View Full Version : 1973 continental c6 auto vaccum modulator

September 3rd, 2017, 05:45 PM
Hello guys.

Recently bought a 1973 Continental 'Town Car'' and am restoring it. The car drives very well and the 460 is very powerful. The autogear box works fine but seems to skip first gear on take off.
It goes there but doesn't stay long and skips to 2nd gear almost straight away. I looked at the modulator and it is a double diaphragm not adjustable.
The main line is on the vacuum port from modulator and the second line goes to the carby via the thermodynamic ?valve .
Do you think the set up is ok and that the auto behaves properly?

Thanks a lot
Regards larry

September 3rd, 2017, 06:39 PM
if it runs through a thermo valve, I'd probably find out if that valve is working correctly and not leaking before getting too far along. Vacuum leaks make all that stuff act stupid.

September 3rd, 2017, 07:19 PM
These are commonly faulty after so many years. Not rebuildable. Best to just replace it and then forget about it. They are available from the usual suspects.

September 3rd, 2017, 08:10 PM
thanks guys. i read the the double diaphragm modulator was later abandonned by ford. i will check the valve for efficiency. i will also try to join the 2 air lines together as it wld set the second diaphragm at the same value as the first one. matter of checks anyway

September 3rd, 2017, 08:13 PM
What I would like to know is how the gear box operates on normal set up. Like how long first gear on before switching? The car was obviously set up for street race with lower suspension, added stabilizer bar etc.

So I am guessing ''they'' did something to skip first gear in order to reach 2nd gear rapidly...

September 3rd, 2017, 08:19 PM
You wouldn't want to do that for any kind of performance application. It would just make it slower. It should wind first out a ways if you put the pedal down. It will upshift sooner with light throttle input. Thats actually most of what the modulator is for, it determines engine load based on vacuum. Less vacuum = higher load, so it holds the gears longer.

September 3rd, 2017, 09:34 PM
Hi gadget. Yes so it seems to make it simple that there are not enough vacuum to ''tell'' the modulator to hold gears.

When i unplugged the 2 lines, I felt the air rushing in. There was a vacuum but not enough on the second line maybe?

September 3rd, 2017, 11:50 PM
Lower vacuum would make it hold gears longer. Thats what happens if the line falls off anyway, it will wind out 1, shift to 2, and may not upshift to 3 or it will take a good long time to do it.

I don't know how that double line setup works though. It may just be bad.

September 4th, 2017, 11:47 AM
The whole dual diaphragm modulator is a new 1 on me, but I'd be interested in knowing what kind of vacuum the engine develops to begin with.

September 4th, 2017, 05:34 PM
Also, as an afterthought if the car was modified, does it have a kickdown lever? Probably a silly question, but....Here in the rust/snow belt I actually miss the FordOMatic ability to start from a stop in 2nd to cut torque in bad weather.

September 4th, 2017, 07:06 PM
thx for your input guys. The car has been totally lpg converted-no dual fuel-and otherwise is running fine but I found lot of dodgy stuff in it.
It seems then, contrary to what I was thinking, that I must have too much vacuum. The setting is simple: modulator to intake vacuum port and other line from modulator to the pvs valve on cooling system.
Maybe the valve is stuck open as I could feel vacuum when I unplugged the line at modulator.

September 4th, 2017, 07:08 PM
and yes i have the kickdown rod that i put back..and remove and it doesnt make any difference. i think all that is a matter of tune up really..but need to find the right settings...

September 4th, 2017, 09:21 PM
If you don't have a vacuum diagram, I'd certainly urge that you get 1. My '75 town coupe had hoses that made no sense, and it was a revision 22 emission control according to the sticker on the B pillar. That thermal vacuum valve in the stat neck should be available - even down under. If not, let me know and I'll find 1 here.
Sounds like progress tho. Good :)

September 4th, 2017, 09:34 PM
yes. found a mustang diagram on the net, for the 460 ci and comparing with my settings, it seems to be ok. checked the valve and it is closed like it supposed to be. otherwise all the hoses are there

September 4th, 2017, 09:42 PM
the car has been converted to full lpg system with special gas evaporator and carby. so all the egr valves and all that are gone. only the basic vacuum are in it lol

September 11th, 2017, 08:48 PM
hi guy. i come back on the vacuum actuator. actually i found a restriction on the main vacuum line that goes to the actuator, around the t section. basically, the inner diameter of the line was less than half of it original size.
what effect would that have on the shifting ?
thanks for your time. larry

September 11th, 2017, 09:08 PM
can't imagine it would help it any.

September 11th, 2017, 09:19 PM
Hi gadget. Yes it seems to keep on ''avoiding'' first gear. Mean also the engine is so powerful that U don't have to put the pedal down at all to keep the car going..maybe that's what the tranny skips the first gear.. ?

September 11th, 2017, 10:32 PM
What happens if you pull the lever to L at a stop, and then move it into drive at 20 or so? It should upshift to 2nd and then 3rd as your speed increases and torque load decreases. Cars of that vintage had many (and sometimes MANY) vacuum check valves. My MK III has a direct 3/16" (4.5mm) hose from the manifold to the modulator.
I can't help but wonder whether the LP conversion messes with the engines ability to produce enough vacuum.
I don't know anything about torque converters, but I'll look in my '70 manuals tomorrow sometime to see what the pump pressures should be.

September 12th, 2017, 07:43 PM
hi markedman. to be honest i havent tried all the ''manual'' shift with the lever. 2nd and 3 rd are going ok and the gearbox is reacting correctly and smoothly.i havent take it on the road since finding that little reduction on the pipe. but may be you are right. it may need a manual shifting to let the valves operating correctly.? and as far as the check valves goes, i didnt find any at all in the engine bay.
otherwise the car is driving verywell. i wld just get a bit more grunt on take off..

September 12th, 2017, 09:44 PM
If you pull the lever all the way down, it'll stay in 1st until you move the lever up a notch.
There's a member here "silver fox" if memory serves, that builds transmissions. He may have seen this situation before. I took pictures of the manual pages covering the pressure specs, but they're pretty blurry.
Something else just occurred to me - is the car right hand drive? Just curious, because if it was built for export, it might not have the same emissions equipment that it would have had for the domestic market. Here, it would have had lots of little plastic check valves in the vacuum system.

September 13th, 2017, 08:31 AM
yes the car is right hand drive. it was actually converted in australia in 1987. the job done is amazing as everything was moved from left to right, even extending vacuum lines etc...and no, i cant see any of the one way valves or non return valve etc on the vacuum lines. but like i said i found a bit of reduction pipe inside the main pipe to the modulator, making the overall diameter of the line 1/2 of it size at some point....i think this can reduce or hold vacuum at some stage. i will drive the car and see if i can feel any difference..

September 13th, 2017, 04:25 PM
Okay, if the car was built for the U.S. market, there would be 2 levels of emission controls: 1 for 49 states, and another more stringent level for California. In either case vacuum check valves would have been installed originally, similar to the attached pic. the 1 shown only allows flow from the green side to the white. It's also the only 1 I have left from my '75 (24 yrs. ago).
WWW:Lincolnlandinc.com has a blog called "Bills Corner" where people from all over write in with ??s. They have diagrams too. Pricey parts, so I don't know what the diagrams might cost, but it might be worth your while to write them and find out.
I'm sorry I can't be more help on this, but with all the mods the car has been thru, I'm out of ideas at this point. If I was there or the car was here....

September 14th, 2017, 07:27 AM
thx very much for your help anyway. when i got that car, it was a real mess. looked good but previous owner didnt give much attention to detail and she could have caught on fire many times after i found electrical wise.wires cut off non protected, wires puled, dodgy connections etc. basically, everytime i look at something, it has to be repaired or put back to original condition.but i am learning about the car at the same time. the check valves are missing because my headlight doors dont stay down for too long for eg.
i think it is a matter of researching and testing so that i get back to what''she'' was before..my aim.

September 14th, 2017, 08:18 PM
by the way, do yu know how to post an album on here ? i cant find the albums link ? i have few photos of the car that i wld love to put on here

September 15th, 2017, 11:30 AM
I just put up 5 @ a time when I have more than that. Use the "manage attachments" button below the submit line. I'd like to see the conversion to rhd.