Cruise control vacuum dump switch help, PLEASE
Thread Starter
Drifting
Joined: Dec 2012
Posts: 1,504
Likes: 73
From: Georgetown TX
Cruise control vacuum dump switch help, PLEASE
89 auto stock
I don't understand this. I have three new brake pedal vacuum dump switches, all different makes, all from different suppliers. None of them hold vacuum. Two will pump up, but loose vacuum very fast. The third pumps up, looses vacuum slower then the other two but holds at about 5 inches.
How can a dump switch work if if can't hold vacuum? I have to be missing something. I only want to crawl under the dash one more time😂
Hope someone can explain this to me so I can get car back together again
I don't understand this. I have three new brake pedal vacuum dump switches, all different makes, all from different suppliers. None of them hold vacuum. Two will pump up, but loose vacuum very fast. The third pumps up, looses vacuum slower then the other two but holds at about 5 inches.
How can a dump switch work if if can't hold vacuum? I have to be missing something. I only want to crawl under the dash one more time😂
Hope someone can explain this to me so I can get car back together again
Instructor
Joined: Jun 2015
Posts: 128
Likes: 13
so, are you saying the 3 switches have all been tried, and none of them have solved the problem?
The minor leak with the vacuum switch is totally ok, your manifold vacuum can easily overcome that leak. You can verify my last statement by checking the vacuum in the line going to the vacuum dump switch. You might have a leak in your lines if your lines are old. Mine are pretty weather checked in the engine bay, but perfect inside the car
Sounds like the dump switch isn't the issue with your system...
Put up a picture of your servo, so I can see if its the same as mine on my '84...
Do you have 12 volts to the cruise brake switch? that 12 volts comes thru the stalk switch , and is ON when the switch is ON.
that switch should be CLOSED when the brake pedal is not pressed. I jumped that switch to rule it out as a problem on mine. It's the main safety shutoff, so if you do that be ready to shut off the cruise via the stalk, your vacuum dump is the second backup.
Be careful, as always.
The minor leak with the vacuum switch is totally ok, your manifold vacuum can easily overcome that leak. You can verify my last statement by checking the vacuum in the line going to the vacuum dump switch. You might have a leak in your lines if your lines are old. Mine are pretty weather checked in the engine bay, but perfect inside the car
Sounds like the dump switch isn't the issue with your system...
Put up a picture of your servo, so I can see if its the same as mine on my '84...
Do you have 12 volts to the cruise brake switch? that 12 volts comes thru the stalk switch , and is ON when the switch is ON.
that switch should be CLOSED when the brake pedal is not pressed. I jumped that switch to rule it out as a problem on mine. It's the main safety shutoff, so if you do that be ready to shut off the cruise via the stalk, your vacuum dump is the second backup.
Be careful, as always.
Thread Starter
Drifting
Joined: Dec 2012
Posts: 1,504
Likes: 73
From: Georgetown TX
i think i have have been going about this the wrong way
First, the hose going down to the switch has no leak as verified with vacuum test. No leak
because it's such a pain to get under dash, I have been checking dump switches out of car at my bench with a vacuum pump. Not one of them hold vacuum, and I'm beginning to believe that's not a problem. I can't believe three switches would all be bad. Today I replaced the switch and I am in the process of putting everything back together. If my back and neck heel by tomorrow, I will try it out.
The problem is is that the cruise control will activate and you can set it to stay at speed selected. Once speed starts to decrease the control will activate again to bring it back to set speed. The problem is that when it activates to increase speed, it does it very hard. Meaning it speeds up to quickly. I think the original switch was bad, and not allowing system to hold vacuum so that each time it needed to gain speed to get back to original set speed, it was acting as thought you were setting the control for the first time
hope this makes sense, cause I'm just quessing. If this doesn't fix problem, then I think it has to be servo. Everything use to work just fine
Mike
Last edited by mlm0; Jun 22, 2017 at 02:48 PM.
Instructor
Joined: Jun 2015
Posts: 128
Likes: 13
there is a 5 wire connector on my 1984 servo, pins labeled A to E
the servo position inductive sensor is located on pins B and D.
the resistance between pins B and D should be 42 ohms , if memory serves.
if that resistance is out of spec, it could cause the surge you're seeing.
the servo position inductive sensor is located on pins B and D.
the resistance between pins B and D should be 42 ohms , if memory serves.
if that resistance is out of spec, it could cause the surge you're seeing.
Thread Starter
Drifting
Joined: Dec 2012
Posts: 1,504
Likes: 73
From: Georgetown TX
Thread Starter
Drifting
Joined: Dec 2012
Posts: 1,504
Likes: 73
From: Georgetown TX
there is a 5 wire connector on my 1984 servo, pins labeled A to E
the servo position inductive sensor is located on pins B and D.
the resistance between pins B and D should be 42 ohms , if memory serves.
if that resistance is out of spec, it could cause the surge you're seeing.
the servo position inductive sensor is located on pins B and D.
the resistance between pins B and D should be 42 ohms , if memory serves.
if that resistance is out of spec, it could cause the surge you're seeing.
if if the new switch doesn't help, I check that
thanks
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski