94 Firebird drag car keeps cracking transmission cases
 

Hi, i am new here and need some assistance. I have a 94 Firebird that I back halved with an Alston setup, subframe connectors and a 10 point cage. It is a drag only car so we gutted the whole thing trying to shortcut things. It has a 406 with an 8 inch converter, 400 trans and Dana 60 w/5.13 gears. I launch off the brake at 5500 rpm and have broken 3 trannys in 2 years. It has a motor and mid plate, poly trans mount and an engine limiter. I like the car and don't want to scrap it but my boss and racing partner is tired of it and wants to move on. Any suggestions?

Possibly something isn't lined up correctly in the driveline...

What's the trans crossmember look like? Is it possible that the crossmember is moving while the motorplate and midplate stay still? Most cars have the crossmember tied into the cage or into the subframes.

where are they breaking ? all with the same engine ?

Solid motor mounts and a solid trans mount? If so, put a urethane trans mount in it. Problem solved. Did this with my old camaro as well. Removed the solid trans mount and problem solved.

says he has poly mount

Sounds like an alignment problem in the driveline. Does the transmission bellhousing bolt up to the engine without extra effort? Once bolted to the engine, does the transmission mount bolt to the trans crossmember easily without having to force or move the transmission/crossmember?

I was going to say like the above post, sounds like something is diffently binding up..

I was kind of thinking that. The trans crossmember is tied into the subframe connectors so i'm pretty sure thats ok. The motor is probably up to high. We didn't do much research on that when we put it together. It was originally a v6 car and I didn't change the subframe crossmember because we used motor/midplates. I did used the v6 mounts to set motor position. Everything bolts together smoothly though.I don't get to race much because of work schedule and transmissions are expensive to just put in and break so I want to be sure it's fixed before I spend more money. It completely shattered the bellhousing and ripped off the mount and broke a front u-joint about two weeks ago. I just built that trans and it was the first pass on it.

Yes, all with the same motor.

whew again is it breaking, possibly rear block mounting off to crank centerline..have run into before

The last trans was a pg. It cracked just in front of the tailshaft. I didn't stall the car very high on that run. The 400 I just broke shattered the entire bellhousing all the way across leaving the rim bolted to the motor plate and lifted the rear of the trans off of the mount. I stalled to 5500 on that pass. The converter was the only thing holding the front of the trans up. It left the line great and when it got to around 6800 rpm, the car felt like it was struggling so I shifted and let off and I could see chunks of the bellhousing in my rear view and banging on the floorboard.

Stock case and tailshaft?

Yes, the case and tailshaft are stock.