Labrauer Posted December 4, 2021 Report Posted December 4, 2021 I thought I wanted to change my drum brakes to disc at one time but now I wish I hadn't. I completed my front disc conversion on my 48 Plymouth Coupe and talked to some guys on the forum here on how to do them. It seemed to be a straight forward easy project. All I had to do is install the conversion and take the poporshing valve out of the old master cylinder and they would work just fine. Well for some odd reason (as a lot of you have had no problems doing this) I couldn't get any brakes. I tried everything I could think of and finally broke down and took the car to a shop to see if they could figure out my problem. Well the guy there said he could fix the problem and also put disc on the rear as well for $700 parts and labor all included. That's cheaper than I did the front so being the dumb ass I am I said go for it. After the car being in his shop for over 2 1/2 years I finally picked it up only to fine I returned around 9 different times because the brakes were not working like they should. Every time he would say they got them fixed only for me to drive the car a day or maybe two and have to return to his shop again. We are now in the third year and I still am having a head ache with these brakes. There was a power booster and a new master cylinder installed with the 2 lb. valve in the brake lines. The power booster and master cylinder are mounted in the old position on the frame under the car. When I drive the car at first the brakes seem to be fine for the first couple of stops but after that they get hard and won't release or get so tight that you can't turn the front wheels by hand and when you come to a stop sign the car will stop on it's own without pushing the brake pedal. I am wondering if any of you know where I should start to get this fixed and working like they should? I had one guy tell me that the master cylinder and booster had to be mounted above the disc brake cylinders in order for them to work like they should. Is there any truth to this? If some of you have done this conversion on all four wheels I would appreciate some pictures or guidance before I go nuts. Oh buy the way the shop closed and the mechanic has sold his house and moved. Quote
Bryan Posted December 4, 2021 Report Posted December 4, 2021 If it's not pulling to the right or left it is something in common with both sides. So it shouldn't be a binding pad. Don't know a lot about brakes but looked up some YouTube videos that might help. Easy Fix for locked-up front brakes? - YouTube Power Brake booster is locking up the brakes | Team Camaro Tech (camaros.net) Master Power Brakes FAQs (mpbrakes.com) Performance Perspectives: Master Cylinder Selection | MOTOR I'm seeing over and over again people saying there has to be a little play between master cyl rod and booster. The mounting height of the master cylinder/booster wouldn't cause your problem. See picture 3. 1 Quote
Andydodge Posted December 4, 2021 Report Posted December 4, 2021 Can you advise exactly what car or brand of brakes you have on the front & rear, what master cylinder and booster..............andyd Quote
Sniper Posted December 4, 2021 Report Posted December 4, 2021 There is no Proportioning valve in the original master cylinder, just a residual pressure valve. My guesses would be lack of proper clearance between the brake push rod and the master cylinder, wrong pressure residual pressure valves installed or you do not need residual pressure valves at all. Push rod clearance https://www.getdiscbrakes.com/knowledge-base/tech-articles/brake-drag-prevention Quicky check is to loosen all 4 of the M/C mounting bolts when the brakes are locked up and see if that releases the brakes, If it does then the push rod is the issue. Aftermarket inline residual pressure vales are generally marked on the outside as to their rating, check that. If the above two checks do not make any difference than you can crack the bleeder valves on the affected brakes. If that releases the brakes then odds are you do not need the residual pressure valves. Quote
Loren Posted December 4, 2021 Report Posted December 4, 2021 Three good answers in a row. We have gotten so used to parts made with tight tolerances that we forget some of the adjustments that can be made for production variations. Most mechanics (if they ever knew) are loathe to change an adjustment because if they were wrong then they think it might be trouble to "get back" to the starting point. One thing that I learned was that small incremental changes don't tell you enough for you to decide which direction right or wrong you are going. So I make a big change in adjustment and see what the result is. If you're wrong it's clearly wrong. If it gets better then you're on the right track. Tiny changes yield no useful information because you could be going the wrong way in tiny increments. A quick check to see if a master cylinder push rod is adjusted right (this should be done whenever a master is changed) is to look into the M.C. reservoir, push the brake pedal and see if the relief port gushes fluid when released. If it doesn't or if it is a feeble gush then the brakes will lock. If the pedal doesn't return all the way every time (weak spring, friction etc.) then the brakes may lock once in a while. I would question the mechanic and ask what they did in the past to fix the problem, if they say they bleed the brakes then this is the problem. I've seen brakes lock from a dropped nut that landed in the linkage to the M.C. Quote
Doug&Deb Posted December 4, 2021 Report Posted December 4, 2021 I did a front disc conversion on my 52 Coronet. I removed the residual valve from the original mc and plumbed in a 2lb valve for the front and a 10lb valve for the rear. I’ve put about 8000 miles since with no problems. My conversion is the simplest way and by no means the safest way of upgrading the brakes. Quote
James_Douglas Posted December 4, 2021 Report Posted December 4, 2021 Sounds like a residual valve - linkage issues is not allowing the master cylinder to back flow like it should... In my 1949 I am using a stock MC in the stock location with a remote power brake booster and 4 wheel disks. The only problem I have is it stops too good... Quote
kencombs Posted December 4, 2021 Report Posted December 4, 2021 Another vote for the master cylinder push rod adjustment. Lack of clearance at that point seems to be a common problem when pairing a new booster and master cylinder. Make sure that is correct before making any other changes. You may well find that is all it takes. Quote
Labrauer Posted December 5, 2021 Author Report Posted December 5, 2021 A big thanks for all the responders with great advice. I won't be able to work on the car this weekend but I will try Monday or Tuesday so I will take the advice and run with it then. I also was thinking it maybe a push rod problem. I have another question if I have a Disc/Disc Proportioning Valve mounted to the master cylinder do I still need the 2# inline residual pressure valve in the brake line also? Quote
Sniper Posted December 5, 2021 Report Posted December 5, 2021 Why the need to mess with the font? It is very distracting. You should not need a proportioning valve in a properly designed all disc setup. Regardless, it's use doesn't affect the need, or lack thereof, for a residual pressure valve. Quote
Doug&Deb Posted December 5, 2021 Report Posted December 5, 2021 Disc brakes need a 2lb valve and drums need 10lb. Quote
JerseyHarold Posted December 5, 2021 Report Posted December 5, 2021 Have you checked the power brake booster for proper operation? Maybe it's binding somehow and keeping the brakes activated. Just a thought.... Quote
jfish Posted December 5, 2021 Report Posted December 5, 2021 I put a dual master cylinder and power booster on my 1962 Fury. There seemed to be way too much free pedal travel (maybe just the opposite of your problem). I found that if the master cylinder was unbolted from the booster, there was a pin with a spherical head that was part of the booster and it pushed on the MC. This pin was adjustable and the brakes would go from dragging to having too much free play. After some trial and error it's good. There was nothing in the literature I received about this adjustment. As others have said moving this pin may give the MC the slack it needs to retract. Quote
Labrauer Posted December 6, 2021 Author Report Posted December 6, 2021 I think my first move would be checking out the pin or rod that goes to the master cylinder from the power booster. I did take the carpet up and removed the top from the master cylinder, pushed on the brake pedal and released it watching the fluid I see no movement of fluid. I also stuck a very small screw driver in the large hole at the bottom of the master to see if I could feel any piston movement. I don't think I felt any movement if I did it was very very little. Quote
Labrauer Posted December 6, 2021 Author Report Posted December 6, 2021 9 hours ago, jfish said: I put a dual master cylinder and power booster on my 1962 Fury. There seemed to be way too much free pedal travel (maybe just the opposite of your problem). I found that if the master cylinder was unbolted from the booster, there was a pin with a spherical head that was part of the booster and it pushed on the MC. This pin was adjustable and the brakes would go from dragging to having too much free play. After some trial and error it's good. There was nothing in the literature I received about this adjustment. As others have said moving this pin may give the MC the slack it needs to retract. Where did you mount the power booster and master cylinder? Is it mounted on the inside of the frame where originally the master cylinder was mounted? Quote
Labrauer Posted December 6, 2021 Author Report Posted December 6, 2021 10 hours ago, JerseyHarold said: Have you checked the power brake booster for proper operation? Maybe it's binding somehow and keeping the brakes activated. Just a thought.... No I haven't not yet Quote
LazyK Posted December 6, 2021 Report Posted December 6, 2021 of the three brands commonly discussed here, scarebird, ECI ,and rusty hope, rusty hope is the only one that would say for sure their kit would work on the stock 15" wheels on my 51 Cranbrook. The other two stated minimum 16". I used the rustyhope kit and have had no issues with operation. I should also state I used an ECI kit for the master cylinder as rusty hope did not offer a dual reservoir master cylinder kit. in choosing the ECI master cylinder kit they were very helpful in telling me which master cylinder to use based on the calipers and the original rear drum wheel cylinder combination. Quote
Plymouthy Adams Posted December 6, 2021 Report Posted December 6, 2021 On 12/4/2021 at 4:15 AM, Labrauer said: Oh buy the way the shop closed and the mechanic has sold his house and moved. You probably were one of the lucky ones that even got their car back.... Certain other forum has a shop closing its doors in the middle of a number of car restorations to the tune of HEY DUDE, WHERE'S MY CAR Quote
jfish Posted December 6, 2021 Report Posted December 6, 2021 12 hours ago, Labrauer said: Where did you mount the power booster and master cylinder? Is it mounted on the inside of the frame where originally the master cylinder was mounted? This booster was on my 1962 Plymouth, so it went on the firewall no problem. I would like to see a setup on a P15 or other frame mount MCs. A friend put a dual MC on his 53 Chevy and he had to install a sealed top and a remote resevoir to make it work. Quote
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