brakes!

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fv50fv
Posts: 45
Joined: March 29th, 2009, 7:10 pm

brakes!

Post by fv50fv »

i have a old d-13 i just replaced the masters and wheel cly. got the rears to work but can't get the air out of the fronts, could the master be sucking air? anyone 's help would to a help!! thetackleshop@aol.com
Dietmar
Site Admin
Posts: 650
Joined: June 24th, 2006, 11:56 am

Re: brakes!

Post by Dietmar »

Yes, the master cyl could be stuck- however, I would look to see that the bias bar is not too tight and not allowing the rod for the front to go in when you apply the brakes. Check to see that there is free play at the bias bar and the rods that go into the masters have some free play when you apply the brakes. There should be a short distance before the rod engages.
Also, I know this is an older car- if you have rubber brake lines( as in stock), it is not uncommon for the lines to actually get clogged and no fluid can pass through. If you open the wheel cylinder bleed screw, a lot of fluid should come out when you apply the brake.

Hope this helps
Dietmar
Rich_G
Posts: 41
Joined: June 25th, 2006, 11:16 am

Re: brakes!

Post by Rich_G »

Double check that you have the correct size wheel cylinders in the front. I had a similar experience after tearing down both the front and rears and put them back together. I spent $$ I didn't have to on new brake lines and consternated over it for a while before I figured out that I had put my front cylinders on the rear (work just fine) and rears on the front (pedal to the floor). I don't recall the sizes but the narrower bore (longer travel) should be on the front. If you are pulling your hair out bleeding the brakes (finding no air) but still have excessive pedal travel you might have done the same thing.

Good luck,
Rich
FM92
South Carolina Region
SR Racing
Posts: 1205
Joined: June 24th, 2006, 1:58 pm

Re: brakes!

Post by SR Racing »

Rich_G wrote: I don't recall the sizes but the narrower bore (longer travel) should be on the front.
No. The larger bore wheel cylinders always go on the fronts! In those rare cases where you have a smaller bore MASTER cylinder IT can be used on the front.

Typically your masters cylinders should both be 5/8" bore. Your slave cylinders are 21mm fronts and 19mm rears.
Some people may use a different master cylinder bore depending upon how much mechanical leverage you have at the pedal.
Some people may use a 5/8" on the front and a 3/4" on the rear for bias purposes but it is normally acheived mechanically via a bias bar.

THe SMALLER the bore on the MASTER the more brake pressure you will have. The smaller the bore on the brake cylinder the less the brake pressure you will have.
Greg Davis
Posts: 137
Joined: June 26th, 2006, 9:55 am

Re: brakes!

Post by Greg Davis »

Because the bleed screw on the front wheel cylinders is BELOW the upper cup it is possible that an air pocket is trapped above the bleeder. Take the shoes off, remove the upper dust cover and take out the metal puck. Take something that won't damage the wheel cylinder wall or the rubber hydralic seal and gently pry the seal sideways. If you hear air escaping, that is the problem. I actually had to remove the backing plate/brake assembly, clamp the cylinders and turn them sideways to bleed the the cylinders and then re-assemble. After doing this I had a rock solid pedal. I know this sounds unlikey, but it may be worth a try.
brian
Posts: 1348
Joined: June 26th, 2006, 12:31 pm

Re: brakes!

Post by brian »

when bleeding brakes that have not had any fluid before or have had all the fluid drained you will have to use a priming method for bleeding. You will need to make one stroke of the pedal then open the bleed screw; close the bleed screw for the upstroke of the pedal. Repeat this process using the small amount of vacuum that's generated to pull the fluid to the wheel cylinder. Never use mulitple strokes of the pedal it will generate bubbles and drive you nuts. You can disconnect the rear master completely if the pedal is not making a full stroke on the front master.
The above post is for reference only and your results may vary. This post is not intended to reflect the views or opinions of SCCA and should not be considered an analysis or opinion of the rules written in the GCR.
cendiv37
Posts: 386
Joined: June 25th, 2006, 7:29 pm

Re: brakes!

Post by cendiv37 »

To add to what Brian and Greg have said.

1. As an alternative to Greg's suggestion, first try adjusting the front brakes up tight to press the pistons and seals back into the cylinder thus minimizing the volume (to be purged of air) in the wheel cyl.

2. To add to Brian's suggestion, I find I get the best, quickest results if I assume there is lots of air in the cylinder and ALWAYS start with "priming" as Brian describes it. To do this I open the bleed screw and then press and hold the pedal and close the bleed screw while the pedal is down. I do this 3 to 4 times and then check the master fluid level. Continue until the fluid is clear and bubble free using a clear bleeding hose. Looping the hose up and inch or two and then down to the catch jar/bottle makes it easier to see what's happening. I then go to the other side (same master cylinder/axle) and do the same. I check the fluid in the master on my way between sides. Once both sides are basically bubble free, THEN I go to the more typical pump it up and hold it down opening the bleeder method. It usually only takes a couple final "bleeds" per side to be completely bubble free.

By combining both 1 and 2, I think the turbulence created in the small volume of a compressed wheel cylinder is enough to get the air out of the fronts even though there is still some space above the bleed screw.

Last suggestion on brakes: Always flush your system with new fluid at least once a year. It's probably best to do it at the end of the season as part of your winterizing process, especially if you are storing your car in a cold location. The enemy of brake hydraulics is moisture. Brake fluid picks up moisture quickly and our systems are not very well sealed. Use new fluid or at least fluid that hasn't been open for more than a few months, maybe a year at most if it was well "sealed" after opening. Your cylinders will thank you for it.

Your mileage may vary as always.
Bruce
cendiv37
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