the valve conglomeration on the rocker cover..

vac pump...
big vac line...
tee with orifice...
orifice output divided feed to mod...
orifice output divided feed to VCV....

You are getting close....dont give up....

[yellit]

I may not have answered your question in my ramblings.....

The adjustable valve that you are using in place of a fixed orifice should go directly on the big brake booster line and the other side of this adjustable valve or orifice should split and feed the mod and the VCV....

The mod line and VCV line should be together at this point...

I am using this setup for explanation...in the original system the fixed orifice feeds the swithch-over valves on top of the rocker cover and they feed the split to the mod and VCV.....

The modulator is just sampling the pressure on the line the VCV is changing.....

[seth411]

So I got MV to read 10 at idle then go to zero at half throttle by moving the store bought valve at the brake booster. If I open it anymore the VCV buzzes constantly but hg still stays at 10.

So I think this is right but why isn't it shifting?

Or could the Modulator be the cause of no shifting?

From the DIY articel:
Once a proper vacuum curve is created, the real finesse begins. There are a number of possible adjustments. The first is the relationship of the control valve linkage to the throttle lever. The later proportioning valve is mounted to the injection pump and is rotated to achieve this adjustment. The early adjustment is achieved by adjusting the rod length such that the lever reaches within 0.5mm of the full throttle stop (see Fig. 1) with full throttle. The size of the vacuum leak, and thus the range of vacuum, is adjusted on early versions by turning the adjustment under the plastic cap. (See Fig. 2).

I am unable to get my adjustment to .5mm could this be a problem?

I also don't understand from what I've read My car should shift with no vacuum. It will barley shift If I coast when no vacuum is applied.

Dose this mean theres no hope and that flare is going to be the new name for my car?

[yellit]

These readings are getting close....

Are you monitoring the vacuum applied to the modulator with the MV gauge ...?

Where is the vacuum line from the modulator attached now...?

Are you sure all the hoses are tight with no leaks...?

[seth411]

Originally Posted by yellit

These readings are getting close....

Are you monitoring the vacuum applied to the modulator with the MV gauge ...?
-Yes I have the MV T'd right as it gose to the modulator

Where is the vacuum line from the modulator attached now...?
-T'd with the main vacuum line to the 2/3 valve

Are you sure all the hoses are tight with no leaks...?
-Everything holds vacuum except the VCV. Though It is disengaged at idle so it shouldn't matter.

Thanks for your help again yellit. I'll let you get back to your lunch.

As of now I can only get a shift from 1st when the MV reads 20hg and the foot is off the pedal. So i assume that I need a dashpot to regulate the the vacuum from the cvc. I think I'm going to pull one from the heater since that doesn't work well.

It looks like I need a wide span of low and hi vacuum for shifting on my car.

I think the tranny is getting tiered of me.


UPDATE": Cars are machines they love you no matter what.

Out of frustration I turned the modulator key 10!! full turns counterclockwise to firm the shifting, and she Shifts!! She Shifts!!

I adjusted the store bought valve thats in between the brake booster line and the VCV and Modulator Line so the hg sits at 15 and goes down to ZERO! NO more flaring and easy down shifts.

I read in one of the many post that you should get the modulator adjusted first, that is if you have great luck or the banjo bolt from an alda!

Good luck to anyone else. It only took me six months!

[Samuel M. Ross]

Seth411,
"yellit" advised me that you had started this THREAD and what the subject was.
IF you want to read more on this subject in a very long THREAD [486 replies] and almost 43,000 reads... in just about 2 years... see it at its beginning: It's CRITICAL... how you set your transmission's vacuum system on your diesel MBZ...
I am the original author of this THREAD and my reason for starting it was to help people exactly like yourself... for I felt there was a lack of understanding among the DIYers struggling with what I subsequently titled their "Auto Tranny-shifter Vacuum Control Systems"... and almost no understanding of the function of the 6+ different restricted orifices available from Mercedes.

Yellit was exactly right... when you changed out the line between your vacuum pump and brake booster reservoir, you created what I see as "THE" classic problem in these systems because the previous OEM "Tee" that tapped into this line as a vacuum source for the "Tranny-shifter/EGR vacuum control system" this "Tee" had a restricted orifice built into it and in addition to this restriction, most of these cars have one or more additional in-line restricted orifices in the system to create different pressure [vacuum] zones so that the EGR system will have a stronger vacuum source than the tranny-shifter portion of this system. AND the official MBZ manuals have NO discussion as to the function of these orifices!!

I read through this THREAD and see that you went through much the same experience I did in that your VMV on the transmission was probably adjusted too far to the right contributing to your problem of getting the system set up properly. I eventually played with my Vac.Mod.Valve [VMV] and for me it was logical to figure out how many thurns there was between the two extremes of adjustment and then put mine about mid-way! From that point on it was a matter of first finding the correct size orifice to restrict the vacuum being supplied to the VMV/VCV circuit and after putting my smallest orifice in this line, then it was merely a case of adjusting the VMV. I never had to adjust the VCV... but I did make certain that it was not clogged with dirt.

The original title of my THREAD I referenced above is: It's CRITICAL... setting up your "Transmission-Shifter Vacuum Control System"... and in one of the latest POSTS in this THREAD I discuss how such vacuum systems are a combination of both "dynamic" [the bleeding VCV] and "static" [VMV]. It might help if you read this discussion which both before and after about POST #481. See It's CRITICAL... how you set your transmission's vacuum system on your diesel MBZ...
I don't pretend to fully understand this subject, but I truly enjoy it and look forward to writing a "wiki" ariicle on it one day... but right now I'm too busy redesigning AC systems and replacing upholstery!
Regards,