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Shifting issue

Booreatta

By Booreatta
in Buick Riviera

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RivNut 25,000+ Points

RivNut

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Here's my opinion. The TCC (Torque Converter Control) solenoid is causing the torque converter to lock up when it's not supposed to. I've had four of the '83-'85 vintage Rivieras with the TH325 transmission and have had to replace the TCC solenoid on three of them. It's not a big job nor is it expensive. You can either have a shop do it, or if you have the tools and room, you can do it yourself. Try "Google" for some articles on how to do it yourself.

Remember, this is only my opinion.

Ed

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Guest pfloro

Guest pfloro

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Hello Boreatta:

Rivnut is correct in that the TCC solenoid may be bad. Here is a VERY easy way to check if the engine computer (ECM) is involved: Drive as you normally would and just as soon as the engine bogs down, lightly depress your <span style="font-weight: bold"><span style="font-style: italic">LEFT</span></span> foot on the brake pedal while keeping the same pressure on the accelerator pedal. This will tell the ECM to electrically de-energize the solenoid. If the engine bog stops, the ECM is at fault. If the problem remains, the TCC solenoid could be the culprit OR something else may be going on...

Since your '84 Riviera's drive train is almost identical to my '84 Toronado's, I have a good feel for the THM 325's shift points. Under <span style="font-weight: bold"><span style="font-style: italic">light</span></span> throttle on a level road, the 1-2 shift should occur at about 10-15 MPH, the 2-3 at about 20-25 MPH, the 3-4 (overdrive) at about 30 MPH and the TCC should apply at about 40 MPH.

Additional info may help with a diagnosis...

1) If you start out from a stop with the 'gear' selector in 'D' as opposed to 'OD', does the bog occur?

2) What about starting out in '2'?

3) Does the bog occur at the same time/speed during each 'drive off' from a stop?

The TCC solenoid in my Toronado has never failed so I haven't personally experienced this problem. However with my understanding of the THM 325

transmission, the torque converter clutch can be electrically commanded to apply (by the ECM) in ANY forward 'gear' but 1st. Hydraulic pressures must be within a certain range and vehicle speed must be around 40 MPH.

FYI: There is a safety reason why the TCC is designed to release when the brakes are applied. Back in the later 70s when TCCs were working their way into transmissions, Ford discovered a serious problem. If you were cruising along with the TCC applied and slammed on the brakes hard enough to lock the driving wheels (rear back then), the engine could immediately stall. Remember with the TCC applied, there is a direct connection between the crankshaft and driving wheels...! Once the engine stalled, the driver had no power steering assist and after one or two brake applies, no more power brake assist. I somehow remember that serious injuries, deaths and lawsuits were part of this issue...

Years ago a friend had an early '90s Olds Cutlass Calais with the V6 (transverse). It would bog down immediately after the transmission shifted into 2nd. By using the 'Left Foot' test, I discovered that the TCC was applying as soon as the 2nd gear shift occurred. In his case, this was caused by a malfunctioning engine computer.

Please keep us posted.

Paul

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RivNut 25,000+ Points

RivNut

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To add some to what Paul was saying about testing for the TCC solenoid being bad. My car was demonstrating what is typically referred to as the "Riviera Chuggle." My car showed these symtoms - after driving for a while on the highway in o/d then pulling off at an exit, my car acted as if it were a standard transmission car that I was trying to bring to a stop without disengaging the clutch; it would try to stall on me. My test is this: upon showing these symptoms, I would shift the car into neutral. That would reset the solenoid and everything would be fine again. It took me a while to figure it out the first time, a few times with the second car, and only once with the thrid one.

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Booreatta 10,000+ Points

Booreatta

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Thanks guys I will be able to get to the car when I get back to town and start checking things out. I had a mechanic tell me yesterday that there is a cable under the aircleaner that some time went slack and would allow the tranny to shift much too early. He was a fast talker but said that there is a self adjustment on the throttle cable, he left me thinking but with out the car at hand it is hard to check it out. I do most of my work but I know nothing about trannys

Any thoughts on the cable, I really appreciate your help

Thanks

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RivNut 25,000+ Points

RivNut

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I've read a couple of article that state the TH325 has the same internals as a 200R4. The latter uses a TV (throttle valve) positioning cable to control up shifts, downshift, firmness of shifts, and shift points all depending on the postion of the TV cable (which is hooked to the carburetor.)

I know of a guy (not me) who rebuilt a 200r4 and test drove it around the block BEFORE hooking up his TV cable - burned up the trans and started all over.

If these transmissions are kissn' cousins and there is a TV cable involved, a frayed, or misadjusted cable could do you a bunch of harm. There are very precise measurements involved in getting this cable perfectly positioned.

I don't have any first hand info on how upshifts, downshifts, etc. are handled on a 325, but if they are in fact similar to a 200R4, be very careful with that cable.

Ed

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Guest pfloro

Guest pfloro

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Lots of good information coming out here...!

As Rivnut stated, the THM 325's internals are pretty much the same as the THM 200R4. <span style="font-weight: bold"><span style="font-style: italic">Both</span></span> use a TV cable. If you look at drivers side of the

carburetor, you will see two cables: one passes through the firewall (the accelerator cable) and other connects to the transmission. The TV controls

the shift points AND hydraulic line pressure which affects how 'strongly' the clutches and band apply.

If the TV is misadjusted one way, the shifts will be early & soft. If misadjusted the other way, they will be late & hard. I am puzzled because the condition you describe seems to occur ONLY when the engine is hot. A misadjusted TV cable will affect the shifts regardless of engine temp... ???

The your TV cable needs replacement, it's a pretty easy job and the cable housing (at the carb) has a built in adjustment mechanism...

You're getting closer...

Paul

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tim63riv 2,500+ Points

tim63riv

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Jayson,

You make an excellent point! If the TCC applies early when hot, you would loose the torque multiplication ability of the converter and the car would fall on it's face. The T.V. cable would not be affected by temperature unless it passed too close to the exhaust pipe or manifold and would bind when hot.

Ed is right, the T.V. cable can cause a transmission to burn down if it fails to low pressure, so be careful. Do not attempt an adjustment without consulting the service manual and following the procedure to the letter!

Tim McCluskey

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