Life span of 34 element sprag in a th400

What type of lifespan are users obtaining with this part?What et and valve body?

When I was running a 34 element, I would get one or two passes out of it. Happened 3 times in a row. Manual VB, conservative line pressure, 3300 lb car.
My opinion is, once you get around 1,000 hp, flipping that OEM HD sprag is going to be a problem.
You have to go with the 4T80E deal. Bullet proof.

I dont like it above 750 /600lbs ft in a street car with fixed line.Strange thing is I have a few customers in the 9.3 to 8.8 range running them w/ a 2.10 first gear and they live.With the 2.10 the anti rotation of the direct drum is higher so its spinning at a higher rpm when shifted at the same rpm and they live.What are your thoughts on that Don?

How heavy are the cars? Are they big tire cars? Slicks? Drag radials? Coming into the power gradually (turbo) or n/a? What sort of converter config? Anything that will help absorb some of the shock load of the shift will help that sprag live longer.

10.5 cars.Combos vary,Procharged,Mod. twim turbo,big n20 motors .When switching to the 2.10 they are still shifting @ the same rpm, just further down the track because of the gear .

Why the durability with the numerically lower gear and increased anti rotation?The increased anti rotation makes the drum harder on the sprag during the ratio change.

I can't tell you what torque value the sprag was seeing when I was flipping them, but I can tell you that right after I switched to the 4T80E setup, when I would shift into second, instead of the sprag flipping, the tires would lose traction. Just go up in smoke. I was probably using too much power at the 1-2 shift at the time. Now, my tires and the track are so bad, I would probably get away with a HD sprag.

How heavy are those cars? Car weight plays a large part.

At the time, I was also using a very tight torque converter. 2400 stall N/C.

They are all @ 3200 plus.

This is the sort of 1-2 shift I was doing back then. I've tamed it down since then.

DRW / Buick V6 Alky v3.2 20L video test - YouTube

Do you know if they're using any sort of torque management during the shifts? Some ECMs have an option to pull timing at the shifts.

Tight torque converters?

No torque management.The turbo car and the procharged set up are both running tight neal chance bolt togethers.2800 to 3000.

Probably close to what I was running. My engine could only twist 2400 rpm out of it without boost and nitrous.
Well, after flipping 3 complete setups in a row within the first or second pass, I was done with the HD sprag. I don't give a second thought worrying about the 4T80E setup. It's obviously taking the punishment much better. Haven't opened up the trans for going on two years now.

edit: May be longer than 2 years. I can check my records if you're really interested.

THM 400 rev. manual w/t-brake clutch & band application

Reverse - Direct clutch & Rear band

1st gear - Forward clutch is applied & the Low roller clutch is holding (needs to see load)

1st gear w/brake on - Forward clutch, Direct clutch, Low roller clutch holding & Rear band applied.

2nd gear - Forward clutch is applied, Intermediate clutch is applied & Intermediate sprag is holding

3rd gear - Forward clutch is applied, Intermediate clutch is applied, Direct clutch is applied & Intermediate sprag is overrunning.

THM 400 Geartrain

1st gear under acceleration - Front planetary/reaction carrier is being held stationary from the low roller clutch locking against the center support, the rear planetary/carrier is rotating with the driveshaft, the direct drum is being antirotating via the sun tube @ a speed determined by which gear set is in the trans (2.48/1st is 84% of input shaft speed). The combination of both the front & rear planetaries gives you first gear.

2nd gear under acceleration - The intermediate clutch is applied & along with the Intermediate sprag holding this stops the dirct drum from antirotating & also releases the low roller clutch which intern eliminates the front planetary/reaction carrier. Now the only active planetary is the rear one thus giving you second gear.

3rd gear under acceleration - The Intermediate clutch stays applied & the direct clutch is also applied which allows the Intermediate sprag to freewheel thus eliminating the rear planetary & giving you 3rd gear.


The low roller clutch is designed to work under load & for this reason it is highly recomended that you do not do burn outs or hard peddle the car while in first gear. The loading & unloading of the low roller clutch causes the rollers to slam against the springs & flatten them. If the low roller fails under load it will send the dirct drum to 3.25 + times engine speed, usally very bad when there is a cast drum involved. Another big issue is the Intermediate sprag also works under load, it needs moments of time to load the sprag elements properly & also the sprag race dementions come into play. Now we are only talking about mili-second, but this is accomplished by bringing the motor down to drivshaft speed during the gear change, where as in the burrnout you are bringing the driveshaft up to enging speed during the gaer change which can & will "shock load" the Intermediate sprag.

Remember when in 1st gear you are antirotating the direct drum then stopping it to get second which in a burnout situation this unloads the low roller rapidly & has to lock the intermediate sprag with out the proper "time" to load. This will cause unnessassary wear & abuse to the sprag, then resulting in premature sprag failure

8.40's-8.50's 3400lbs+ over 100 passes 34 element sprag. Havent touched the trans.

You forgot to cross your fingers and knock on wood.

There was a time in my development where I was using a 34 element for quite awhile. I don't remember what the change was with my combination back then that made the difference, but whatever it was, all of a sudden the 34 element sprag didn't like it at all. One to two passes and it was out for the count.
The direct drum was stabilized, also.

Dont know about. Just know its been working flawless.

Always runs flawless,... up until the run that you need it most.

Hasnt let me down in 100 plus passes. I cant complain.

I wouldn't complain, either. I wouldn't change a thing until you have to. Why spend the extra big bucks for the huge gain in intermediate torque capacity that you most likely will never use. I did the same thing. As long as the 34 element was doing it for me, why fork out the big bucks. As performance stepped up for me, I had to make a choice, either step back in performance to a level where the 34 will live, or move forward with the project and put something in the trans where I won't have to give a second thought as to whether this will be the run that it flips or not. Changing out complete direct drum and intermediate sprag assemblies 3 times within a span of 4-6 passes wasn't floating my boat. It's kinda like getting away with the stock driveshaft as your project moves forward in performance levels and finally installing the right driveshaft and u-joints and feeling relief that you've got the right part in there and don't have to worry about it.