QuestionHi Knuck, You answered a previous question for me on the Modulator Valve for this truck, still haven't found it though! Anyway, we have drained the transmission oil, cleaned the pan, replaced the filter and put in new oil. The truck takes off with power in drive and reverse (it wouldn't move before) but will not shift out of first. I bought a modulator valve, but is it worth trying to locate and change it? Or is the tranny trash?
AnswerHi Gina,
That darned modulator!
If you are standing under the vehicle, rear driveshaft directly over your head and looking toward the front of the vehicle, look to the back of the transmission, NOT the transfer case (if 4WD), on the right (passenger) side, slightly above the pan and just below the center line of the tail housing you should see the small round vacuum diaphragm (modulator). If you can't find it, snap me a picture of the rear of the trans because GM used vacuum modulators well into the '90's on just about every THM-350 an yours should be no different unless it is a 700R4 (4-speed OD).
Ok, now the fun part. The modulator only controls the shift timing, it does not exactly control the actual shift, only that the engine is ready for the next gear, if you catch my drift. The governor is the device that physically allows the trans to shift up or down.
Based on what you have stated, I'm thinking the fluid was probably pretty burnt and/or black/thick. If that was the case, it is entirely possible that the governor is sticking and not allowing the trans to up-shift. The governor in your trans is located inside the tail housing, bolted to the output shaft, just forward of the speedo gear if 2WD and you'll need to remove the T-case to access it if you have a 4W edition.
If first and reverse seem strong, I'd say the trans is worth at least the effort to see if it can be saved. A six-month major component reprieve should be welcomed.
Looking for a reputable service technician? My advice on finding a good technician is: Steer clear of the dealership and 'chain' stores like Firestone, Sears, Pep Boys, Monro Muffler/Brake, Midas, etc. as they usually only employ ONE ASE Certified Tech just so they can say they do and chances are, that guy is the asst. manager or manager and is not in the store to diagnose/repair vehicles anyway. Find a service location in the link below or get some names out of the yellow-pages and do a drive-by. Garages that employ ASE Certified Technicians will be marked with the 'Blue-Seal' insignia. If unsure about whether a place employs Certified Techs, just ask to see their credentials. ALL ASE Certified Technicians will be PROUD to show and display their certificate(s).
Thanks for the question, I hope this information was helpful to you.
Fred
Knucklebusters Used Auto & Truck Parts, Inc.
www.knucklebusters.us
570-453-0910
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