Mystery Transmission Leak - Modulator Valve?

[The_Handier_Man1]

From: LJ-TJ  (Original Message)
Sent: 10/10/2005 12:00 AM

Hey Guys, Just had the old Winni out and was going through tranny fluid like crazy.Dosen't look to be leaking from the pan.Somebody said if the modulator valve was bad it would blow out the exaust.Anyone ever herd of this and if so where is it and is it hard to replace.Thanks. T.J.



From: cooneytunes
Sent: 10/10/2005 2:08 AM

No, I've never heard that, I could be wrong but there's no way for tranny fluid to get into the exaust.....now I've seen it blow back out of the dipstick..but this would be caused by a pressure build up...it also will lose it out of the bellhousing....or the converter cover and maybe it's being flung on the exaust pipe and burning up, so if it's disappearing there has to be some kind of leak near your exaust pipe or manifold...not going through your exaust, but leaking onto your exaust.....so it would be hard to spot........but a bad moduator valve, I wouldn't think could cause a loss of fluid..it just wouldn't let the fluid flow to the right bands......and your shifting just wouldn't happen correctly.....Does your fluid look dark and / or smell burnt? Also could be leaking somewhere near your radiator or one of the lines that go to bottom of the radiator.  And if it was leaking there,,,,,there's a chance it could get on one of the exaust pipes...put a big piece of cardboard underneath, (like one from a kitchen appliance so it will go from under your radiator to where your driveshaft begins) get it up to temperature, shift through all your gears, put it in park and look for a leak with it running.....shut it down and let it sit, see if you can find a leak...there has to be one....

Timmy



From: Im-still-Lefty
Sent: 10/10/2005 2:54 AM

Hi, A bad diaphram in the modulator valve will cause transmission fluid to be sucked into the intake manifold,due to the vacuum line hooked to it, and burned in the combustion chamber. Causing a whole lotta white smoke. Lefty



From: denison
Sent: 10/10/2005 8:39 AM

I know that Chevy/GM transmissions used a vacuum based modulator valve for shift control, but I thought all 727s used the rod that connects to the throttle linkage for shift/kickdown control.
My tranny leaks mostly from the shifter shaft, and when sitting still drips onto the exhaust pipe. If I only park for a day or two I dont see any oil drips on the ground. And when I drive away, the oil burns off the exh. pipe and I dont notice it. Mine leaks about 3 pints in a month or two, then seems to stop leaking - as the oil level has dropped below the level where it oozes from that shifter shaft seal.
If your tranny fluid was leaking into the cooling system, you would see a scummy effect on the top of the coolant wherever you could look at it.... inside the cap, or an overflow recovery bottle. Those rubber hoses connecting the tranny fluid lines to the radiator are old enough to be leaking.



From: elandan2
Sent: 10/10/2005 11:57 AM

727's don't have a modulator valve



From: LJ-TJ
Sent: 10/11/2005 5:16 AM

Thanks fella's I got a cement floor to work on underneeth the rig today.I'll let you know what I find. T.J.



From: Slantsixness
Sent: 10/11/2005 7:14 AM

No, 727's DO have a "modulator valve", but it is NOT connected to the intake vacuum, it is connected to the throttle linkage, as Dave stated. Only the vacuum modulator valves have the tendency to dump trans fluid into the intake, and produce huge white smoke clouds out the tailpipe.

Leaks on 727's (and all othe RWD chrysler transmissions, by the way (except the Allison) are as follows:

The most common for small leaks:
Pan gasket improperly installed. Commonly people use silicone seal or "blue goo" on the pan gasket. This is DEAD wrong. Use NO sealer and try to use the all rubber, or the new neoprene gaskets, although the cork gaskets will work fine, they are susceptible to damage from overtorquing the pan bolts (and excessive over torquing will cause the case threads to strip too!)

Another small leak problem is the rubber O-ring or paper gasket at the speedometer gear housing.

Major leaks:

Not really the transmission, but:
The steel cooling lines can rust through. Replace them if they are corroded. If you grab one and bend it a little and it breaks in two, then you know for sure they are bad and need replacement.

When it's the transmission itself:
Front main converter to pump seal. This ones a pain in the butt to replace, but it's the most common seal to fall apart.

Rear tailshaft seal... easy to replace, but you'll lose some fluid changing it. The new seals DO NOT LOOK LIKE the "old" or "original" seals, especially if you do NOT have the trans mounted parking brake. If you have a trans mounted brake, you will have to remove the driveshaft and the brake before you'll even see the seal (TJ, in your case you will not have this brake, so don't worry)

I would recommend replacing all the seals, filter and gaskets, along with adjusting the bands.  However, only the front main pump-to-converter seal would require removing the transmission, and if it's still ok, I would leave for a warmer summertime project, rather than a cold winter thing!

Good luck!

Tom



From: denison
Sent: 10/11/2005 10:19 AM

Ha!! Tom (slantsixness) failed to mention the other (minor) leak possibilities; the dipstick tube has an "O" ring or grommet where it goes into the tranny case. That can die of old age, but can be replaced without too much trouble, i.e. the tranny in place. I have replaced mine. And like the dipstick tube grommet, the fluid level is also higher than the seal around the shifter shaft when the engine isnt running, and that can leak. Mine does. From the looks of it that can only be replaced when the valve body is out of the tranny. My shifter-shaft seal leak is small and will have to wait till I remove the tranny for rebuilding.



From: Slantsixness
Sent: 10/11/2005 12:41 PM

Damn!

I can't get 'em all!

The shifter seal can be replaced by removing the valve body. You can remove the Valve body with the trans still installed, but it's not a "simple" task, either way. It's imperative that you service the valve body before reassembly, too, or you could have all kinds of little problems (like the little ball bearing check valves, to be specific)!

The dipstick tube was a brain fart....I can't remember EVERYTHING! Simple though, remove the bellhousing bolt that holds the tube, twist and pull out, replace the little O-ring (smear a little trans fluid on it when you do, so it'll reassemble easily). Put it back in, trying NOT to twist the tube, as that can damage or unseat the new O-ring, and you're smiling again!

Tom



From: rshaw500
Sent: 10/11/2005 1:55 PM

If it were your modulator valve you would know it right away.   You would be going down the road and leaving a very big trail....(I mean a very big trail) of smoke.   It would be white smoke.   
Rick