Disc Brake Conversion Failing

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Son2PopsCuda

Son2PopsCuda

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Hey Fabo Fam's, it's been a long time and A LOT has been done to the Barricuda. I will post plenty of pics of whats been done and also post all of the parts that are up for grabs. But I do have a question for anyone that can help. The car is 67, I did a 68 disc brake conversion up front. the brakes were stopping but not locking and really doesn't feel much different from drum/drum application and the pedal does feel pressure. I replaced the drum/drum MC with a disc/drum MC and also replaced the stock distribution valve for what I think would be the correct proprtioning valve. Welp after all of this only one wheel is locking and it happens to a rear one at that. All of the wheel come to slow stop except the passenger rear. Pleeeeaaase help. MC was bench bleed, no air in the system (I've bleed and bleed the system) new shoes in the rear, new pads up front, new everything and no locking. Any suggestions?
 
Is it power or manual? Which master cylinder? Most have better success with manual using the 15/16 bore master cylinder. It produces more pressure than the 1" bore and usually has a greater assist with manual brakes.
 
If you're locking a rear, you messed something up.

How about pics of your setup?
 
RustyRatRod said:
Is it power or manual? Which master cylinder? Most have better success with manual using the 15/16 bore master cylinder. It produces more pressure than the 1" bore and usually has a greater assist with manual brakes.
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Not sure what bore? it is manual and was told it's for disc/drum application. it's from FVP off of RockAuto.

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That doesn't look like a disc/drum master cylinder. Are the front and rear reservoirs the same size? If so, it's drum/drum.
 
jos51700 said:
If you're locking a rear, you messed something up.

How about pics of your setup?
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the rear bowl on MC has to be filled when I bleed the front brakes so I though the setup was correct being that the front brakes are being fed from the correct bowl.

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RustyRatRod said:
That doesn't look like a disc/drum master cylinder. Are the front and rear reservoirs the same size? If so, it's drum/drum.
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thats exactly what I was thinking, I called up the so called manufacturer stated that the product number was indeed for a disc/drum application. what's more interesting is that the original MC actually has a significantly smaller bowl up front and it's a factory drum/drum application. the old style with bolt down the middle of the wing on the cover.
 
Son2PopsCuda said:
thats exactly what I was thinking, I called up the so called manufacturer stated that the product number was indeed for a disc/drum application. what's more interesting is that the original MC actually has a significantly smaller bowl up front and it's a factory drum/drum application. the old style with bolt down the middle of the wing on the cover.
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I don't care what the online or voiced description says, I think it's wrong. Call Dr Diff. He can set you up with a correct one.
 
RustyRatRod said:
I don't care what the online or voiced description says, I think it's wrong. Call Dr Diff. He can set you up with a correct one.
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Would a car without a proportioning valve run a larger resivor to increase line pressure to the front? Totally Spitballin' here. Just wondering.... but yes, these people MAKE mistakes, and even sell crap that dont work. Knowingly....
 
Ironracer said:
Would a car without a proportioning valve run a larger resivor to increase line pressure to the front? Totally Spitballin' here. Just wondering.... but yes, these people MAKE mistakes, and even sell crap that dont work. Knowingly....
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**** if I know. I'd never try it. Brakes are one thing I want right. You hear what I'm sayin? lol
 
Ironracer said:
Would a car without a proportioning valve run a larger resivor to increase line pressure to the front? Totally Spitballin' here. Just wondering.... but yes, these people MAKE mistakes, and even sell crap that dont work. Knowingly....
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yeah I'm definitely not going to find out and I also agree with them selling crap, hell I called the so called manufacturer and they don't even make the part only sell it. It would be the same as Wally World selling brakes with there label and not knowing who actually made the part.:mad:
 
RustyRatRod said:
**** if I know. I'd never try it. Brakes are one thing I want right. You hear what I'm sayin? lol
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Yessir! As much Time, Hard Work, and what Lil Cash some of us have, the Thangs better stop when we want em to!!! Not to mention, the fact that we ain't scoring parts like we usta
 
Ironracer said:
Yessir! As much Time, Hard Work, and what Lil Cash some of us have, the Thangs better stop when we want em to!!! Not to mention, the fact that we ain't scoring parts like we usta
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EXACTLY!!! Someones giving me a refund for an unusable part. I already had one, I don't need two.
 
Son2PopsCuda said:
yeah I'm definitely not going to find out and I also agree with them selling crap, hell I called the so called manufacturer and they don't even make the part only sell it. It would be the same as Wally World selling brakes with there label and not knowing who actually made the part.:mad:
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Wow, that's Crazy! Sub contract Crap. Probably Xinjiangese
 
The master cylinder decodes as a 1" bore, which should be correct for a factory KH disk/drum system. The larger reservoir does not change line pressure at all, the line pressure change comes only from the bore diameter. The reservoir split is different for a disk/drum master cylinder because each type of brake requires a different amount of fluid volume to activate. So the line pressure out of the master cylinder should be the same for both ports, just backed by a different volume so it doesn't suck air. The combination valve will change the line pressure balance front to rear.

Other than changing the master cylinder and distribution block, did you do anything to the rear brakes at all? Because locking one wheel in the back is only possible with trapped air, a brake line issue, or a brake adjustment issue on that side. The master cylinder and combination valve sends the same pressure all the way back in a single brake line, so, to have one rear brake lock and not the other means the issue is on the rear brake side of the line split at the rear axle.
 
So I just read that a metering valve allows the rear brakes to engage first and than the front brakes after a predetermined pressure. The proportioning valve I put on has this metering valve. I'm set it up without the metering valve and let you guys know the end result. :thumbsup:
 
Brake fluid or gear oil leak on the shoes can cause a single wheel to lock early.
 
72bluNblu said:
The master cylinder decodes as a 1" bore, which should be correct for a factory KH disk/drum system. The larger reservoir does not change line pressure at all, the line pressure change comes only from the bore diameter. The reservoir split is different for a disk/drum master cylinder because each type of brake requires a different amount of fluid volume to activate. So the line pressure out of the master cylinder should be the same for both ports, just backed by a different volume so it doesn't suck air. The combination valve will change the line pressure balance front to rear.

Other than changing the master cylinder and distribution block, did you do anything to the rear brakes at all? Because locking one wheel in the back is only possible with trapped air, a brake line issue, or a brake adjustment issue on that side. The master cylinder and combination valve sends the same pressure all the way back in a single brake line, so, to have one rear brake lock and not the other means the issue is on the rear brake side of the line split at the rear axle.
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I haven't done anything different. bleed the MC, bleed the Front, Bleed the rear. there wasn't any air spitting out any of lines at the time of bleeding the system.
 
Son2PopsCuda said:
So I just read that a metering valve allows the rear brakes to engage first and than the front brakes after a predetermined pressure. The proportioning valve I put on has this metering valve. I'm set it up without the metering valve and let you guys know the end result. :thumbsup:
Click to expand...

Yes, that is true. But, like I said, that's BOTH rear brakes. If only one is locking, that problem is between the T block on the rear axle and the rear brakes. Even if the metering valve is messed up, it would effect both rear brakes equally. It sounds like you have more than one issue here.

Son2PopsCuda said:
I haven't done anything different. bleed the MC, bleed the Front, Bleed the rear. there wasn't any air spitting out any of lines at the time of bleeding the system.
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The metering valve requires the brakes to be bled in order, so that the metering valve sets correctly. Passenger rear, drivers rear, passenger front, drivers front is the correct bleeding order.

But even if the metering valve were misadjusted, it would effect both brakes equally. In the rear at least you have one problem that's between the "T" and the rear brake. Air, brake line issue, brake line adjustment or contamination.
 
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