89 Jimmy/K5 doesn't have a standalone brake proportional valve, does it?

[MrTruck805]

Sorry if this is a stupid question but...

I'm having some problems with the brake light coming on in my 1989 fullsize Jimmy. Brakes go pretty far to the floor, and it just doesn't seem to have it's normal stopping power. I'm planning on doing a flush and replacing the master cylinder. I've been doing a lot of reading on the forums about braking problems, and a lot of people are mentioning the proportional valve, and having to push back in a button that pops out.

On and 89, there is no standalone proportional valve right? It looks like it's built into the master cylinder? Autozone doesn't list a brake proportional valve as something that can be bought when they list parts for an 89, unless it's called something different.

Again, sorry if this is a dumb question. Any insight is much appreciated.

 

[onetonbb74]

Check the front frame crossmember under the radiator...it should be there and a brake light switch is hooked up to it that turns on your brake light if pressure is too low.

 

[MrTruck805]

Thanks for the reply, much appreciated! What do you think, while I'm at it should I replace the proportional valve? The part is going for about $90-150 on autopartswarehouse. It's an 89 Fullsize Jimmy with about 200k miles.

 

[frankin5]

Check the front frame crossmember under the radiator...it should be there and a brake light switch is hooked up to it that turns on your brake light if pressure is too low.

On the 89 it is on a bracket below the master, with the brake light switch. When was the last brake job. Have you tried adjusting the rear shoes. Do you have any fluid loss. could have air in the system.

 

[MrTruck805]

On the 89 it is on a bracket below the master, with the brake light switch. When was the last brake job. Have you tried adjusting the rear shoes. Do you have any fluid loss. could have air in the system.

That's what I thought, it seemed to be attached to the master cylinder. The truck is new to me so I'm not sure when the last brake job was, but the fluid is dirty and my moisture meter is maxing out at 4% when testing it. I know it's not the best way, but since they are fairly cheap and the truck has a lot of miles, I'm just throwing parts at it. I will look at the rear shoes though.

Can anyone recommend a good website for Jimmy/K5 parts? I'm not having much luck finding a brake proportional valve that looks like it will fit.

 

[496truck]

Stop. Just stop. (ironic because the thread is about brakes)

Don't just throw parts at it. You need the brake system to function properly and stop your 6000 pound truck. Prop valves very rarely fail..... ever. So, unless it is leaking or the front or rear brakes lock up with little to no effort.... it's not the prop valve.

Look into the brake systems. Check the hoses and lines. From your location rust is not usually the issue but I wouldn't rule it out. Dry rotted and cracked hoses can expand/contract when you step on/release the pedal.

As mentioned before, check the rear brakes. Sounds like they could be cleaned and adjusted or all out replaced. You could have a leaky rear wheel cylinder.

Check the fronts too. You could have a leaky caliper causing pressure loss.

 

[MrTruck805]

You're right 496, it's better to find out exactly what is wrong than to throw parts, but I'm doing a flush anyway and the master cylinder was $40 shipped, so why not. I will definitely try to pinpoint the problem though.

It is not leaking fluid anywhere, but I will surely check the front calipers, rear brakes/cylinders, hoses, and lines.

Stop. Just stop. (ironic because the thread is about brakes)

Don't just throw parts at it. You need the brake system to function properly and stop your 6000 pound truck. Prop valves very rarely fail..... ever. So, unless it is leaking or the front or rear brakes lock up with little to no effort.... it's not the prop valve.

Look into the brake systems. Check the hoses and lines. From your location rust is not usually the issue but I wouldn't rule it out. Dry rotted and cracked hoses can expand/contract when you step on/release the pedal.

As mentioned before, check the rear brakes. Sounds like they could be cleaned and adjusted or all out replaced. You could have a leaky rear wheel cylinder.

Check the fronts too. You could have a leaky caliper causing pressure loss.