1980 TH350 Originally Mated to a 260 V8

Discussion in 'The "Juice Box"' started by Bridgford, Apr 21, 2017.

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  1. Bridgford

    Bridgford OK, no progress in 11 yr

    In 2001 I bought a 68 Skylark Custom Convertible 350 4bbl that the previous owner had had the engine rebuilt about a year earlier. Somewhere along the line (probably before the engine rebuild), the ST300 was replaced with a TH350. When I bought the car, it had lost any desire to go forward, however it would back up just fine. Now that my 3 daughters are on their own, I am finally getting back to working on the car. From what I can figure from information on the trans, the TH350 came from a 1980 Olds with a 260 V8. Presuming this trans was built to mate with an anemic tiny V8, can I buy a rebuild kit and make it substantial enough to be reliable when mated to a PP code '68 350 which I think was mildly built up?

    My evidence for what the tranny was originally hooked to is based on the pictures below and the following link:
    http://www.teufert.net/trans/t350-3.htm
    The VIN portion on the transmission 3=Olds, A=1980, M=Lansing, the rest is the sequence number.

    Thanks,

    Dale
     

    Attached Files:

  2. BQUICK

    BQUICK Gold Level Contributor

    That should be a T350 with lockup converter. Nice setup when rebuilt properly.
     
  3. BRUCE ROE

    BRUCE ROE Well-Known Member

    I have run a TH350 90,000 hard miles with a 350 engine and 4100 lb. A decent trans,
    but no match for a TH400. I would chance it after a rebuild; look to see that the full
    number of plates is used in the clutch packs. Bruce Roe
     
  4. Bridgford

    Bridgford OK, no progress in 11 yr

    My concern is that if the trans had a code of LD, which if the reference material is right, would have been built for an Olds 260 V8. I assume that the vast array of TH350 codes over its production run meant that each code was built to meet the requirements of that specific engine it was to be mated to. Would this trans accept the same quantity of clutch disks and steel plates as one built for a Buick 350 with 250 HP? Or, more to the point, can I use all of the disks that come with the rebuild kit, even if the trans wasn't originally built with that quantity of disks?

    Thanks,

    Dale
     
  5. BRUCE ROE

    BRUCE ROE Well-Known Member

    Part numbers were changed for every model of every year. For a trans there probably was
    some fine tuning of the valve body to match the car/engine, but mostly a TH350 is a TH350.
    Things like output shaft length are obvious, and things like electrical contacts for the
    emissions system don't affect shifting. A bit of shift tuning might be advantageous, even
    on the original setup. Most of such things can be done in the car. What is to worry, is they
    put in some light duty part for a smaller engine, seen sometimes as less than a full set of
    clutch pack plates, also note release springs. For a 400 that means changing the
    piston, not sure about a 350. Bruce Roe
     
  6. Bridgford

    Bridgford OK, no progress in 11 yr

    Thank you Bruce, that is the type of thing that I wanted to know. I intend to try rebuilding it myself. I have a 1972 Pontiac service manual that I will reference, once I get it back this weekend. I have a couple of months to speculate before I can get to work on the car. I expect that the accountants would drive how many parts would be put into the transmission based on the power output of the engine. Save a couple dollars on a transmission and it adds up if sales are high.

    So if they used fewer clutch pack plates in this particular transmission, if the rebuild kit I get has all of the clutch packs possible, will the part that the clutch packs go into hold all of them, or will I need different parts? Will most of the vendors that sell rebuild kits also sell the springs and other internal parts?

    Thanks again for your input.

    Dale
     
  7. BRUCE ROE

    BRUCE ROE Well-Known Member

    My experience is with TH400, which is probably easier to rebuild, at around
    the same cost. Rebuild kits never have ALL of the parts that ought to be
    changed, some more than others. None had the extra clutch, had to find one.
    No springs in my kits, usually they are OK.

    TH400s had a 4 clutch plates (TH375), 5 (standard), and 6 (thinner piston,
    for large big block cars) in the direct clutch pack. In addition, the steel plates
    between the clutches could be several different thicknesses, I probably have
    found 6 variations to fine tune the clearance. Check yours out. Bruce Roe
     
  8. Bridgford

    Bridgford OK, no progress in 11 yr

    Thanks Bruce, I will be working on it this summer, I hope.
     
  9. sean Buick 76

    sean Buick 76 Buick Nut

    I would just take it to a trans shop and get a good rebuild done. I have a TH-350 that can handle tons of power they can be built right up... Your combo should be fine with a stock rebuild.
     
  10. Mark Demko

    Mark Demko Well-Known Member

    X2, I know the 350C trans used behind the 231 V6 used one less clutch per pack
     

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