I had a local shop rebuild my trans this spring. Its pretty much got every upgrade other than the lightweight drum, full bearings, red eagle clutches, welded in center support, HD sprag, HD retaining ring ect. I just broke it after only a few passes on the trans brake. I made some passes(about 12 total over the past few months, 5 on the trans brake) and once in awhile it wouldn't go into 2nd gear. I never even launched higher than 2500rpm's on the brake..I was hoping to atleast get some 3500rpm launches in before it broke I finally completely lost 2nd gear last weekend doing some street driving. The 2nd gear sprag and sprag race were broke and of course sent metal all through the trans chewing up a some other parts too. I was surprised it was working at all once I saw how bad it was broke..1st and 3rd still worked fine. Whats the max power level a th-350 can be reliable with a trans brake on a full weight (3400lbs w/driver) car?

I'm probably making around 550-600 flywheel HP, which I thought would be ok from what I've read? Not sure If I just had bad luck of If I'm pushing the limits of a th-350. The car definately has easy high 10 sec power (123+mph in good not great weather) I just got to get these trans problems worked out.

The good news is the trans shop the built is going to take care of me and fix it with little or no cost to me but I'm trying to figure out if I still want to use the trans brake valve body or just go back to foot braking it for reliability and eventually switch over to a th-400. w/trans brake Any thoughts?

 

I like to see these transmissions get ditched at about 550 Hp. The cases are weak, the valve bodys don't sit well on the case unless the case is milled, sprags break and god knows what else?

Turbo 400 is the way to go.

 

If you have serious power, just use a powerglide.

You don't break the sprag going down the track. You break the sprag coming out of the water box in second gear letting the tires grab. Always come out of the water box and let off the throttle in high gear.

You can still break the sprag in a TH400.

 

I have been running one for awhile, and putting alot more power through it.
the car weighs 3270 ready to race, with driver. I also use a transbrake, and leave at 4800, and on nitrous it usually 60 foots in the 1.2's depending on the track the front tires come down right before the 60 foot clock, or if the track is good, 100-120 feet out. I dont have many special part in the trans, other than the improved sprag, and revised clips for the sun gear.it has raybestos clutches in it (no band). recently I have been running 1/8th mile so i changed to a 4.56 gear and when crossing the finish line the shift light is on in 3rd (which is set to 7500 in 3rd) that works out to over 130 in 1/8th mile so feel free to check the hp with varios calculators. needless to say, I have been wondering what to replace it with, but it works so well I have no reason to.
were any of the clutches burnt? I wonder if a clutch was dragging and causing the sprag to drag. Is there any way you can get some pics?
Also like stephen said, it would be very hard on the sprag comming out of the water box in 2nd

 

What Stephen said. I ran a th350 for 5 years and never broke one internally. I did break some cases, but a JW bell fixed that. I traded that 350 for a blowed up glide and some cash, and the guy is still running it. It seen many 4000 rpm launches getting 1.45 60s. I went to a glide over the winter and wouldn't go back. My car 60s a .015 quicker with the glide, but I'm running a 5.67 gear.

 

https://www.thirdgen.org/forums/orga...ck-saddle.html


If your running the intermediate roller clutch (sometimes confused with a sprag) your going to have problems. Have your trans shop keep the wave steel in the intermediate clutch (it will reduce the shock load on the intermediate roller clutch}.

Scott's trans in the link posted above is built with the sprag intermdiate drum, and a heat treated stock input shaft , and alto red clutches that are at least 2 ys old by now.

A upgraded sprag intermediate drum will add 200-300 ( depending on who's drum) to the cost of the build.

Mike.

 

With my old trans I did 2nd gear burn outs never shifting to 3rd for years and never broke it(got lucky). I changed my line lock button location to the shifter handle so I could shift to 3rd before leaving the water box and I broke this trans.. just my luck lol

Thanks for the input guys...I think a th-400 or powerglide is in my future once I blow this trans up again.

 

Well, from reading the rest of the responses here I don’t think that this is going to be a popular answer, but if you want something reliable that you can play with and not blow up then run a TH400. The only reason to run a TH350 in a car is if it’s a serious race only car that you’re looking to get every last fraction of a second out of with lighter parts and less rotating inertia. The TH350 is just never going to be a beefy, bulletproof transmission, so if you’re going to run it in anything resembling a “fast” car, then resign yourself to having to do regular maintenance to keep it on piece, and that is just too much of a hassle for anything but a dedicated race car.

Since you’re talking about taking it on the street… to me it’s a no brainer…

 

Sounds like you need to find a new transmisson builder to me, both 87_TA and I are running 800hp big blocks in front of the TH350, we have both had some up and downs (bellhousings & cases) but the the alto clutches in mine are 3 seasons old now with close to 200 passes off the brake @ 3500+ Listen to converter guy he definetly knows what he is talking about. I have no doubt if you had a solid build to begin with the trans would love the 550 hp motor.

 

My TH350 has a stock rebuild with a shift kit in it and has been living strong for nearly 4 years now... No transbrake though, but a ton of 11 sec passes on it and severe beatings while street driving. I'd agree that something is wrong with the builder, not the transmission itself.