Is my transmission slipping?
 

ALDA removed, full boost @ 1500~1700rpm; theoretically giving me full torque way earlier than the initial design.

Starting from a stop, if I give more than 25% pedal I stop accelerating and get a THUMP-THUMP-THUMP-THUMP that shakes the car and is OBVIOUSLY coming from the transmission. It stops when I let off, and it shifts faster up into 3rd than I would prefer.

Only does it on the 1-2 shift.
In any other gear, it lugs down the way every other 617 does when started in too high of a gear.

Vaccum to the transmission changes nothing, Bowen cable adjustment only changes how soon it attempts to go from 1-2; the thumping still occurs.


Any suggestions?

How solid were the shifts before the ALDA adjustment?

Sounds like a band slipping, increase the modulator pressure and see if it solves the problem before you destroy the band. Or if you can do the operating pressure test, that would be a better start.

Adjusting the vaccuum to the transmission doesn't change how it shifts.

Is there another modulator I should be playing with?

Yes, the hydraulic pressure modulator on the side of the transmission. If you don't have a manual, do a search on modulator and transmission here and in the tech forum (not sure where they are).

The 1-2 shift is a brake band, and without enough hydraulic pressure to engage it completely it will slip as you describe. Could also be worn-out, but if so the transmission has to come apart anyway, might as well try the modulator adjustment (operating pressure increase) first.

Found the DIY:
http://www.peachparts.com/Wikka/Trans722VacMod
I'll give it a go tonight!