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Thread: TH-350

  1. #1

    TH-350

    I have a 1972 Nova with a 327 .030 over 10.5 compression. 250 @.050 cam with .555 lift Mechanical / Solid lifter cam, AFR 195 heads, Weiand Team G with a Holley 800 double. TH350 combo with a shift kit and a B&M 10" 3600 torgue converter stalls between 3600 - 3800 rpms with a 12 bolt posi with 4.56 gears.

    The problem is a year ago I was going through the traps at about 7500 rpms. I ususally shift around 7300 rpms...The last time at the track I only went through about 6200 rpms...the next pass only around 5800 rpms...my final pass only around 5500 rpms...I have ran a best of 12.57...then 13.00...then a 13.20 as the rpms drop.

    The car comes out of the hole great with the torque converter...it feels like the tranny is slipping but I am losing rpms so that doesn't make sense...

    Also it doesn't "chirp" the tires as I go from first to second gear like it used to...

    Any ideas? Time for a rebuild? New shift kit? Valve body? Torque Converter?

  2. #2
    Senior Member RACING JUNKIE
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    Doesn't much matter if it is the converter or trans at this point...if the converter is going then the trans will need to come apart also.

    Does the engine run the same as it did? No chance the valve springs are worn out or ANYTHING like that. Might explain the loss of ET. I would expect a trans/converter problem to show itself in the 60' times.

    jmo

  3. #3
    Senior Member RACING JUNKIE
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    LOOK ELSE WHERE, NOT TRANS. IF YOUR RPM'S WERE GOING UP & ET & MPH WERE GOING DOWN THEN I WOULD LOOK THERE.

  4. #4
    The engine runs the same as it did before up to about 7300 rpms...It pulls as hard as ever in first gear...but when going from first to second it isn't as snappy as it used to be but still goes right up too about 7300...but when I go from second to third it just seems like it is slipping but it just won't go over 5500-6000 rpms...

    I guess that is why I didn't think it was engine related...I will have to check my springs but doubt that they are the problem...

    Willing to try anything at this point...

  5. #5
    Senior Member RACING JUNKIE
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    I'd be pulling the tranny and while I had it out getting rebuilt I'd send the converter out and get it cut open too, your problem is definetly not in the motor IMO>Cp
    ***IN GOD WE TRUST***

  6. #6
    Senior Member RACING JUNKIE
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    Quote Originally Posted by cepx111
    I'd be pulling the tranny and while I had it out getting rebuilt I'd send the converter out and get it cut open too, your problem is definetly not in the motor IMO>Cp
    I've narrowed it down to something on the car.


    OK Now I don't want to insult you but just a thought.

    Have you checked to make sure the throttle is still opening all the way? One time my NOVA slowed down all of a sudden and after looking things over discovered the throttle cable pulled through the sheet metal of the firewall a bit and the throttle blades were not opened fully.

  7. #7
    cepx111 - Where would you recommend sending the converter to have it checked out?

    Tod74 - lol...I am not insulted at all. My carb throttles are opening all the way. But that was good advice as often times I get so focused on one thing I forget to check out other options.

    I was also told that because I am running a single plane intake with a manual / automatic valve body that the "kickdown" passing gear line was never connect to the intake from the tranny. If that wasn't connected properly that the transmission wouldn't get anough vacuum to apply enough pressure to the clutches to make them work properly. Hence my transmission is going to need to be rebuilt. They also said that if I go to a full manual valve body that I wouldn't have to worry about hooking up the "kickdown" line. Does this make any sense to you guys? Thanks!

  8. #8
    Senior Member RACING JUNKIE
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    Quote Originally Posted by toohipz28
    cepx111 - Where would you recommend sending the converter to have it checked out?
    PTC in Alabama, ask for Kenny Ford.

    About that kickdown cable, when I ran a T350 I just pulled the cable all the way out and crimped it down, that way your fooling the tranny into thinking your at WOT all the time which will increase line pressure. I ran one that way for 4 years in my 81 Z28 dragcar, never had any trouble, screw a manual valve body, it didnt cost me nothing to pull that cable out and clamp it down.
    ***IN GOD WE TRUST***

  9. #9
    Senior Member RACING JUNKIE
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    Quote Originally Posted by cepx111
    Quote Originally Posted by toohipz28
    cepx111 - Where would you recommend sending the converter to have it checked out?
    PTC in Alabama, ask for Kenny Ford.

    About that kickdown cable, when I ran a T350 I just pulled the cable all the way out and crimped it down, that way your fooling the tranny into thinking your at WOT all the time which will increase line pressure. I ran one that way for 4 years in my 81 Z28 dragcar, never had any trouble, screw a manual valve body, it didnt cost me nothing to pull that cable out and clamp it down.


    the way I read his last post he is talking about the vacuum modulator valve not the kick down cable.I could be wrong. Also, what happens if you don't use a kick down cable at all?How does that work with a th400? I ran a th400 in my chevelle and don't remember any type of cable at all...just a vacuum modulator.I had it rebuilt and don't know what was done to it but I could manually shift it or put it in drive.I also never had it shift out of low on it's own with the shifter in low.Someone told me once that a th400 will do that(shift out of low on it's own)

  10. #10
    Todd - I thought he was referring to the kick down cable...Not the Vaccum Modulator. The kick down modulator is what I was told that if not hooked up properly with a manual/automatic valve body will result in not enough pressure to apply the clutches under WOT...hence my now slipping clutches in high gear...and now the car won't go into reverse until it warms up. Which makes even more sense because third and reverse are together on the TH 350.

    Someone was telling me that I could have my current valve body modified relatively cheaply to manual to avoid the problem...???

    I don't understand how crimping the kick down cable would work though if it needs vacuum to work though?

    I appreciate everyones advice! This is my first automatic transmission and have alot to learn! Again Thanks!


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