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New update -

I changed the power wire to the solenoid and also installed a new switch thinking that might be the problem… no change. I what did learn is the transmission does not start locking and unlocking on its own until I drive for 20 miles or so and the trans gets real hot. During the first 20 miles the lock up works prefect as it should.

So I was talking to someone else and they recommended changing the soliend in the picture above. My question... how to get the part out ( I guess it's actual part is located under the pan)

2. where can I buy the new part?

I assume I leave the plug connector and black part seen in the picture alone.. change the part below inside the pan?  

hmm.. could the pressure switch be going bad...  or the sealing rings not holding pressure to keep the switch closed..

do you have oversized tires that  have reduced drive shaft speed???? so you are right on the margin

i found some info on the pressure switches..

lock up pressure switches  (GM part numbers with color strip ID..    PSI nearly equals MPH..)

white  38 Psi  8633363

purple 40 Psi 8641265

pink 44 Psi  8633361

white 50 Psi  8633397

Brown 52 Psi 8633360

blue  54 Psi  8633364

i searched for some of these numbers..   could not find some.. i did notice that some of the transmission parts suppliers do sell them under their own number.. .

which one your transmission has?????????????  my TH350 delco catalog is long buried in an unmarked box in storage..

why unmarked.. one of my local parts stores closed one of their stores..   they tossed out every paper catalog from that store.. as they had duplicates for them at their main store.. i was in heaven.. i filled my car with them..  boxed them up.. stored them for some time in future where i can set up the catalog racks..


depending on where you live..  there might be transmission parts stores around..   you might be able to pick one up online..

some gm dealers.. some stores sell AC delco parts..  

please use if you can.. a oil pressure switch socket on the new one.. so you don't crush the edge crimp with the channel lock pliers..  

The solinoid is under the pan. It is held down with two 5/16 bolts and has one wire on it.  If you only lose lockup when its hot it could be that those bolts are not tight enough. If they are loose that could be your problem.  

Big help, thank you all.  And yes.. the truck is a K5 blazer lifted 6 inchs with 35in tires.

I will drop the pan and check things out...  

Ok.. lots of updates...see pics below.  I dropped the pan and looked around.  I noticed first the wire to the solenoid is cracked and about 5 spots.  Could this be causing the problem?  Doesn’t seem to be shorting out on anything….but it didn’t look right. Is there a special type of wire to use here?

The pressure switch is 48 psi as seen in the picture.   I’m going to replace this … with the nature of my issue should I get a lower psi switch? Like 40 psi?

Any input would be greatly appreciated. thanks









 

While the pan is off I guess I should also replace the  solenoid. Here is what I have now…



Here is what I found online – look ok?  http://www.ebay.com/itm/350C-TH350C-THM350C-350-LOCK-UP-TCC-SOLENOID-ROSTRA-NEW-/290548707122?pt=Motors_Car_Truck_Parts_Accessories&vxp=mtr&hash=item43a60d6f32#ht_1726wt_795  

dropping the pressure is probably what i would ***

as is replacing the TCC solenoid..

there is somewhere a test port that you could screw a long hose and a pressure gauge into for pressure testing that circuit.. so you will know exactly what the actual pressure is during a test drive..

these are like 25 bucks at harbor freight



Engine Oil Pressure Test Kit ITEM # 98949  the gauge on this goes to 140PSI.. so  it should be able to tell you what the governor line pressure is at lower speeds..  the hose is 66 inches long.. perhaps not quite long enough. but its cheep..  

here is what I'm looking to buy -

TCC solenoid- http://www.ebay.com/itm/350C-TH350C-THM350C-350-LOCK-UP-TCC-SOLENOID-ROSTRA-NEW-/290548707122?pt=Motors_Car_Truck_Parts_Accessories&vxp=mtr&hash=item43a60d6f32#ht_1726wt_795


44psi switch (one I had is 48psi) http://www.ebay.com/itm/Trans-converter-pressure-switch-GM-350-350C-250C-375B-/220823315854?item=220823315854&vxp=mtr#ht_500wt_810


Seems about right?  or should I go even lower.. like 40 psi?