87350formula

Ok, 87 350 formula, the cruise does not work. I removed the diaphram thinking it was bad because it wouldn't hold when both vacuum lines were plugged. Well, after removing I discovered there is a small winding that I assume magnetizes when charged causing a small metal "plug" to plug the hole allowing the system to hold vacuum. When I plug both vacuum lines and plug the third hole the diaphram holds vacuum. There is a five pin connector to the diaphram. I assume I need to check for power at the connector when the multi function switch is on. But, I don't know which wires to test. Any help is appreciated. Thanks.

chevymec

iTrader: (5)

A bad brake lamp switch was cause the cruise to be inop also.

87350formula

What? A brake lamp switch? The brake lights work. I suppose the cruise is linked to the brakes to kick off when the brakes are applied?

chevymec

iTrader: (5)

Your brake lights might work but there is a different circuit that will disengage the cruise and tcc. If you can get ahold of a scanner look for someting that shows brakes applied or released.

87350formula

Thanks for the responses

GTA Jim

FWIW, I've heard that if the third brake light is out, the cruise won't work.. I can't see how this would happen and have no idea if this is true..

The cruise in my 90 GTA didn't work when I go it 14 years ago... I took the vacuum servo apart and measured the coil resistances and checked for leaks but it seemed OK. I went to a dealer and had them diagnose the problem.. They said it was the vacuum servo and wanted almost $300 to install a new one.. I declined the work. They charged me around $40 bucks for the estimate.

I got a servo from a wrecker (these things are common) for about 30 bucks.. That fixed it.. The cruise has worked perfectly ever since.

87350formula

GTA Jim, interesting idea. My third brake light doesn't work! I would
assume the third brake light is on the same circuit as the rear tail lights meaning the bulbs are burned out since the rear tail lights work. But maybe they are hooked up to the same circuit as the switch mentioned above by chevymec. I'll work on that today.

UPDATE: both bulbs work fine so obviously the third brake light is on a different circuit than the rear tail lights. Maybe there is some truth to the third brake light idea. THis would point to a faulty brake light switch, correct?

87350formula

Well, I removed the access panel from under the driver side dash and found two switches are activated when the brake pedal is depressed. One switch has two connectors while the other has one two pin connector and a vacuum line. The one with what appears to be a vacuum line was broken. When I google the part number 25523376-7075 I get cruise valve! Is it possible this is the cruise switch with just two wires that also "runs" the third brake light? Therefore, when this switch is broken both will not work? I have attached an image of the switch. The item shown broke off of the threaded tube that is still in the brake pedal braket. What are your thoughts?

BADCAM70

Guess what my 3rd brake light is inoperative also and my cruise control is also down so i am following this with great interest.

regards Mats

87350formula

Badcam, I figured out the situation for my 87 350 auto car. Don't know if this applies to other years. As stated above there are two switches. One operates the brake lights and the third light IS on the same circuit as the tail lights. I didn't have continuity to the third brake light. I fixed that and all operate together. The switch I listed above is the cruise control and lock up converter deactivation switch. It will deactivate both when the brake is applied. My switch was broken so I replaced it. Therefore, I don't think there is necessarily a link between the third brake light and the cruise not working. I confirmed this when all three brake lights worked when the cruise deactivation switch was removed.

HCR13

iTrader: (5)

I just replaced the actual turn signal stalk a week ago, where the cruise controls were located, and since then my cruise has worked fine, I have an 87 LB9. I'd check that aswell... and my 3rd brake light is out, so thats not an issue...

bigbird90650

How hard was it to replace the turn signal arm? Any tips for a first timer? Thanks.

HCR13

iTrader: (5)

its not hard at all. The arm itself just pops off when you yank it. You are probably thinking you have to take the steering wheel off (which I thought I had to also) and such...nope. All you do is yank the stalk outward and it comes right out. The actual switch mechanism is inside the column. The stalk just controls it. The "hardest" part is that you have to find the connection/pigtail under the hush panels (only on cruise control) for the cruise control. I found the old one, tied a small, strong wire to it and pulled it out. Once the old electric cord was out, tie the new one from the new stalk and pull it back down through the column and connect...easy stuff!

Formula-Finatic

So this is a dead post that I'm replying to(as usual) but I think some information can be added on the subject of the cars third brake light. Long story short you will have no power in your cruise circuit if that light is out. Friends Nissan Quest had no cruise and that was the culprit. My cruise went out after checking fuse and vaccume I figured looking at a wiring diagram would be beneficial to see if that lamp is in the circuit. Yup if there's no continuity(no current able to pass) through that "high centrally mounted brake lamp" I think they call it you'll have no cruise control. Hard to tell it was out until I had a buddy press the peddle as I stood behind the car. Should mention my car is a Canadian made 87 TA with the lamp in the wing. I'll end with its pretty common to have this type of circuit in 80's gm cars.