124 upshifts way too soon. Tranny experts help! - PeachParts Mercedes-Benz Forum

muleears · #1 04-03-2007, 06:43 AM

I have a new to me 124 with 217K on the clock that upshifts way too soon. The 1-2 shift is @5mph then at @22mph it shifts 2-3-4, so I am in 4th at 23mph. Accelerator pedal position makes no difference in shift points, floored or slow acceleration it shifts the same. No records from PO, but was a one owner car. Here is what I have done so far (with a great deal of advice from GSXR)

Fluid/filter change with Dexron III

Vacuum appears ok, car shuts off instantly, don't know how to check vac. to tranny (but I have a mityvac). All I know so far is there is 9in. of vac. going into the top center of the vacuum amplifier at idle.

Have adjusted the bowden cable its full adjustment range and it has had no effect on the shift points. Cable does not appear to be broken. When detached from linkage there is resistance and it returns to the same spot each time it is pulled.

Replaced kickdown switch with known good one with no effect.

When shifted manually it operates much better (shifter bushings are worn) it will accelerate to redline in each gear, shifts are smooth with no clunks or flaring.

ALDA has been adjusted so performance 0-20 is acceptable.

The car is driveable just slow. Any help would be greatly appreciated.

pdrayton · #2 04-03-2007, 07:34 AM

9" is a bit low - should be around 13 if I remember correctly.

I would check the vacuum first, and then adjust the vacuum valve on the side of the ip.

To check vacuum, pull the line that goes to the vac modulator on the tranny off the vacuum valve on the IP and see if it holds vacuum. Mine wouldn't because the modulator cap was split and spilling vacuum.

First you have to get the vacuum at the correct level to the tranny, then you can start troubleshooting the rest of it. see http://pauldrayton.com/uploadfiles/merc/Service/W124/Index/602_603/07MechElec.html
for testing procedures.

Use the mityvac to trace where your vacuum problem is and then fix that.

muleears · #3 04-03-2007, 09:20 AM

I tested the vacuum pump and it is pulling 23in. of vac. I'll check the modulator to see if it holds vac. and adjust the vac. valve today. Will adjusting the vac. valve send more to the amplifier? Should I adjust till I get about 13in. at the amp? (I'm checking this at the line that goes into the top center of the amp.) I'll adjust the Bowden to somewhere near the middle until I get the vac. squared away. Thanks for the advice

jshadows · #4 04-03-2007, 10:21 AM

The vacuum will affect more the smoothness of the shift rather than where it shifts. This sounds to me more like a bowden cable problem which adjusts the shift point based on the pedal position (light acceleration or stomped to the floor). Given your description your vacuum is ok. If it wasn't you'd have violent shifting into each gear as there would be little or no modulation. It also sounds like the clutch packs are fine since you're moving into each gear smoothly and without flaring.

Yours is shifting so fast that it sounds like the cable is completely disconnected from the actuator on the valve body. Based on your statements though it sounds as though the cable is ok...could be something quirky in the valve body too.

Check the fluid level again when it's hot and level. I suppose you could be getting too much pressure which would force faster shifts (and can damage the valve body).

A kickdown switch failure is generally going to stop you from getting into 3rd or 4th (not your case)...so not there..best way to test this is to just pull the plug and if shifts are ok then.....

BTW, what model transmission? I'm guessing a variant of the 722.3xx.

muleears · #5 04-03-2007, 12:21 PM

Tranny model number is on the passenger side just above the pan correct?

jshadows · #6 04-03-2007, 12:33 PM

sounds about right..year of car will go a long way for starters

muleears · #7 04-03-2007, 12:37 PM

It's an 87 124, 217K miles.

jshadows · #8 04-03-2007, 04:41 PM

Well, nothing special but a run of the mill 722.3xx.

this is pretty much in-line of what I said with a few more things that are not so easy to check with DIY tools

"Check pressure control cable engagement, condition and
adjustment. Check full throttle stop by accelerating engine and
ensuring throttle valve rests against full throttle stop. Readjust
throttle stop (if necessary). Check governor pressure. If governor
pressure is too high, replace centrifugal governor. Repair or replace
valve body."

The governor pressure being too high could be too much fluid or a faulty governor (as stated above)..the control pressure cable is the bowden.

Though this is a PITA it might be worth pulling the bowden cable for starters to be sure. This can be done by plucking off the ball joint on the accelerator linkage, squeezing the black plastic piece held in the square bracket where the adjuster is and then feeding it down past the transmission.

The connection at the transmission requires moving the clip fastening the cable to the transmission and then turning it 1/4 turn to remove. When it is pulled out it should be attached to a thin metal shaft that is attached to the piston on the valve body. If the cable is broken or is connected to nothing then this is a problem. You should be able to stick your finger in the hole and feel the metal piece with a 90 degree hook in it to latch on to the cable assembly. Inspect the cable and see if the latching assembly is still there (assuming it was disconnected somehow).

If it's not the cable then it's either something went awry in the valve body or in the governor. I hesitate to speculate which one but my money (like in the random NCAA b'ball pool) would go on the valve body. What exactly I don't know as it's beyond my area of understanding of these beasts.

I think you can find a rebuilt v. body for about $300 (cheaper than a transmission and can be done without removal). The governor I think can be serviced while the tranny is still on the car as well.

PM me with an e-mail address if you want the manuals...they explain the operation pretty well though actually checking operating pressures etc. is like I said beyond the DIY tool set AFAIK.