Uh-oh, 1984 Riviera transmission problems, help !!

Discussion in 'The "Juice Box"' started by buicksg, May 29, 2020.

  1. buicksg

    buicksg Well-Known Member

    My 84 Riv was doing just fine, until a couple of days ago when the transmission suddenly started acting up. I checked the fluid after driving, it was at the bottom of the cross hatch on the dipstick, so I put half a bottle in, still same problem. Fluid is perfectly clean, no problems there. Has about 64K miles.
    From what I can see, it is OK for about the first 10 minutes or so of driving, and then it starts slipping out of gear and/or not going out of 1st gear. I drove it yesterday, and it seemed to shift from 1st gear to 2nd at about 45mph. But still haven't established whether it does that all the time or not. The only thing for sure right now is that it's fine for about 10 minutes, then starts malfunctioning after that. When I took it out on the highway the other day, it started acting up after I downshifted to pass someone, not sure if that has anything to do with it though.

    I was looking for the vacuum modulator line, but I can't seem to find it anywhere. Also, does this car have a TV cable like the Ford cars do? There is a 2nd cable under the throttle cable, might be a kickdown don't know.
  2. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    No vacuum modulator. As far as I can tell, it should be the THM325-4L transmission, and yes, it has a TV cable. I would check the adjustment on it first. Taking a look on Rockauto, I see a shift solenoid.


    When I googled the transmission, I got a link to the AAC club,


    The mention the TCC going, nothing about a shift solenoid.

    Maybe read through this,

  3. buicksg

    buicksg Well-Known Member

    Thx. for the info. So that extra throttle cable under the main one is a TV cable. Will have to have that checked. The key thing seems to be that it acts up when hot and running for a while, shifts OK when cold.
  4. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    Maybe it's the shift solenoid. Not sure what's involved in replacing it.
  5. buicksg

    buicksg Well-Known Member

    Too bad it's not on the outside of the trans, according to that link it's apparently in the pan. Looks like it would be easy to replace once the pan is down, assuming that's the issue.
    My trans place suggested by phone that it could be the governor (just a guess over the phone), is that on the outside of the trans? I know that on my 70 Toronado it was on the drivers side of the transaxle unit right by the steering column.
  6. telriv

    telriv Well-Known Member

    Could also be the trans. filter is clogged & needing replacement. While your in there you could check the TV cable.
    Next could be the governor. IF it sticks will cause shifting problems. But since it appears to be OK cold I DON'T think that may be the problem.
    But by your description it could also be it's time for an overhaul. When it's cold the fluid is thicker than when it's warm. You could try a bottle of Lucas No Slip. It has helped solved a few problems for me in the past.
    It's worth a try & not that costly & easy to do.

    Tom T.
  7. buicksg

    buicksg Well-Known Member

    Thanks for the info. Good point about the fluid being thicker when cold. If the filter needed replacing, wouldn't the fluid look dirty? I may try that Lucas stuff. What about Marvel Mystery oil? Would that help?

    BRUCE ROE Well-Known Member

    Try a filter replacement. But in my opinion after so many decades it is
    way past time to go through the trans and replace all the soft parts. If
    low miles that may cure a leaking pressure seal, perhaps before the
    trans is seriously damaged. Bruce Roe

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