THM 350 Transmission Rebuild Part 2

Описание: This is part 2 ot the THM 350 Transmission Rebuild.
*Briefing Document: THM350 Transmission Disassembly*

*Key Points:*

*Transmission Identification:* The Pontiac THM350 is identified by its *bell housing's "valley" shape,* unlike the "peak" on regular GM bell housings. Universal bell housings existed in the 70s and 80s, but this transmission is not one of them.
*Original Condition:* The presenter notes the transmission appears to be in original condition. The presence of original *"flon ceiling rings"* indicates it likely hasn't been rebuilt. However, the presenter acknowledges that the transmission could be "flat rated," or patched up without a full rebuild.
*Step-by-Step Disassembly:* The video guides viewers through each step of disassembly, identifying components such as the pump, stator, linkage, servo, accumulator, modulator, governor, valve body, clutches, bands, bearings, and gears.
*Component Details:*
*Pump:* Includes a stator, "flon ceiling rings," and an intermediate piston. The **bushings in the pump are critical and will be replaced**. The pump has a shim for end play and is a crescent type.
*Linkage:* The shifter linkage is connected to the front of the transmission and is removed with a 15mm socket.
*Case Saver:* A metal part resembling a "Texas map," including the anti-clunk spring, designed to protect the transmission case from wear.
*Anti-Clunk Spring:* A metal spring placed in the case along the center support to reduce noise and vibration during shifts.
*Kickdown Cable:* Also known as the passing gear cable, it is used for downshifting during acceleration. **Unlike the 700R4, it only affects downshifts and not line pressure**.
*Servo & Accumulator:* The intermediate servo and accumulator are identified, noting the importance of the o-ring. The o-ring is found to be flat and the spring is broken.
*Modulator:* Controls shifts and may have an adjustment screw. It uses a flat o-ring and is held in place by a hold-down bracket.
*Governor:* Regulates shift points based on vehicle speed. The governor has a filter that needs to be installed for proper oil flow.
*Valve Body:* Contains a manual valve and an s-clip. The gaskets are brown, indicating age.
*Intermediate Sprag:* A one-way clutch that prevents the intermediate drum from turning backward. **Correct orientation is crucial; it should be installed counterclockwise**.
*Check Balls:* The THM350 uses four check balls, and a common modification is to eliminate three and only use the one by the modulator.
*Troubleshooting and Wear:* The presenter points out common wear areas, such as worn bushings, flat o-rings, debonding friction material, and grooves in the speedometer driven gear.
*Performance Enhancements:* Modifications for firmer shifts include removing springs from the accumulators, replacing the wavy plate in the intermediate clutch with an extra steel plate, modifying check ball locations, and blocking the accumulator piston.
*End Play:* The video emphasizes the critical nature of end play clearance. Shims are used to achieve the correct clearance.
*Importance of Details:* The presenter stresses observing the orientation of parts, ID marks, and snap ring placement during disassembly.
*Filter:* The transmission has an old factory felt filter which will be replaced with a screen filter.

*Key Quotes:*
"That's how you identify a Pontiac from a regular general motors".
"...this transmission has not been worked on I mean I'm very surprised 1980 we're are in January 2016 so you do the math that's a long time long time...".
"I'll tell you something about this 350s there is a part that is called case saver it's a metal little thing that looks like a little Texas map where you have your your anti-clunk spring...".
"This is the kick down cable or the passing gear cable. It only works for passing here. You go pedal to the metal, it opens the kick down valve and it down shifts to second or to first depending on the speed that you're going".
"...the clearance the employee so that's very important we're gonna on the rebuild we're gonna take care of that...".
"That's why it's very important for you guys to want to know Sprag rotations on the unit that you're working on if you don't know your Sprag rotation before you take it out mark it do a mark on it take a picture...".

*Conclusion:* The video thoroughly overviews the THM350 disassembly process, highlighting critical components, potential wear points, and common modifications. The presenter's practical experience makes this video valuable for those learning about or working on THM350 transmissions. The rebuild process will be shown in "part two" of the series.


*Hashtags:* #THM350 #TransmissionRebuild #CarRestoration #DIYMechanic #AutomaticTransmission #Pontiac #TransAm #Automotive