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Old 03-15-2006, 08:33 PM
Badkitty Badkitty is offline
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69 chevelle disc brake conversion problem

Ok...so i decided to convert my old drums in front to disc. a friend had done the same with his el camino not long before. He got his parts from a junkyard off a corvette. Everythign worked and he even kept his old single resevoir master cylinder and did NOT change his proportioning valve. He also used same old power booster. dont ask why, but it all still worked great

My parts came off 69 chevelle SS...hooked it all up. Got a ns MC unit for SS from kragen. NO booster tho.

Now the first time i did all this and bled brakes, the rear worked great and the front did not work. Pedal went half way then rear grabbed.So i bled 4 more times and still same deal. So i went and got another MC unit, for same car, yet on this one the lines were reversed. by that i mean this : my front line is threaded 1/2'' and rear is 7/16'' so on first MC unit the front line went to rear(close to firewall) hole and rear went on front hole. Well this new one is backwards, front line hooks to front and rear to rear. This second unit NONE of the brakes worked. No matter how many times i bled them.

So i bought a THIRD unit , again for same year and make. This one came like the first one and again same thing happened.Rear brakes work, front do not.

How can my friend's work and mine doesnt ? remember he did NOT change his P valve and had old resevoir. What do you guys think i need now ? im stumped. Do i NEED to change P valve that mounts to the body or get an inline adjustable valve. I have never attemped this before.

I know thats alot to read and take in, but ANY help would be GREAT!! thanks.
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Old 03-15-2006, 08:41 PM
dougbfresh dougbfresh is offline
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Maybe this will help, Stainless Steel Brake is a great outfit:
http://www.superchevy-web.com/tech/03s6sc_ssbc/
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Old 03-15-2006, 08:45 PM
Badkitty Badkitty is offline
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ok i did most of that....my question now is does the P valve on the REAR lines affect the front at all? or just limit to GREATER pressure ,the new MC produces,to the rears.?
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Old 03-15-2006, 09:04 PM
dougbfresh dougbfresh is offline
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That would be my guess, but I'd call Stainless steel Brake and tell them where your at and see if they have a proportioning valve for your application. An adjustable one is probably a good option in your case to try to tune it the way you need since it sounds like your rear brakes are getting too much pressure too soon.
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Old 03-15-2006, 09:09 PM
Badkitty Badkitty is offline
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well its not that they get it too soon...my pedal will easily go half way down,as if nothing was hooked up, then is starts to get stiff for rear. the whole problem is the front get NO pressure at all. period. There is no air in the lines or nothing after 6 full bleedings.

do you happen to know how the lines should arranged on the MC unit? like front lines hook to rear hole(closer to firewall) and rear to front holes? that was the other thing that was confusing. i didnt know which way was right as i got 3 different units and 2 were reversed from the stock one i had for drum
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Old 03-15-2006, 09:31 PM
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justen justen is offline
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You may need a valve, The el camino's alot of times came disc brakes, so they were interchangeable from disc or drums, But I'm a bit skeptical about the master cylinder if the old style will work for sure or not. I guess it was me, I would get my thread size off the master cylinder reservoir, and go to a hardware store and buy a plug, (there cheap couple cents) and plug off the rear brakes, and then try and see if your front brakes and master cylinder creates enough pressure. If it does, then most definitely need a adjustable valve, if not then your gonna need a master cylinder off a different car like a 74 chevy nova or some aftermarket place. Make sure you have no lines that are kinked or collapsed.
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Last edited by justen; 03-15-2006 at 09:34 PM.
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Old 03-15-2006, 09:40 PM
Badkitty Badkitty is offline
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alrgiht cool. I will try the plug thing. my problem is im selling the car now, after owning it for 10years, but i dont want to sell, obviously , in its current state. So i cant afford to buy too many parts to try to get it working.

I am sad that i have to sell, but the last time i drove it was 4yrs ago when gas was $1.05 a gallon. Now its $2.55 and the car gets 6mpg. not too mention i dont make as much oney as i used to, im having a car, and i bought a house. So i cant afford to finish the car, as everything i need now costs more than $600 a pop.
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Old 03-15-2006, 09:47 PM
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When you get done with your experiment, give us a update what you have learned. This way you can kind of trouble shoot and find out what it really needs.
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Old 03-15-2006, 10:40 PM
Racerock Racerock is offline
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Without getting into it too much:

-Adjustable prop valve in line with the rear, after the factory valve

-Make sure the large reservoir goes to the front

-There are some factory valves that for some reason require you to go back to one of the rear drums, after bleeding the front, and crack them for one pump. After that, the brakes tighten up.

(happened to me on my parents caddy)

-If, after bleeding the rear, the brakes seem fine, and then you go to the front, and it is like there is a ton of air in the system, try the above.
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Old 03-16-2006, 11:10 PM
Trader Ray Trader Ray is offline
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You did not mention bench bleeding the Master, have you done that? Also, some will be surprised to know that you can over center the proportioning valve by bleeding so many times. Under the rubber plug on the prop valve there is a pin that protrudes when the brakes are applied, have some one hold the brakes down and push the pin back and see if that helps, I never heard of that untill I lost brakes on a s10 I had years ago and it worked on that vehicle. Of course brakes are very important so after anything you try that you read anywhere make sure they are right. I would hate to read you have a fender bender at the end of your driveway.
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Old 03-17-2006, 12:34 AM
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You should have been able to swap from the SS with little trouble-it seldom seems to work that way though LOL.Thing is if the donor car has power brakes you need the booster and the rod from the brake pedal.Can use a manual brake cyl if the cup depth or rod length matches.There were a lot of configurations in the same year so it's important to match as much as possible from donor car.

Good point about the plunger in the factory prop valve.You have to hold it out to bleed the front brakes.Going over center can be an issue also-if pushing the pin back in doesn't work sometimes you can pop the brake pedal real fast and it'll reset.Usually the large reservoir is for front brakes and usually the large line is front.It really sounds to me that you have the wrong master cyl or rod length.There should be around 1/16" to 1/8" ballpark clearance in the rod to piston.You can measure how far the rod is from the firewall and then how deep the M/C piston is from the back side of the bolt flange to get an idea,or put a small piece of clay in piston and bolt M/C back on.Then remove and see how much of the clay it got.You should use the prop valve from the disk brake unless you use the aftermarket valve(I don't know anything about that one).Make sure you hold out pin to bleed and check rod clearance.

Tim
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Old 03-17-2006, 12:49 AM
Badkitty Badkitty is offline
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well first im going to try pluggin the REAR out on the M/C..and go from there. Its the simplier one to start with.

Whole pedal rod length thing, would that really affect it to the point of the REAR working great but absolutely NO pressure in front? I will then check on this pin on the P valve. i just NOW remember when i first got the car i had to replace m/c but couldnt get front to work..at that time i just paind a mechanic $80 to bleed it. I have no idea what he did. I've bled brakes before and worked fine. just cant understand why im having such a hard time with these.
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Old 03-17-2006, 01:39 AM
firebird79455 firebird79455 is offline
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You're right about the plug to see what happens.Just be careful about the type-you don't want to damage the inside flair on the M/C port,you need a tube or flare type plug.

Yes the rod length is important and any extra play loses a lot of pedal travel.Is it causing the problem?I doubt it,but I would check it before I went too much farther.If you aren't using the booster-you can probably feel it by pushing pedal by hand-an inch or so at the top is good ballpark.

Brake systems are totally matched from the pedal to the wheel cyls.Any time you adapt a different part you have to match whatever parts may be affected.Unless you buy an aftermarket kit-a donor car sitting right next to it is the absolute best way.

Shame you have to sell the car,I had a 70 Elk for about 20 yrs.Would still have it but it rusted faster than I could fix it.It was a constant battle.

Keep us posted

Tim
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Old 03-17-2006, 08:04 PM
Badkitty Badkitty is offline
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i have another important question. i know that the LARGER resevoir and brake line is for the front brake , does it matter where this set is on the MC unit?

Something i forgot to add...was..the front brakes actually work enuff, to keep from HAND turning the front wheels...yet u feel nothing when car is moving. I just remembered this and hope this significantly reduces the solutions to my problem

i just went ouside and looked at what i've got. this is whats confusing me....the LARGER line(REAR BRAKE LINE) is connected to the smaller resevoir and is closest to the firewall. The smaller line is connected to the LARGER resevoir and is further from firewall. Now since these are different sized threads its impossible to install wrong. yet is possible i got the wrong MC unit AGAIN.

Another question i wanted to know is, im not going to use a power booster. Engine produces 7inches of vaccumm at idle. Yet i cannot find a MC unit for MANUAL front disc. All units for front disc are for power assist. Does this make a difference.

i really appreciate all your feedback and the speed at which u do. thanks.

also could something like this help my situation? since im using the old drum/drum P valve? the only reason i didnt change was my friend didnt either and his worked fine.didnt even install a adjustable valve either.
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Last edited by Badkitty; 03-17-2006 at 09:14 PM.
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Old 03-17-2006, 10:33 PM
Trader Ray Trader Ray is offline
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Just a thought, I have had several s10 pickups with non power front disc brakes. You may find one for it at a junk yard cheap. I would say that for sure that the prop valve is different between drums and disc. The placement of the large reservoir would not matter as I have seen different configurations on various vehicles. That is what the prop valve does.
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