Brake Conversion issues.

[Dynamo Dan]

Figured I'd start a fresh thread in the correct category, of this ongoing hair pulling fun. 

1970 Monte Carlo, 383 Stroker, Turbo 350, full disk conversion. New Booster,new vacuum pump directly connected to booster.  We replaced the master with a Corvette Dual and a disk/disk Proportion Valve. Bench bled, vacuum bled, and manual bled brakes, we are 99% sure air is eliminated. 

Car off 2-3 pumps brakes are nice and solid. Hit the key to turn the vacuum pump on brake slowly sinks to the floor. Clamping off the rear brakes seems to improve this but it will still slowly sink. 

Master kit is from Southwest Performance, 1" bore. I've heard good/bad about their stuff. But it showed up fast and I'd heavy and looks good. 

Being that this was a rear drum car, it had the little valve on the side of the master which was in the front brakes, which I removed when I installed the prop valve in place of the distribution block on the frame rail. I redid the flares on a couple lines so they correctly hooked up with the proper fittings. Inverted flare on everything. 

So dumb question here. The line going from the master to the prop valve is quite large compared to the front and the line running to the rear is also a larger line. Do I need to replace this lube with smaller to increase pressure? Or would installing. 2 pound Residual value in the line help eliminate the drop and squishy pedal..

 

I'm no brake guy. At this point I'd be slapping the rear drums back on. Lol!!! 

 

Thanks everyone. Big help so far. 

[jft69z]

Decreasing line size will do nothing to 'increase' line pressure. System pressure is system pressure.

I left the line sizes as is when converting to 4 w disc, no issues. You shouldn't need a residual valve either, unless the master was placed in an odd location, like a street rod or something.

I did pressure bleed my brakes when I had some air issues, did get a few more bubbles of air out of the system. (I usually vacuum bleed, unless that isn't completely effective, or I suspect there are air pockets left).

[Dynamo Dan]

Master is in stock location in firewall.

Maybe let it sit again and try bleeding again. Never fought one like this. It's got me stumped. At least now if you hold the brake the vacuum pump cycles on them back off. Old master it would run forever if you held the brake.

 

I did also adjust Freeplay a bit on the push rod. Forgot to mention that. 

[cny first gen 71]

I'm not really familiar with conversation or vacuum pumps but normally if your holding light pressure on brake pedal and it fades down its usually a bad master cylinder, on stock systems anyhow. 

[Dynamo Dan]

This one will pump solid with the key off/pump off. Hit the key to trigger the pump with your foot in the brake and I expect a bit if drop but not clear to the floor. It did this with the old master as well. If line size isn't the culprit I'm down to think we have a rotten booster. I'm getting pretty confused at this point as well. 

[jft69z]

Usually a symptom of a bad booster is a hard pedal, all the time. One test is exactly what you are doing, key off, hard pedal, engine run (or in your case, power up vacuum pump), and the pedal should drop a bit.

Check for tubing leaks too, inspect every one real careful. I'm sure you've done it, but it may only weep out when you have a lot of pressure on the system. Like Steve mentions above, if you have a creeping pedal, there is a leak somewhere (or air still). Either in the master itself, or someplace else in the system. Could be a tube fitting, caliper piston, etc. In my case, I had a slight leak, at pressure from the front caliper plugs at the bottom, where a bleeder would normally go, (they were drilled at both locations, top & bottom). 

Freeplay is an often overlooked adjustment, glad you checked it. Should be .020" between the booster pushrod & master cyl piston pocket, in most cases btw.

[Dynamo Dan]

We gained ground once I had the Freeplay figured out. He had just bottomed out the adjustment as it was on the old booster. I probably adjusted it out 1/4" to get about 20 thousandths Freeplay. As far as the booster to master I don't see any adjustments there. I did also have him hold the brake and I cracked the lines at the master after bench bleeding and got a bit more air out, and this master has plugs on the opposite side as well I verified were tight no leaks.   I've been all over the car and can't see any leaks at any fittings but I do hear an odd noose when he applies the brake I think is the proportion valve adjusting, or fluid going thru the crossover since it lays on the cross member so I'm hearing it.  Pistons and pucks all seem square to the rotors, fronts are 2 Piston Wildwoods backs are unbranded single piston with sizable pistons and the lousiest e brake setup ever. And I've cranked on the arms and pumped the pedal so much it's crazy. I even had to add a spacer to the ebrake cable under the floor to get enough adjustment to properly set the e brake but even then it's going down 6-7 clicks off it stop to lock the brakes. 

There was a note that if the e brakes were not properly set you will have little to no brakes so I went back thru even used a pry bar and pushed the pad simulating braking and having him pump the ebrake to see it it would go to the next click of adjustment. No luck.  

One thought and I doubt it matters is how the rear brake line has to make a small loop to go from the fitting to the flex line to the banjo fitting. As I had him push the pedal when I had the bleeder open to see what kind of pressure we had. And sadly it was minimal pressure. But the bleeder is fairly small on these.  I need to see if my other buddy found his pressure gauges and maybe see what kind of rear brake pressure we have.  

I am pretty sure it's something now in the back as if I clamp off the flex line from the line to the axle, solid brake, and minimal movement when the booster hits. I had to head home for dinner so I gave up for the day.  

 

I will take some pictures and upload the pics tomorrow. I have to run down and pick up the new one wire alternator, and figure out how to bypass the Voltage Regulator and keep the idiot light on the dash functional. (I'm starting a new thread in that section as well later). 

[jft69z]

You may be on to something with the rear calipers & the e-brake adjustment being a possible cause. If the pads aren't close to the rotors at rest, it'll take a lot of pedal travel to get good brakes. Just something else to consider, clamping the flex lines can cause internal damage that you may not see, and could cause other troubles. If and when you get everything figured out (and you will), if it were mine, I'd consider replacing the lines just to be safe.

[Dynamo Dan]

The pads are lightly dragging on the rotors when released. But could be tighter I guess without any issues. 

I was using a special hose clamping pliers but definitely it's a 50+ year old hose. Was only going as tight as necessary. I wonder if the hose itself has internal restrictions due to its age and with what little was being forced out with the pedal press. Definitely want to get my hands on that gauge now. 

 

Thanks again. 

[jft69z]

Any clamping of the hose can cause internal damage, generally not recommended. For troubleshooting purposes, it's one way to narrow down your problem, just something to think about replacing down the road as a safety consideration (especially if they're 50+ years old).

[jft69z]

11 hours ago, Dynamo Dan said:

As far as the booster to master I don't see any adjustments there.

Some have an adjustable pushrod in the booster/master cylinder area (mine didn't). Not too easy to find anymore either... I ended having to cut mine down a bit when I replaced everything, as the master was slightly engaged when everything was tightened down. If you look directly in the small holes on the bottom of the master, you may see the piston slowly move forward as you tighten the master cylinder mounting bolts down, not good. Get a real bright light to see down in there....

They make a measuring tool to check that clearance, but I found that unless the pushrod is exactly the same diameter as the measuring rod on the tool, the clearance will be inaccurate (the rod will travel further in the machined hole in the piston if it's thinner than the booster's actual rod).

 

https://www.amazon.com/Power-Brake-Booster-Adjustment-Tool/dp/B079QGXY55

 

[Dynamo Dan]

Going to have him turn it over to a professional shop on the brakes. Did some more reading find the rear brake kit is a Jegs Special, no name calipers. And low and behold they say use a 1 1/4 master is recommended. But I dropped off the alternator as I had other engagements today hopped in and checked the brake pedal back to sponge and wouldn't pump up. No evidence of leaks. So I'm pretty well done trying to figure it out and stick to electric stuff and fabrication. Lol!! Thanks JFT69z for the help on both threads.  

[jft69z]

You're welcome. Keep us updated on any progress or resolution to the problems, it may help one of us down the road.

[cny first gen 71]

8 hours ago, Dynamo Dan said:

Going to have him turn it over to a professional shop on the brakes. Did some more reading find the rear brake kit is a Jegs Special, no name calipers. And low and behold they say use a 1 1/4 master is recommended. But I dropped off the alternator as I had other engagements today hopped in and checked the brake pedal back to sponge and wouldn't pump up. No evidence of leaks. So I'm pretty well done trying to figure it out and stick to electric stuff and fabrication. Lol!! Thanks JFT69z for the help on both threads.  

Dan be careful where you take it, you dont want anyone that's going to start throwing parts at it hoping they get the right thing. Try and find a shop that's familiar to disc brake conversions. Good luck with it.

[Dynamo Dan]

Thanks. Thankfully we do have a few good shops around here. Had a similar issue with another I helped with but it was Hydroboost that one local shop was able to sort out. 

I'm honestly thinking we have a restriction somewhere in the rear brake line someplace. I have a pressure gauge that screws on the bleeder I'm going to try today when I'm redoing the new alternator harness 

[jft69z]

5 minutes ago, Dynamo Dan said:

I'm honestly thinking we have a restriction somewhere in the rear brake line someplace. I have a pressure gauge that screws on the bleeder I'm going to try today when I'm redoing the new alternator harness 

I have a snap-on brake pressure gauge set that I used when I was working on my system. I was taking readings with no vacuum assist, and then with the vacuum applied. It'll be interesting to see what values you come up. Let us know what numbers you get. Thx.

[Dtret]

If you pump up the pedal pressure then open the rear bleeders you should get a relatively equal blast of fluid in your face. If not then I would look for a restriction. But if you’re running original hoses ..... If you put rear calipers on then you only have one hose left to replace. I’m assuming that you put a new line kit on the rear axle housing with the conversion 

[Dynamo Dan]

I got the alternator in and the regulator conversation done about the time the owner got off work. He wanted to drive it so we tested the brakes and well it will about put you thru the windshield from 50, but won't lock them up, said he will live with it. But I did mention if they go soft I'd be changing that last hose from the Hardline to the axle block. As it was a bit weak when you open the bleeders. 

[Dynamo Dan]

Figured I was finished with this car but still having some issues. One I'll never install a Sniper unit again, total garbage, think it has itself sorted out cycle the key and it loses its mind.

... 2 the brake thing is ongoing. They are okay... Not spectacular. But the owner is wanting to know if we add a vacuum can of it would help the added vacuum pump not run when you have your foot on the brake at a long light. It pumps up and shuts off when you first start as expected, but one press of the brake and it will just run till you release the brake. 

[MC1of80]

Then there is a vacuum leak somewhere. My pump only comes on when I have low vacuum and shuts off at required vacuum. Even with my foot on the brake pedal. 

Check the booster. Sounds like it leaks with pedal pressed. 

[Dynamo Dan]

That's my guess as well and confirms it. It shuts off white your foot is off the pedal and originally would run a few seconds and shut off with the brake on, but when I swapped to that Corvette Master and cussed my way thru that, it went back to running with the foot in the pedal.  Thanks.