Brake Bleed'n problem

[47convert]

We're trying to help a friend finish a deuce coupe that he had (partly) built about 7 or 8 years ago and we are having a lot of trouble bleeding the front brakes. The master cylinder is a typical 4 wheel disc master from a mid 80s Vette. The rear brakes were bled without any difficulty but the fronts are a real problem. With the rears bled we get a hard pedal at about 1/2 stroke with no fluid at all in the front lines. When we bleed the front we get a small bit of fluid and a typical amount of air bubbles but it never becomes just fluid. We changed the M/C, The cross fitting ($ ported Tee and the lines from the cross to 1/2 way up the sides towards the front wheels. I tried using the Bench bleed tubes on the rear cylinder to allow more pedal travel while bleeding the fronts without success. Tried using a vacuum bleeder but it won't pull fluid through either. The vacuum gauge goes up to about 15 or 16" of vacuum and stays there for quite a while before gradually dropping off toabout 8" and it stays there - I think the leak is from the threads on the blleder not an internal leak anywhere in the system,

[bcal]

Stoopid question, but I only ask coz I've done this myself, are the bleed screws at the top of the calliper?

Or another stoopid one. Have you got the front and rear reservoirs mixed up? nearly done that once :oops:

[Dave]

Stoopid question, but I only ask coz I've done this myself, are the bleed screws at the top of the calliper?

I almost hate to admit this but I have also swapped the calipers left for right on the front of a car way back in my younger days and had a problem exactly as you describe! Ended up going to a local brake shop in despair who put it on the hoist and had a great laugh! Hey I was about 19 and still learning!

[slocrow]

I'm by no means an expert on anything but do have a few thoughts. I think that if the calipers were switched putting the bleeders on the bottom then you'd just be unable to get all the air out and have a spongy pedal. This is a all disc system, correct and are you using external, in-line residual valves of the 2# nature? Finally, does the master have an operating residual valve internally that is still functional? I'm thinking that is the problem. You effectively have two working on the same system line and I think it will lock up the rears and prevent the needed travel. Then again I could be all wet.............Frank

I can't read your drawing but are the front lines going first too the rear and then splitting and then going to the front up their own side frame rail?

[flt-blk]

I'm going to the calipers too.  Ensure the bleeders are pointed up.  Make
sure they are clean inside.

I had a 10 yr pause in building my Commander and the calipers had built
up some sludge inside.  I completley disassembled them for cleaning,
now they bleed just fine.

I suspect there was some residual fluid inside and the system sat open.  
You know how brake fluid attracts water, and the sludge was born.

[Dave]

We're trying to help a friend finish a deuce coupe that he had (partly) built about 7 or 8 years ago and we are having a lot of trouble bleeding the front brakes. The master cylinder is a typical 4 wheel disc master from a mid 80s Vette. The rear brakes were bled without any difficulty but the fronts are a real problem. With the rears bled we get a hard pedal at about 1/2 stroke with no fluid at all in the front lines. When we bleed the front we get a small bit of fluid and a typical amount of air bubbles but it never becomes just fluid. We changed the M/C, The cross fitting ($ ported Tee and the lines from the cross to 1/2 way up the sides towards the front wheels. I tried using the Bench bleed tubes on the rear cylinder to allow more pedal travel while bleeding the fronts without success. Tried using a vacuum bleeder but it won't pull fluid through either. The vacuum gauge goes up to about 15 or 16" of vacuum and stays there for quite a while before gradually dropping off toabout 8" and it stays there - I think the leak is from the threads on the blleder not an internal leak anywhere in the system,

A little trick that helps me when i bleed brakes is for the fronts jack up the rear if you have a under the floor m/c and for the rears jack up the front. It makes the system appear that the m/c is mounted higher than the calipers and rear wheel cylinders helping to remove the air.
Dave

[timkins]

One of the replies stated that maybe you had changed the reservoirs front to rear. What difference would this make? The reason I ask is mine was changed and the car still does not stop the way I think it should after I installed 11" brakes in place of the stock Mustang II that was on the car. I also installed all new brakes (drum) on the rear. I posted a message a while back for spongy brakes and this was not mentioned. Did I do something wrong??

[Bruce Dorsi]

We're trying to help a friend finish a deuce coupe that he had (partly) built about 7 or 8 years ago and we are having a lot of trouble bleeding the front brakes. The master cylinder is a typical 4 wheel disc master from a mid 80s Vette. The rear brakes were bled without any difficulty but the fronts are a real problem. With the rears bled we get a hard pedal at about 1/2 stroke with no fluid at all in the front lines. When we bleed the front we get a small bit of fluid and a typical amount of air bubbles but it never becomes just fluid. We changed the M/C, The cross fitting ($ ported Tee and the lines from the cross to 1/2 way up the sides towards the front wheels. I tried using the Bench bleed tubes on the rear cylinder to allow more pedal travel while bleeding the fronts without success. Tried using a vacuum bleeder but it won't pull fluid through either. The vacuum gauge goes up to about 15 or 16" of vacuum and stays there for quite a while before gradually dropping off toabout 8" and it stays there - I think the leak is from the threads on the blleder not an internal leak anywhere in the system,

..........

(1) I don't think the 'Vette M/C has residual pressure valves internally.  ...However, since your m/c is mounted under the floor, you may find that you will need a 2psi rpv in the front circuit.

(2) What calipers are you using?  ....On some calipers, the bleeder should NOT face upward.  See:
http://www.mpbrakes.com/troubleshooting.htm

(3) The fact that you can build & hold vacuum, without pulling fluid through, sounds like a possible blockage.  .....If you remove the lines at the caliper, do you get  
adequate volume of fluid?

(4) Are the hoses in the front circuit deteriorated to where they restrict flow and/or collapse under vacuum, or allow  air to get in?

(5) Is the piston of the m/c returning all the way (against the retaining ring) when the brake pedal is released?  ...If not, the compensating port in the m/c may be blocked.

(6) If the rear brake circuit is preventing you from getting enough pedal travel to bleed the fronts, you can open a rear bleeder and use the "hose in jar of brake fluid" method to prevent air ingestion in the rear brakes.  ......However, your method of using the bench-bleed tube on the rear circuit should allow the fronts to bleed properly.

(7) As far as I know, it does not matter if the front brakes are connected to a certain port of the m/c if it is a straight bore m/c and NOT a stepped-bore m/c.   .......Generally, but not always, the front brakes are plumbed to the m/c port closest to the pushrod.

( Any possibility that the hydraulic brake switch threads are blocking off the side ports of the cross?


Good luck, Mike.  .....Please let me know what you find, so I can learn too!

[enjenjo]

One of the replies stated that maybe you had changed the reservoirs front to rear. What difference would this make? The reason I ask is mine was changed and the car still does not stop the way I think it should after I installed 11" brakes in place of the stock Mustang II that was on the car. I also installed all new brakes (drum) on the rear. I posted a message a while back for spongy brakes and this was not mentioned. Did I do something wrong??

I had a fellow here that has been working on his brakes for 4 years, he went from Mustang brakes, to 11 inch brakes, to 12 inch brakes, two boosters, and three master cylinders, Mustang, stock Vette, and aftermarket Vette type. The best he could get was just barely acceptable, never good brakes. Several months ago, he bought yet another new booster, and master cylinder, I talked him into bringing them over before he installed them. I checked them with my handy dandy tool, and found the pushrod adjusted too long on the master cylinder side of the booster. I reset it, and he went home and installed it, the brakes are now killer. He brought over the old booster and master cylinder, it was out of adjustment too. I have installed a couple more boosters since then, and they were both out of adjustment. This is something that is seldom checked, and in my opinion, is one of the biggest problems in bad brakes. As bruce said, if the transfer port is blocked, the brakes can't be bled properly, and they will never be right.

[Bruce Dorsi]

I checked them with my handy dandy tool, and found the pushrod adjusted too long on the master cylinder side of the booster.

Frank, you've mentioned this tool in the past, but I don't recall any details of its construction.

Are you willing to share some pics or a description, or is it CLASSIFIED?

[47convert]

Thanx for all the responses, these are all very good points, but I've checked most of them and I'm pulling what's left of my hair out. . The Vette Cylinder doesn't have built in residual checks and there is a 10# check in the front line. The lines DO go towards the rear for about a foot, then thru the cross (where the brake liight switch is installed and up both sides to the front. I don't like it, but don't see a problem with it. I replaced the M/C and the cross fitting as well as part of the plumbing due to this "cross" being slightly different in configuration from the original. The calipers are typical "large" GM style and we do have the bleeders at the top. I made up some lines  and reversed the two ports (reserviors) to try it and the problem remians the same. The Vette uses the port closest to the front of the (original) car to supply the front brakes. I know that differs on some cars but this does seem to be correct. There is very little difference in the size of the two reservoirs on the Vette Cyl because , I guess, of the large disc brakes on the rear of the Vette. But I did check to make sure the lines are run to the correct port. I have wondered about the adjustment between the booster and the M/C, because on the bench we can shoot fluid across the garage, but in the car it doesn't seem to have that much effect. Tomorrow, I'll temporarily eliminate the booster and see if I can bleed them that way. Thanx again everyone for your valuable advice and thoughts. It's appreciated!

[Bruce Dorsi]

The Vette Cylinder doesn't have built in residual checks and there is a 10# check in the front line.

Mike, a 10# residual valve in a disc brake circuit will cause a problem in most cases, even with the big GM calipers.  .....Ten psi is usually sufficient to cause the pistons in the caliper to keep the pads against the rotor, causing the front brakes to drag.

If you are using a Wilwood rpv, or one of it's clones, it may be faulty.  ....If I remember correctly, Enjenjo went nuts trying to bleed brakes with a faulty rpv a few years ago.

Is there any possibility the rpv is installed backwards? ....That could account for limited fluid flow.

[enjenjo]

It's not a secret, I posted some picutres of it here a while back. I'll post more, including how to use it.

[Dirk35]

I also had the sludge problem on my front caliapers. They sat while building the truck with just cut lines (open to air). When I put them on, the back brakes bled easily, but when I went to the front brakes, I couldnt get ANY fluid to transfer through. After pumping and pumping, I thought I might have dust and moisture combined with the fluid left in, so I left both the front bleeders open after presuring up the system.

Went back the next night, and pumped again, and it shot sludge and brown (dark brown) brake fluid back the length of the entire truck on the passenger side. Took almost an enitre big bottle of fluid to get to clean looking fluid for the fronts. I ran all new brake lines and new M/C on the truck, so it came from inside the front caliapers only.

I still need to bleed them again as the pedal will presure up properly, but will be spongy after a couple of days.

[47convert]

The residual valve is in the correct orientation. I always use 10# in the front - I think I have an extra 2# - I'll swap it and see what happens - Thanx