Rear disc update once again

[swervin ervin]

OK. Here goes. This is for anyone who is wondering where I'm at with this and also, maybe someone can help me with my problem.

First let me state, I'm no dummy. I can bleed brakes and understand how it all works. So, with this said, here's my problem.

I've got everything hooked up. My new custom park brake cables came today. Went on great and they work fantastic. This isn't the problem. The problem is I can't get a good pedal, no matter what I do. Here's what I've done. First, I used all new parts. Disc/disc master cylinder, disc/disc combination valve, 80-85 Seville calipers. The whole nine yards. I have bled everything, many, many, many, times. Bench bled the master, even called the company I bought it from and had them send me another one. So, I'm pretty sure the master isn't the problem. I even went to Advance and bought some cheap regular calipers made for a Monte Carlo to try, thinking it may be the Seville calipers. Still nothing. Called the techs at Master Power Brakes, where I got the master can valve at today. He said it may be my initial park brake adjustment. Tried his suggestions. Nothing. I'm about to pull out what hair I have left here.

The only thing I've not changed that maybe could be causing this is the new combination valve. I've searched everywhere on the net I can think of trying to find a valve off a 77-78 Seville, which had 4 wheel disc brakes. I can't find anywhere that sells these things. If I could find one local, I could try it and if it fixes my problems, could send the brass one I bought back for a replacement. I could also take the Seville valve back for refund too. I hate to send it back without knowing if it's bad. I already did this with the master. I plan to call them tomorrow and see what they say about the valve.

I'm no expert on combination valves, but I'm thinking it may not be allowing enough pressure to the rears. This is a disc/disc valve and is supposed to take the place of using an adjustable proportioning valve. For sure, I know there is no way any air can be in the lines or calipers. I've bled them to many times. I've bled the calipers on the brackets, off the brackets, upside down, sideways, and any other way you can think of. I've gravity bled, vacuum bled, done the two man bleed job with the peddle. Even bought a one man bleeder kit. Pretty neat little item. A plastic bottle with a magnet on it. You hook it up and pump the brake pedal.

So, I'm at the end of my rope here. Something that should be so damn simple is driving me totally nuts. If the combination valve isn't it, I don't know where to go next. So, does anyone know where to get a valve for a 77-78 Seville at?

[plumbcut]

Hmm... I would think that at this point you should buy a pressure gauge and related fittings to where you can mount it in-line with your brake system.. first at the master cylinder pressure fittings, then before & after the combo valve, then at the calipers..

Exactly how does the pedal feel? Is it that bad? I know from swapping out a few master cylinders/vacuum boosters that I always end up with something a little different than what I started with. Not always for the better either. Did you try a test drive to see how it handles itself on the road? When you vacuume-ize the brake booster, does it get worse?

keep on truckin'. You'll figure it out eventually.

pc

[swervin ervin]

Rip, everything is new. I replaced the brake hoses on the front and the one rear last year with new rubber ones. I used stainless hoses for the new disc install at the end of the hard lines to the calipers.

I've been doing more of my research on this tonight. If this is my problem, everyone hide their guns, cause I may just blow my brains out.

I started thinking, I know this is bad sometimes. I was thinking to myself. I said self, didn't you read somewhere not to use synthetic brake fluid? Well, sure enough, I did read this. I read it on the info Master Power sent with the master cylinder. They say not to use it because it can trap air. This was plainly in the troubleshooting list they send you. Well, as luck would have it and me being so damned anal about things and not one to cheap out, I have been buying the best brake fluid Advance sells. Guess what? It's synthetic. It's the Valvoline SynPower brand.

So, here I go again. I plan on flushing the entire system tomorrow and put regular ole brake fluid in it. I don't know if this will do anything, but it's sure worth a shot. I don't put much faith in this fixing anything though. But I'm picking at straws here.

Anyway, back to your regular programming.

[swervin ervin]

Here's what I've done. I used solid plugs in the master to see if it's good. With the plugs I have a good pedal. Put the front line on with the solid plug for the rear still in. Good pedal. Hook the rear line up, real soft and low pedal. So this tells me it's in the rear side, which I knew it would be. So then, I clamp off the rubber hose at the rear brake tee. Good pedal. So, this tells me it's from the tee to the calipers, somewhere. I've got new hard lines from the tee the the stainless hose going to the calipers. No leaks anywhere. I've pretty much ruled out it being the Seville calipers when I used regular, no park brake calipers. By nature, rear calipers are a biotch to bleed anyway. But with everything I've done, no way any air should be in them. So, my thinking is the combination valve is not allowing enough pressure to the rear. It's a much longer run anyway and requires more pressure and volume than drum brakes. But, this should be no problem with a disc/disc master and valve. What really pisses me off so much is I thought I would bypass all the crap by going with the proper stuff and not trying to make old stuff work. Man, what luck I have.

I thought about getting a pressure gauge and checking the pressure. It will be next on the list is the fluid or valve doesn't fix anything.

[swervin ervin]

Oh, on the pedal feel part. It's a real low, mushy pedal. You can feel when the fronts catch. It's not the booster. It's new too from a few months ago. I've tested it and if it was bad the pedal would be hard anyway.

[ElGracho]

Mike, this sounds like a shuttle valve problem.

I've had the same problem myself, on my 87 diesel after I rebuilt the rear brakes. There is a shuttle valve in the combination valve. It's the spool that is in the center of the valve. When either the front or the rear brake system gets a leak (or is vigorously bled...) the spool will shift blocking off that port of the brake system. This allows most of the braking from the other side of the system as a backup in case of brake failure when you really need them.

To shift the spool back, you are supposed to be able to bleed the other side vigorously (the fronts in your case) to move it. When I tried that, it didn't work and my valve moved back on it's own while I was reading about what to do next.

One thing that would make me wrong, on the factory truck combination valves, when the shuttle valve spool shifts it actuates the electrical switch on the combination valve causing the 'brake' light in the instrument cluster to come on. Is it possible that this has happened but you no longer have the indication?

Hope this helps, I'm anxious to see what it turns out to be.

[swervin ervin]

Joe,

thanks for the suggestion. I called MP brakes and talked with a tech about the disc/disc combination valve I bought from them. He said disc/disc valves don't have the thing you are talking about. These are used in disc/drum valves. If when bleeding, the brake warning light comes on, all you have to do is get a pedal and the light will go out. The disc/disc valves won't stop fluid flow to any wheel or side of the system. In other words, they don't need to be reset.

My brake fluid idea above is ruled out also, I think. The Valvoline SynPower fluid is synthetic formula, not silicone. Silicone is a no-no, as it will cause all kinds of problems, so they say. But the fluid I'm using is compatible with conventional fluid, so I know it's not silicone based.

The tech a Master Power Brakes is talking with an Engineer about my problem because as he put it, he doesn't have a clue of what's wrong. I told him to join my club. Anyway, he is supposed to call me back.

I called Streetrod Manufacturing, where I bought the calipers and rotors from. Talked to Skip about it. He didn't know either but offered some suggestions to try. He said to pinch off all three rubber brake hoses and see if the pedal gets rock hard as it should. If it does, release one at a time to see if I can isolate it this way. I'm just about at the end of my rope on this deal. It's pissed me off so bad, no way am I giving up now. I will find out what it is if it's the last thing I do. Which it may be if I keep pitching fits. My heart my decide to give up.

All jokes aside, I've taken a step back to try and look at this thing from the outside. I don't have anyone around here that I know of who has done this swap. I know it's a lot easier to spot things someone else has done wrong. But, I've done nothing wrong that I know of. It's got to be something simple and I can't see it. I'm thinking maybe a air pocket has gotten in the lines or somewhere and won't bleed out with normal bleeding procedures. I come real close to buying a pressure bleeder kit, but I don't want to spend 100 bucks on something I'll never use again. But, if all else fails, I may end up getting one. For sure, these brakes will work cause I'm not giving up now.

Anyway, back to the drawing board. Wish me luck with the engineer at MP. I'm probably going to need it.

[Low87]

Originally Posted by swervin ervin

rear calipers are a biotch to bleed anyway.

Mike said biotch!

[LOHRTBT]

lol!!
Hope you get it straightened out soon Mike!

[C&C Chevy]

Originally Posted by Low87

Mike said biotch!

[swervin ervin]

Well, I think I may have found the problem. Go back and read what I said about hiding all the guns so I couldn't blow my brains out if it was something I caused. Everyone start hiding. Now before I get all excited and say for sure it's fixed, just let me say it's not complete yet. Notice the yet. I've got a ton of air in the rear lines and calipers to get out yet. My one man bleeder wasn't doing this job to satisfy me and I'm waiting until the wife and son get home so I've got some help to pump the pedal. Anyway, here's what I found today.

The tech at MP Brakes called me back and said he talked to the owner who said right off the bat for me to bypass the combination valve and try it. Said to put an adjustable proportioning valve in the rear line. Well, I go to Doug Herberts and buy a Wilwood valve. Planning on bypassing the CV. After looking and thinking about what all this would involve, I said, forget it. I have had it. I'm not about to go through all that crap. So I pull the CV just to look and see what's up. I take the outlet fitting for the rear brakes off. I'm looking and blowing with an air hose to see if something comes out. Guess what, it does. I see a tiny, white, piece of something sticking in the hole where the arrow is pointing. I pull it out. It's about 3/16" long and maybe 1/16" round. I'm thinking, what in the hell is that and where did it come from??? Then it hits me. Like a ton of bricks. Don't everyone laugh too hard.

See, when bench bleeding the master, the plastic fittings they give you were too loose or I thought so anyway. The one for the front was fine. But the one for the rear port was loose. So what did my dumbass do, Yep, you guessed it. I wrapped a little teflon tape around the threads. So a piece of the teflon came loose and went into brake line going to the CV.

Now, where is that gun of mine? I feel like a giant weight has been lifted from my shoulders. One reason I'm in here now is because I have a headache from thinking and worrying about this crap. For sure, I'll know tomorrow if it fixed it or not.

[plumbcut]

persistant bastards always prevail. this buds for you

pc

[swervin ervin]

After doing the stupid teflon tape deal, and knowing better than to try something like that, I'm not so sure about being a leader to anything except the dumbsh.t club.

Now many times have you seen me say to be careful with the tape and silicone?? Then I go and pull the stunt.

Oh well, sort of like a southern baptist preacher. Never does what he preaches. Don't matter though. If it's fixed, I can take all the ribbing in the world and grin while driving with my new rear disc brakes.

Going to take something to dull the pain right now. And no, it's not alcohol either

Tylenol works for me.

[ElGracho]

Cool, glad you found it! Now finish polishing up the article so we can all copy it...

[shavedchevy]

DOH!!!!!!! Doesn't it always seem like the littlest things are the biggest PITA. Oh well live and learn.... That is, if that fixes the problem

[swervin ervin]

I feel pretty confident it will fix it. I can tell by the way it's bleeding now. It's different than before. I have a lot of air coming out the rear bleeder fittings now, like it should be when you have all the lines taken loose.

Anyway, I think I'll see if Phoenix (Eddie) will do my drawings in Autocad for me. It sure would look a ton more professional than my scribling. If I had access to a CNC I would make brackets and sell them. The way I made mine, I'd go broke making them to sell.

[plumbcut]

time to patent the brackets and design and register 73-87reardiscs.com.... I know chvchk is pretty good w/ web design, she could integrate automated ordering, add some nice flash animations, hmmmm the list goes on & on. It might not make you rich but a little extra side money is always nice. It might make you enough to fund a complete resto-mod (whats left anyways) of your truck(S). A complete rear discs kit for the 2wd's would be VERY appealing to a lot of people...

pc

[bigblock73]

Mike, if Eddie can't/won't do your drawings, I can.

Glad you found the problem!

Get ahold of me when you finish the article so we can get it posted.

[swervin ervin]

Well, it looks like I didn't find the problem. Although it may be related to what I found. I bled a quart of fluid through the system and still nothing. It's just like it's been since I started trying to bleed from the beginning. I plan on calling MP Brakes on Monday and get them to send me another combination valve. I hope it's bad or maybe stopped up with the teflon tape somwhere. I can't see anything wrong by looking at it, but it may be possible something is wrong internally. I don't know. I'm so fed up with this crap, if I had brakes I'd drive the damn thing off a cliff. If a new combination valve don't fix it, I don't have an idea on what to do next. I have done every troubleshooting tip there is. I am at loss what to do besides a new valve.

I'm just about ready to give up and except the fact someone don't want me to have rear disc brakes. The bad part of this junk is how simple everything is to assemble. I fully know how a hydraulic braking system works. It's not like I'm learning as I go. It's about enough to make you do bad things.

Now, I won't know anything until next week sometime. Maybe this is a good thing. I sure need some time away from this mess.

[NeCrOmAnCeR]

Have you thought of using a residual pressure valve on the rear lines? It helps keep 2~10 lbs in the rear lines (2 lbs for disks). It may be possible that the calipers are pushing fluid away from them. Then when you step on the brakes the master cylinder must make up for it. Had to do this on a disk conversion on a Toyota 4WD. Just a thought. Wilwood makes them also.

This can also be caused by allignment problems with the calipers, if they are not perfectly parallel to the rotors the "spring" in the brackets will compress the calipers like when you do during a brake job. Hope this description makes sense.

[swervin ervin]

From everything I've read and heard from the ones who know about all this, residual valves are used for disc/drum brakes of course, and also are needed when the master cylinder is mounted below the calipers, as in under the floor in a rod setup.

Under normal operating conditions and installations, a residual valve will cause the calipers to drag by holding the pads against the rotors. Residual valves are needed in a disc/drum setup to keep the shoes out close the drum to overcome the pullback of the springs hooked up to the shoes. If you didn't have one in the rear line, the pedal would need to travel a great distance before the shoes made contact with the drum. When the master is mounted below the calipers, gravity will let fluid syphon back to the master, causing a long pedal. So a 2 lb. residual valve is used to stop this.

There is something not working right. No way in the world I shouldn't be able to get a pedal with the parts I'm using. I'm hoping it's the valve. I don't know what else it can be. This is the only part out of the new parts I've bought not changed.

We'll see next week if it's the problem. Keeping fingers crossed here.

Thanks for the suggestion.

Oh, forgot to add. Around 80 or so GM started using low drag calipers on some cars to help increase gas mileage. These calipers are the smaller, metric ones. These calipers must use a quick take up master cylinder or else you will never get a pedal. I asked about if the Seville calipers are low drag and was told no, by two different companies. It makes sense if they were low drag, how would the park brake work by being adjusted to .030". From what I know, the low drag calipers are only made without a park brake, as in the small metric ones used on front.

[87 STEPPER]

Mike,

Are you shure that the fluid lines in your system are of the proper size to deliver the proper flow and pressure required for there correct operation?

What im getting at is maybe the lines for the rear sys. are either too small or too big and not allowing the proper amount's of flow & press. from the m/c to the c/v or the c/v to the caliper's.
If any combination of these lines or all of 'em are the wrong size you may not ever get the pedal right.

And what i mean by the correct size is the internal diameter of the line.
Not does the threaded fitting screw into it's respected connection.

Remember you now have a totally custom system (Rear only) with a host of different component's that were not designed to complement each other and work right togeather so you may think the line size is right but they could be wrong.

Of corse i could be wrong but at this point ya don't know.

It's just a sugestion and it's a good ? to ask the eng. @ MP brakes.

Hope this help's.

[swervin ervin]

Bruce,

I have already asked them about this. Stock brake lines are 3/16" going to the front brakes all the way from master to calipers. Rear line is 1/4" from master to tee at rear axle. Then from tee to calipers they are 3/16", same as stock. I asked them if this is OK, was told yes. It makes sense. These calipers were used on stock Cadillac Sevilles with the same size brake lines.

Thanks for the suggestions everyone. Keep them coming. Even if I have thought of it or not, it helps to have more than one head working on a problem.

Tomorrow I'm calling MP brakes to get the CV exchanged. It should be at my house by Wednesday, since they are only a couple hours away from me.

[87 STEPPER]

Hey Mike,

I forgot to add in my pryor post...... you asked if anyone knew where to get the caddy valve?............. have you tried NAPA they seem to have thing's other parts store's don't.

If they don't have it then the only other place would be the junk yard.

[swervin ervin]

Bruce,

I searched every parts place you can find for this valve, even GM. I can't find it anywhere. I haven't looked at a junkyard, but the odds of finding a 77-78 Seville around here is slim to none.

Rip,

I know you can use a master cylinder from a corvette. Not sure on what year though. Really, I doubt it matters what master you use as long as it's a disc/disc master and will has the correct bolt pattern to mount to the booster. It has to have the right depth for the booster rod also. The master cylinder I'm using is a Corvette style according to what MP Brakes says.

Proportioning valve, or as it's real name is, combination valve, I don't know. There seems to be some kind of mystery about these things. First, in order to make things simple, you need one that will bolt up to the craddle, and all the fittings will fit it like stock. I don't know if any GM disc/disc valve will work or not.

Again, the only calipers I have seen mentioned with a built in park brake are the El Dorado/Seville calipers. There are several you could use without the park brake. One thing you have to careful of is not to get some low drag calipers. These were started around 1980 to help gas mileage. If these are used, you must use a quick take up master or else you'll not ever get a pedal.

Anyway, I contacted MP Brakes today. I've got another CV coming. We'll see what or if this does anything later in the week.