Bleeding brakes

[Bub]

It's time to get that old brake fluid out of my 98Z. At the last autocross in the fall the pedal was fading all the way to the floor. I plan to use the two person technique, moving from the farthest wheel from the master to the nearest. Never done this before so any tips or tricks would be appreciated.
Bub

 

[OneQuartLow]

Is that a Chevy Z or the other?

If it has ABS then it may require special effort to bleed out the pump. Haven't worked on either of those since the late 80's so can't help much.

David

 

[dkcase]

Other Z ??

Oh, yeah... the Datsun..

 

[satterfi]

Do yourself a favor and buy a Mityvac. It's much easier and the job is done better.

 

[jason07-1zzfe]

I like my pressure bleeder.

 

[OneQuartLow]

Bub, assuming it has ABS it's worth cycling the pump to get that fluid out. Depends on the system how to accomplish this.

Satterfi, I've used vacuum pumps but not a Mityvac. Are they that much better?

Have to throw in my vote for speedbleeder(.com) valves. Slightly on the luxury side of things but they sure simplify the job.

David

 

[jason07-1zzfe]

What about ABS requires special procedure? And what is the special procedure? I've heard that it does need special treatment...then I've heard that it doesn't. And no one can tell me what the special procedure is.
I simply flushed my system completely with a pressure bleeder untill all new fluid came out.
Should I have done something for the ABS?
Then I read in a somewhat recent C&D in the big brake test article, Brembo said that with ABS cars it may need a couple subsequent bleedings a few days apart. That was why their two tests were different.
My stopping with ABS is not what I'd like. Seems to actually increase distance sometimes. But then it is 13+ yr old design. So maybe they all sucked back then?
Anyway,
What is the TRUTH about ABS and BLEEDING?
Thanks

 

[satterfi]

OneQuartLow

A Mityvac is a hand operated vacuum pump. I like speedbleeders too. I use them on my bikes, but I like the Mityvac on the cars because I can pull a vacuum and with the bleeder valve cracked open I can walk around to the reservoir and fill it while fluid is being sucked out. I made a larger vacuum reservoir that holds a quart of fluid.

 

[OneQuartLow]

They look to be of higher quality than the imitations I've used. Recently broke my plastic "Help aisle" special so will look into them. Thanks.

[ January 17, 2003, 02:07 PM: Message edited by: OneQuartLow ]

 

[jason07-1zzfe]

What exactly does removing the fuse/relay do? I thought the pump would only cycle if the computer sensed lockup? (how can you simulate that?) Removing fuse should just turn off the computer?

And the way I uderstand ABS design (and that probably isn't saying much). Is that the fluid normally goes straight to the caliper, but when the comp senses lockup it opens up a valve in the appropriate circuit relieving pressure back to the master cylinder.
So basically when flushing the only thing that would not be changed is that return line, correct? So does it really matter? If there was air in that return line, wouldn't it rise to the surface and escape once returned to the master-cyl?

[ January 17, 2003, 03:37 PM: Message edited by: Jason Troxell ]

 

[OneQuartLow]

Jason, on the simple systems I know the pump has to both relieve and apply pressure. It isn't arranged to allow bubbles to escape so cycling is necessary. Better, don't let the system run dry enough to allow bubbles inside. If bleeding, keep the reservoir full. If changing lines, block the brake pedal so gravity won't empty everything.

You're right, for simple bleeding the benefit is marginal. More important if air got in or you're flushing. For a spongy pedal I sure start with the four corners and worry about ABS later, only if necessary.

On cycling the pump, some systems do it as part of their diagnostic after losing power. When I pull a relay on the jeep I jump 12v from the battery to the leg that activates the pump. Makes that same special sound, but up close.

David

 

[Bub]

It's the chevy Z, sorry for the confussion. I think the ABS motors only need to be cycled if the unit goes dry, if you keep fluid in the master, there should'nt be a problem. Thanks for the ideas, the mighty vac idea sounds like a winner.
Bub

 

[OneQuartLow]

Jason, you're right it can vary by system. And yes, old systems were less than ideal. Still do a pretty good job for the masses though if they remember to keep their feet planted and stop modulating. Unless on gravel, or snow, or ...

Where bleeding is concerned, the difference is that the ABS pump can hold fluid the normal pedal-pump bleeding action won't remove. Again, varies by system and bleeding method which might explain the conflicting advice you've heard.

Usually some trick is required to get fresh fluid into the pump. DIY manuals usually say to just bleed & do it again later. Dilution method. Service books say a scan tool is necessary to cycle the pump, but it's the same thing you hear at 5mph. For me it's been easy to simulate by removing & replacing a fuse or relay.

 

[UncleS2]

ABS: Yes, ABS systems may require different procedures, may vary from mfg to mfg. I understand that some systems are very "unfriendly" to the home mechanic.

Speedbleeders: I really like mine! Makes brake bleeding a one-man job(at least for those of us without ABS!). When weather gets warm, I'll change my brake fluid again.

 

[shoz123]

I recently found out that with Ford ABS sytems they are considered a diagonal system with two parts. Meaning the front right,left rear are one system and the front left, rear right are another.

The proper method of bleeding is right rear, then left front, then left rear and right front.