Brake Issues
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Cross-Country
Joined: Jul 2019
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Brake Issues
Hello,
I have a 1988 f250 that has had some brake problems for a while now. For years now, when you press the brakes I get a noise that sounds like air escaping from under the pedal. All the research i've done has pointed to this being a vacuum leak with the brake booster. The only thing that is mixing me up is that the leading indication of a faulty booster is a stiff pedal and mine is actually very squishy. From what i've seen the leading causes for a spongey pedal is air in the lines or a bad master cylinder. None the less, I am well overdue for a brake bleed so I am doing that in the next few days. Any suggestions on what to do to really test where the problem is? I done the first test in the link below on the brake booster and it passed with no problems seemingly.
https://www.yourmechanic.com/article...-brake-booster
Another thing I've commonly seen is issues with the RABS in these trucks so I'm not sure if that is also contributing to my problems or not. Is there anything special I need to do when bleeding the brakes with this RABS unit? I've seen some people online talk about bleeding with the RABS valve. Is that necessary in this truck or can I just bleed the brakes like a normal car? Any help or experience with this is appreciated.
I have a 1988 f250 that has had some brake problems for a while now. For years now, when you press the brakes I get a noise that sounds like air escaping from under the pedal. All the research i've done has pointed to this being a vacuum leak with the brake booster. The only thing that is mixing me up is that the leading indication of a faulty booster is a stiff pedal and mine is actually very squishy. From what i've seen the leading causes for a spongey pedal is air in the lines or a bad master cylinder. None the less, I am well overdue for a brake bleed so I am doing that in the next few days. Any suggestions on what to do to really test where the problem is? I done the first test in the link below on the brake booster and it passed with no problems seemingly.
https://www.yourmechanic.com/article...-brake-booster
Another thing I've commonly seen is issues with the RABS in these trucks so I'm not sure if that is also contributing to my problems or not. Is there anything special I need to do when bleeding the brakes with this RABS unit? I've seen some people online talk about bleeding with the RABS valve. Is that necessary in this truck or can I just bleed the brakes like a normal car? Any help or experience with this is appreciated.
More Turbo
Joined: Dec 2021
Posts: 554
Likes: 186
Ignore hissing booster till you get brakes bled. Some hiss for years and still do their job flawlessly.
You start to bleed the brakes like a car, do rears first. Not a bad idea to bleed the RABS, but look at the condition of it, if it looks nasty leave it for now. Do front brakes like a car. Get in truck, see how pedal feels. If all good then you're done.
If still spongy you gotta bleed ABS, break out the blue wrench if needed and be VERY careful about what you heat and for how long. Once the bleed port is freed loose close it, do a quick bleed at the rear brakes again, then do the RABS. Get in cab again, try pedal again, if still spong you might have a RABS issue - crawl under truck, disconnect RABS harness, go back in cab, try pedal again. Good pedal -> electrical issue with RABS control (brainis under the dash).
Still bad pedal -> internal bypass inside the RABS. Crawl under truck, take end cap off RABS (32mm wrench?), pull spring out, do some measuring and cut/grind a suitable bolt to go where the spring used to go. Leave spring out, put bolt in, put end cap back on, get back in cab, try pedal if it's solid you do indeed have internal RABS issue and you need to either replace the RABS or bypass it entirely. Most ppl bypass, personally I went off the deep end and installed a full-ABS system off an early SD truck in its entirety (axles included) and couldn't be happier.
You start to bleed the brakes like a car, do rears first. Not a bad idea to bleed the RABS, but look at the condition of it, if it looks nasty leave it for now. Do front brakes like a car. Get in truck, see how pedal feels. If all good then you're done.
If still spongy you gotta bleed ABS, break out the blue wrench if needed and be VERY careful about what you heat and for how long. Once the bleed port is freed loose close it, do a quick bleed at the rear brakes again, then do the RABS. Get in cab again, try pedal again, if still spong you might have a RABS issue - crawl under truck, disconnect RABS harness, go back in cab, try pedal again. Good pedal -> electrical issue with RABS control (brainis under the dash).
Still bad pedal -> internal bypass inside the RABS. Crawl under truck, take end cap off RABS (32mm wrench?), pull spring out, do some measuring and cut/grind a suitable bolt to go where the spring used to go. Leave spring out, put bolt in, put end cap back on, get back in cab, try pedal if it's solid you do indeed have internal RABS issue and you need to either replace the RABS or bypass it entirely. Most ppl bypass, personally I went off the deep end and installed a full-ABS system off an early SD truck in its entirety (axles included) and couldn't be happier.
Thread Starter
|
Cross-Country
Joined: Jul 2019
Posts: 62
Likes: 0
Ignore hissing booster till you get brakes bled. Some hiss for years and still do their job flawlessly.
You start to bleed the brakes like a car, do rears first. Not a bad idea to bleed the RABS, but look at the condition of it, if it looks nasty leave it for now. Do front brakes like a car. Get in truck, see how pedal feels. If all good then you're done.
If still spongy you gotta bleed ABS, break out the blue wrench if needed and be VERY careful about what you heat and for how long. Once the bleed port is freed loose close it, do a quick bleed at the rear brakes again, then do the RABS. Get in cab again, try pedal again, if still spong you might have a RABS issue - crawl under truck, disconnect RABS harness, go back in cab, try pedal again. Good pedal -> electrical issue with RABS control (brainis under the dash).
Still bad pedal -> internal bypass inside the RABS. Crawl under truck, take end cap off RABS (32mm wrench?), pull spring out, do some measuring and cut/grind a suitable bolt to go where the spring used to go. Leave spring out, put bolt in, put end cap back on, get back in cab, try pedal if it's solid you do indeed have internal RABS issue and you need to either replace the RABS or bypass it entirely. Most ppl bypass, personally I went off the deep end and installed a full-ABS system off an early SD truck in its entirety (axles included) and couldn't be happier.
You start to bleed the brakes like a car, do rears first. Not a bad idea to bleed the RABS, but look at the condition of it, if it looks nasty leave it for now. Do front brakes like a car. Get in truck, see how pedal feels. If all good then you're done.
If still spongy you gotta bleed ABS, break out the blue wrench if needed and be VERY careful about what you heat and for how long. Once the bleed port is freed loose close it, do a quick bleed at the rear brakes again, then do the RABS. Get in cab again, try pedal again, if still spong you might have a RABS issue - crawl under truck, disconnect RABS harness, go back in cab, try pedal again. Good pedal -> electrical issue with RABS control (brainis under the dash).
Still bad pedal -> internal bypass inside the RABS. Crawl under truck, take end cap off RABS (32mm wrench?), pull spring out, do some measuring and cut/grind a suitable bolt to go where the spring used to go. Leave spring out, put bolt in, put end cap back on, get back in cab, try pedal if it's solid you do indeed have internal RABS issue and you need to either replace the RABS or bypass it entirely. Most ppl bypass, personally I went off the deep end and installed a full-ABS system off an early SD truck in its entirety (axles included) and couldn't be happier.
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