Turbo400 modulator

[Dvldog8793]

Howdy
Any opinion on a type/brand or source for the vacuum modulator on the turbo 400? This trans is on my m1009 cucv.
Thanks!

[Robyn]

Pretty basic stuff here.

Remove the old one and take it to your favorite parts store (NAPA, AUTOZONE) and get one for the civvy version of the truck.

If there are choices, just match the new one to the original.

If you are having modulator troubles, be sure that the vacuum control switch on the IP is functioning properly.

Also be sure that your vacuum pump is producing a nice steady 25 inches or better on a vacuum gauge.

If the vacuum pump shows a low or wobbly gauge reading the tranny will shift poorly.

Good luck

Missy

[Dvldog8793]

Howdy
Thanks...I've already checked the lines and different vac conections. I plan on checking the modulator using the float method. Toss it in the pond and if it floats it's good, sinks it's bad. If that doesn't improve things then the control valve will probably be next. The vac pump tests good.
Thanks Robyn!

[Robyn]

Keep us posted

[Dvldog8793]

Howdy
Replaced Vac Mod. Vac at the input line to the control valve/switch/whatever was a steady 21. Also adjusted this switch. Cleaned and replaced all vac lines. Also fflip floped the lines to determine the right order.
Still has intermittent mushy late shifts. MOST of the time it shifts great when cool or after driving on highway. MOST of the time it has mush shifts when it has been idling or town driving. BUT neither all the time. Fluid/filter has been changed and had NO nasties in the pan, just normal grey matter.
I have a new switch that will be going in today.
Does anyone know if the small rubber vac line "adapter" that is on my original switch is needed? I looked at it and it appears to just be a rubber splitter to no where....? It mounts direct to the vac in connectors on the switch with a small rubber dead hole and vac in/out. This is a military rig with only 60k miles.
Thanks

[Robyn]

The little adapter is likely not needed, especially if its a dead end and goes nowhere.

Be sure your vacuum at the pump is good even at speed.

Connect a gauge with a T fitting and put the gauge under the wiper and watch it under real time running.

It needs to stay steady at all times.

Late shifts are usually harsh and not mushy.

Early soft shifts are associated with too much vacuum to the mod for the given throttle angle.

Late harsh shifts are normally seen with too little vacuum for the given throttle angle.

Check the vacuum at the mod during driving and see what it reads.

Light throttle should show high vacuum and heavy throttle should show low/er vacuum.

This sounds like the vacuum switch is bad

Missy