How the !@#$ do I remove the tranny modulator?

[EvilManor]

Anybody know how to remove/replace the trans. modulator on my '69 caddy? I've pretty much degreased/cleaned the exterior of it but still can't see what's holding it in place. It will turn indefinitely clock or counter clockwise. I've even tried pulling straight out and it doesn't even budge.

I went to the parts house and the somewhat smaller version appears to have a lip for some sort of keeper ring, c-ring, or whatever it's called, but can't seem to see one on mine.

Any ideas? If I can get my shifting issues fixed I'll be driving it to the Casket Races!!

[hotroddwayne]

Should be a "C" shaped tab that straddles the modulator valve, held tight with 1 bolt. Remove the tab & the modulator slides out. Use a mirror & flashlight to find it. KEEP IN MIND that the GM modulators are adjustable... remove the vacuum line & there's a spring loaded screw down in that vacuum hole. Make sure you have GOOD vacuum first, then if you do... turn the screw to adjust the shifting. Is it shifting too late or too soon? If memory is working you turn the screw clockwise for later shifts, but don't hold me to that. Try both ways, hopefully you'll get it the first try. Don't get real agressive with your first adjustment, just a couple turns @ a time. Hook up the vacuum line & take it for a spin. You may get lucky & only have to adjust the one you have! Good luck, keep us posted...

[EvilManor]

Should be a "C" shaped tab that straddles the modulator valve, held tight with 1 bolt. Remove the tab & the modulator slides out. Use a mirror & flashlight to find it. KEEP IN MIND that the GM modulators are adjustable... remove the vacuum line & there's a spring loaded screw down in that vacuum hole. Make sure you have GOOD vacuum first, then if you do... turn the screw to adjust the shifting. Is it shifting too late or too soon? If memory is working you turn the screw clockwise for later shifts, but don't hold me to that. Try both ways, hopefully you'll get it the first try. Don't get real agressive with your first adjustment, just a couple turns @ a time. Hook up the vacuum line & take it for a spin. You may get lucky & only have to adjust the one you have! Good luck, keep us posted...

There's a bolt holding a "C" shaped tab?

It's shifting late. Shift to 2nd is about 35-40 and shift to 3rd is 55-60.

[Custom Coffin Works]

There's a bolt holding a "C" shaped tab?

It's shifting late. Shift to 2nd is about 35-40 and shift to 3rd is 55-60.

Assuming you check the tranny fluid level first, it sounds like a slight vacuum leak for it to be doing that. Replace both hoses (one at the mod and the other on the manifold) first. If you go to turn that screw, do it in VERY small amounts. It doesn't take much to make a difference. If you do have to replace it, there is a small rubber O-ring that is on the shaft that goes into the tranny. Once you remove the clamp give it a firm pull straight out. Sometimes that o-ring hardens and makes it a pain in the ass to remove. To reinstall the new one, put some tranny oil on the O-ring of the new Mod and push in slowly. If you break that ring you have to but a whole new mod. Hope that helps.

Eric Unser
Custom Coffin Works.com

[EvilManor]

Tranny fluid should be fine, but I'll double check it.

Vacuum lines have been replaced at both ends.

Something else I failed to mention is after replacing the lines and trying to remove the mod, (not sure if that's relevant) when the car has set for a while (next day). It takes a while for what seems to be air pressure building up before it will move forward. After driving it other than previously mentioned shift problems it's fine.

I really appreciate all your help!!

[hotroddwayne]

Since there's a pause before the car will move, definitely check the fluid level. Transmision fluid has to be checked HOT, so start the car & let it run for several minutes, pull out the dipstick, wipe it off, put it back in all the way again & pull it back out immediately... and look at your fluid level. If it still hesitates you might want to change the tranny filter. It's a horribly messy job since most pans don't have a drain plug. If you decide to change the tranny filter i'll explain it to you later.
Anyway, here's "the gospel" from TCI transmissions:

Is there a right way or a wrong way to hook up my vacuum modulator?

Answer: Since the transmission is so dependent upon the modulator to function properly, a good vacuum signal must be transferred from the intake manifold down to the modulator. The best way to insure this is to utilize hard steel line to carry the vacuum signal with approximately three inches (maximum) of rubber hose on each end for the connections. This setup will prevent the hose from cracking or burning in areas that are close to the exhaust system and will also reduce the chances of the hose collapsing onto itself. Most modulators require a minimum of 15 inches of Hg (Mercury) at idle to function properly.

What does the vacuum modulator do?

Answer: The vacuum modulator is a canister that contains a diaphragm and a calibrated spring. The diaphragm senses changes in engine vacuum due to throttle position/load changes and transfers the diaphragm motion to the modulator valve in the transmission. The calibrated spring opposes the diaphragm movement. This provides the means for the transmission to adjust internal pressures based upon torque demand by the engine.

Are there any adjustments that can be made to the modulator?

Answer: Stock factory modulators are pre-set and most are sealed. TCIŽ StreetFighterŽ modulator-type transmissions are all equipped with adjustable modulators. By turning the adjusting screw (found in the vacuum nipple) counterclockwise, you will lower the spring pre-load. This will cause earlier shifts. By turning the adjusting screw clockwise and raising the spring pre-load, the shift points will go up. The range of adjustability is only a few mph either way.

There you go bud, counterclockwise will make it shift earlier!

[EvilManor]

OK (thanks for the help everyone) finally found the tab holding the modulator in. There's a set screw in the end of the mod. but adjusting it either way doesn't seem to change anything.

I went to get a new one and all the one's found at parts stores were small in comparison. I realize that sometimes parts are different, but didn't think they would be that much smaller. The part that inserts into the transmission seem to be the same, but the body of the mod was quite a bit smaller.

After cross referencing the part# of the mod no one seems to have it in stock. Should I keep searching or try one of the smaller ones?

[Morella]

The part that inserts into the transmission seem to be the same, but the body of the mod was quite a bit smaller.

Ask Mr. Goodwrench, or the CLC board. Those guys know everything.