Measuring transmission modulator pressure

[FresnoBob]

I wish to thank everyone who has helped me solve the many issues with my 66 230 SL.   The list of components that now work because of advice from this forum include: fuel pump, radiator, water pump, CSS, cold start valve, shift linkages, relays, mufflers, etc.  My car is now running pretty darn well and I am grateful for the assistance. 

However - I struggle to find the correct method to measure transmission modulator pressure.  Where is the "test port"?  What type of banjo fitting is needed?  The one below?

http://www.brakeconnect.com/product/banjo-bolt-m8-x-1-0

The transmission shifts better now that I've turned in the modulator pressure adjustment screw, but I'm adjusting blind.  I drove a friend's 66 230 SL and his car actually chirps the wheels when shifting into 2nd gear.  I'm far from that point. 

Thanks again for your advice. 

[ja17]

Transmission shift problems can be caused by incorrect fluid level, improper ignition timing causing low engine vacuum, improperly adjusted engine linkages causing the transmission solenoid to not function correctly, stuck transmission solenoid or linkage (rust), improper wiring of the transmission solenoid or a host of internal transmission malfunctions or mal-adjustments. Make sure your basics are correct before scrambling the critical adjustments.

First of all, make sure that your transmission 3 position solenoid is working and the linkage is free to move. Also check to make sure that there is 15 lbs. of vacuum available at the engine. There is a modulator test plug (12mm) rearward from the modulator. Hook your test gauge to this port. For the test, disconnect the vacuum line going to the modulator and plug the line going to the intake mqnifold. With the engine running at idle (solenoid in rear position) and vacuum disconnected the modulator pressure should read 12.7 psi plus or minus 1.5 psi. Pressure reading just off idle (solenoid in center position) vacuum disconnected, should read 41.24 psi. Lastly, kickdown pressure is measured with the vacuum disconnected and the throttle switch disconnected so that the transmission solenoid is at center position, next the kickdown button on the floor is pressed manually and the pressure should read 65.41 psi. Once all the pressures are set, re-connect the vacuum line and test drive.

Modulator pressure at idle (vacuum disconnected) is set by turning the tiny square adjustment screw (1 turn equals 2.1psi ). Kickdown pressure can be adjusted by turning the adjustment on the transmission solenoid linkage (shortening or lengthening).

Also refer to Early BBB 27-0/1, 27-8/5 thru 27-25/5

Adjusting modulator pressure lower may soften shifts, and/or cause slippage and/or early shifts in all gears.  Adjusting the modulator higher may cause hard shifts and/or late shifts, in all gears. Adjusting the transmission solenoid rod will cause variations in kickdown activation. Individual shifting problems in specific individual gears is usually not related to these adjustments.

[FresnoBob]

Thanks Joe.  Yes, the 3 position solenoid works perfectly, the timing is spot on and the vacuum is above 15 psi and the kick down switch is also working well and downshifting appropriately.  The fluid is just above the line, but I'm not sure how to remove a small amount of transmission fluid, which was changed last August. 

If I understand correctly, the modulator adjustment screw only changes the pressure at idle and the 3 position solenoid linkage adjusts pressure during kick down.  How do you change the pressure above idle?

What I most notice comparing my transmission shifting to Pete Petersen's 230 SL is the positive nature of shifting from 1st to 2nd and 2nd to 3rd.  On his car, when aggressively accelerating, the car quickly and crisply goes from one gear to the next, but on my car, the transmission slips into the next gear, and often too early. 

Pawell showed me the correct setup for the M8 x 1 bolt and banjo fitting and location of the test port.  I'm heading to the car parts store shortly to buy the necessary parts and then I'll advise the readings.

[Pawel66]

Joe writes "pressure reading just off idle..." this is your above idle reading. "Just off" as you do not have to rev up - the throttle switch should make your solenoid and rod move just as you press the pedal a little from idle position.

I assume you have the throttle switch adjusted?

From your description you may indeed have too low pressure. When you check it, please note Joe's indication on how much you can change it with adjustment screw. You may start increasing pressure with the length of the rod first and then fine tune with adjustment screw. Please read from Tech manual - shorter rod, lower pressure - or vice versa - I have good memory but short...

[FresnoBob]

I'm cobbling together the necessary parts from various Internet sources.  This will be quite a contraption once I'm done, so I'll bring it to the PagodaFest and loan it to anyone that needs it.  I'm assuming an M8 banjo bolt needs a M10 banjo fitting, which is what I ordered, but I haven't been able to confirm this is correct.  It will take a couple of weeks to get all the parts, so I'll report back once I have measurements. 

[StevenF]

Joe,
Would the same advice apply to a 71 280sl?
Regards
Steven

When I stop in drive and shift to reverse, my engine revs all over the place and my transmission tunnel makes a loud shifting /grinding sound sound and my car jerks. 

Regards
Steven

[lurtch]

Hello all,

I fabricated these two special tools when I was doing this job years ago. I through-drilled a 10mm bolt and silver soldered a fitting to it, then ran tubing up to a gauge set hanging on the dashboard.

It was interesting to watch the modulator pressure climb then drop as the shifts occurred. Transmission fluid can be seen in the right hand tube. If I remember correctly, the pressure measurement on the left hand gauge was at the manifold tap. And YES - - my modulator pressure was way out of adjustment.

Larry in CA

[ja17]

Yes Stephen,

Your "71" should be basically the same. Sounds like your modulator pressure may be low in reverse. Make sure that the trans linkage and solenoid  moves to the middle position when reverse is selected and the accelerator is moved above idle.

[StevenF]

Thank you Joe

[ja17]

Steven,  check the adjustment on your reverse band first. Loosen the 22mm locknut, turn the 10mm bolt in until snug then back the 10mm bolt out 1 3/4 turns, then tighten down the 22 mm lock nut.

[Pawel66]

I'm cobbling together the necessary parts from various Internet sources.  This will be quite a contraption once I'm done, so I'll bring it to the PagodaFest and loan it to anyone that needs it.  I'm assuming an M8 banjo bolt needs a M10 banjo fitting, which is what I ordered, but I haven't been able to confirm this is correct.  It will take a couple of weeks to get all the parts, so I'll report back once I have measurements.

Bob, I am sorry, I am not sure there about this M8 and M10 fitting... I had a set, M8 was the thread diameter on the hollow bolt. Sometimes they give you a hose inner diameter on these connectors, I am really not sure if M8 bolt shoud be M8 banjo or M10 banjo...

[mbzse]

.../...I'm assuming an M8 banjo bolt needs a M10 banjo fitting.../...

An M8x1 bolt needs an M8 fitting.
The hollow bolt and the pipe fitting from the water pump air release can be used, if you cut it. See attached (courtesy of SLS)
Note: Hollow bolt is M8x1 which is fine pitch metric

[FresnoBob]

I checked, and I'm positive I have the M8 banjo bolt and fitting attached to the correct test port, which can be seen in the attached picture. 

Does the transmission need to be in gear to measure modulator pressure? 

I read no pressure at all at idle and above idle in neutral, and above 100 psi at idle when in gear.  Am I doing something wrong? 

[ja17]

Do you have the vacuum disconnected?

[FresnoBob]

Yes, I have the vacuum disconnected at the intake manifold, which is taped closed. 

Is using a liquid filled gage acceptable?