checking vacuum diaphragm / modulator

[yob_yeknom]

Not my Explorer.

A guy with a '91 model is having problem getting his tranny to shift from second to third. It'll only shift if he lets off the gas and then back on it.

Did some searching and found that a bad vacuum diaphragm or vaccuum modulator can cause this problem. Supposed to be easy to check by finding fluid in a line or something.

Are these the same part, just calling them different names?

How exactly do you check them?

Thanks.

 

[Opera House]

Thats about it

Presence of fluid most common problem. Sometimes hoses have split that connect the modulator. You can put a mity-vac on to see if it holds a vacuum. This is a $12 part and at this age I would just replace it. It is a pain to get at.

 

[FIRE and ICE]

the usual way to determine if the vac mod is leaking is to check (remove one by one ) a vac line connected to the vacuum octupus AKA tee located under the hood at the top rear of the engine.
If you have power brakes just follow the hose from the brake booster to the octopus.
If the vac mod is bad you will usually find trany fluid in one or more of the lines
It is a pain to replace but not impossible with ordinary hand tools.
i attacked it from the top -- took out both frnt seats,console and peeled back the carpet.(remove the plastic moulding where carpet meets the door trim)
next remove the manual shift access plate on the floor (hunp) you should be able to see the vac mod on the side of the tranny.
Unbolt it after removing the attached hose

PUT A PAN UNDER THE TRANNY TO CATCH THE FLUID WHEN YOU PULL OUT THE VAC MOD !!!!!!!!!!!!!!!!!

 

[hillrad]

My 94 was burning about a quart/1000 miles.

Suspected the vacuum modulator as the transmission had no visible leak. I checked the intake line several times but never found fluid.

I went the double jointed left handed (which I am NOT) finger and wrist scraping on my back rust in the eyes without removing the exhaust from under method.

 

[yob_yeknom]

What does the vaccuum modulator look like and where is it located?

Thanks.

 

[hillrad]

If you continue your search...someone has posted the diagram from a repair manual.

 

[slim]

I just changed mine last week. I was burning 4 quarts of tranny fluid a week, and it ran like crap. I had no trouble because I have a body lift. If you have any thoughts of a body lift I would do the lift first.