disc brake conversion kits????????????? expert opinions?

Well I am having fitts trying to bleed this puppy. Hope I did it right?
we have a Corvette master and a residual valve. What do you think??? New connection to rear

Wdaguy:

My guess is that red valve is a 10 pound valve going to rear drums?

What do you have on the front lines? A 2 lb valve with disc brakes?

That master looks too dry around the fittings, did you "bench bleed it"?

Are the check valve installed in the correct flow direction?

Are you still having problems bleeding?

M1D

Interesting.. The Vette master was bench bled was I suppose to take something out of the master.? sounds like I need a pressure bleeder? We have been using a hand held suction type.

I may be cofused fro M1 directions page? "all you would need to do is use the Corvette master and then install the inline 10 lb residual valve in the rear brake line:".[/i][/u][/b] this was a 68 Vette mc not 65?. Do you think I need to install the Blue residual valve for thr fronts? We have brakes but squishy pedal it really doesnt pump up. It will stop but not very imppressive.

bleeders are at top. Iit has some free play. I would say it seems like the left front locks up first, but doesnt swerve or pul l because of it....??

wdaguy wrote:bleeders are at top. Iit has some free play. I would say it seems like the left front locks up first, but doesnt swerve or pul l because of it....??

do you think its ok without the 2lb valve for the fronts? I am suspecting just more bleeding?

well I took my friends advice who didnt run the 2lb.. his work great without it.. he loves the flat brackets set up????????

Many things contribute to a spongy pedal.

But first, the valve question.
Heres the rules.
Its been said that if your master had valves internally they should not be combined with other vaslve, There should be only one valve per system.

Whats not been said is only old time brake systens "That did not have an external proportioning valve" (like your 65 single line system) will have a built in valve.

Most every other master cylinder built, I dont care 65 vet, or 68 vet or what ever, If the car had an external proportioning valve, the master cylinder had no internal valves!

Reasons for valves. The most need for a residual valve on disc brakes is only when the master cylinder is gravetationaly below the calipers. You don't really need the valve for you early disc brake conversion as long as you promiss never to park your van with the front end up a steep drive way, causing the callipers to be above the master cylinder. This elevation/gravity rule also applies to the drum brakes. However the drum brakes "Require" a TEN pound valves which is intended to keep enough preasure on the sheveron style seals in the wheel cylinders to keep them sealed so air cannot get in and fluid cannot escape. The preasure must be there to keep the seals pushing tight. But not pushing the shoes against the drum too much. By the way, if you leave your drum brake vehicle in storage, be shure to pump up the brakes at least once every couple weeks or that 10 Lbs will deminish and the cylinder will seep.

I use two 2lb valves on my four wheel disc set up. one for the rear and one for the front. Best mounted at the master but definetly befor the "T" in the lines.

There should be almost NO free play in your brake pedal linkage, that equals strait up pedal loss. But you must also make sure the master is not being held slightly on. I also wrote a piece on adjusting that little cam bolt at the bottom of your pedal on the push rod. Its too much to re-write here but it is very important and can be mistakenly placed 180* out with no free play and cause about an inch pedal loss.

The number one reason for pedal loss on disc brakes is the caliper "Hanging up" on the bracket (no mater what bracket you use) I wrote about this too. You must make absolutly sure the bracket is not flexing even the slightest amount. If the bracket flexes 1/64" it will equal almost a full inch of pedal loss. The other common pedal problem is improper bleeding and incomplette bench bleading.

When bleading brakes always start with the wheel furthest away from the master. (furthest away by Line length) then the next closser and so on. First start by opening the bleader and waiting for the fluid to appear on its own at each wheel one at a time, all four wheels. Then go to pumping the pedal, again starting at the furthest away wheel. (pumping the pedal on a system that is complettly empty will often ruin the master. Vacuum bleaders are crap on drum brake systems. Remember the 10lb sheveron seal rule? Sheveron seals work in one direction only. When you try to suck the fluid to one cylinder, yes you get fluid from the master but you also suck air into the other wheel cylinder because the suction wilkl collapse the seal. You can go back and forth until you start to throw tools and cry with insanity. Presure blead is what you need. Doing it old schooll with one person at the pedal taking exact instructions from the person at the wheel, not the other way around. Make sure the drum brakes are adjusted correctly first, Improperly adjusted drum brakes steels alot of pedal.

Bleeding brakes with a factory type "differencial/proportioning valve" can have other bleeding problems caused by Lock out.

Spongy pedal. there are two basic but very different situations that people generally call"spongy pedal". Either there is air in the system OR there is a mechanical problem. (or both) You must diognose this first or you will frustrate yourself to death.
Heres how you tell, On a level parking spot with the vehicle in park, with the brakes at rest, push the pedal down ONCE! and make note of where it stops. then lift your foot and push the pedal down again right away and now make not of where it stops. Repeate this four or five times. If the pedal is stopping at a higher high each time(pumping up) then you have air in the system. If it rises on the second and/or third stroke only, then you proboly have poorly adjusted drum brakes. If the pedal always goes to the same applied (down) position then you have a mechanical problem. It is best to do this test while looking at anything except your foot or leg you can best"sence the high by feel" and re-try it several times letting the brakes rest in between trys. If you have power brakes this test should also be done with the engine off and the boster vacuum displaced by pushing the pedal two or three times to lose the boost reserve.

M1D

Ther are many mechanical problems, I discused the most commun here.

Another problem that will make for a spongy pedal (especialy with the absence of the residual valve) is loose or improperly adjusted wheel bearings. the hubs will flex while driving, as they do this they will push the caliper to and fro. If there is not residual valve keeping 2lb presure the flexing rotor will simple move the caliper pistom only firther into the caliper ( especialy if the caliper does not slide freely on the bracket) and you will then have to make up all that space with the brake pedal before the pads connect and tighten. That will make for a much lower pedal. If the wheel bearings are allowing for much more flexing do to poor adjustment the problem wil be compounder that much worse. This will be amplified even worse again if you did not clean up the hub to make sure the rotor is sitting down flat and true, or you over torqued the wheel nuts, either of which is known to cause the rotor to woble slightly, again pushing the pads away to making too much space.

M1D

Thats not a half bad idea donivan65. But I think I would not disconect the rears once you know they are right there is no reason to open that circuit again. In fact the "other circuit" being open while trying to blead the next may cause a "feel" problem and make you think you have a problem with the circuit you are trying to bleed. Factory differential valves have a piston that moves over to block the circuit that "blew a line", this willl make that "useless side" of the master cylinder still build pressure so as to provide for a decent pedal hight. The thing about a "bench bleed" is you plunge the piston deeper then it moves when installed, getting the air out of every nook and crany.

I called thems the rules cuz thats what you asked for. LoL!!

One thing I discovered is alot of people, including myself in the begining(35 +years ago) have this idea that since brakes seem big, bulky, dirty and heavy duty, the tollorances of workmanship can be slopy or the "Oh thats good enough" attitude will do. But as a mater of fact nothing is further from the truth. Heres an example of how exacting the tollorances are. Most vehicles only need loose 10 thousands of an inch thickness off the rotor and there will be insuficient rotor mass to the point of about a 41% braking efficiency loss under full braking.

Each of these mechanical problems I have addressed (like wheel bearings, caliper hang up, rotor fit/woble, adjustments and so on), each one can rob 1/8" to 1" of pedal travel if not right. Think of it, you only have about 2.5" pedal travel on good brakes and another couple inches to the floor. It only takes a little bit of carelessness in workmanship on one or two items to loose that 2" of good pedal. It dosn't take much!

I say this without prejudges, I am not commenting on any persons work here. I am saying only that my own poor work habits of the past have expirienced me to the reality of how important the small details and measurment tollorances are. I can't say it enough, attention to research, detail and a high standard of craftsmanship will make the absolute difference in saved time, money and frustration. "attention to detail" especialy fit and adjustment tollorances.


Hope this helps.
M1D

A few more bleeding tips.

Sometimes bleeding a new system is best done first by gently pumping the pedal, useing you hand on the pedal and being sure to make full strokes.

Agressive actions on the pedal during bleeding may cause other problems.

It is best to push the pedal down with the bleeder open and hold it down untill the bleeder is closed then let the pedal up, each time, rather then "pumping" the pedal a bunch of times to try and make presure and then opening the bleader.

After all air seems to be gone. pound on the brakes a few times, and push the pedal as hard as you can. These two actions will loosen any lodged bubbles. The blead each wheel again.

If either of the master reseviours run enpty, you have to start over again.

I much prefer the clear hose on the bleeder screw into a jar of fluid so I can see when the bubbles are gone. and if the person on the pedal messis up you wont such air back in.

M1D

Well your right about doing what you have to, to make it happen. When you have too many variables you sometimes have to throw out the rule book and approach the problem from a completely off the wall angle.

Just a thought here, I have not yet heard of a vapor lock type of problem before, but, I have had rear brakes un able to blead problems before. You may have had this same problem I say because what you did will fix this same problem.
I mentioned the factory style pressure differential valve (built in to most proportioning valves) that can go into "lock out". They do that when there is too much presure difference between the two brake circuits, a piston shutles to the low presure side and plugs that circuit. It is sometimes very hard to get it to unplug and re-center itself as it has no springs, it just floats. If a brake line blows under presure, or if when bleading you pump up the pedal too agressively when the fluid has not yet filled all the lines you can actually shutle that piston with so much force that it will jam to one side, especially with used valves. The circuit will be locked out and you will not be able to blead that side without re-cenering the valve. The way to re-center the valve is to open the line that is not locked and pump the pedal to get the presure happening only on the opposite side of the differential valve to push it back to center, re-opening that circuit. If you are too agressive doing this though you will likely just slam the valve to the other side and lock the other circuit out. That is the valve that also trigers the light.

M1D

Should I let the blue one go? 2lb

You should keep the blue 2lb valve. You need only one 2lb valve for both the calipers. It needs to be in the line from the master before the "T".

If you have a combonation valve that is a different story. A combonation valve is three valves in one. It has a presure differential valve, a proportioning valve, and the residual presure valve for the drums. Some combanations valves also have the 2lb residual presure valve for the discs as well. Either way you should not combine two residual presure valves onto the same circuit
If you combine two residual vales in the same circuit of different values, the valve with the higher value will dominate and the other will be useless. If you combine two of the same value, the one closest the master will function properly and the other down stream will remain dorment.

M1D

Ok I will put one 2lb for the fronts. So really there is nothing special about the Corvette master other than size? A stock double M/c would be the same?
I was thinking they had pressure valves internally.

Donivan65; you have a valid point

If someone is running a "Combonation valve" they should not have other residual presure valves in thier system.

But If the 2nd gen valve is only a "Presure differential" valve (I don,t know what it actually is) that differential valve would have to be right after the master cylinder and then the "Residual presure" valves down stream of it or it would in fact cause the problems you descride.

Usually a tripped differencial presure valve will re-set itself during bleading providing one is easy on the pedal during the bleading. But sometiimes you have to crack the line on the good circuit to get it to reset. If you pound away on the pedal trying to pump up the system you will cause the valve to trip.
The exception to this is when using an old/used valve that may have never been tripped in its past life and has some sludge in it. I have had such valves trip and jam in the triped position.

In the tripped position there will be problems bleeding, and likely unable to blead one circuit because the piston locks off the bad circuit. The system willl bleed very easily if the differential valve is kept from tripping, and that is done by using a pressure bleader at low presure or going easy with the foot and being carefull not to pump up the preasure during bleading. Bleading is all about "flow" not presure. You have to flush out the air bubbles with flow, presurization can sometimes cause intrapment of air bubbles in iregular shaped spaces.


The vet master is desired because of its lower reseviour high and the fact that the lines come off the correct side. Other then that there is nothing special about it, you could use any double master with the correct boar size.

wdaguy: what are you using for a proportioning valve?
M1D