Vacuum Modifications - lost top end power - Page 2 - PeachParts Mercedes-Benz Forum

legasea · #16 03-21-2008, 11:28 AM

I bypassed the EGR already. That helped and I replaced my cracked vac modulator cap, that helped too. When I started, the VCV was at 15 so I lowered it to 8, but that was too low, created hard shifts in all gears. so I found 12 was acceptable. I just can't seem to get the car to stay in second gear for long enough. It wants to shift to 3rd way too soon. If I crank down on the bowden cable, it makes the 1-2 and the 3-4 shifts too late. So I have the bowden cable where I want I think, but still get an early 2-3.
Is that what the K1 spring kit is for or am I just dealing with an old trans on its way out? Odd that it shifts great when I barely press on the pedal though, only shifts early if I get on it a bit.

Brian Carlton · #17 03-21-2008, 12:05 PM

Quote:

Originally Posted by legasea

Got my new modulator cap today, put it in and tested with mityvac. It now holds vacuum as before it dropped right down. I was expecting miracles after replacing it but I think some additional tuning is still in order. If I accelerate slowly (1/4 pedal) it shifts great through all gears!!! If I give it moderate acceleration (1/2 pedal) I have hard/late 1-2 shift, a super early 2-3 (almost immediate) and a great 3-4. Where do I begin and at which component? I have not checked throttle linkage position yet...not sure exactly where to measure distance.

Questions to solve these issues:

Hard 1-2: Adjust VCV or Modulator? I believe (& will check again) VCV has a vacuum of 10 coming out the top. Should 10 be fine and how much acceleration should it take to get down to 5, and then 0? If VCV is OK, should I mess with modulator and turn 1 notch CCW to allow more vacuum or should I allow more vacuum out of VCV?

Late 1-2 Shift - adjust Bowden cable? Should cable be relatively taught or should i still be able to take the end at the socket and pull it out a couple inches?

Early 2-3 - also Bowden cable? K1 sping kit?

I rarely get boost any more either. I think I lost it when I dropped the VCV vacuum from 15 to 10, or possibly when turning the bowden cable. Is boost controlled via kickdown switch? If so, what does it look like and where is it?

I just wonder if this is as good as I am going to get it being its 25 yrs old. I am confident I have no more leaks, just not sure if I am going to resolve all problems or if i should live with what I've got. Sorry for the many loaded questions.....can you tell I am spinning in circles?

You can't soften the hard 1-2 without softening all the shifts. If you've got no flaring, then you can increase the vacuum level at idle on the VCV. Raise it from 10" to 13" or so and see how you like the results. If it starts to flare on the 2-3, you'll need to return it to 10".

The 1-2 is always a bit late for most folks. If you want to make all the shifts earlier, then adjust the Bowden cable for a bit more slack. Try two turns on the adjusting nut and see how it works for you.

Early 2-3: This is referred to as a "stacked 2-3 shift". It's common in older transmissions.........the vacuum and/or Bowden adjustments will affect it but I cannot be sure of what the results will be. The Superior spring kit usually corrects the situation if a new spring is installed.

No boost: None of your vacuum adjustments has any effect on the boost. If there is no boost, check the pressure banjo bolt and all the lines to and from the overboost protection valve to the ALDA.

Mister Byrnzoil · #18 03-21-2008, 01:12 PM

the superior spring kit has a host of options for softening or firmening(?) shifts. But pay particular attention to this thread...

ruff ro raggy, little balls everywhere