I have a Master Power Brake disk upgrade on my 65 Dart. I did a 8 1/4" rear upgrade this weekend and, although I didn't know it, the drive shaft has to be shortened so I iwll have to wait until Mon to get it to a driveshaft shop. After I bled the brakes I thought I would have a better pedal-w-the bigger rear brakes but this is not the case. My issue is-w-the amount of travel in the brake pedal. The pedal has to get about 3/4 to the floor before the brakes get fully engaged. I looked at where the piston goes into the MC and it seems like the MC piston and the pedal rod have to travel about 1" into the MC before ANY resistance in the pedal is felt.
I know that changing to a larger bore MC would mean more effort so I can't go this way but maybe I can get some better insight as to the choices I have. Again, the kit is from Master Power Brakes and I don't know the MC they include-w-the kit or if I would want to replace it-w-the same one. Do I look to change the pivot point on the brake lever or look at another MC that will bolt up-w-a smaller bore? I don't know the current bore size.
I am so sick of the piss poor brakes in the car AFTER spending all this time and $ on kits, rear end swap etc that I need to just get it friggin right if possible.
Thanks
Howard

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65 4-door Dart
70 Chrysler 300
2004 Cummins Ram 3500
1968 Dart GT Convertible-project
Chordomafoundation.org

Are the rears adjusted properly? Out of adjustment rears will cause a low pedal.

Will they "pump up" or do they just stay low however much you pump?

Do you have any brake hose clamps? Something like these at the top of the page. You can clamp off all 3 rubber lines, the pedal should be rock hard with very little travel, if not your problem is "above" the clamps, probably the master. If the pedal is hard with all 3 clamps on, remove the rear clamp, if the pedal drops, your prob is back there. If the problem is not found then put the clamp on the back again, then remove one of the front clamps, and try again.

Another good test is to get all 4 wheels up and have an assistant try to turn the wheels while you ease down the pedal very gently. When the brakes barely begin to drag the rotor, hold the pedal steady there as the assistant tries to turn the wheels, both fronts should drag about the same, as should both rear wheels. This is not a scientific test, but should lead you in the right direction.

TopHat

Changing the pivot point to allow more master cyl stroke with the same pedal movement, will give you a higher pedal effort. A master cyl with a smaller bore will reduce pedal effort, but require a greater pedal movement.

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

I have the rears adjusted so there is a very slight drag on the drums. just enough to make a little resistance. This is how I've done it for 40+ years but I'm not saying it is right-it was taught to me then and it has not made me wreck. It makes the brakes hot but only for a few miles as I "break in" the shoes/drums. At one point I remember brake companies would curve the shoes or something like that?
they don't pump up so I don't think it is an air issue.
I don't have these clamps but I do have some vise grips-w-the swivel circle I've used before on brake hoses-I think I'll try your trick-it is a great tip!
I will keep this in mind as well but I should think isolating the problem area-w-the clamps should produce some sort of indication. In reading so many posts about pedal feel, travel etc. I came across a few that mention that this is a normal thing. Being it is a converted single well all drum car and now has disks up front & rears in the back would this still allow me to get a good hard pedal that isn't 75% to the floor?
I have been having trouble lately getting information from Master Power Brakes. I did this conversion 6+ years ago and they have changes the entire set up so they can't tell me much about replacement parts found at local auto suppliers. If I need to replace the master I am thinking an manual master from an aspen would be the same yes? Mine has the lines on the left which go directly to a proportioning valve "block" directly under it. I have a feeling this is more of a distribution block as opposed to something that actually changes any proportioning??
Thanks-Howard

_________________
65 4-door Dart
70 Chrysler 300
2004 Cummins Ram 3500
1968 Dart GT Convertible-project
Chordomafoundation.org

Well it sounds like the rears are adjusted properly.

The fact that it wont pump up makes me think too, that the problem is air in the lines, or it could be a bad master.

The wheel turning trick was mainly for if you did not have a way to clamp off the lines.

I did my upgrade with Volare calipers and a master for a 74 RoadRunner. The 74 master still has the 4 bolt flange for the firewall, Aspens may be new enough to use the 2 bolt flange, I'm not sure. I am not running a proportioning valve, I know I should, but I'm not. My brake pedal has less then 1 inch of travel before I start to stop.


TopHat

So would you say that the rod pushing into the MC 1" before any resistance in the pedal is felt is normal or should I feel pressure right as soon as the rod makes any movement into the MC? It is like there is built in 1" approx free travel in the MC.
Thanks
Howard

_________________
65 4-door Dart
70 Chrysler 300
2004 Cummins Ram 3500
1968 Dart GT Convertible-project
Chordomafoundation.org

No that is not normal. There should be a "small" amount of piston movement before resistance is felt, but 1 inch is way too much. I would guess a "ballpark' distance would be approx 3/16 to 1/4 inch, at the cyl, not the pedal. There will be movement with very little resistance, as the clearance between the pads and rotors, and shoes to drums is taken up. You should then feel a very noticable resistance, and not very much pedal travel.

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

I spoke-w-Master Power Brakes today and the MC I could use to replace mine would be for a 73-76 non power disk/drum Dart. I can get one but they first suggested I try bench bleeding the MC again which I will do.
When I talk about the 1" movement before there is resistance felt I mean ANY resistance. I don't even think this 1" I am seeing is taking up any space between the rotors/pads etc.
After calling around I'm finding it is 3-4 days for a new MC and about $125.00 after shipping. I hope I can get mine to work because I'm paying for too many things right now on this car. Drive shaft shortening/rear axle-w-complete brakes and up next is power steering.
It is getting to be a drain on the wallet.
Thanks
Howard

_________________
65 4-door Dart
70 Chrysler 300
2004 Cummins Ram 3500
1968 Dart GT Convertible-project
Chordomafoundation.org

It does sound like your present master cylinder is defective if there's really no resistance for the first inch. If there's minor resistance but not enough, then it sounds like the master and/or lines still need bleeding. If you need a new master cylinder, try for a Raybestos MC36426.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Another tip for bench bleeding the master is to gently tap the sides of the bore with a hammer, just gently, it can help dislodge tiny air bubbles that could be causing your problem. Though I have never had a problem with any mopar cast iron master as far as bench bleeding goes. When I have problems it is usually with a gm product.


TopHat

I spoek-w-Master Power AGAIN-they were very helpfull. I bench bled the master AGAIN and all the lines AGAIN and I still have the same issue. The tech at MAster Power said to plug the lines from the MC and if it still has the pedal coming in at 3/4 of the way down then it is a bad MC. I was about to do this and the sky opened so I'll have to wait until tomorrow. I'd really like to setup a better bleeding system than my current "tube in a bottle" set up. I have a unit I can create vacuum with by using compressed air and I was thinking of making an isolated fluid container. Any ideas on how to go about this? I also have an idea for putting an air connection on another MC lid to give pressure. I've seen kits like this and maybe this is better??
Thanks-Howard

_________________
65 4-door Dart
70 Chrysler 300
2004 Cummins Ram 3500
1968 Dart GT Convertible-project
Chordomafoundation.org

I plugged the MC as per the instructions from Master Power Brakes and sure enough there was a great pedal for the first time. I can't explain it because I've isolated and bench bled the MC prior to plugging. I then added the rear brakes and had the old, low/poor pedal. I called MPB back and asked about the "Compensating valve" that came-w-my set up and they said it couldn't hold air if it was mounted the way it should have been which is was because it came-w-a bracket for mounting it properly. I mentioned to the tech about the fact that I had replumbed the back lines and some of the brake line was higher than the wheel cylinder and had some up & down bends to get around the U bolts. My tubing bender doesn't give me tight radius bends so the lines ended up being higher above the axle than I wished plus I was using stock size lines that were woo long and made some bends to lose some extra length. I cut the line on the right rear and rebent it, added some spring coil from Mopar for protection and reflared the lines so they lay close to the axle and got rid of the extra bends used to compensate for the longer than needed hard line and this seemed to enable me to get the rears bled and still have a great pedal. I can't believe these bends trapped air but I have no other variable except this "compensating valve". I am thinking of getting rid of it if I continue to have problems when I do the fronts today. It makes it a PIA the bleed the brakes-w-one man because there is a piston in it that will move to one side if you bleed the brakes by pressing too hard/fast on the pedal and this operation locks out the side you are bleeding. It is made to sense low pressure from a leak or fault in the system and cut off the problem circuit and turn on a brake light.
Thankfully it appears the MC is good and I will do the front calipers this AM. I've never had an experience like this in all my years of messing-w-brakes but that it how this car has always been. I should have sold it when I first got it and took out the headliner trying to find a foul odor. I was in the back seat and dropped the left rear corner of the headliner and got a face full of dead mice, mouse turds and nesting goodies which left me-w-a chest infection but a delightful mid day snack of freeze dried new born rodent. Wish me luck-like someone steals the car.
Thanks-Howard

_________________
65 4-door Dart
70 Chrysler 300
2004 Cummins Ram 3500
1968 Dart GT Convertible-project
Chordomafoundation.org

More info please on this "compensating valve" you're talking about. There are proportioning valves, and there are residual-pressure valves, and your system should have both, but "compensating valve" is not standard terminology. Please explain what is being "compensated".

Assuming your rear brakes themselves are in good repair, it sounds like your residual pressure valve is either missing or improperly installed. If you are not using a master cylinder with a built-in residual pressure valve, the external RP valve should be installed right at the master cylinder outlet for the rear brakes (that's the frontmost outlet on the master cylinder).

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

A third possibility is a metering valve, or hold-off valve that would be in the front braking loop. It delays the front disc brakes until the back drums have reached operating pressure.

Sorry for wrong name for the valve. It is a combination valve and has two functions as mentioned in the previous 2 posts. It is a proportioning valve and a hold off valve. In addition there is a 10 lb residual valve for the rear brake (which are all brand new including all the hardware & wheel cylinder).
I have diagnosed the problem with zero doubt to the front calipers. As I mentioned in a previous post I plugged the MC and had a great pedal at maybe 20% down and it was solid from that point so I don't see there is any reason to look at the MC any further. In addition I rebled the rears and reconfigured a "problem" with a line that I made that had too large a loop in it and was holding air. With the rears now OK and the fronts plugged I had the same pedal as-w-the MC being plugged-great! Then the fun started again. I spent 5 d@mn hours trying to get the air from the front calipers. I rerouted the lines thinking they were trapping air bled them at least 5 times while tapping the calipers and lines to help release air but I had zero success. I then clamped the hoses going to the calipers and had the same high/hard pedal as when the master was plugged so it has to be the calipers holding air. I went out tonight and got a pump so I can reverse/pressure bleed the lines but I think this will not help. I talked-w-Master Power Brakes again and they said I may need to tilt the calipers while I am bleeding them to see if they are on the car in a position that is making them trap air. I told them I remember haveing a poor pedal the entire time since the kit was installed (my fault for not getting a better grip on the problem)but that I considered it "normal" after doing all I could to get the air out. The brakes after the initial installation was much better than now but still nowhere near where it should be now that I know what "normal" is for manual brakes-It's been decades since I had a manual brake car. I also told them it is crazy to have to tilt the calipers every time a line is removed from the system and the brakes need bleeding and I got no response so I will attack it again in the AM armed-w-a few types of bleed systems including the speed bleeder fittings if the reverse bleed doesn't do it. Lastly I'll remove the calipers and see if there is some kind of internal issue. I just put new organic pads on and I know the piston moves freely.
Sorry for the long story and thanks for the help-this is nuts!
Howard

_________________
65 4-door Dart
70 Chrysler 300
2004 Cummins Ram 3500
1968 Dart GT Convertible-project
Chordomafoundation.org