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hydro-matic question

Discussion in 'The Hokey Ass Message Board' started by oldsrocket, Dec 17, 2006.

  1. oldsrocket
    Joined: Oct 31, 2004
    Posts: 2,145


    Maybe somebody can shed some light on this issue. I am having a few issues with my hydromatic. Mainly two main issues:

    1. When I am slowing to make a turn and the tranny doesn't shift into first and I start to accelerate out of the turn the carb bogs and the car wants to die. If I slow enough to let it shift into 1st gear and then accelerate out of the turn it's fine. Down shifting into 1st a really hard shift.

    2. The car does not like to shift into reverse. It is a real hard shift and then if I'm not on level ground the car chokes and dies. I can get it to go in reverse if I shift to reverse and keep my foot off the pedel, and slowly back, or when I'm on level ground, But if I ever have to shift into reverse on a hill I'm screwed.

    I thought it was the carb. So I rebuilt the carb. Made all the adjustments to the factory specs (float level, float drop, pump rod, etc). And I have quite a lot of experience with rebuilding carbs, so I know it's good. Installed it back on and the problem still exists. I haven't messed around much with auto trannys and was hoping someone could offer some advice. Maybe a vacuum issue?

    BTW- The carb is a Rochester 2GC
    The Motor is a 1956 Pontiac 316
    Fluid level is good
    No noticable external leaks

    Any help would be appreciated. Thanks
  2. rocket8
    Joined: Sep 14, 2006
    Posts: 621

    from antioch CA

    i have the original hydramatic in my 52 olds, and ive been having the same problems you are having, and no avail, have been able to fix them. downshift into 1st and your reverse problem must be common seeing that it happens to me as well. im getting ready to just throw down the $$ and have the fucking thing rebuilt...nobody wants to do them its a damn shitty situation! if you find how to fix the damn problem, PLEASE, let me know! haha good luck my friend
  3. flatford39
    Joined: Dec 3, 2006
    Posts: 1,746


    My guess is that it is a vacuum problem. If I remember there is a modulator valve on the passenger side of the trans that the vacuum line runs to. Have you checked that out yet???
  4. Just happen to have my Hydra-Matic book in the house and was contemplating whether to tear one apart or not.This is what the diagnosis section says about rough 3-2 or 3-1 downshifts and I quote:

    "Check for binding throttle linkage causing engine to idle excessively fast.Make sure engine idle and transmission throttle linkage are adjusted properly. Check accelerator shaft for binding at floor mat."

    "Disassemble rear servo and check for broken accumulator check valve or sticking check valve plunger.Also check to see that rear servo exhaust valve operates freely in it's bore.Interference between exhaust valve and servo gasket may cause valve to stick open."

    "Disassemble,clean,and inspect control valve assembly,with special attention to TV and compensator valves.Check passages in case under control valve.Restricted exhaust hole in case or restriction in control valve body may delay application of rear servo until after the car has stopped,causing a severe downshift after stopping."

    Those are the three possibilities they list.
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  5. Do you have access to an old MoToRs Manual? I have a 1958 issue which has 2 1/2 pages devoted to trouble shooting the single coupling type. One more page devoted to the later Jet-Away which is what I think you have.

  6. yorgatron
    Joined: Jan 25, 2002
    Posts: 4,228

    Member Emeritus

    you have to adjust the shift/kickdown linkages and adjust the bands,i like to throw in a truck size can of Trans-X too...
    of course,if it's the controlled-coupling hydramatic you're SOL...:(

    Attached Files:

  7. oldsrocket
    Joined: Oct 31, 2004
    Posts: 2,145


    Bringing this topic back up.

    How can I tell if I have the dual range or the controlled coupling model? I heard that one version has park and the other version doesn't. That park is engaged by a pawl when put into reverse while the car is off.

    My tranny doesn't have "park". It would be the second type I mentioned.

    Is adjusting the bands and linkages a tough job and what type if improvement should I expect? what is the process? I plan on getting a manual soon, but I'm not sure which version my tranny is in order to by the correct manual.

    Also- I plan on hopping up my 316. It's a small motor, but I think the potential is there. She definately likes to run. I plan on putting in a hotter cam, spiced up ignition, and multi-carb intake system.

    Should I expect any ill effects of taking the extra power to the tranny and what if any modification would be needed by swapping the carb system out?

    Thanks fellas...
  8. Dirty Old Nash
    Joined: Jan 13, 2007
    Posts: 24

    Dirty Old Nash

    No "Park" definitely means the (older, better) dual-range hydramatic. The dual-range also had an iron case and weighs a ton. The "controlled coupling" unit is also called a Jetaway and had an aluminum case. Easy to distinguish with a magnet. I found this link with a good short history of the different models:

    If you want to try adjusting it yourself, I'd look for an auto-trans shop manual from the era. Lots of cars used these in the mid-50's. I found the manual for my Nash-specific Hydramatic unit on eBay for $15.

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