brake problems

[dmbturbo69]

just picked up a 93 sho last weekend and on the way home the brakes went all the way to the floor. when i got home i replaced the master cylinder. then a few days later i was driving down the road and the brake pedal went down to the floor again. I also bled them all the way around. Im going to do it again tonight and try bleading the abs also just in case.

Could there have been some air stuck somewhere in the system?

 

[CerberuS]

Make sure theres 0 leaks.

And yes , air can do a spongy-pedal to floor.

And they are a pain to bleed , only a couple bubbles can do those symptoms , has to be completely airless.

 

[dmbturbo69]

I know how to bleed brakes, I am wondering is there somehow air stuck in the abs block making its way out at startup when abs checks itself?

I bled them again tonight and man they worked great like a brand new car on my way to round lake to unlock a house, about 30 miles round trip. When i got home and got back in it an hour later they are going to the floor again. Not quite as bad as before but still pretty much to floor. I see a little fluid on top of abs block it looks like may be coming from the hose that runs from master cylinder res. to top of abs block.

 

[dmbturbo69]

Alright I have replaced the master cylinder, front calipers (because I broke the bleeder valves)

I have bled the system 3-4 times now and every time it ends up back at the floor, sometimes one hour later, sometimes a week later.
One of the times I was bleeding the shit out of it kick in abs a few times and bleed again I got the hydraulic unit/pump to leak on me a bit.
It doesnt seem like I am loosing fluid @ master cylinder.
Now the drivers rear caliper is sticking so I am replacing the hose as it is an original car has 165k.

The day after I bought the car it would not shift into gear, the fuse had popped, and I have heard the sensor on the bottom of the master cylinder to cause brakes to go to the floor and blow this fuse?

What should I do? I have a used abs block here that I had shipped to me assuming this is the issue? Should I try changing this sensor first? How could it cause the pedal to go to the floor like that?

thanks

 

[rangerj]

In order to PROPERLY bleed the ABS it takes a special tool to cycle the ABS pump and its valves. The tool sets the valves in the proper position for bleeding. If the problem is not air in the system, nor a leak, then it points to a bad master cylinder. A failing master cylinder will intermittently allow fluid to bypass the cylinder seals in the master cylinder. Did you buy a rebuilt master cylinder, or is the replacement off of another SHO? You could also have a connection that is sucking in air, such as a bleeder, or the sensor under the master cylinder. When you rebleed the system do you get more air out? Were any of the metal brake lines replaced? If so was the proper ISO style flare used, as opposed to as double flare? .Just some thoughts.

 

[dmbturbo69]

stock lines look good, no rust. The master cylinder is brand new not rebuilt. Bleeders are all good, just replaced sensor on bottom of master cyl. I know of the ABS tool and have someone who will borrow me one, just waiting to see if the sensor takes care of this issue. If not then I will put in ABS pump and use abs bleeder.

thanks