Automatic Transmission

[n/a]

Howdy Folks!

Been trouble shooting my automatic transmission for about 3 weeks now.  To date, I can't figure out what the problem is and wanted to see if I could get your thoughts and ideas.

A little background:  The car is a 1965 230SL.  The transmission is original to the car but I have no idea if it has ever been overhauled or repaired.  I bought the car (wasn't running) in October and have been working to get it running right ever since.  The previous owner had the car 8 years and claimed there were no repairs to the engine or transmission while he owned it.  There are no repair or service records prior to 1995.

The problem...

The transmission won't up-shift until the cars speed is quite high.  According to MB, the car should up-shift from 2nd to 3rd at 25 Km/hr during partial throttle operations.  Mine upshifts at 45 Km/hr regardless of throttle position (Kick-down switch is not engaged)

Up-shifts from 3rd to 4th are similarly late.  MB states it should up-shift at 45 Km/hr, but it won't up-shift until 67 Km/hr is reached, again regardless of throttle position.

Downshifts occur at too high a speed (down-shifts come early) and I feel quite certain that solving one will solve the other.

Here's what I've done so far.

1.  Verified the operation of the idle switch, kick-down switch, and double acting solenoid.  All three of these components appear to be working as designed.

2.  Verified linkage from shift lever to transmission is correct.

3.  Verified vacuum line from the intake manifold to transmission modulator is not leaking or clogged and that it is providing vacuum to the modulator.

4.  Changed the transmission fluid and filter.  Both looked very clean.  The fluid was clear, looked like new, and didn't have a "burnt" smell to it.  I don't know much about automatic transmissions, but I must say I was surprised how clean everything was when I pulled the pan.  It all looked brand new.  There wasn't any debris or sludge in the pan.

5.  Checked the modulating pressure.  MB says it should be 41 psi with the vacuum line removed and the double acting solenoid disabled (fuse pulled).  Modulating pressure was 36 psi.  I adjusted the pressure to 41 psi.  Following this adjustment, kick-down pressure was 60 psi, 2.5 pounds below MB specification of 62.5 psi.  Following these adjustments, no improvement was noted, if anything, up-shifts came even later (1-2 Km/hr).  This was very disappointing, I thought for sure the low modulating pressure would have had more of an impact on the operation of the transmission.

6.  I did NOT adjust the length of the linkage from the double acting solenoid to the modulator valve.  It seems that if modulating pressure is correct, and it is, then the transmission should shift properly when operating within the partial throttle envelope.  For the time being, I've left it alone.

Now what?  The transmission is very consistant in its shifting behavior, it's quiet, and the shifts are solid with no slipping.

I'm suspicious of the vacuum modulator diaphragm.  On American cars, transmission fluid will be sucked into the intake manifold if this diaphragm is ruptured, creating smoke, lots of smoke! Enough smoke to provide misquito relief to the entire county.  My car doesn't smoke at all.  Perhaps there's no fluid on the inboard side of the modulator diaphragm?  Anyone know for sure?  If the diaphragm is ruptured, I assume the modulator would react as if the engine was trying to produce high power, thus delaying the shift points.  This would correspond with the symptoms I have.

I appreciate any ideas or suggestions.  Thanks in advance.

Have a Safe and Happy New Year.

Tony M


Tony M
1965 230SL (Auto)

[hands_aus]

Tony,
That linkage from the 3 position solenoid to the modulator works for the three positions not just kick down.
Could it be that the linkage rod is not allowing the modulator to achieve the correct pressure? Remember that you said you disconnected the solenoid while testing its value.
Did you check the modulating pressure with the solenoid in operation?


Bob (Brisbane,Australia)
early 250 SL, RHD

[ja17]

Hello Tony,
Remove the side inspection cover on the transmission tunnel and observe the operation of the linkage and solenoid during a test drive. A second person will be required. Mke sure the linkage and solenoid moves to the center position after the gas pedal is depressed. The third (forward)position should be engaged only during kick down when the switch is activated under the gas pedal, at full throttle.
It is absolutely necessary to make sure the solenoids, throttle venturi switch, linkages and wiring are correct before tamprring with factory settings. According to the factory transmission manual, basic modulating pressure, maximum modulating pressure and kick down modulating pressures should be checked if you are having shift problems after all the other inputs are checked.
The modulator adjustments are a bit involved. If the metal seal on the modulator adjustment has been broken, then there is a good chance someone has tampered with this adjustment. Changing the length of the linkage rod on the transmission will also change shifting characteristics, but the pressure settings should be checked afterward. Be sure to record any changes you make so you can return them to their original settings if needed! the factory tramnsmission manual gives a little more specific information on these procedures than the BBB. I will scan or send you this information.
Also, the engine will suck-in transmssion fluid and smoke, if the modulator diaphram is ruptured.
Make sure that solenoid is moving the linkage to all three positions first! good luck, keep us posted.


Download Attachment: Automatic Transmission with solenoid.jpg
45.9 KB
 


Joe Alexander
Blacklick, Ohio

[n/a]

Joe

I removed the inspection cover and verified the solenoid is moving into all 3 positions.  It seems to function properly, though I haven't done this while actually driving, only while sitting idle and manipulating the switches by hand.  I'll try it while driving and see if it appears to function properly.

The modulating pressure adjustment has in fact been tampered with before.  There was no seal or safety wire on the threaded shaft.  I didn't check the basic pressure reading (rats!) but I'll do it as soon as I get the chance.  I've avoided messing with the linkage rod between the double acting solenoid and the modulating valve.  When adjusting the length of the rod, should I be adjusting rod length to reach a specified pressure or just drive the car and see what works?

Thanks

TonyM

quote:Originally posted by ja17

Hello Tony,
Remove the side inspection cover on the transmission tunnel and observe the operation of the linkage and solenoid during a test drive. A second person will be required. Mke sure the linkage and solenoid moves to the center position after the gas pedal is depressed. The third (forward)position should be engaged only during kick down when the switch is activated under the gas pedal, at full throttle.
It is absolutely necessary to make sure the solenoids, throttle venturi switch, linkages and wiring are correct before tamprring with factory settings. According to the factory transmission manual, basic modulating pressure, maximum modulating pressure and kick down modulating pressures should be checked if you are having shift problems after all the other inputs are checked.
The modulator adjustments are a bit involved. If the metal seal on the modulator adjustment has been broken, then there is a good chance someone has tampered with this adjustment. Changing the length of the linkage rod on the transmission will also change shifting characteristics, but the pressure settings should be checked afterward. Be sure to record any changes you make so you can return them to their original settings if needed! the factory tramnsmission manual gives a little more specific information on these procedures than the BBB. I will scan or send you this information.
Also, the engine will suck-in transmssion fluid and smoke, if the modulator diaphram is ruptured.
Make sure that solenoid is moving the linkage to all three positions first! good luck, keep us posted.


Download Attachment: Automatic Transmission with solenoid.jpg
45.9 KB
 


Joe Alexander
Blacklick, Ohio

Tony M
1965 230SL (Auto)

[n/a]

Bob

I reconnected the pressure gage this morning to the modulating pressure port and did some additional testing.  Here's what I found:

Basic pressure = 10-12 psi.

Note:  This is the pressure shown with the solenoid hooked up, in idle position, and the vacuum line connected from the manifold to the modulator.

Modulating pressure = 40 psi
Kickdown pressure = 60 psi

Note: Both these pressures are taken with the vacuum line disconnnected.  Kickdown pressure utilizes the double acting solenoid to move the modulating vavle lever forward.

I went driving, and found that Basic Pressure is rising in direct relation to the gas pedal.  (pedal down = pressure up)  I don't know that this is normal but it seems to make sense.

I checked the double acting solenoid and it seems to be functioning properly while the car is in motion.  Idle brings the linkage aft, partial throttle operation centers the linkage, and kick-down pulls the linkage forward.

Perhaps I should put the modulating pressure back where I found it and start working with the solenoid/modulator linkage?

I'm going to think on this for awhile before I do anything stupid.  Then, after much thought and contemplation...I'll do something stupid!

Thanks

TonyM

quote:Originally posted by hands_aus

Tony,
That linkage from the 3 position solenoid to the modulator works for the three positions not just kick down.
Could it be that the linkage rod is not allowing the modulator to achieve the correct pressure? Remember that you said you disconnected the solenoid while testing its value.
Did you check the modulating pressure with the solenoid in operation?


Bob (Brisbane,Australia)
early 250 SL, RHD

Tony M
1965 230SL (Auto)

[ja17]

Hello Tony,
Your pressure readings look fairly good and it sounds like your hook-ups are correct. Unfortunately you are correct higher modulating pressures usually bring later shifts. Did you try tightening the valvebody bolts in the transmission when the filter was off? Sometimes they are loose and cause an internal hydraulic leak.
I would try adjusting the linkage but count the turns so you can put things back if needed.

Joe Alexander
Blacklick, Ohio

[n/a]

Joe

No, I didn't think to check the torque on the valve body, but I'll put it on my list.

Over the past few days, I've wondered about the centrifugal governor or a valve associated with it causing problems.  I would assume the governor pressure is part of a "differential pressure equation" that is continuously underway within the transmission.  I also assume low or high centrifugal governor pressure would impact shifting points.  (It seems I remember hearing about folks changing out governor springs in their Ford C-4's to modify shift characteristics for racing.)

Any thoughts on this?

In the next few weeks, I'll pull the transmission pan and check the torque of the valve body.
Thanks Joe!

Tony M

quote:Originally posted by ja17

Hello Tony,
Your pressure readings look fairly good and it sounds like your hook-ups are correct. Unfortunately you are correct higher modulating pressures usually bring later shifts. Did you try tightening the valvebody bolts in the transmission when the filter was off? Sometimes they are loose and cause an internal hydraulic leak.
I would try adjusting the linkage but count the turns so you can put things back if needed.

Joe Alexander
Blacklick, Ohio

Tony M
1965 230SL (Auto)

[n/a]

Joe

I've been busy working on other items requiring attention over the past 3 weeks.  Today, I finally got back to the automatic transmission.  I tried linkage adjustments with no encouraging results.  I went to extremes in both directions and the only thing that seemed to change was how smoothly the tranny shifted, but not where (speed) it shifted.  I still haven't checked torque on the valve body bolts, but I'll do it in the near future.

The car drives fine except for the late (high rev) shifting.  Seems a shame to pull it out of the car and pay for an overhaul with this being the only problem.  Do you know where I can get hold of a "hydraulic flow" schematic?

Lastly, do you know of a skilled mechanic capable of and willing to overhaul one of these tranny's?  I don't have a problem pulling it out of the car and crating it.

If anyone else has any idea's or recommendations, I'd love to hear them.

Thanks

quote:Originally posted by ja17

Hello Tony,
Your pressure readings look fairly good and it sounds like your hook-ups are correct. Unfortunately you are correct higher modulating pressures usually bring later shifts. Did you try tightening the valvebody bolts in the transmission when the filter was off? Sometimes they are loose and cause an internal hydraulic leak.
I would try adjusting the linkage but count the turns so you can put things back if needed.

Joe Alexander
Blacklick, Ohio

Tony M
1965 230SL (Auto)

[ja17]

Hello Tony,
 I have the factory workshop manual on these transmission and can copy the flow chart for you. Before giving up consider checking the valve body bolts for tightness. Some times the problem is in the valve body itself (something stuck).
The modulator diaphram is probably ok. The engine will smoke if ruptured often fouling out #6 sparkplug. There is a small spring which acts on the modulator diaphram. I have never seen one break, but you may want to look at it as last resort. The diaphram and spring can be removed from below.
Before giving up you may actually want to remove the valve body (drops out the bottom) to make sure the gasket has not blown causing an internal hydraulic leak. It is unusual that changing the three position solenoid linkage length did not make a big difference. Something must be stuck or maybe an internal hydraulic leak. Good Luck,


Joe Alexander
Blacklick, Ohio

[n/a]

Joe

Getting hold of some actual transmission documents would be wonderful.  I've decided it's difficult to troubleshoot when you don't know "what's in there?".  I'll check the torque on the valve body bolts.  I've been giving some serious thought to pulling the valve body out and checking all the sleeves, springs, and plungers for condition and freedom of movement.  Obviously, this would have to be done with great care to ensure all parts are returned to their original positions.  This would confirm the condition of the gasket you referenced, too.  I assume it's standard procedure to install a new gasket regardless of the previous gasket's condition?  Do you know if they are available?

I hadn't thought of the modulator spring, but it seems like a reasonable suspect.  I'll go ahead and order a new diaphragm and replace it while checking the spring.  I know the old one isn't leaking, but it may be 40+ years old and living on borrowed time.  Seems like cheap insurance.

As always, I appreciate your ideas and assistance.  I'll keep you posted on my progress.

1965 230SL with GA 230SL - 002462 transmission

Cheers!

quote:Originally posted by ja17

Hello Tony,
 I have the factory workshop manual on these transmission and can copy the flow chart for you. Before giving up consider checking the valve body bolts for tightness. Some times the problem is in the valve body itself (something stuck).
The modulator diaphram is probably ok. The engine will smoke if ruptured often fouling out #6 sparkplug. There is a small spring which acts on the modulator diaphram. I have never seen one break, but you may want to look at it as last resort. The diaphram and spring can be removed from below.
Before giving up you may actually want to remove the valve body (drops out the bottom) to make sure the gasket has not blown causing an internal hydraulic leak. It is unusual that changing the three position solenoid linkage length did not make a big difference. Something must be stuck or maybe an internal hydraulic leak. Good Luck,


Joe Alexander
Blacklick, Ohio

Tony M
1965 230SL (Auto)

[ja17]

Hello Tony,
Re-torque of the valve body is not difficult. Removal of the valve body is a bit more difficult. Dis-sassembly should be the very last resort. These units are  very complex on this compact four speed tranmission. I have found that if the gasket is still good the problem is usually not in the valve body but who knows. If you tear into the valve body be prepared to send the transmission out for a rebuild.
 The valve body gaskets are available in a kit with pan gasket and some minor seals. Often times the gasket will part completely intact and can be re-used. I can help with information and visuals. I have some partialy dis-assembled units around for pictures if needed. I am hoping that you may find a simple fix.
Joe

Joe Alexander
Blacklick, Ohio

[n/a]

Thanks Joe
I'll keep you posted.
Tony

quote:Originally posted by ja17

Hello Tony,
Re-torque of the valve body is not difficult. Removal of the valve body is a bit more difficult. Dis-sassembly should be the very last resort. These units are  very complex on this compact four speed tranmission. I have found that if the gasket is still good the problem is usually not in the valve body but who knows. If you tear into the valve body be prepared to send the transmission out for a rebuild.
 The valve body gaskets are available in a kit with pan gasket and some minor seals. Often times the gasket will part completely intact and can be re-used. I can help with information and visuals. I have some partialy dis-assembled units around for pictures if needed. I am hoping that you may find a simple fix.
Joe

Joe Alexander
Blacklick, Ohio

Tony M
1965 230SL (Auto)

[hands_aus]

Hey Tony M

What was the end result of all the tests and adjustments to your auto transmission?

Did you finally get the trans to change at normal speeds?



Bob Smith (Brisbane,Australia)
RHD,1967 early 250 SL, auto

[n/a]

Bob,

I've never solved the puzzle.  I pulled the valve body assembly out of the car and went through it completely as Joe recommended.  I found one of the sliding valves was "a little sticky".  I cleaned it up with some scotch brite and it worked very smoothly.  I figured that was the problem and was anxious to get it put back together (I used a new gasket set)  No such luck.  The car ran the same.  Since then, I've acquired manuals and spent a lot of time studying the transmission.  Unfortunately, my business has been consuming my life for the past year and I've gotten very little hands on time with the car.  Things are getting better now and I look forward to some "quality time" in the shop with the SL.

If there's a bright side, I've been driving the car fairly frequently.  I probably put 5,000 miles on it in the last year.  Other than looking goofy with my head snapping back everytime it shifts to the next gear, the car drives fine.  If I fix the tranny, my head won't snap back anymore but my wife said it won't do much for my looking goofy

I think there are two likely culptits to the tranny problem.  The governor could have a stuck valve, broken spring,leaking O-ring, etc. or the low (or high) volume pump could have a pressure valve that is faulty.  In order to check these items, the tranny must be removed.  I've spent the last couple of months acquiring parts for the change, including a used tranny.  I'm planning on swapping out the two tranny's and seeing how the "new" one performs.  The previous owner reports it ran fine in his car when removed.  Regardless, I can tear into the original transmission and see what I can find.  Anyone know of a good supplier for transmission gasket kits?

I'll advise of any progress.  Sorry I've been away for so long.  I need to get back into the car and the group.  It's a lot of fun.

Regards,

Tony M

quote:Originally posted by hands_aus

Hey Tony M

What was the end result of all the tests and adjustments to your auto transmission?

Did you finally get the trans to change at normal speeds?



Bob Smith (Brisbane,Australia)
RHD,1967 early 250 SL, auto

Tony M
1965 230SL (Auto)

[TheEngineer]

Have you checked your rear axle ratio? I installed a 3.27 axle and this moved my shift points up by MPH x 1.25. The up shift at light throttle (very light throttle) should be at about 2500 RPM. That is true for all gears. From standing start, the transmission starts in 2nd gear unless the shifter is in the "2" position. Then it starts in 1st gear and shifts into 2nd at about 2500 RPM. Then you must move the shifter to "4" and it will shift into 3rd at 2500RPM and into 4th again at 2500 RPM. With my rear axle ratio I turn 3000RPM at 62 MPH. The only pressure that is adjustable is the modulator pressure. The working pressure is a function of the modulator pressure. The shift points are considerable higher at lower manifold vaccum, like when one hits the pedal. You may want to rig a vacuum gauge and observe it. If your engine does not pull a high vacuum it affects shift points.

[hands_aus]

Hey Tony,
Thanks for replying. I read these topics with an eye for the future.
I was just reading the "Diagnosis of troubles for automatically shifting" on the cd 280SL manual

No. 10 says

"Upshifts occur independent of gas pedal position (except kickdown) always at full throttle shift points."  sounds like your situation

Possible causes  
1. Under pressure line loose or clogged
2. Modulating pressure control sleeve 25 stuck.  

I think that you need a copy of the Autotransmission service manual.
The CD has all the information for each model but no part number lists.

Bob Smith (Brisbane,Australia)
RHD,1967 early 250 SL, auto

[Ben]

Sorry to dig up an old thread but does anyone have the factory transmission book for these auto transmissions ?

I have some information about checking/adjusting but I's like to see a bit more info before i pull things apart !

Regards,
Ben in Ireland.
'64 230SL 4sp.

[ja17]

Hello Ben,

I have the factory manual on the unit if you need any information.

Joe Alexander
Blacklick, Ohio

[Ben]

Thanks Joe, I havent got near it yet but I noticed last night that when I start it in "N" it tries to move, never did that before, also I noticed that the solenoid for the accelerator linkage does not move when "4" is selected !

It has me confused since it was not like that the other day !

Have I more than one problem or is it all related ??

Regards,
Ben in Ireland.
'64 230SL 4sp.

[ja17]

Hello Ben,

Pressure switches on the transmission activate the solenoid.  Hmm, lack of pressur, still thinking front pump or converter.

Joe Alexander
Blacklick, Ohio

[Ben]

I will pull off the pan to see if there is any debris and check the bolt tightness.

I have a good used transmission arranged anyway so I'll get stuck into that job at the weekend !

Thanks for your help and advise Joe, it does all point to a lack of pressure indeed!  :?

Regards,
Ben in Ireland.
'64 230SL 4sp.