hi guys, currently just finishing up my build on my vl, has a built jatco 4spd, was thinking the other day is there a point where boost going to the trans via the vacuum line becomes to much and does damage ??? surely 20ish psi is not doing any good going to the diaphram in the trans ? any one put a one way valve in line or something ? is it something that gives trouble at all ? i could be overthinking it and itll be fine but just wondered if anyone else has thought of this before. cheers sean

yeah you probably are. The modulator uses vacuum to operate not pressure! It can handle vacuum of 25Hg+ when shutting throttle from WOT, so I'd expect it won't mind going the other way. I think a one way valve may cause it stay in gear though and not allow an upshift on light throttle. maybe best ask a tranny guy to be sure to be sure.

yeah i know it works on vacuum just wondered if boost would affect it at all. good idea ill maybe speak to a trans guy. was just curious

They should be able to handle a backfire so I wouldn't think 30-40psi would hurt them.

Surely it has a one way valve so it only gets vacuum.

well the factory line just joins up to the back of the manifold, no one way valve visable from manifold to trans.

my vl is being tuned at the moment and the trans is having a few issues my tuner seemed tot think he had another vl awhile ago and there was something done with the line to the modulator, im gonna give MV automatics a call tomorrow, thats where the box was built, and see what they have to say. so no one else has any input ?? ---------- Post added 21-09-12 at 12:54 ---------- Spoke to MV's today and the modulator does need to see boost. So that sorts that out. Doesnt fix my issues im having though.