tmacie

Hey everyone, I've searched but all I have found is 1st gen related. I'd like to temporarily bypass my RWAL dump valve (under the master cyl) for troubleshooting purposes. I have a brake pedal that sinks to the floor with the truck running. the pedal still falls with all 3 rubber lines clamped. Bench bled the new MC 2 times.

My questions are:

1: Are the input line and nut and the output line and nut the same size?

2: If they arent, what sizes are they?


Thanks,
Travis

dozer12216

This has not been a active thread. ABS brake diagnois must not be popular.
Eliminating the Dump valve will not help your situation IMO.
I gather the pedal goes to floor with pressure applied over a short period of time. Even with hoses clamped. So wheel cyls are not leaking. Problem must be in MC or booster. It has had two MC you say. You know that after bench bleeding you still have to bleed the brake system, right!!!
Sounds like MC's are junk or the booster is leaking internally. Will it still supply boost after engine is shut off for a few minutes??? By the way, you ruined the hoses when you clamped them shut. The metal braiding destroys the inside lining. The hose may not leak but, will block fluid on release. The abs module cannot store fluid.

1workinman

I have a 95 it does the same thing.rebuilt master cylinder. bench bled. bled system several times. New master cylinder repeat bleding. By passed abs. New rear brakes drums wheel cylinders. Front calipers pads ect. No leaks found. The vacuum booster deforms and the master cylinder moves forward when I pressure up the system. I am sure it will not help but I am going to replace the vacuum booster with either a 97 hydroboost or one off a k30 chev. Probably a power steering pump and what ever else it takes to have some brakes for a change. I have searched on the first generation and it is a popular swap. If you ever find out what your problem is please post the cure. Jim

tmacie

Thanks for the input, All I would like to know is if the threads are the same so I can bypass it for the time being.


Thanks,
Travis

1workinman

I cut the lines and installed a compression fitting and a piece of line. Good luck.

tmacie

You couldn't find a flare union that would match the threads?

blackimpala

Unless you are talking about a different kind of compression fitting, I would never use them on a brake system.

Floyd

tmacie

I'm talking about a flare union, NOT a compression fitting.

Now, does any one know the nut/thread size for the RWAL Dump Block?


Thanks,
Travis

1workinman

I think that O Relly sells brake line fittings . Good luck

tmacie

I know where to get the fittings, i was jsut hoping to not have to take the block off and drive there to test to see what fitting and line size I need. I was hoping some one could tell me so I could just drive there get the fittings and do the work once. If no one knows by weds, I will make the sacrifice and I will post up my findings.

Thanks,
Travis

1workinman

OK if I can find the the block that I took off my truck I will try and find out for you. Jim

tmacie

Jim, that would be greatly apreciated!!! Don't go out of your way though. my situation is a little odd, my truck is 20 min from my house, and the parts stores are 20 min back towards my house so you see where its kinda a pain.


Thanks again,
Travis

1workinman

I too would like to know where to get a better supply of brake fittings> There is a web sight that does conversions from vacuum to hydro boost on jeeps and a few dodges. I talked to the guys and they are good to work with. I had thought I might give the guys a call and see if they would be willing to sell me the brakes fittings and I will buy a good double flaring tool. I am going to try to find the block today. The holidays are eating up my spare time Jim

gmctd

If you're seeing no wet leak-sign on any wheel, along the frame, or under the master cylinder, then the mc is leaking internally - 'rebuilt' ones are the worst, as water oxidizes the aluminum versions, rusts the cast-iron versions, leaving pits in the bore - new replacement piston-cup rubbers cannot seal to pits - install a new mc for best service and reliability

Low brake-pedal results when the rear wheel automatic brake self-adjusters stop adjusting - increased rear wheel-cylinder travel due to normal shoe-wear causes increased master cylinder piston travel = brake pedal travels nearly to floor B4 braking begins = can put master cylinder pistons into etched pitted area(s), causing pedal to slowly go clear to floor - worser the leak, faster the bleed-past.

Now, if the pedal is sinking to floor without being pressed, engine running, that is vacuum booster leak, or internal hydraulic leak in hydro-boost from heat-hardened seals\cups\o-rings - booster rebuild is required in either case

tmacie

gmctd,
I'd agree with you however this is the 2nd NEW MC and it does it a tthe exact same rate, and it does it at the same rate with the original MC. There are numerous threads here and other CTD sites that describe this problem to a T and it has either been a faulty RWAL valve or one with air. I have bled the RWAL very well and the problem still exists. I am trying to take the next logical step and eliminate the RWAL valve with a $3 piece of brake line instead of spending $200 to replace it on little more than a whim. I am also trying to save some time by finding out if the RWAL fittings are common ize or some off the wall size before I drive 20min each way to where my truck is vs a parts store.

Travis