1976Oldswagon

this, and I have a vacuum leak.

my friend in school who's family does transmissions told me there is a vacuum line running to the transmission, this would explain both problems...one problem though-I can't find it to save my life.

car is a '76 cutlass cruiser (455) and TH400.

where is this vacuum line?

Qwik71442

modulator connects on the passenger side above pan rail by dipstick tube and goes to intake vacuum

1976Oldswagon

thanks man

oldcutlass

It needs to have manifold vacuum on it.

MDchanic

If you can't find the line to the vacuum modulator, then perhaps it's not there...

- Eric

Rickman48

If that's not it, could be a broken spring or stuck weight in the governor!

67442HT

Check all basics first, and that is a vacuum line connected from manifold vacuum to the vacuum modulator on the right side of trans and it is getting vacuum from the engine.

1976Oldswagon

I found a severe vacuum leak, but the symptoms are still there...the hose between the trans and the manifold is metal, and as far as I can tell intact.

I bottomed out REAL bad the other day, and there are fresh scratches on the trans where the vacuum line goes in.

how does it work, and how hard is it to replace/repair?

MDchanic

Are there signs of ATF in the vacuum line / hose?

If so, replace the modulator.

If not, pull the line off the manifold and give a good suck on it (or get fancy and use one of those hand pumps with a gauge).

If the vacuum leaks down, and the lines are all good, replace the modulator.

- Eric

1976Oldswagon

I won't be able to get it on a lift until tuesday, I will report back then, thanks for your help.

MDchanic

No need for a lift - just pull the vacuum line and look and feel for ATF.
Similarly, no need for a lift to suck on the end of the line.

- Eric

Rickman48

What's a lift??
In my 60's, and still doing transmissions on the ground!!
Spoiled kids?!?!

oldcutlass

Some modulators are adjustable, so if everything checks good and it still does it, stick a small flat head screw drive into the inlet on the modulator and back off 1-2 turns.

TripDeuces

Check the plastic connectors at all the junctions where vacuum lines are tied together. If there's a crack in one you can miss it easily. Ask me how I know

1976Oldswagon

the steel line runs all the way to the transmission, I can't easily check it. from under the hood there is no residue of ATF, and the transmission and line holds its vacuum. to double check it, I disconnected the line from the steel one, plugged it with a pencil, and started the engine. still a severe vacuum leak. so I replaced a mile and a half of vacuum line, and checked all the connectors I could, not including the ones under the carb. tomorrow I can get a blowtorch and use the blowtorch method to find the leak.

could a vacuum leak somewhere else in the system cause the trans to shift late? all lines directly related to the trans are connected.

Rickman48

The modulator has rubber connections at both ends of the steel line!
Check under the car, too!

Curious - how does this 'blowtorch' method work??

oldcutlass

Blowtorch???

1976Oldswagon

my line is metal till it enters the trans, and holds vacuum from under the hood.

the blowtorch method for diagnosing vacuum leaks-
get a blowtorch, propane works best. start the engine. turn the blowtorch on DO NOT LIGHT. run the gas over the vacuum system untill the engine races, when it does, the propane is entering the manifold and burning-thus telling you where the vacuum leak is.

courtesy of my auto shop instructor.

1976Oldswagon

FOUND IT!!! damn vacuum advance distributors...what is this modern sorcery?

the hose goes straight into the same set of vacuum lines as the one that goes to the transmission, explaining the shifting issue...the distributor had gotten so loose that I could turn it by hand, I don't even think there is a bolt on it anymore...thanks for the help fellas, I got it from here.

Rickman48

Never heard of that method - and if you've got a bad wire, bet it scares the hell outa ya!

oldcutlass

Same theory as starting fluid!