BA71SS Posted May 19, 2008 Share Posted May 19, 2008 I have a TH 350, with a 2800 stall, unknnown make shift kit, behind a 454 with plus 450 h.p. which has developed a severe shift problem. At first it would not shift into 3 rd, then things got worse and it would not shift into second either. When it would shift to second the engine compression would not slow the car down when I let off the accel. First and reversse are both fine with no slippage and when it had second there was no slippage. This came on all of a sudden and w/o warning. I checked the oil and it is fine and the vac line to the mod is in tach. Do I start pulling it out? I was wondering if the shift kit had a part failure. Any help is appreciated. Quote Link to comment Share on other sites More sharing options...
Heckeng Posted May 19, 2008 Share Posted May 19, 2008 You broke a sprag I think! I've done the same thing. th350s can take a lot of abuse, but you have to be careful with some things. Don't downshift above your stall rpm or you risk breaking your sprag which is probably what happened. You won't have any engine braking and can lose second and third. If you like the th350, you might consider upgrading to a heavy duty sprag setup. It'll run you several hundred dollars not including the rebuild that you already need, but that would probably do you. Check out this thread about what you can and shouldn't do with a th350 and also a th400. TH350 and TH400 discussion Quote Link to comment Share on other sites More sharing options...
kc8oye Posted May 19, 2008 Share Posted May 19, 2008 yeah, i wouldn't reccomend running a TH350 behind a big block.. i've never heard that one about downshifting above stall tho scott.. I used to downshift all over the place with my TH350 and never broke it.. but then, I was runnning a small block :> Quote Link to comment Share on other sites More sharing options...
monte70car Posted May 19, 2008 Share Posted May 19, 2008 had a 350 behind my big block for a while until i got the 700 in 2001 Quote Link to comment Share on other sites More sharing options...
Heckeng Posted May 19, 2008 Share Posted May 19, 2008 The downshifting changes directions of the drums and sprag almost instantaneously, and puts massive pressure on the sprag which can break the framework that holds the roller bearings in place. That doesn't matter if it's a big block or small block, just be careful! I have a buddy (yeah, the infamous "buddy" post) who runs a 68 camaro which is pretty heavy, I think 3400 pounds or so, with a 496 and a th350 and he runs high 9's with a tranny that he built himself. He is a mechanic, and focuses on transmissions, but he is only running a couple hardened parts, and not even the heavy duty sprag assembly. TH350s can be very strong for very cheap. Just know what not to do to keep them going! Quote Link to comment Share on other sites More sharing options...
BA71SS Posted May 19, 2008 Author Share Posted May 19, 2008 Thanks for the diagnos Scott. Guess it is time to get out the jacks and get the car up enough to drop the tranny. I'll also see if there is a 400 avail. around here, if not I'll redo the 350 with the HD parts and put in back in. May as well do it right while it is out of the car. Thanks again. Butch Quote Link to comment Share on other sites More sharing options...
Heckeng Posted May 20, 2008 Share Posted May 20, 2008 Best of luck, let us know what you or the tranny shop finds out. Quote Link to comment Share on other sites More sharing options...
kc8oye Posted May 20, 2008 Share Posted May 20, 2008 so are you saying the reverse j-hook's are out of the questions? (get the tires burning in reverse, slam it into drive and burn them the other way to make j-shaped burnout marks) Quote Link to comment Share on other sites More sharing options...
Heckeng Posted May 20, 2008 Share Posted May 20, 2008 OUCH! That hurts just thinking about it! Quote Link to comment Share on other sites More sharing options...
kc8oye Posted May 21, 2008 Share Posted May 21, 2008 Leo's TH400 has survived a number of these 'manuevers' Quote Link to comment Share on other sites More sharing options...
BA71SS Posted May 21, 2008 Author Share Posted May 21, 2008 Ok on the follow up report. I'll be getting the tranny out myself and most likely the shop down the road from me will be taking it apart. Been awhile since I had a tranny apart. The owner there likes the muscle era cars and enjoys working on them. I'll get down there thursday afternoon and speak with him and see what his schedule is like. Thanks again Butch Quote Link to comment Share on other sites More sharing options...
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