Disc brake swap - master cylinder question.

[Belvedere-II]

I'm swapping the front drums to discs and have a couple questions. I'm using the later A-body spindles and calipers (11 inch rotors, slider calipers) and swapped in a Master Cylinder from a 71-75 B-body.

My questions are:
1. Does it matter if the caliper is to the rear of the spindle, or does it have to be towards the front? I've heard both, but anyone who has knowledge please help.
2. When replacing the master cylinder on my 1965 power booster, there is a spacer that was on the old single reservoir cylinder, does it stay or get removed?
3. When installing the new master cylinder, should the booster pushrod be firm against the MC piston, or barely touching it? Without the spacer removed, the master cylinder piston gets pushed in a little with the pushrod, with the spacer, it doesn't come in contact with the piston.

I know there are articles out there, but of the ones that I've read (one was an E-body, the other was a later B-body) none of them clearly defined the details on the master cylinder. I got a new one from Rock Auto (part # 10-1515) and currently the brakes work but if I slam them on I don't get wheel lock up. It stops, but not as good as I would have hoped.

We used an adjustable proportioning valve for the rear, and I have new wheel cylinders on the drums. We bled the brakes completely, but still not as firm as I would have hoped. (the MC was bench bled on the car to get all air out of system).

Thanks for any advice/suggestions on this.

 

[67 coronet]

1)caliper is better on rear but can be mounted in front if need be.most important is for bleeder screw to be on top of caliper.
2/3)your master shouldnt colaps at all when installed.the rod should be very close or just touching the piston.
did you bench bleed the master before installation on the car?the pedal wont fully compress the master cyl plunger on the car and you can have air traped at the tip of your master.always bench bleed in a vice and depress the piston completely with rubber lines imersed in the fluid,from the output holes,until you get no bubbles.takes upto 15 full depretions of the rod.then install on the car.

 

[Belvedere-II]

The master cylinder was bench bled on a vise, but it seemed that there was still air in the lines so I attached fittings/tubes to the outlets and looped them into the fluid and pushed the pedal several times until there wasn't any air in the tubes. We installed the MC, then bled the brakes, rear to front.

It's just odd that I cannot get wheel lockup at all, so it makes me think I'm not getting full pedal pressure. When I go in reverse and hit the brakes hard, I can sometimes get a chirp, but not really locking up.

Thanks for the input... I'll keep checking things out.

 

[dpstark2]

Whenever I've gone through my brakes, I've had issues with bleeding. I've tried 3 different master cylinders in my car trying to get the right pedal travel and feel following a disc conversion, and I've tried different pads and rotors and calipers. So, like many here, I've had my brake lines empty a few times. It seems to me that I always end up bleeding the brakes again after I've heated the fluid a few times and I inevitably find bubbles. I've also had issues with connections seeping slightly on the first use- so check all your connections and watch your fluid level. I've had the best luck with good old fashioned get-a-friend-to-pump-the-pedal bleeding. It's a pain, but it seems to work best for me.

 

[Belvedere-II]

I've had the best luck with good old fashioned get-a-friend-to-pump-the-pedal bleeding. It's a pain, but it seems to work best for me.

I had a brake bleeder kit with me, but my friend and I bled the brakes the old fashioned way... like you stated. We got fluid and no air bubbles out of each corner. I'll keep an eye on it and see if it starts feeling better. Thanks.

 

[67 coronet]

someone else on here just solved a similar problem by adjusting up the rear brakes tighter.i would double check your rear brake adjustment just to be sure.if your adjustable prop valve to the rear is all the way open,you should get rear lockup very easy.then you need to adjust it from there.if you dont get rear lockup with the valve wide open then it may be an adjustment issue.

 

[Belvedere-II]

someone else on here just solved a similar problem by adjusting up the rear brakes tighter.i would double check your rear brake adjustment just to be sure.if your adjustable prop valve to the rear is all the way open,you should get rear lockup very easy.then you need to adjust it from there.if you dont get rear lockup with the valve wide open then it may be an adjustment issue.

The adjustable valve is on the rear line (the front reservoir) and the knob shows "less brake" and an arrow going counter-clockwise. Normal driving it feels okay, but hard braking and I realized that the rear brakes are doing all the work.

I asked a Mopar shop and they told me that it could be that I have the wrong master cylinder, that I should stick with what was on a car with the brakes I'm using, so I got a late 70's A body cylinder and will try that. The part number I have for the one on the car is for a 71-74 B body. The bore sizes are different, and there appears to be an additional valve in the new master cylinder in the front reservoir - which is bigger than the other front reservoir but still smaller than the rear reservoir. If that makes sense.

 

[5.7 hemi]

You need to "bed in the pads" on the disc's. Drive on an empty road, go about 40 and get agressive with the pedal, but do not come to a complete stop, then do it about 4 more times, again no complete stops as this will burn the pad to the rotor. Drive for a bit to let the rotors cool, then let it sit for about 1/2 hour or till the rotors are cool to the touch. Go back out and repeat the process. Last time, now you can start adjusting the rear brakes with the adjustable proportioning valve, fronts need to lock up first then the rear.

I did this procedure with my 64 polara, and my 06 pt cruiser (skipped the rear adjustment for obvious reasons) and the brakes work really well. The instructions from Wilwood (for my 64) and the instructions with the new rotors and pads (06 pt cruiser) basically said the same thing. Hope this helps.

 

[Belvedere-II]

You need to "bed in the pads" on the disc's. Drive on an empty road, go about 40 and get agressive with the pedal, but do not come to a complete stop, then do it about 4 more times, again no complete stops as this will burn the pad to the rotor. Drive for a bit to let the rotors cool, then let it sit for about 1/2 hour or till the rotors are cool to the touch. Go back out and repeat the process. Last time, now you can start adjusting the rear brakes with the adjustable proportioning valve, fronts need to lock up first then the rear.

Yeah, this is basically what I did and have done it a couple times. At first I thought my rear wheel cylinders where locking up, and they did need replacement, but I still have the same problem. Driving around here you don't have much choice but to do what you're suggesting, but I did that when we first installed the brakes: drove it around the block a few times, used the brakes to slow, but not stop, lather, rinse, repeat.... still, rear brakes get way too hot, fronts are still cold.

I'm trying the other master cylinder first...it was twenty bucks so if it solves the problem it is the easiest and least expensive fix. I'll post what I find out. Thanks!

 

[5.7 hemi]

Do you have the lines hooked up right from the mc?

 

[Belvedere-II]

Do you have the lines hooked up right from the mc?

That was my first concern, but yes, they are.

The original block that fed all brake lines from the single reservoir is still there, but only holds the rear brake line from the master cylinder and the line to the rear. We couldn't disconnect the brake fitting to the rear, so we plugged the two holes that went to the front lines, and left the rear line attached.

For the front lines, we used a new block and tee-d off the front brake line to the two front calipers. Thanks!

 

[5.7 hemi]

I'm at a loss now, but will keep thinking on it and make some calls.

 

[Belvedere-II]

I installed the new master cylinder, and we bled the brakes again, and I test drove it again, and the only thing I can honesly think is that the adjustable proportioning valve is defective. When I hit the brakes, the rear still seem to be holding more than the front, and when I come to a complete stop and let off the brakes it takes a couple second before the car rolls forward (on idle) as if the brake is slowly letting up. So in essence, it feels like the rear brakes are dragging.

It feels better now with the different MC, but the rear still seems to be an issue. I have the valve adjusted all the way out (less brake), but when I turn it in a little the rear holds even tighter. I guess the next stop is to take it to a shop and pay some ridiculous amount to figure it out.

 

[67 coronet]

other then the adjustable valve,what else is in the system?is there an original diverter block from the original 4 drum system or did you install a prop valve?oops,sorry read the above post.check the rear brake hose(rubber one at the diff)to see if it is collapsing internally.

 

[dpstark2]

Is there any chance you have the rear shoes installed backwards? (There is a front and rear shoe.) Or the auto-adjusters installed wrong? One thought is that the rears auto-adjusting too much (possibly while moving forward). Second, it's possible you have residual pressure in the rear after a stop (which might mean a bigger problem with your factory distribution valve). Does the factory valve have a residual pressure valve or hold-off or anything built in? I believe in this application you would want it gutted- i.e., just a distribution block.

My (later) FSMs have pretty good diagrams of these. Admittedly, I don't know the earlier B-bodies, but my '67 block failed in a most unpleasant way- it's a dual MC setup, and the internal shuttle would not return to center after it stuck once. Again- I don't know your setup, but I'd suspect the way you have the front section bypassed might be an issue.

Hmm. Also- did you double check that the inlet and outlet of proportioning valve are correct? I can kind of see this behavior if you have it backwards.

Sorry to toss ideas like this- but I hope they help.

 

[5.7 hemi]

Rear shoes are like a "mullet hair cut" short in the front, long in the rear, lol!

 

[Belvedere-II]

All good suggestions, so thanks for all the input. I'll check the rear hose and see what's going on with it. Also, the brakes used to work great when they were four drums, and nothing has required me to remove them so they're still in the same position as before. But then one day after hard braking they didn't work so well anymore, and since I had already bought the disc kit I decided to install it.

I'm not aware if there is anything in the original 'distribution block' that split the front/rear brake lines that would cause this, it's weird this is happening. I've done two-wheel to four-wheel disc conversions and never had an issue such as this.

I can check the adjustment, but the drum pulls off easily on both sides, so it's not like they're adjusted too tightly.

The adjustable valve is in correctly: the inlet line is higher than the outlet line and the markings state for it to be installed that way. It could be defective, that's always a possibility. I'll keep trying to tackle it until I figure it out.

Thanks for all the feedback/input and suggestions, it gives me more to look at. I swear, all the brake jobs and swaps I've done and I've never experienced something like this before.

 

[BBDart]

Did you put a 2Lb residual valve in the rear brake line,It keeps the pedal up and stops the rear brakes from dragging!!

 

[Belvedere-II]

Did you put a 2Lb residual valve in the rear brake line,It keeps the pedal up and stops the rear brakes from dragging!!

No, I haven't tried that, I did call a shop that's done a few of these and he didn't mention it. The guy told me that he doesn't even use a proportioning valve... not sure how that's possible though.

From what I have read they use a 2lb for the disc and 10lb for the drums, and the valve is to hold pressure for braking. My problem is that I have too much pressure in the rear lines, and when I let up it feels that the brakes are dragging. I was looking at this page and it explains it a little differently, so can you elaborate?

Thanks.

 

[BBDart]

When I did the disc conversion in my 65 I used 73 up A body upper arms and discs and prop valve,residual valve in the rear line and a manual disc drum master for a 73 340 dart..It has worked perfect!! same setup in my 64 440.Maybe the master you were using might have a prop valve in it if so you can run a line direct from the master to the rear brakes?