gingerbreadman1977

i only have 11 vacum at idle meaning sometimes my kickdown works and sometimes it doesnt when i floor it....more often than not it doesnt. cable is adjusted properly so it must be vacum modulator.

who is running one of the more sensitive vacum modulators that should improve my kickdown strike ratio . is it a B&M part?

TimAT

Most of the auto parts store here carry replacement modulators- and a good many of them are adjustable. In the nipple for the vacuum hose there's a screw- 3 turns either way from where it came out of the box. Don't recall which manufacturer it was, but they said any more and you risk popping the diaphragm.

Try disconnecting your cable completely- assuming it's a TH 350 or 350C. See what happens then. Vacuum usually has more effect on the "feel" of the upshift and it's timing than detent downshift.

ssenay72

advanced autoparts sells a b&m one.

larrywalk

The vacuum modulator generally affects the part throttle downshift (and up shift) point(s). This can be adjusted by turning the internal screw as noted above.

Full throttle up and down shifts are affected by detent regulator pressure (throttle cable shifts the detent regulator), and by the governor. One can shim the detent regulator spring to raise WOT shift points a bit, and also modify the governor flyweights to raise the shift rpm. The governor springs affect the 1-2 shift more than the 2-3 shift; for the latter, cutting down the weights helps most.

Have fun with this one!

jordan89

I have the B&M Vac. mod. and it works great.

gingerbreadman1977

everyone we have to rewind a bit because my gears change fine. up and down no problem. its just the kickdown that im not happy with . when im in 3rd and babying it if i floor it then it doesnt go to 2nd as it should. my kickdown cable is adjusted properly so it beats me.

TimAT

OK- You adjusted your kickdown cable per the manual? Remember- ALL cables stretch a little over time. There's a lot of adjustment available- nearly 3/4 of an inch IIRC. Nothing says you can't adjust it so it comes on a little sooner- or later- as needed. Back it up a few clicks and try it.

gingerbreadman1977

i dont have the stock style kickdown bracket any more Timat. it is adjusted so that when i pull the the kickdown out fully and i mean yanking on it fully thats where my full throttle is also. i guess i could adjust the kickdown some more for testing but then i wont be getting full throttle.

7T1vette

The vacuum modulator isn't involved in the WOT downshift process at all. At WOT, there is no vacuum generated until higher RPM levels. Downshifting is executed with an electrical 'kickdown' switch and a solenoid-valve inside the tranny (on some units) or the TV cable which signals the tranny of a WOT condition on other units. Low vacuum at idle is an entirely different issue and doesn't affect downshifting, unless it is a closed-throttle, manual downshift.

TimAT

Setup your throttle so it gets WOT without the kickdown cable connected. Then go back and set the kickdown so it gets pulled fully about 3/4 throttle, it should not stop the carb from getting to WOT. If it does, move the cable housing a little closer to the lever on the carb. It'll be a trial and error thing.

corvettedave383

my vette runs around 7 hg vac at idle, ive got a standard vac modulator, and it kicks down fine, everytime