: Simple silly brake question


bbeardb
03-22-2008, 10:20 AM
Hi all,

I'm actually embarassed to be asking this, but I need input as to why my brakes seem weak on my 87. I've just replaced all the pads and shoes, and bled them with my mityvac (the girlfiend hates to help) so I don't think there is any air in the lines. Unless I can screw up with a mityvac... I don't know.

Anyway, I push on the pedal, and it goes to the floor. But if I pump, it seems to work fine. To me, it's acting as if I need to bleed it, but hell, when fluid is coming out and you close the bleeder, it's bled.

Yeah, i feel like a moron...

ike
03-22-2008, 11:31 AM
sounds like air in the lines, or a faulty master cylinder. also check the lines for leaks as that may cause your symptoms also.

RedRunnertc
03-22-2008, 12:29 PM
Did you bleed the LSPV?

tacotoy
03-22-2008, 12:39 PM
yep.... probably air not at the wheel but up high in the line.... grab a few extra bottles of brake fluid and get your girlfriend to step on the brake pedal while you bleed.... rear right rear left bpv front right front left all as you are looking at the rear of the vehicle....

Quick Draw
03-22-2008, 07:06 PM
yep.... probably air not at the wheel but up high in the line.... grab a few extra bottles of brake fluid and get your girlfriend to step on the brake pedal while you bleed.... rear right rear left bpv front right front left all as you are looking at the rear of the vehicle....

I thought it was the other way around... I thought you started at the wheel closest to the resevoir... Am I crazy? Probably.

ziggy428
03-22-2008, 07:44 PM
I had that problem too, air is higher up in the lines. Probably just need to bleed longer. Also if you've lifted your truck and haven't relocated the LSPV sometimes it seems like it feels spongy too. Its bled after a few minutes when you see no air bubbles. I've heard you have to keep the exit line submerged in fluid but I'm not really sure what the proper way is. I can't remember if those trucks have a brake booster pump but that could be another source of trouble.

tacotoy
03-22-2008, 08:59 PM
I thought it was the other way around... I thought you started at the wheel closest to the resevoir... Am I crazy? Probably.

you start furthest away to try and push as much air out in one bleed as possible.... that way you avoid thinking you are done and still having bubbles in the line. but if you want to do it the other way then let me know so i can avoid being in front of you

00regcab
03-22-2008, 11:22 PM
sounds like air in the lines, or a faulty master cylinder. also check the lines for leaks as that may cause your symptoms also.

if it was a faulty master cylinder, even if he pumped it it would go back to the floor.

my moms pathfinder is kinda like this. The pedal is SLIGHTLY mushy the first time you hit it, but if you hit it, let off then hit it again real quick its super firm.

i didnt get all of the air out of the lines last time i did the brakes on it...

air in the lines sounds like your symptom.

ike
03-22-2008, 11:34 PM
when the master cylinder is just starting to go out you can pump them and gain firmness.

00regcab
03-23-2008, 12:57 PM
when the master cylinder is just starting to go out you can pump them and gain firmness.

yes, but then as you sit and hold the pedal it'll slowly fade back to the floor. I had this problem in my car.

spindleshanks
03-23-2008, 02:06 PM
I agree that you probably have more air in the system. I've been told that if you apply too much pressure to the brakes when bleeding, you can break up the air bubbles into smaller ones that are difficult to get rid of. In ABS setups these tiny bubbles can get into the system and wreak havoc, and are very difficult to coalesce and remove.

I don't know how well your auto brake bleeder works, but if you grap some 1/4" vacuum line at the parts store and press it onto the bleeder valve , then run it into a clean, full jar of fresh brake fluid(a clear glass or jar). This eliminates the possibility of any air returning to the system while the bleeder is open. Using this method, you and the person pumping the brakes can afford to be out of sync a bit without ruining your progress.

Using this method, if there is any air in the system at all, you will actually be able to see the bubbles in the jar. Keep doing this repeatedly, like Rich (Tacotoy) said, for a couple bottles of fluid.
Not sure if this is what you need, but it's a handy little technique.

Keep in mind also that brake fluid naturally absorbs moisture, up to 2% its volume per year. It's supposed to be replaced regularly. An old tech ref manual of mine suggests every two years or 30k miles. This is not as much an issue for us as for people in humid areas of the country. You should probably get all the old fluid out of the system before going through all this trouble.

Don_G
03-24-2008, 05:53 AM
Both the vacuum bleed and bleeder-hose-in-a-bottle can let air get sucked in around the threads of the bleeder valve. I have a Motion-Pro vacuum bleeder, so I speak from experience.

Sounds to me like it's time to try a pressure bleeder like the one from Motive. I have been thinking of getting one, as it lets one man do the job.

mrdoug
03-24-2008, 08:14 AM
Keep in mind also that brake fluid naturally absorbs moisture, up to 2% its volume per year. It's supposed to be replaced regularly.

Am I reading this right? How do you replace _all_ the brake fluid? I'm assuming you don't drain it like other fluids (ie, open a plug, drain, replace plug, fill). I'm going to be concentrating on my brakes in the next couple weeks (got a warped disc and need to bleed the brakes, check the pads/shoes).

Both the vacuum bleed and bleeder-hose-in-a-bottle can let air get sucked in around the threads of the bleeder valve. I have a Motion-Pro vacuum bleeder, so I speak from experience.

Sounds to me like it's time to try a pressure bleeder like the one from Motive. I have been thinking of getting one, as it lets one man do the job.

Don, I've been looking at a one man bleeding device and can only find super cheep plastic things in the local stores. Got a link for this device you speak of?

bbeardb
03-24-2008, 08:39 AM
Am I reading this right? How do you replace _all_ the brake fluid? I'm assuming you don't drain it like other fluids (ie, open a plug, drain, replace plug, fill). I'm going to be concentrating on my brakes in the next couple weeks (got a warped disc and need to bleed the brakes, check the pads/shoes).

Don, I've been looking at a one man bleeding device and can only find super cheep plastic things in the local stores. Got a link for this device you speak of?

To replace, personally I would bleed a whole bunch (which I've done a bit of lately.)

I think what he is talking about is this:

http://www.germanautoparts.com/tools

Looks interesting. I agree that air does get by the threads when vacuum bleeding. It is hard to tell if air is in the lines or working its way through the bleeder threads when using the mityvac.

Chalkie
03-24-2008, 10:05 AM
Am I reading this right? How do you replace _all_ the brake fluid?

You keep pumping fresh fluid through all the lines until they all run clear and new looking.

ike
03-24-2008, 08:25 PM
X2, to replace your brake fluid you just bleed the hell out of them until you are sure that you are getting new fluid out.