Cruise control is dead!

[ridindirrty]

Whatup LVC crew! Recently did some brake work where I had to re & re the master:wrench . I no longer have cruise control since the job was done. The only thought I have on this thus far is as follows; At one point in the job I yanked back pretty hard:bash: on the pedal to access one of the master cyl. studs and I heard a cracking sound. I think this may have been something being damaged in the brake light switch, which i believe also disables the cruise control when the brakes are depressed. Only thing is, my brake lights still work as they should . Any thoughts on what might be going on here? Cruise worked flawlessly up to this point. Am I way off track here? Any suggestions? I miss my c.c...help:L !

 

[Elessee]

I don't think the brake lights have anything to do with it..
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I'm reading the shop manual.
Volume B Chassis Electrical.. section / page 37-05-8

Speed Control System with Resume:
Adjusments:
Vacuum Dump Valve:

It shows a picture of a "vacuum dump valve" touching the "pad on brake pedal". It must be somewhere up there under the dash.

That valve is attached to the end of a vacuum tube/line..

So, i guess that when you step on the brake the valve opens (closes?) and that the loss (or gain) of vacuum sends a signal that deactivates "speed control".
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Reading .. "The vacuum dump valve is adjustable" .. it should be adjusted so it is closed (no vacuum leak) when pedal is in normal position... suggests 0.050 inch clearance.

"Dump Valve Black Housing Must Clear White Plastic Pad On Brake Pedal With Brake Pedal Pulled To Rear Most Position."

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The pic shows that the vacuum valve is attached by way of a little spring clip.
It looks like if you pull the pedal up too hard the brake-pad will force the switch to be pushed upwards and out of it's spring clip-holder.

So, if you're lucky, maybe the spring-clip detached and you heard the click.. If not lucky something got broken..

good luck with it.. i see 54 pages of information and diagnoses on this speed control.. if you got a question, ask and i'll search.

 

[jeffmo]

While not on a Lincoln, I had the experience on another car with the cruise being dead. The culprit was the switch that "kills" the cruise when the brake is depressed. It was a little switch that went bad. On this particular vehicle it was the same switch that turns on the brake light as well. See if the brake lights go on when you apply the brake. So, you might see if you can find that switch (if the Lincoln has one - something "kills" the cruise with brake application) and see if it is out of adjustment, or broken. Just a thought. The previous post might be correct, but I would pursue whatever "kills" the cruise when the brake is applied since you were working in the area of the brake pedal.

 

[Magic Al]

The post above sounds correct, it's probably the vacuum switch. Cruise is disengaged either electronically by application of the brakes (your brake lights work so that's OK), or mechanically by opening the vacuum dump valve. Since cruise worked prior to the brake job, it's in that vacuum circuit.

 

[Elessee]

ok.. i really didnt wanna do it but since there was some question about it, i climbed under there and looked.

There's a thick (1/2") rubber vacuum hose (Black/W) attached to a black plastic threaded valve/valve housing. This valve touches the upper portion of the brake pedal lever.

This valve mount and assembly is located immediately above the brake light switch and is not a part of it and not connected to it.

Since the throttle speed-control is primarily a cable attached to a vacuum motor, it seems reasonable that releasing the vacuum would release the throttle speed control / accelerator pedal.
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Upon inspection of the real thing, i now have serious doubts that the vacuum dump valve could be pushed out of it's mounting bracket without damaging something.. but who knows.. there's always hope.

 

[Elessee]

While i'm logged in, i have a couple more thoughts..

you could bypass a broken dump-valve by plugging that vacuum hose, sealing the vacuum leak, and thus regain speed/cruise control.

But, the consequence is that when you hit the brakes, speed control is still active. So, you got one foot on the brake and "one on the accelerator". This doesn't sound safe to me

 

[Magic Al]

Yes, you could plug that line. The vacuum dump valve is a secondary, or backup safety device in that the electrical brake light circuit should disengage the cruise also. Yes, it would be an unsafe solution to drive w/ the line plugged.

 

[Elessee]

Yes, you could plug that line. The vacuum dump valve is a secondary, or backup safety device in that the electrical brake light circuit should disengage the cruise also. Yes, it would be an unsafe solution to drive w/ the line plugged.

Being the curious sort, i took another look at the manual. It first lists components of the IVSC (integrated vehicle speed control) system.

They include the following:

A servo (vacuum servo-motor) assembly.
A speed sensor (on the tranny.. but not needed for vehicles with electronic cluster).
A stoplamp switch.
A vacuum dump valve.
An aspirator (?).
A horn relay.
along with a couple of check valves, some wires and hoses..

So, I have to wonder if hitting the horn is a third way to disengage the system.. After all, in a panic / warning situation, a common reflex is to honk the horn.
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The vacuum dump valve is up there under the dash but is well exposed. R 'n R seems easy enough: Pull the vacuum hose off and unscrew the threaded housing.. simple. Reinstallation requires setting the correct clearance but that's about it..
And it seems like the sort of part that is only rarely scavanged from boneyard vehicles... I've noticed that MK7 brake switches are often missing but I never looked for the dump valves. Chances are the yard would sell the little plastic things for a dollar or so categorized as a miscellaneous switch..

 

[ridindirrty]

Great leads

Sorry I haven't checked back in on this one in awhile, when i first posted i heard nothing for quite some time so i kind of gave up on it:sleep: . Been screwing around with door lock nonsense in the meantime. These are some excellent leads and i intend to chase them down ASAP. My cruise worked perfectly up until i did that brake work and i want it back:runaway: ! I've been doing some extended interprovincial driving:steering and not having this feature is just wrong. I'll follow up with my findings. Thank you as always for the in-depth info. Nice to know that someone figured out where I was coming from on this:yourock: .

 

[OldSchool1]

Yes, you could plug that line. The vacuum dump valve is a secondary, or backup safety device in that the electrical brake light circuit should disengage the cruise also. Yes, it would be an unsafe solution to drive w/ the line plugged.

You read my mind almost verbatim.