Long story short I have had the car running for a while now but every time the car sees the dyno it breaks a trans case or tailhousing. I think the stock type driveshft was partially to blame as it is 56" long and 3" necked down to 2.5" on one end.

I replaced the driveline with a 3.5" chromoly high speed balanced shaft from Bloomingthals in OKC to eliminate that theory.

I looked at the trans angle and it was pointed downward somewhat extreme just looking so I shimmed the mount up .5" (any more and the case hits the floor)

I have the BRP style mount plates on the engine and the lh8 pan. Also moved my perches so the engine sits where it naturally wanted to. Crossmember went back to the same place it was with the 700r4/350 sbc.

Pinion angle looks to be slightly on the positive side.

I know ideally the trans should be positive and the pinion negative (correct) but that doesn't seem to be an option...

What have you guys done? I think it's only been a dyno problem because I am sane and 6500rpm in third would be well over 130 mph on the street...I don't do that haha

I can't afford to wipe out another built 4l60e but I really need the car to be dyno tuned as the idle sucks and I'm losing at least 20rwhp with my mail order tune.

I can measure my angles, but I honestly haven't messed with the pinion angle since before the swap. My trans is sitting at about 4.5* down. I ran it to 7000 rpm on the dyno in 4th gear (1:1) which is 161mph and no problems.

The calculating pinion angle thing still confuses me for some reason. Maybe someone can give a good explanation. Do you have a digital level or angle gauge?

craftsman angle gauge thing

mine was only spinning 6500 but it was a stock recut shaft...not sure what it even came from and it was only low speed balanced so it might have been mostly a driveshaft problem

yours is also a t56 not sure if its shorter or longer but my shaft is 56" long which puts the "critical speed" before driveshaft failure at around 5800 rpm

thanks for the reply!

I just looked up a critical speed calculator and I don't have enough information about my driveshaft in front of me to calculate it. I do have a 4" diameter aluminum shaft and I think it is under 50" long of the top of my head.

Thinking back I still had my old 3" steel shaft when I did the dyno, but it is an aftermarket driveshaft. When I went to disc brakes in the back I also wanted to go with a 1350 pinion and u-joints front and rear so I just had a new driveshaft built and the rear gone through.

my angles after shimming the tailhousing up as far as I can are:

trans -3 (down towards the ground) flat against tailhousing rear surface

rear pinion +1 (up towards the car) across u joint strap flat surfaces

I think this puts me in close to perfect, albeit not optimal because normally you would want negative pinion angle, but perfect in that under torque the pinion and tans should cancel each other...correct?

I am trying to decide if I am dyno safe now

trans -3 (down towards the ground) flat against tailhousing rear surface

rear pinion +1 (up towards the car) across u joint strap flat surfaces

youre still missing the critical piece of the puzzle; ds angle. you need that to figure the working angles at either side of the ds. remember that WA's need to be as close to 1* as possible without going under, and they arent supposed to be any more than .5* different.

also, remember that the angle of your trans has no correllation to ANYBODYS number that they post online. you dont know how level the ground was, how much of a rake their car has, was the front on stands, were both ends on stands.......

take the third measurement and report back with your findings. you can also point you pinion down if needed to get better numbers.

how do I measure that? just place the angle gauge on the bottom of the driveshaft at each end?

my numbers are as the car sits at ride height on the ground, I was able to crawl under barely to get these numbers

driveshaft angle is -1*

so if the information I have is correct I calculate a 2* working angle on both front and rear as the car sits

I do have slapper type bars adjusted so the rubber contacts the frame at rest...this should limit pinion rise drastically correct?

anything else before I hit the dyno?

if your numbers are all taken in the same direction (+/- oriented the same way), then you do have 2* working angles and you should be good to go.

got a dyno pull with no apparent damage...must be getting close haha