GMC transmission questions,(UPDATED)

[AMGeneral]

Digging up an old thread again....

I'm still working on this M211 trans,turns out the 3/4 clutch pack was toast in it.

Today I finally finished installing a replacment trans(another 302M,donated from another truck) it tested well within suggested pressure limits,Now it shifts 1-3 with ease,4th is still not there,maybe a stuck piston in the valve body,at any rate I gotta pull the governer and valve body and clean em up again.

I also noticed the reduction unit is stuck in Low range,so i'll probably run some Dextron 3 through it and clean it out like the last one.

I also got the hardtop installed with the help of MDSA,good to see this old truck coming together.

After this one i'll probably move on to the M135 w/winch.

Updates soon hopefully

 

[Gunfreak25]

Ya'll are making me glad I have a Turbo 400 in my GMC.

 

[AMGeneral]

Well,I am back to square one here,


The replacment trans still will not shift up beyond 2nd gear,and requires it to be at just about governed speed to do so,this is after I have....

Cleaned the control valve,governer,trans pan,flushed the entire trans twice till the oil came out clean,then cleaned the control valve and governer again.

My oil pressures are 105 PSI in any Foward range,Idle speed warm oil,210 PSI both Reverse ranges idle speed warm oil.

Adjusted all my linkage as per the TM,(throttle rod and shifting linkage).

The engine easily accelerates to governed speed of 3400 rpm(verified with an electronic tachometer)

The engine is running fine,no missing,plenty of power,base timing set correctly and timing advance working as it should.

The trans makes no unusual noises and engages with no hesitation in any range.

The oil pressure makes a slight drop during the 1/2 shift up or down,but returns to 105 psi quickly after the shift.

I have tried both 30W oil and Dextron 3 trans fluid,same result with either oil.

I have not noted any slippage when if shifts,it engages quickly and firmly.

Any suggestions?

 

[NDT]

By "cleaned the control valve", do you mean make sure every spool is completely free to move back and forth? It is acting as it is stuck in F-2 Hilly.

 

[AMGeneral]

Yep,completely disassembled and cleaned every moving part and ensured it had free movement within it's respective port.

 

[AMGeneral]

Bump

 

[papabear]

Here's an even stranger symptom (to me).

My M211 will shift "perfectly" from a stop thru all gears to high. Whenever she feels like it, she will downshift...and won't upshift unless ya stop and start over again!!!

 

[AMGeneral]

Worked on the GMC again today,pulled the control valve off took it apart and checked everything again,bright and shiny,all plungers/valves/springs in their correct places. I pressure tested all the ports within the trans with clean air,everything worked as it should,bands,clutch packs applied/relased as they should,so i'm out of ideas on the trans.


PB sounds like the control valve need taken apart and cleaned as well as the governer assembely.