Brake/ABS warning lights

[RedD250]

My Brake and ABS lights are staying on after the self test, sometimes. They will usually go out after I drive a little bit. They will also randomly come on while I'm driving. Brake pedal sometimes becomes very firm like there is no power assist, but the truck still stops easily, it's not like panic inducing or anything. Not sure if this is related or not, but my transmission also started randomly going in/out of overdrive at the same time this problem started, only at low speeds under light throttle. On the open highway over 55 it will stay in o/d.

Booster/master cylinder are both new, and I flushed out all the old fluid and bled the brakes when I installed these parts 6 months ago. Oddly enough, no warning lights came on then, and the booster was completely dead. I had to stand on the pedal with both feet and literally lift my ass off the seat to get enough pedal pressure to stop this thing lol.

Fluid resorvior is full, and no sign of leaks anywhere. I don't see any wires disconnected. The only wire I see under the hood is the connector on the combination valve. Brake warning light wire on the parking brake pedal is connected firmly. I haven't had a chance to do a vacuum check yet, but my vent flaps and cruise control are working fine, so I'm assuming there isn't a vacuum leak. All the vacuum lines are connected.

The ABS hasn't worked since I got the truck, because I have locked the rears up a couple times in panic stops, but the light has never come on until yesterday when this problem started. Any suggestions?

 

[sdeeter19555]

Check your vacuum at the booster...low vacuum will pop the brake light.

The ABS may just be the system at fault...unplugging the module behind the glove box temporarily will rule that out.

 

[RedD250]

I'm thinking it may be my vacuum pump starting to go out. Vacuum test was fine. The problem has not occured for several days now, but I don't think a leak can be intermittent? On another note, the overdrive slipping turned out to be the TPS. Odd that both of these issues would happen at the exact same time. I got the delete kit from Geno's and it's working great.

 

[RedD250]

I'm pretty sure I figured this out. My vacuum line from the vacuum pump to the booster won't hold vacuum, which is either a bad line or the original squeeze clamp thing that holds it onto the pump is bad (it was really loose, I didn't even need pliers to get it off). The line that goes from the junction off the check valve to the vacuum sensor on the fender was also leaking, and possibly the vacuum sensor too... I was not able to test that, as the nipple broke off when I went to remove the line. Found a new one online, so I'll know for sure when it gets in. The vacuum pump is pulling 28 in/hg, and my check valve, cruise control line, and booster all hold vacuum just fine. The leak is slow, which explains why this was an intermittent problem. Also explains why the lights went off when I accelerated, and explains why the brakes would sometimes be rock hard and sometimes be normal, and explains why the lights would go off if I applied more pedal pressure, only for the pedal to slowly keep going lower and lower and the lights to come back on. Also explains why it seems to be worse when it's really cold outside. The overdrive issue that cropped up at the same time was a failing TPS. I replaced it with the TPS delete kit from Geno's and it's fine now.

 

[Ozymandias]

After 30 years you probably have to replace almost all rubber parts in the engine bay.
Especially these tiny hoses age always very fast.

 

[RedD250]

Yup. I don't have the correct adapter thing on my vacuum tester to fit into the small line that goes to the heater controls, so I haven't been able to test anything on that side. But everything does work, it opens and closes the flaps as it should. Slowly, but it does work. Takes several seconds when I switch from vent to heat before the air starts coming out on the floor. Not sure how fast it should be. God help me if there are any leaks on that side lol... talk about a pain in the ass. Hopefully if anything there is leaking, that line is so thin that the vacuum pump can keep up and compensate for the leak lol. It pulls well over the amount of vacuum needed. I think the manual said 8.5 to 16 in/hg and I've got 28.