I am not shure what the exact procedure is on a 93 but I would not use the mighty vac. I had bad luck with mine and had do it the old fasion way by having the wife stomp on the old brake pedal while I bleed the brakes. I just pulled most of the old fluid out of the resevoir and filled with new.

 

You've got it, for the most part.

I took the opportunity to rotate my tires and grease the chassis, so I had the whole car on jack stands, and all four tires off. This makes it easier for a few reasons. You can stand with one foot in the car pumping the brake, and filling the resevoir.

I don't believe in speed bleeders or anything, too much chance to screw up. If you allow air into the ABS, you're towing it to a shop. This way is slow enough that its not really screw-upable, but its quick enough that you're not there all day long.

The sequence is to start as far away from the resevoir as possible, which is the front right wheel, then the front left wheel, then right rear, and finally left rear. I'm not sure if this matters on a Corvette with 4 lines for 4 calipers, but its imporant with cars that share lines for the rear brakes.

Anyways, I find it best to get a length of line that will fit over the bleeder, and run it into a milk jug or even a soda bottle. The soda bottle will need to be emptied three or maybe four times.

Draining 3/4 of the resevoir then filling with clean fluid seems to be the best method, that way you don't get much of a chance to get air in the system. Takes a little longer, but feels safer.

I prefer Valvoline SynTech. I needed about 1.1 quarts. Good luck.


[Modified by NoWorries, 8:44 PM 1/18/2003]

 

Wouldn't that be the right rear wheel first, the left rear, right front, and finially the left front? ;)

 

If I had allowed air into the ABS, how would I fix it without towing it to a shop?
Anything is possible right?

 

:lol: You'd think so, but the ABS system is located behind the drivers seat, and the brake lines all go there first before going to their respective wheel. :)

Blk91, I think you need a vacuum pump or something to remove air from the ABS, I'm not sure how to fix it. I've heard its hard, and I don't know how to do it. Its much easier just to not get air in the system. :) At work I've had to use a hydraulic mule(sp?) which is a resevoir with about 55 psi of pressure to bleed some helicopter hydraulics...I'd assume that would work too...but I don't know how you'd get a good pressure seal into the resevoir.

I hope your question was mearly hypothetical. :) :cheers: :seeya

 

You need a Tech 1 to run the ABS pump in order to properly flush it when you are flushing the lines. The ABS pump gets its fluid from the master cylinder so everytime you start the engine and the ABS does the self-test, a little fluid will pass from the ABS back to the master. That's one reason why the fluid in the resevoir gets dirty so quickly!

The local Corvette-trained mechanic at my dealership did not even recommend flushing the ABS if it is working properly. He said it was not a good idea to run the risk of getting air in to the ABS unit. It will flush itself in time.

The different bleed sequence is correct because of the position of the ABS pump in the car. The Mighty-Vac works fine but speed bleeders are easier to do with only one person and you have no equipment to hook up. BTW, the flush will take one quart to flush the lines. I recommend the Ford (Mororcraft) High Performance fluid. Has a very good wet boiling point. Castrol LMA is another good fluid for street use.

 

My car sits for the long Ohio winters so I try to flush the system every other year. I have used the Mity-Vac but it is a PIA to use. The problem is that when you loosen the bleeders to evacuate the system, it sucks air through the threads. Eventually you get it done but it takes awhile. I never mess around with the ABS module itself. Next time I will try the speed bleeders. I also use the Valvoline Syntech and have had good luck with it.
:chevy

 

Nice write up Iani. Your "dumb" question really isn't. I have read that its not dirt getting into the system thats a concern, but moisture. It seems that this type of fluid attracts moisture and even if you never open the system some will get in and eventually cause problems. Having read and said that, I feel that that is also debateable. While we obsess and fuss over this, my 10 year old S10 pick-up has had only one flushing when I had to replace a caliper. Never had any problems with it. Maybe were all crazy!
:chevy

 

Lani, you are thinking way too much!

Brake fluid: DOT 3 and DOT 4 are compatable. Everything mentioned was a DOT 3 as a matter of fact. Both fluids are also good choices. Brake fluid is good for about 2 years, and should be flushed. It turns black as water enters the system, nothing can be done to prevent this, entry is through the hoses and master (largely).

ABS short story: You can get air in the abs modulator. The device retains fluid under pressure behind a set of "gates" which pulse the fluid pressure to the wheels. If air gets in the abs controls, it is very difficult to get out. You need to control it with a Tech 1 as mentioned as you flush.

You do not flush brake fluid by opening all the valves and draining all the fluid out of the system, this would allow air into the system and make getting it out very difficult. Never allow your master to drain. We can talk about gravity bleeding later, but it does not include "draining" the fluid, just flushing.

The bleed order is different for different years, for some reason that escapes me. Could be the placement of the bleeder on the abs module, which some early models do not have as a place to start.

 

I used this thing:



I connect a hose to the brake bleeder, break it loose, and pressurize the pump. As it sucks the fluid out I keep topping off the master cylinder. I let the fluid go down to about 1/2" from the bottom of the master clyinder then slowly fill it back up again. Pouring slowly as not to make any bubbles. I repeated the process until clean fluid was coming out on the pump end. Which was pretty hard to tell. I was deceived by a dirty resevoir. Once fluid got low enough I noticed how dirty the resevoir was and not the fluid. I used just over a quart. I think I filled the resevoir three times on each wheel. My car has 2 resevoirs. One for the front brakes and the other for the rear brakes.

 

Does anyone know If I had allowed air into the ABS, how would I fix it without towing it to a shop?
LAst night I started flushing the system and had my better half pump the brake pedal for me.
Long story short there is now air in the ABS from pumping with no brake fluid in the resivor. :cry


How can I go about fixing this at home?

I had installed the quick leeders and bleed the brake 3 times and still I have no brakes.

 

:eek: I'm going to start looking now, I'm not sure how similar my '87 is to your '91, I'd assume they're pretty similar.

I'll get back to you with whatever I find in my service manual, and looking at my system.

 

Hmmm...I'm in the process of a move, and my whole library is backed into boxes. I've never been good at organization, and I have no idea where my service manual.

Looking at the ABS unit behind the drivers seat, there doesn't appear to be any way to bleed the unit from inside the cab. There is something that could possibly be a bleeder that exits the box at the rear of the box. If your car is jacked up high enough to climb under, take a look at the rear of the plastic box that is just forward of the left rear tire. Hopefully that is a bleeder valve.

Good luck. :eek:

 

Hey Lani,

Good questions. :) I think the first important part about ownding a Corvette is realizing that Chevrolet has not now, nor have they ever had, a clue. You'll find some members here that think Chevy is God, and shouldn't be tampered with, then you'll find members that change every part of the car for a better part. ;)

The service manual is great for telling you how to fix some components, but I don't put much stock in their suggestions. The automotive market has improved a lot in ten years, and there are better fluids and components available now. Still, its important that whichever fluid you use is compatible. As PeteL said, Dot 4 and Dot 3 are compatible, while Dot 5 is not. Dot 5 is not recommended in ABS applications due to some sort of bubbling or cavitating in the regulator. Most of the Synthetic fluids today say where they can and can't go. I chose to go with Valvoline because its a decent price, with a very high boiling point. I think as long as its a name brand, and says it will work, it'll be fine.

You keep refering to the "Prime Pipe", I'm not sure what that is. It sounds like one brake line running to the ABS where its then seperated into four seperate lines. The Corvette isn't like that, you've got four lines running to the ABS, somehow I think they must mix in the ABS unit though. The ABS operation is still somewhat confusing to me. Hopefully bleeding the ABS is how to fix Blk91's problem, but others have had problems in the past with no luck, so I doubt that there is an easy fix.

The brakes will work with the ABS not working, the earlier designs won't work in extreme cold(kind of ironic), so you have to get the interior temperature up before you get ABS.

I checked my car and there is no in-cab bleeder for the ABS. There may be right outside of the ABS unit, I don't have a suitable jack to get under my car to see right now. :(

Your question dealing with dirt isn't dumb. I've read that a lot of the black is water, but some is from deteriorating rubber hoses. My friends 1990 454SS lost the right front break when a piece of the brake line flaked off inside and blocked the caliper from getting pressure. I don't know how much heat has to do with the discoloration either...I'm sure that the brake fluid gets pretty hot sometimes.

My worst experience bleeding was on my Honda motorcycle clutch slave. I let the fluid drain because there is no ABS unit, obviously. The lines are only a few feet long too. It took me a whole quart to get the clutch bled correctly so that it would work. The slave cylinder has this weird Tear-Drop shape, and air has a very convenient place to get trapped, and in the end, the only way I could get it bled was to have two people, one on a wrench to tighten, and me pumping the clutch lever has fast as possible. As soon as it got hard, I told my friend to tighten it. It was a whole lotta work, something I hope to never have to do again. :eek:

 

When I first got my car, I had the dealer flush the system and fill with dot 4 fluid for $90. Kind of steep, but a few months earlier I flushed my wife's 96 accord and when done the abs light was on. The problem was a blown abs fuse, and the diag costs were $150, so I was afraid of a repeat and wanted piece of mind...

 

QUOTE]Does anyone know If I had allowed air into the ABS, how would I fix it without towing it to a shop? LAst night I started flushing the system and had my better half pump the brake pedal for me. Long story short there is now air in the ABS from pumping with no brake fluid in the resivor.[/QUOTE]

Normally the ABS unit is in a straight through mode (acts almost like a staright piece of brake line). You can get air into your ABS unit or even run your brakes dry when flushing your brakes, but do not start the car up at all, becuase it goes into a test mode. The test mode will get air into the internal passages, if this happens the ANS unit will need to be bled by the dealer.

 

Anyone with a 91 had this or a simular experiance?
I called the shop that does the work on my car and they say that I shoud be able to fix it myself. I cant find my book on the car.

 

I ran my MC dry during a bleed :rolleyes: It was dark out, I wasn't paying attention, ran it dry rather quickly :eek: .

no air ever entered the ABS unit. I just had to have wifey pump the pedal 10 zillion times and I ran around all 4 wheels until I (she) got a firm pedal again.

again, I did NOT have to touch the ABS unit at all. The air eventually cleared out through a bleeder. and I started the motor plenty of times to see if the brake light was on. evidentally, the ABS unit only cycles (test) at a certain MPH.

No more brake bleeding in the dark :D

 

I used the Mityvac-if the lines get opened you have to start with the bleeder screw on the ABS unit behind the drivers seat,there is a bleeder screw on the unit,1992 vehicle. :cheers:

 

:iagree: Will not cycle until you go into reverse or forward at >3-4mph.

I won't use the Valvoline stuff any longer because it was requiring a new flush every six months. I autocross so I'm sure that is the reason. My fronts would lock up and I would know it is time to bleed the system. The next event, no lock-ups. That's the fluid. Switched to the Ford Blue stuff. Will see this season if it is better for my application.
Never had to bleed the ABS unit, but it is as described from the manual that others have already stated.
I agree that Dot3 Dot4 are pretty much the same. They achieve the rating by the boiling points wet/dry and a few other specs as well.
I have the speed bleeders and they do work great. No pumps and I don't need the wife to perform this task. I usually do this task while I am swapping race/street tires, so the car is up on jacks and the wheels are already off. I do follow the Right Rear, Left Rear, Right Front, Left Front sequence as well. States so in the manual. :seeya


[Modified by Goody, 8:34 AM 1/21/2003]