Slow Brake Pedal

[Essex85]

Hello all,

I've read through a lot of posts today and nothing quite fits my dilemma. A little background first. I have an ;'88 Chevy K2500, with power assisted brakes. When I bought this truck, last year, it would stop just not very good. So I decided to change the drum shoes in the rear. Well I had found that they were missing several components and I wanted to do a disc swap anyway so I just tossed them. Flash forward a few months, I have the disc swap installed on my rear axle but now I can't get a solid pedal to push on (with the vacuum from the engine) and it will take the brake pedal a good five to ten seconds to return back to it's starting place.

So I suppose my question would be, does anyone have any ideas as to what would cause this?

• I believe the booster is good, is solid when I pump and the engine is off, then when I keep it pressed and start the truck it will drop.
• The calipers bleed screws are all pointed up (the rears are on a slight probably sixty degree angle though
• Bench bled master cylinder (several times now) and plugged the ports and it is solid
• Checked for any kinked lines anywhere and can't seem to find one
• Have pressure bled the brakes and ensured a good steady flow from screws

Well if anyone can provide any assistance I'd sure be grateful. Thanks again!

[chevy_man]

Did you put a proportioning valve in? And are you using junkyard parts or new parts?

Also is yours hydroboost or just vacuum boost? All the vacuum boosted ones I've driven have stopped fine, but they do take a second to return. However not the 5-10 seconds you describe.

[Essex85]

No I am still using the stock prop valve, as far as the parts go, anything that I have put on has been new. Now the woman I bought the truck from had said her boyfriend had put some old parts on, but none were related to the brakes, so it should be completely stock or new parts.

It is also a vaccum driven booster. As far as stopping, it seems that it will stop just not in a hurry. Now naturally I haven't tried anything over about 15 mph or so just to be on the safe side. It feels almost as though I have air in the lines, but I am fairly certain that is not the case. Thanks again!

[travis00]

Originally Posted by Essex85

No I am still using the stock prop valve, as far as the parts go, anything that I have put on has been new. Now the woman I bought the truck from had said her boyfriend had put some old parts on, but none were related to the brakes, so it should be completely stock or new parts.

It is also a vaccum driven booster. As far as stopping, it seems that it will stop just not in a hurry. Now naturally I haven't tried anything over about 15 mph or so just to be on the safe side. It feels almost as though I have air in the lines, but I am fairly certain that is not the case. Thanks again!

Try bleeding it a few more times. Chevys are known for getting a lot of air in the lines and even with a pressure bleeder it can take a while.

[Essex85]

Hmm, really? Didn't know they were known for that. Okay, I will go ahead and give it another couple bleeding runs. Thanks again!

[abig84]

my 90 1500 did the same crap when i got it. the brakes would start to grab at normal height then the pedal would go down about a inch or two then grab the bottom kinda like when you have a leak in the line.

it was that stupid rear abs thing. you can try bypassing that if you try bleeding again. its the little thing bolted to the side of the master cylinder. the lines go from the master into the prop valve. then into that thing then to rear brakes. i bypassed mine and havent had any problems since

[Essex85]

Hey,

Thanks for the suggestion. I may go ahead and get sometube that size and just make a quick patch and see if it works. Thank ya!

[beefdawg]

Originally Posted by travis00

Try bleeding it a few more times. Chevys are known for getting a lot of air in the lines and even with a pressure bleeder it can take a while.

REALLY, this is an answer?

so it's missing some components??? like what? the stock brakes are more then adequate to stop this truck,

Try finding out what the problem is before throwing parts at it.

but anyhow. When you switch to rear disc, you need to remove the stock prop valve and install an adjustable one.

nowthen back to: "it would stop, just not very good. How is the vacuum to the booster, if the engine has a miss, the vacuum is going to be low. Is the booster any good? Is the master cyc working the way it should, or is it going to the floor, or half way to the floor. Look at the rear axle, is there an anti lock up valve. (this valve has the brake line running to and from it and connected to the rear axle with a rod) does it work, or is it disconnected?

[Essex85]

Hey,

Well to start with, the components that were missing were an actuating arm had busted and on the other shoe the guide bolt at the top of backing plate had rusted up and broke, figured it'd be pricey either way.

As far as the vacuum to the booster I don't have any particular guage on it so I can't give you a surefire answer but the diaphragm inside it does seem to be holding.
The master cylinder should be working correctly. It is tight with a good spring return when I bench bled it. As far as that goes, I have had two MC's and both have been fine on the bench just put in the truck it doesn't seem to want to push the pedal back up. When I step on the pedal it goes to the floor with a slight resistance and then just takes some time to return to the starting position.
I may be misunderstanding the anti-locking valve, but no I don't see anything that fits that description. Now I do have the ABS thing underneath the master cylinder, but that's it.

Thanks again!

[Bubba_Jeep]

I'm "0" expert on ABS systems, but have read that ABS system bleeding requires a specific procedure. So if you haven't done so, I'd suggest you do some serious reading on the procedure is.

[abig84]

Originally Posted by Essex85

Hey,

Thanks for the suggestion. I may go ahead and get sometube that size and just make a quick patch and see if it works. Thank ya!

when i bypassed mine i didnt have to use any brake lines. but you will need a flare tool or a adapter of some sort. the line coming out of the prop valve to the abs thing is the size as the one going to the back of the truck, just different thread size

[Essex85]

Bubba_Jeep -> Did not know that there may be, I will def. look into that. Thanks

abig84 -> Awesome, I have plenty of spare fittings and a flare tool. Thanks!

[mud truck junkie]

one way to tell if the dump valve for the abs as it is called is messing up is to have someone push on the brakes and see if the prop valve moves you should see the pin come out if you remove the black rubber piece off the end of it I have fixed them temporarily by smacking the hell out of the dump valve. If you smack the hell out of it and then the brakes work you know thats your problem. I would bypass it any way though.

[Essex85]

Sounds good, I'm planning to try it this weekend. I'll let ya'll know how it goes! Thanks again.

[Essex85]

Wanted to thank ya'll. It was the abs. I bypassed it and she stops like a champ once I bled the brakes again!

[abig84]

Originally Posted by Essex85

Wanted to thank ya'll. It was the abs. I bypassed it and she stops like a champ once I bled the brakes again!

cool. i guess thats a common problem. i asked a friend about it and hes had to do it to a few trucks. and to get your brake light to go off just unplug the box next to the master cyl

[Essex85]

Cool thanks, I was starting to wonder about that!