M6 Transmission question

[ezrstl48]

48 DeSoto Coupe, just finished going through the engine and have it up on jack stands to test everything. Up on jack stands the transmission is not shifting by itself into the high range from 1st or 3rd. I have 134 tractor oil in the Fluid Drive convertor, 10W in the trans and the pressure checked good at 40 to 45 psi at the trans. The Relay on the inner fender checks good and sends power to the different terminals as rpm comes up. I can hear the solenoid on the trans as I put elelctrical power to it. I am going through the troubleshooting portion of the manual and will be doing the Mechanical Inspection portion this evening.

My question; is it possible that the transmission would need the weight on the car going down the road to allow the transmission to shift properly? As it is right now it does not make the 'click' or 'clunk' into the high range as I bring rpm up and let off the throttle.

I have a couple other interesting things to add about the adventure that this has been and look forward to posting those soon.

BTW, the 134 in the trans case doesn't seem to work as well as the 10w oil. Seemed much tougher to get into gear...

Tim

[greg g]

I can not answer your question directly, however there is a very good section on the Semi automatic trans on the Imperial club website. It is in the repair section and is a technicians guide for trouble shooting the trans.

However, there is a governor in the system that senses speed, and allows the transmission to shift. So if the solenoid is doing its job, it could mean that the governor is not holding up its part of the bargain.

Welcome to the forum. This section is usually for folks postig tech tips that they have discovered, rather than technical questions. You may get more answers posting to the general discussion area, then post here as to what you have found when you effect your repair.

You can copy your original post into a dialoge box in the general section.

[Dodgeb4ya]

It won't shift into high range up on a lift unless you goose it hard and quickly let off on the gas-then right back on the gas.. I occasionally have forced one to upshift doing this-just lucky I guess. 40-45 is excellent trans oil pressure. The problem is when you let off the gas the driveline slows down too much as does the input shaft-the governer tells the solenoid to dump oil pressure and that prevents the upshift.

Best to get the car out on the road for a proper test.

Bob

Edited November 16, 2011 by Dodgeb4ya

[Tom Skinner]

Correct. One must try driving it to be sure.

One more thing to do is run the electrical diagnostics for this problem first to determine if its a short or bad wire or relay etc. The trouble shooting diagnostics are real clear as to the correct seqeunces to test it out.

Tom

[hemsbydodge]

Just read the thread on m6 problems, my desoto has exaxtly the same fault, again it is up on axle stands, and i cannot get it to upshift.

The previous owner had fitted a light to indicate if it was in low or high, and this light does indicate that the relay is sending the signal to upshift

At idle the generator is only producing a few volts, this rapidily raise to about 10 volts with a increase in throttle position, this then trips the relay, and a voltage is senced at the soliniod as just a blip on the digital meter, but it does not seem the change up.

I have change the transmission oil ,but i was advised to use 90 w oil ,by roberts motors, which is correct?

I have also checked the old cloth wiring for defects, no grounds/broken wires could be found either.

thanks shaun

[Tom Skinner]

One more thing. If you painted everything up real purty like - you had better use star washers on everything - every connection - especially the ground.

I had hell to pay when I lost ground by painting everything real pretty and not respecting the Truth. A Ground is a MUST - or no (ticky no shirty) no worky righty. It is essential to maintian a good ground from the M6 Transmission functions or Glitches like this will prevail. The Bell Saw Strap must make metal to metal contact with the block to finish the circiut for the Transmission seleniod as well as a good ground to the fender for the Selenoid.

Get out your pocket knife and make it come true.

Tom

Edited March 21, 2012 by Tom Skinner
spelling

[Dodgeb4ya]

Don't use 90 weight in it!!! NO NO NO! 10 weight only. With out the wiring hooked up the trans should upshift almost imediately. The electrical system on these transmissions is used only to control when a upshift or downshift occurs.

Eliminating the 6V electrical to the transmission imediately lets the oil pump build up to 40 LBS or so and will push the direct speed shift rail forward and cause a direct speed upshift-even at 5 MPH.

So I'd pull the fuse on the transmission relay on the drivers inner fender panel and go for a quick trip around the block test drive. Accelerate up to 10 or 15 MPH and let off the gas in either range-it should imediately upshift! NOTE-It will not downshift at all until you come to a complete stop and hold the clutch pedal in for 2-5 seconds-oil pressure needs to drop to zero lbs..Do not back up with out the fuse in place.

If it still does not upshift you probably have an internal gear issue or oil pressure problem. Grinding/banging upon upshift is a blocker ring and sleeve issue. Make sure the trans is full of 10W and the idle is around 450 RPM.

M-5 is the model of hydraulically operated transmiisions up to 1948. M-6 is 1949-53 and is a slightly different transmission with a bit different diagnostics.

Bob

Edited April 11, 2012 by Dodgeb4ya

[itspatndave]

Wow can I get a wiring diagram for the M6 trans.

[52b3b Joe]

This help??