Transmission modulator leak (not the diaphragm) - update

[rgafitanu@gmail.com]

Hello,
I have a leak coming from the modulator. It just started a couple of days ago and it appears to be only about an ounce after shutting down the engine and it stops after that. It appears to be coming from the modulator. As I understand there is a "primary chamber" where the vacuum from the manifold acts on a diaphragm (changed that a year ago). This is bolted to a bigger housing with a plate and a gasket where the actuator from the 3 position solenoid meets with the modulator plunger.
The amount of oil that came out when I changed the diaphragm was about an ounce too leading me to the conclusion that this is the oil leaking out now. Therefore the leak is from the bigger housing, most likely the gasket. Looking through some cross section drawings of the modulator it is unclear how the 3 position solenoid actuator connects to the modulator plunger.
My question is: would I be able to remove the modulator housing with the plunger to replace the gasket or that actuator will be in the way?
My transmission appears to be a 230 (attached).

[rgafitanu@gmail.com]

Nobody? Some help would be appreciated, the exhaust is already in the way so it would help me to know if I can do it without dropping the transmission.

[ja17]

You should be able to replace the diaphragm, gasket, and o-ring without transmission removal. Remove the rear mounting plate and let the unit drop a little if you need more room to work.

[rgafitanu@gmail.com]

So I took the modulator out and replaced the worn o-ring. I put everything back but when driving it, shifting up took an eternity with the engine racing in the middle of the shift making it very hard to lock in the higher gear. Back on the lift to see what I did wrong, I also ordered a filter kit thinking it would be a good idea to change the transmission fluid too. The quart that came out with the modulator appeared quite muddy. Now the long shift happened occasionally before too but only 2-3. After removing the oil pan picture 1 shows what I found. I was expecting to see a filter like in picture 2 as shown everywhere.
Was I missing the filter or is it an outdated filter?

[rgafitanu@gmail.com]

I removed this "filter" hoping something would be behind the metal screen but just the valve body.

[rgafitanu@gmail.com]

The old oil was quite murky with some rather fine debris in it. Would this be because of lack of or outdated filter? I hope I am not facing something worse.

[Mike K]

I had a similar shifting problem on my '71 280SL. When coming up a very steep incline, the gear shifter would not lock into position 2,
it kept slipping and for about 7 to 10 seconds as I tried to accelerate, the car was revving and almost hunting for the next gear until I moved the shifter back to position 3 and it would then engage and move off normally.

I thought I had a serious transmission problem...

I replaced the Xmission mount and also replaced the filter & fluid- there was a certain amount of fine debris in the Xmission filter pan.
Once I had done this work, the problem was immediately and completely solved.

On a very steep incline the gear shifter now stays in position 2 and the car accelerates normally. I've also noticed very much smoother auto gear shifts in normal drive mode.

A couple of things to check:
Have you checked your transmission mount?
I assume you also drained the fluid out of the torque converter?
Does your filter have the u-shaped rubber gasket?
Also make sure that you have the filter pointing in the right direction (see pic below)

Here's a thread I posted with pics:
https://www.sl113.org/forums/index.php?topic=25341.msg181334#msg181334

Best,
Mike

[rgafitanu@gmail.com]

Took the modulator out again to check it but it was OK, I changed the oil, put everything back but the upshifts are bad. It looks as if the shift is made of 2 stages, it releases the lower gear and then locks into the higher gear. However it release but it doesn't lock, the engine races and I have to play with the throttle to make it lock into the higher gear.
I placed a camera in the tunnel to see the double solenoid linkage and I realized that under reverse or drive the linkage was moving back to the middle position. Apparently the idle speed circuit is shorting or interfering with the double solenoid circuit. I disabled that one but no change in the shifts.
Next I unhooked the vacuum tube from the manifold to remove the throttle "bias" on the modulator. Now it will not initiate the shift, the rpm just increases but stays locked in the lower gear. If I release the throttle it shifts and it will stay locked in the higher gear.
Earlier when I was disassembling for the oil/gasket change, while unscrewing the vacuum pipe at the modulator a small piece of bakelite fell. Now the only bakelite part over there is what they call insulating plate between the modulator housing and transmission body. Another fact is that the leak is still present around the modulator which would indicate that the bakelite plate may be damaged or cracked and leaking. Considering the fact that it has a gasket at the body, an o-ring and I get about a pint of oil every time I am removing the modulator housing I am assuming that there is some precise pressure behind the insulating plate that helps making the shift. So a leak there disturbs the shift.
Next I would try to turn the modulating screw all the way in to see what changes if that spring is fully loaded.
I have to find my 8mm banjo connection to check the 3 modulating pressures and to open it again to see if the bakelite plate is damaged.
Anybody has any experience with this?

Thanks,
Radu

[rgafitanu@gmail.com]

I think I found the cause. The modulator screw needed adjusting, now the car shifts properly. Now I have to fix the electrical circuits. I believe that the idle speed increase circuit is separate/independent from the double acting solenoid circuit. Can somebody please confirm this?
This means that at idle when the solenoid rod is moved back it shouldn't come back to the middle position when shifting to reverse or drive.
The GRN/ORG wire coming from the idle increase solenoid to the pressure switches must be shorting the other circuit somewhere disabling it.

[rgafitanu@gmail.com]

Anybody? Some help?
Are the pressure switches supposed to disable the backward position of the double solenoid (the idle position)? I ran another wire from the switches to the CSS and the idle position is still disabled in Drive or Reverse. So it's either the positive wire to the CSS or the switches are messed up.

Thanks,

Radu

[cfm65@me.com]

Hi Radu,
As far as I understand the CSS and the two way solenoid are two separate circuits.
If I am correct, the CSS increases idle speed when the auto box is put in gear.
The throttle switch, at the front right air intake, senses throttle position. During idle, the two way solenoid is pulled back, when the accelerator pedal is moved, the throttle switch senses throttle movement and will enrich the mixture in order to increase power for pull away.
I believe when the kick dn switch is engaged, the throttle switch will again enrich the mixture, to increase performance.
Radu, this is the best I can do, until someone more knowledgeable can help us.
This diagram might help.

Regards
Chris

[ja17]

There are two hydraulic switches on the automatic. One is activated when the selector is in a forward drive gear. The other is activated when the selector is in "R". When activated the electric solenoid on the intake slightly advances the engine linkages increasing idle. There purpose is to create a constant idle speed whether in gear or neutral. (Constant idle solenoid). This circuit only comes into play when at idle, in or out of gear.

The intake venture switch and the kick-down-switch control the position of the three position solenoid on the transmission. if the  kick-down-switch is activated from a stop the transmission will start off in first gear. Otherwise second gear starts are used. The kick-down-switch should also cause a downshift for passing during normal driving. At engine idle the venture switch will lower load on the engine by lowering the pressure in the transmission via the three position solenoid.

[rgafitanu@gmail.com]

Thank you Joe and Chris, I understand the function of these two circuits. I am baffled, I just wired the 2 pressure switches on a new wire to the CSS and the CSS directly to +. The 3 position solenoid still goes back to the middle position when I shift to drive or reverse. My understanding is that at idle the 3 position solenoid would be in the rear position regardless of the transmission position. That's what I get from all the wiring circuits. Mine doesn't, when I shift to R the solenoid goes to middle, N back to rear, D middle again.
I thought that the original wiring shorted so I used new/separate wires. But it didn't change the behavior. I think I am left with:
- transmission not properly grounded, pressure switches don't make a good ground, finding another path through the 3 position solenoid making it release the rear position set by the idle switch.
- the 3 position solenoid blew its insulation and while still functioning correctly may be affected by that and malfunction.
- one or both of the pressure switches blew the insulation, still function but creating the malfunction.
Anybody has seen something like it?

[cfm65@me.com]

Radu,
The throttle switch at the intake ventury is adjustable. If you loosen the screws the switch can rotate a little. I suggest you turn it anti clockwise and start from there.
Remember, the throttle switch senses throttle position and when the pressure switches increase idle speed, the throttle opens and therefor the throttle switch will react accordingly. I am not sure if what you are getting is correct or not, hopefully Joe would clear this for us.
Regards
Chris

[ja17]

Good advice Chris. Yes make sure the throttle switch is working correctly. Sounds like its time for you to check the engine linkages.

[cfm65@me.com]

Tks Joe.

[rgafitanu@gmail.com]

Joe, Chris,
The throttle switch works correctly, I opened it and cleaned it a few months back. I also checked the linkages, they are where I left them a while back, slightly rich. I believe that this is an electrical issue. I checked this forum several times. It appears to be clear that the 3 way solenoid and CSS circuits are independent, so the rear position of the modulator rod should not be affected by positioning the shift in drive or reverse. The CSS, the 3 way or the harness has a ground fault or a short that gives me this problem. I will put the meter to the idle switch side of the 3-way to see what happens.

[rgafitanu@gmail.com]

Back to the original leak. Even after changing the modulator gaskets twice I still have the leak. It appears to be coming from the top of the transmission. Both sides of the housing above the band valve covers are wet. Could it be the vent leaking? I don't think there is anything else on top that can leak.

[Pawel66]

I have just come across this thread today while looking for someting else.

Radu, have you sorted the influence of R and D on the 3 position solenoid? I think it is as simple as your throttle switch is mowing the 3 position solenoid when R or D are engaged, because it is not set to compensate for throttle movement done by CSS that is engaged by R and D. You put in D, CSS acts, throttle moves, throttle switch opens, 3 position solenoid moves to the middle. Throttle switch should open later, after the point when throttle is open by CSS, when you touch the pedal.

That is what Joe and Chris were saying, I think. I wrote that because I had an impression you were stuck a bit... But maybe you got help via PM  .

[rgafitanu@gmail.com]

Thanks Pawel,
I actually fixed it about a month ago with help from this forum. I also posted my fix on your recent thread. Learning something new everyday.