MainePorsche

Thanks Jim.
The only true pressure I can measure is the Operating/Working Pressure (for the wheels can't move) which should be the highest of the three pressures to measure. A low pressure here would imply a faulted Regulator valve. From what I've read the spring involved with this valve is known to fail. If this were the case, it looks like I could take off the side cover of the valve body to check and replace these parts WITHOUT opening the dreaded valve body and have little bits all over. I could do the same for the range selector valve as well.
If anyone knows, would doing this through the side cover to replace these parts be fraught with peril ?

Lizard928

If the one spring has failed it is highly likely the rest of the springs in the body are close to going too.

MainePorsche

You speak wisely Colin.
I'll check the Operating Pressure. I'll probably find it to be low.
I'll then remove the valve body and send it to Greg.
I try to do all I can to keep her operating like the day Fritz and Bruno sent her off the line in Stuttgart. This car really runs, and all functions, well. It looks as if I have to turn this over to another. I haven't not completed a job on this car as of yet.
I have confidence in where this part is going.
This has been a long thread, and I really thank all for your help, and support. I've actually learned much along the way.
Kindly,
Craig

GregBBRD

Backtracking some, I think we determined that the shifting mechanism was indeed operating....at least the "park" section (which is mechanical) is operating. (Whe you put the shifter into "park", it engaged and locked the wheels.) It might be worth re-removing the pan and making sure that the plunger that moves inside the valve body is still "attached" to the inside shifter.

After that, I personally think you are ready to either remove and repair the valve body or remove and have the transmission "problem" isolated and repaired.

Crazy problem. I've never encountered anything like this. I'm really interested to "see" what the problem is.

MainePorsche

Hey there Greg.
Are you referring to the range selector's arm engaging the follower of the detent plate ?

ammonman

I think Greg is asking you to drop the pan and check to see if the detente plate is still connected to the sprung linkage that moves the shift valve inside the valve body. It was held in place with a circlip originally, but starting in '87 the circlip was eliminated and the linkage was staked to the detente plate. See page 37-163 in the WSM for details. Seems a sound place to start. The shifter could be moving the detente plate but if there's no connection between the detente plate and the shift valve you would stay stuck in whatever gear the shift valve is resting in. The stake might have worn and allowed the shift valve to become disconnected from the detente plate. Worth a look as you'll have to drop the pan to remove the valve body for service anyway.

Mike

MainePorsche

Mike,
Thank you. That image on 37-163 was very helpful. I was using a MB 722 pdf as my reference. The image on page 1.8/7 at the bottom of the first pdf shows where the selector lever comes into the transmission and engages the detent plate. This is an area of potential dis-union. The image on 37-163 is the linkage 'after' the detent plate which when engaged, acts on the selector valve (1) as seen in the second pdf attached.
Also note components 45 and 46 in the second image. I've read the piston spring in 46 is known to fail, and if the regulator valve 45 loses function the overall Operating/Working Pressure of the transmission will be faulty.
I will go back under and inspect these linkages/unions, and then post back.
Thanks again.
Craig

MainePorsche

Well Guys,
Back again. Today (after AM hockey), dropped the pan and inspected the linkages and their movements.
1. The follower of the selector valve engages the detent plate, and their movement appears normal.
2. Posteriorly, the detent plate engages with the sprung linkage (as described in 37-163 WSM) and appears to move normally.
3. On the other side (R) of the valve body the piston for the control pressure control valve rests appropriately against the reversing lever.

Are there any specific 'pearls' for removal of the valve body. I do note the difference in the hexagon bolt sizes (M6x50 & M6x55), and will take care. Are there other matters I need to heed ?
Thanks,
Craig

GregBBRD

Don't wear your favorite shirt and don't let it hit you in the head. Take the smaller rear "pressure portion" off too. The metal "separator" plate should fall out, when this comes off.

MainePorsche

Guys,
Quick question here.
What is the normal Operating/Working Pressure for the transmission ?
I'm about to measure it.
Thanks.

G8RB8

149-159 PSI with stationary car in drive at stall speed with vacuum disconnected. From the WSM

MainePorsche

Thanks Jim.
Sorry, I should have looked at the WSM first. I was focusing on the MB 722 trans docs you had sent.
Craig

G8RB8

http://members.rennlist.com/pirtle/s4atrans.htm This is probably more useful. I'm not sure what I sent before is right although it is what's in my copy of the PDF manuals it says 1978-1979 and is the only one I could find.

G8RB8

Condition: Transmission slips in all selector lever positions
Correction: 1. Check modulating pressure, adjusting if necessary. If not
adjustable, check movement of modulating pressure control
valve. Clean modulating pressure safety valve in shift
valve housing upper section.
2. Check whether vacuum line from intake branch to vacuum
box is plugged. If yes, replace.
3. Check operating pressure. If too low or not available:
a) Disassemble and clan shift valve housing. and service
operating pressure control valve.
b) Remove and inspect primary pump, replacing if necessary

MainePorsche

Couldn't measure the Pressure.
The g-damn pan gasket 'lipped in' in one area when I put back, and once up to temp/pressure -> big leak.
MF'n POS !
Will rectify tonite. It's cold, and I'm frustrated and I didn't want to lose the time - I want to diagnose this damn thing.

Ah... I feel better already.