Well, I had DRM put the spring in my Master Cylinder, then I bench bled it useing Napas little bleeder kit, 12.01 dollars!. After doing this till no air bubbles came out, I went ahead and opened the ABS prime pipe till fluid was steady.
Then, with the car jacked up level, I did RR, LR, RF, LF. I did this 3x's and no air what so ever.
But when I drive it around the block, I can panic stop, but it goes all the way to the floor. It does stop, but it seems like its low on fluid, not really mushy. It probably is mushy, but after 3x's, youd think???
Now , when I pushed the pedal for the first time, while bench bleeding, you could feel the piston going in and out of the master cylinder as I pumped it to bleed it. Now its smooth. No leakeage out of the MS.
Do, I need to adjust the rod? Or, rebleed?
This is a 93 with C5 fronts, Stainless Lines, and Valvoline synthetic ABS fluid.
Thanks

 

You speak of bench bleeding the master but did you bleed the master itself once installed and before you did your four point bleed? Have someone press and hold your brake pedal and crack open the line at the master for the front first. Close the line then tell your assistant to release the pedal and wait 15 seconds then press and hold again then open the line again and purge the air. Then repeat until there's no air. Always close the line before the pedal is released. Then repeat the same process for the rear.

This is from my helms but it says to only do this before you bleed the calipers. I do it before and after just to make sure a bubble hasn't traveled up to the master during the caliper bleed.

 

Thanks, I need to read that manual more often. I use the heck out of it, but sometimes I just do what I think is enough, which was bleed it manually, but not enough times.
Steve

 

Steve- I have some similar symptoms and was wondering if you resolved the problems yet and what you found?

 

Yes I resolved the mushy brake issue. I bled it using the gravity first, one caliper at a time for an hour just let it bleed. Then I did each wheel 10 times, well my wifes leggs did the pushing on the pedal.
I did bleed the prime pipe first, by gravity, I opened up the puka in the rear where the ABS is and the bleed vlave is on the side. I opened it, with a big rag under it and let it go till it was solid fluid (doesnt sound right, solid fluid).
Then I did the normal bleed routine of pumping and releasing and I kept doing it till clear, say NEW, fluid came out each caliper. Now it brakes really well.
And the BIAS spring makes the front NOT dive like it used to under hard braking.

 

Perhaps there’s some hope for me after all. This week I built a power bleeder for the brakes. I bought the pump/container and male/female air fittings from Home Depot. Used cap off of old master and old pool air gauge. I’m all set for this weekend. I have never been able to bleed the prime pipe it only ever dripped. With the added pressure I expect great things. Getting new fluid in the rest of the system and the new master should improve the brake pedal.

 

Well new master, new fluid, no progress. I can’t really believe the pads, rotors or flex lines are causing this. After reading a few posts, I’m thinking somehow the ABS is a factor in this equation. It shouldn’t be this tough, its not a complicated system normally. Need some new ideas starting with ABS.

 

The ABS prime pipe is the first thing you need to bleed. That is straight from the GM service manual. Then you do the right rear, left rear, right front left front. I had to do mine over 10 times each cylinder, after bench bleeding the master cylinder, and the ABS, Now I have good brakes.
All you do is open the bleed valve and let it flow till it is solid fluid. Then shut, then do exactly as the service manual tells you to bleed. Powqer Bleeding should eliminate allot of the air quickly. ALso, once you are done, go out and make the ABS work, supposedly this will get all the air out of the ABS.

 

greetings,

i received an e-mail from pcolt last night regarding this issue. i too have a brake problem (88 vette) i have been chasing for months with no resolve, specifically; insufficient braking.

new bench bled m/c, s/s brake lines, pads, rotors turned, system flushed 4 times +, no vac leaks, booster holds vacuum and no leaks, booster ck valve ok, correct brake fluid and stock pads, proper pad bed - in. ***i have no air in pedal nor does the pedal travel to floor, feel mushy or hard***

i have never fooled with abs however, i would think that "standard" bleeding should get all the air out ofthe lines, calipers, and the abs. when i bled mine, i bled with ignition both on and off. now that may have been an effort in futility but, the abs has to have power to work while in service, right? at any rate, if right or wrong, it didn't make any difference at all.

when you speak of the abs "prime pipe", what-where is it on the abs unit? is it a standard "bleeder"? could i-we accelerate the bleeding process by depressing the pedal while bleeding the abs or does it specifically have to gravity flow to bleed corectly?

lastly, were your brakes similar in problem with his and mine in that, if you had to panic stop, the car would glide 9so-to-speak) to a stop and / or require an excessive amount of foot power effort on the brake pedal?

pcolt, what part of orlando are you in?..i am over by the west oaks mall fyi.

 

On the side of your Master cylinder, there is a rubber hose, with a regular clamp on it, that is the hose that goes to the ABS unit. Behind the drivers seat is the ABS unit under the carpet. When you open it, the Prime pipe will be towards the center of the car, on the right side of the unit. It will have a rubber boot over it . It will be very obvious. You might be able to push the pedal down to accelrate the bleed process when doing the prime pump. The prime pipe is supposed to bled first, according to GM.
Before I bled the brakes with my wife, the brakes were mushy and would go all the way to the floor, but the car would come to a stop. Not a comfortable feeling.
The biggest thing that made a difference, was bleeding each brake over 10x's till fresh fluid came out. When this was done, brakes were fine.
ALSO,read this, since you changed your master cylinder with a different one.
http://forums.corvetteforum.com/show...0&page=1&pp=20

 

humn...there is no rubber hose at my master cylinder, only hose is for the booster vacuum.....at the abs, is the bleeder a "standard" bleeder?.......

 

Then yours is different. I would refer to a service manual, or hopefully someone will step in and assist your year. My 93 I think is an oddbal year.

 

i imagine so since mine is an 88 and see no reference of hose in helms....thanks for the reply.......

 

Mail Man - I'm east Orlando, past UCF in Lake Picket road area.

Power bled the brakes yesterday, did prim pipe first and needed some pressure to push it thru. The brake pedal will not help with that bleed process. There is a standard bleeder on the side of the ABS and the rubber hose is on the side of the master which is the prime pipe out, then becomes metal. Power bled all wheel cylinders, same problem. Everything goes to the ABS and I feel it is such a unknown area to most of us, I don't know what the heck the thing is capable of doing.

I think most of us have extensive auto experience. I grew up in the business with my father. Doing brake jobs since I was 10 (not telling my age) and much more. Changed everything under the sun in my Datson 280ZX and most of the brake parts. That car will launch you thru the windshield if I stop hard. Never needed any help, things were straight forward.

What the heck is going on with the corvettes? I have never seen more wacko problems with brakes in my life. To many parts changed with no improvement. That is not a methodical way to do things. Brakes should be an easy system to troubleshoot and repair. I keep thinking there must be a common link to some of these problems, like bad braking but everything individually looks good.

 

Hmm, I recommend taking it to Midas for a check, which is free, and have
them bleed the brakes. At least you can see if they do something different, or if there is air in the system. Steve

 

i should have checked but, what year do you have again?...as in my previous post, i have no rubber hoses affixed to the m/c in my 88 coup, just the hard lines and my m/c is dual resovoir....

it sorta feels like i have little or no rear brakes but again, i am NOT sure. i got really busy today and didn't have time to converse with vette guy at a local dealership...may try on tuesday......

i never had this problem with brakes at all EXCEPT 1 time with my 81 corvette but, that didn't have abs. in that car i had little or no brakes too so, after a bit, i replaced the external proportioning valve, re-bled, then had brakes that would send you through the windshield!.....

i have inspected all the hard lines and all is well.....i hate when i drive my toyota because when i go back to the vette, i am severely disappointed (in the brakes that is!)...have you tried to disable the abs to see (if anything) it would do or react?

 

94 - I have had that thought about the ABS and many more but I have no clear path on what my approach will be. Trying to figure what will give me valid information. The ABS seems to work fine. I can't lock the wheels on pavement but on dirt all the normal things happen. Pedal comes back at me, I can here the motor run and the lights come on. Before I get to aggressive on the ABS I need to read some more to get a plan. But in the mean time I thought I would really rough up the rotors and pads just to see. I have had someone stand on the brakes while I looked at the lines, and saw nothing strange.

 

Not sure if this is true to C-4's, but it is to C-3's, and so far only one person (steve40th) has mentioned it in conjunction with a C-4, but he also says his brakes work fine now, so maybe it is true of C-4's as well. When bleeding the brakes by the pumping method ,the proportioning valve in c-3's will move to block off the side that has air in it, thereby negating any amount of bleeding you do by keeping air trapped in the valve. The "correct" procedure to use (as explained by a couple of different Corvette tech's with about 70 yrs experience between them) is to do your brake work, making sure not to touch the brake pedal after you start so the proportioning valve will stay centered, and when your done, gravity bleed the system one wheel at a time, starting with RR, LR, RF, and LF. If you do accidently un-center the Proportioning valve, you must then Reverse bleed the system (I did this by using a pump type oil cal full of brake fluid with a 1/8" vaccuum hose over the end of it and the bleeder screw tip so I could still get a wrench on it. then force fluid backwards through the system to the master cylinder reservouir, making sure you have room in it to prevent overflow. Also, make sure the cap is on loosely to prevent splashing fluid from getting anywhere you don't want it. Reverse bleeding and gravity bleeding have a shared advantage, you can do them both alone. Also, when reverse bleeding, the fluid and air are moving in the direction the air naturally wants to move in, making it easier to remove the air from the system. This "might" work for the ABS as well, but I've never tried it so I don't know.

Note: As I said before, this is a C-3 procedure that should work on C-4's, but if anyone knows differently, please post so I don't steer him wrong!

 

Exciting to see everyone who has brake problems! I too see im not the only one in this boat. I put a new MC in and new synthetic fluid. Only to bleed my system 5 times and still have a somewhat hard pedal. I bench bled mc, installed, and bled again.. Then did the standard bleeding procedure for all wheels... Each time i do it, the braking improves. Guess I will need to do it a few more times.

Another point - never noticed how many ppl in C4 tech that were from Orlando.. I too live near the west oaks mall..

 

MAYBE IT IS SOMETHING IN THE WATER DOWN HERE IN ORLANDO!....last i remember from another thread pcolt had "chimed", he was going to try an upgraded brake pad. i wonder how he made out. i have tried 2 sets (or was that 3?) of stock brake pads and my brakes are still crappy!! pcolt, any results?