So ran my trans for two seasons in Top Dragster but had to tear it down and send it off for recertification. Freshened it and back together with a larger blower. Took it out first time and destroyed the band so bad it ate the drum and smoked the clutches. Pulled apart, new drum, clutches, and band. Cleaned everything out, flushed the cooler, had come mverter flushed by reputable trans company. Back together and first pass did the same thing. Had 225 lbs of PSI, only got to 180 degrees. Not sure what the problem is, converter is spragless so don’t think it can be in there. Both times brake set, as soon as it released felt like it blew the tires off but no tire spin...just band eating slip.

Have the Sonnax servo on that. Corrects Pin Bias as you know.

the band wont hold the drum if it is trying to turn,could be valve body related or shifter alignment.

Nemo,
With the power level you are making now,you need to raise the line pressure in the trans to 275 psi and Do Not use a wide band.But use a good used band from a OEM GM core,and 72 in pounds and back off 3.5 turns. It would not hurt while the trans is out to up grade to the Sonnax servo kit.

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Who made the band you used?

Have the sonnax servo kit, it was set 72 inch pounds and 3.5 turns. FTI standard width band, fti valve body, shifter is aligned in 1st and 2nd.

Give Greg a call or email, he knows what to do to fix it. I've got plenty of 3.80-3.70 passes on mine with no issues.

Why not the wide band? I stepped up to the Sonnax wide Kevlar band when I put the blower motor in. Also have the Sonnex bias servo

I had used the wide band before with no problems (although that was 17 lbs of Boost instead of the 24+ now), last time I ordered parts FTI said they had no wide bands available due to some material problems but they had a standard width pro-mod band they recommended. Don’t think it’s a band problem, servo is good, has to be a pressure problem just can’t figure out why. Only change I made was a different converter but it’s spragless so cant think of anything in there that would do this. Checked all passages after last one so don’t think I have a obstruction...once I can see a material problem but twice back to back I have something happening I’m missing.

Ive seen an issue where a servo was hanging up and not releasing properly. Same symptons was burning bands and clutches up in 1 or 2 runs. We went back to just a standard dual ring servo and never had the issue again.

keith do you air check the high and servo systems when apart

I was having similar issue, finally took apart the sonnax servo deal, and it was full of tranny much that was causing the piston to stick in the servo housing. cleaned it out, and re lubed everything and been good since. I have the older Red version of the sonnax servo.

It may be a gasket on the valve body issue, even if it only has one now,use a gasket on each side of the plate.it must be sending some amount of pressure to high while in first

Not an expert but: possibly a timing problem? Spring pressure in clutch packs not synchronizing properly with band apply/release?

I do air check, apply and release was good. I will have the VB apart so I will donthe gasket thing.

i also think you need more pressure,i dont think main line pressure is causing your problem.if you do go up on pressure and go to 275 i recommend the sonnax green spring and or the 28821-10K servo kit.

I dropped it off at a local trans guy that builds powerglides for tons of fast cars to give it a look over and see what, if anything I’m Missing. He talked like he may throw another valve body and pump on it just to make sure it’s fixed. Going to send the converter back to get looked at, bad thing is topeka is two weeks so hoping I can get it back in time...otherwise may need a rental converter for the National

i here you on the time thing i waited untill today to find a servo issue in mine.good luck
i dont think the convertor could have anything to do with it

Nemo, Give me a call tomorrow and lets go over a few things for your builder to look for. 13867365816

Greg