ABS bleeding

I have a 1996 chevy Silverado with a Kelsey-Hayes EBC310 ABS. I am needing to replace the master cylinder but am afraid I will ot be able to properly bleed the system because of comments I have read about air getting into the ABS. Can anyone tell me if this is true?

Reply to
stryped
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Oh horseshit, Stryped! Read the book, do the bleed as specified. This is not rocket science.

Reply to
hls

"hls" wrote in news:toWdnZixTu7l6WHWnZ2dnUVZ snipped-for-privacy@giganews.com:

I see this at the AZ page on ABS for OP's vehicle:

"Bleeding the EHCU

------------------ "Bleeding the EHCU requires the use of the TECH-1 scanner or its equivalent and the appropriate cartridge. Additionally, 3 tools, J-39177 or equivalent, are required. Bleeding cannot be performed without this equipment. "The EHCU must be bled after replacement or if air is trapped within the unit. It must be bled after bleeding the master cylinder and before bleeding the individual wheel circuits."

There's more, too, here:

I'm glad I don't have ABS.

Reply to
Tegger

1996 will need a GOOD scan tool and some clips for the valves to bleed the ABS unit. A Tech 2 or other high end unit is needed to activate the bleeding procedure to get the air out IF you get air into it.

BUT there is a way around this, the catch is that you have to pay a LOT of attention to do it, and it takes about an extra quart of brake fluid.

You start by flushing the system with new fluid. To do this you break loose one rear bleeder and one front bleeder. Then you use a turkey baster to remove as much of the old fluid out of the master. Now fill it with clean fluid and WITH THE ENGINE OFF AND THE KEY OFF! you crack the front bleeder and let the fluid come out. KEEP THE reservoir FULL as you do this. Continue until you get clean fluid. Repeat with the rear.

Now for the tricky part. Remove one pad on the front caliper, then GENTLY you push down the pedal to push out the piston just a SMALL amount while making sure the master stays full. Now on the back you remove the drum and gently pump the wheel cylinder full with a clamp holding the front piston so it cannot move any farther.

Now for the fun part. Bench bleed the new master, then install it and connect it up. Now GENTLY compress the rear wheel cylinder and the front piston. This will push new fluid up through the master and any air that got into the lines below the master. If you do it gently and correctly you end up not getting air into the ABS and new fluid in the system.

Reply to
Steve W.

Why does my hanes manual in the section on how to replace the master cylinder not say anythign about bleeding the ABS. Is it possible most of the time you dont have to?

Reply to
stryped

I wouldn't trust a Haynes manual for oil capacity let alone ABS function.

Note how Haynes likes to cover ALL variations of a vehicle with one manual? The phrases they like is "others similar" and "others may differ". With ABS that difference can cost you your life.

The KH310 is a 3 channel ABS unit. One channel each to the front brakes and one channel to the rear brakes. If your changing out downstream parts (steel lines, rubber lines, wheel cylinders, calipers) You usually don't have to bleed them because the air is past the unit.

If on the other hand you are changing upstream parts (connector lines, master cylinder, ECU) you need to bleed the unit to make SURE no air stays in.

The method I posted is a Q&D shortcut that does work 99% of the time as long as you don't let a lot of air into the lines from the master cylinder. If you let them drain out then you WILL have to bleed it and without a scan tool to cycle the modulators in the unit you can't.

There is NO other way to get the air out of the unit.

Reply to
Steve W.

how are abs units bled at the factory?

Reply to
jim beam

When you take your truck to a shop like Midas do they have those scan tools to do this?

Reply to
stryped

I have read elsewhere that driving and slamming ont he breaks will cylc ethe valve? ALthought, I dont think this will work on me, the ABS light is constantly on in my vehicle.

Reply to
stryped

Not only won't it work with the light on (that light means the ABS isn't working anyway) it won't purge the air unless there is also fluid flow and the valves need to cycle more than once.

Also this system has a three section unit. The only way to purge the system would be to make sure ALL the circuits activated. That means you need the right front to activate, then the left front and the rear as well. Got a good controlled way to KNOW that they all activated by slamming on the brakes? I sure don't.

I have read on the internet that if I spray myself with AXE body spray that all the hot women will jump on me. Think I believe it????

As for the other post. I don't know. I would suspect they might since they do brakes. BUT a LOT of those shops make the employees provide there own tools so ??????

Reply to
Steve W.

Any good way to figure out why the light is on without a reader?

Byt the way thanks for that procedue. I plan on using it when I replace the master cylinder.

Reply to
stryped

Is there a combination valve in my truck? If I bleed per your procedures do I need to do anythign with this? The directions on the autozone website say somethign abotu using a special tool to hold the valve open when bleeding.

Reply to
stryped

Nope. If you had a different unit then I could tell you a jumper sequence that would flash the code on the light. The 310 though requires a reader. You can rent the Actron unit from some parts stores and it will read the code. It will NOT allow you to bleed the unit though, just pull the code. The nice thing about the ABS unit is that if you repair the fault properly the light will go out and the ABS will work.

Reply to
Steve W.

No. The light means an error has been recorded. The reader tells you what the error is.

You basically can do no diagnosis of any sort without the reader. The light exists only to tell you to use the reader.

--scott

Reply to
Scott Dorsey

Can I check the wheel speed sensors with an ohmeter?

Reply to
stryped

They are not that easy to test. They are basically modified hall effect sensors and generate a frequency that the ECU calculates into a speed.

The easy way to test them is with a scan tool. You can drive down the road and see what speed and frequency the ECM is getting from each sensor.

Reply to
Steve W.

No they're not, they are permanent magnet generators. Very basic.

The EBCM uses both frequency and signal amplitude.

Reply to
aarcuda69062

And the interruption of the magnetic field through the inductance coil by the reluctor which generates the A/C waveform is called? The Hall Effect.

Either way a resistor can't be used to test them. And an ohm meter is useless unless you want to see if they are open. The best method is with a scope and watch the waveform coming off the sensor wile in motion. BUT I'm kind of doubting he has this available. OR knows how to use the info.

True but ABS function is controlled through the 150K signal on a KH system.

Reply to
Steve W.

No, you _are_ wrong, that is NOT the Hall effect.

Wikipedia's page is actually quite good and has it right.

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Reply to
Mark Olson

Actually, it's called 'reluctance.'

He's got two codes indicating open circuits so an ohm meter isn't useless and I bet his ohm meter is also an AC volt meter which would give him some direction on the 'signal missing' code.

He can also get direction with an AC volt meter. We both know that millions of these systems were fixed over 20 years ago with a DVOM, no scan data, long before lab scopes came into vogue.

Yup!

Reply to
aarcuda69062

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