i put discs on the front of my 53 back in january. bled out fine, but it took all of the m/c travel (7/8 bore) to stop. fast forward, i put a 1" vette m/c in, and now 1 caliper will not bleed. i get fluid pumping out at the hose connection, but it won't go that extra inch to the valve. i'm going to warranty it out at ho-riley's but i thought it was a bit strange. btw, it stops great with 3 wheels, pulls a bit to the right, though when is tech week, i'm getting antsy.
so... I have all new lines running from a non-power 1" vette m/c under floor to original 53 rear drums, 76 a-body discs. rpv's in the proper locations. 1/4 line running to t for the fronts, then 3/16 to the calipers, 3/16 all the way in the rear. bled the air out, finally. Question... I had 1 disc hooked up in the front, both rears and it would lock up the brakes at low speed in the driveway, stopped hard with just a little pull. now with both discs, it won't lock up the brakes in gravel, and stops, but WORSE than with drums all the way around. brake pedal doesn't go to floor, about 1/2 way and gets solid, car feels as if it coasts to a stop, like in sand. I'm thinking the rears are "bottoming out" before there is enough travel to actuate the fronts. Is the solution to go with larger wheel cylinders? the calipers would have paired with 1 1/8 wheel cylinders on the original and 1 1/8 power m/c, the 53 has 1" wheel cylinders iirc with a 7/8 bore m/c. or should i pony up to 4wdisc like the m/c was intended for?
Do you have a combination valve? If you do it may have shifted when you bled the brakes and byp***ed the front circuit.
nope, just hooked direct from m/c to brakes, only rpv's in the way. also, it is evn harder to get stopped in reverse, good thing i have a big yard
I did a similar conversion over the winter (actually started last fall) - at first I plumbed it WITHOUT a Proportioning Valve - for curiosity sake - I DID have RPV's front and rear. The braking was well UNDERWHELMING. I wasn't impressed to say the least. BTW I am using 11-1/2" rotors and GM calipers with the stock '47 ford rear drum brakes. Over the winter I finally put EVERYTHING in the system - proportioning valve - 2psi RPV to the front etc. I also have a power booster that was in there last year too. And for comparison's sake I too have a "corvette" style master. NOW - It now stops GREAT. Guys can say all they want about not needing all the gizmo's, but the factory used them for a reason - and I am more of a believer now than ever. Question for you: When you say it is locking up - is that the fronts - rears or both??? It sounds like REARS and that would make perfect sense - here's why I say that - a disc brake requires about TWICE the LINE PRESSURE than does a drum brake - (a result of the servo effect you get with drum brakes) so if you are running WITHOUT a proportioning valve you are basically putting the SAME PRESSURE to both sides of your system - so at about 500 psi your REARS are locking and your fronts aren't even 1/2 way there yet - result your REARS are effectively preventing your FRONTS from applying fully. Enter the proportioning valve - this gizmo allows you to acheive a PRRESSURE DIFFERENTIAL front front to rear - this is done with a little piston that is backed by a spring - the piston moves allowing you to do 2 things - reduce rear pressure while allowing the VOLUME differential required to do so. It's really quite ingenious if you think about it. Other things to consider on your system: Any reason you're NOT running a Proportioning valve? Are your RPV's installed properly? Are your hoses GOOD - they fail all to often and FOOL us by acting like a 1 way valve.
That actually happened to me. I had this wierd problem where it felt like my car was was getting held back for about 100 yards after every stop. I bled the system, replaced the wheel cylinder, replaced the master cylinder, re-bled the system, rebuilt my calipers, re-bled the system, it wasnt till a friend let me borrow a brake pressure gauge that I found the rear brakes holding pressure and tracked it back to the hose. Replaced it, problem gone. If the lines are good, look into installing one of these: http://www.ssbrakes.com/products/detail/3434/?make=Street%20Rod%20Accessorie***odel=Adjustable+Proportioning+Valves&year= Just as an example. If you hunt the net you can get one new for about 25 bucks.
According to this, I need a combination valve. http://www.mpbrakes.com/mpfaqvalving.htm I can't lock up the rears, so none of there answers seem to apply to my problem. Why won't a larger m/c lock up the rears, and why did it stop better with only 1 front brake? I've spent more cash on damn brakes than anything else.
front locked up with 1, not 2. rears won't. not even doing their job. haven't tried one yet, want the right one. yes. I think. new hoses, everything on front. new lines, wheel cylinders on back I'm stumped.
So let me understand.....when I caliper wasn't working at all it actually would stop while locking up the workign front caliper, but now with BOTH front calipers working you can't stop for **** and neither will lock up??? To me this suggest a fluid volume issue. Remember the calipers really don't take alot of VOLUME if the pads are CLOSE to the rotors - on the other hand IF you are running those GM LOW DRAG CALIPERS you might have a problem right there making your volume requirements front to rear TOO LARGE to be working properly - again having the rear drums HOLD the fronts from building pressure - enlarging the rear wheel cylinders would help if that was the case. The "vette" master - will work fine with a disc/drum setup - but things have to be working in harmony. FWIW I am using the origional wheel cylinders in the rear ('47 truck) I seem to recall them being dual bore - 1-1/8" and 1" . I still revert to my origional post - that the rears are "holding" back your fronts from building enough pressure - a Proportioning valve will definitely help - as it allows the differential in FLUID VOLUME as well as FLUID PRESSURE differential. I would still agree that looking into your rear cyclinder size is a good idea. Selecting the proper portioning valve i may be easier than you think. The easiest way is to pick a vehicle that closely resmblems your own. In my case I have 11-1/2" rotors - I have a truck (high C.G.) and drum brakes - same sized tires front/rear etc etc. While cruisin' ebay I found a brand new proportioning valve for a 81 ford 1/2 ton truck - with 11-1/2" rotors - rear drums - similar weight/C.G. - price was right. Sure there was some educated "guess" factor - but it appears to be working great. I would reccomend similar approach for you. look for a similar application - it will be way cheaper than adding rear discs which will add all sorts of other complications - like a parking brake....
Brakes are a hydraulic system. The engineering that goes into them is tremendous. Your brakes functioned with 3 because 1 caliper was stuck allowing all of the volume in the front to go to one wheel. Now with both calipers free, the master doesn't have enough volume for both callipers and bottoms out before the front will work. The rears are getting fully extended in the process. You need to find out if your front calipers require a larger bore/stroke master and then select appropriate slaves for the rear. A proportioning valve will be mandatory to balance the system or one end will be maxed before the other. There is no subs***ute for professional advice in this area. Just remember that brakes are a package deal. All of your choices must take the rest of the system into account. Good luck!
i bought a summit adj. prop valve, and I'll also try wheel cylinders from the same car the discs came from. not at the same time, I want to know what fixed the problem
Consider this: The Master cylinder displaces "X" amount of volume (based on stroke versus bore size) this equates to the SAME volume going "into" each side. Your pedal is setup (***uming) for drum brakes - meaning it has "X" amount of mechanical advantage (aka Pedal Ratio). The hydraulic system itself can have a mechanical advantage/disadvantage based on MC bore size versus disc brake piston/wheel cylinder bore size. Each component requires a certain amount of FLUID VOLUME to function properly - your system must provide THAT volume (and then some) to result in ANY PRESSURE at all - if your rear wheel cylinders are using excessive vloume that can be the start of your problem right there - are the REAR BRAKES adjusted properly??? Misadjusted brakes will potentially use a BUNCH of volume - possibly so much so that you don't have enough to build pressure in the fronts (or backs for that matter) - which makes sense when your "single" caliper actually functioned. Jack the rear of the car up and have a helper depress the pedal slowly - how soon does the pedal actually lock up the rear brakes - spin the tire to see when. If it's CLOSE to the end of pedal travel - that indicates a problem. If you can't build pressure in the rears you are likely to be no better in the fronts - or vice versa. How much Pedal Stroke do you have?????? Which calipers are you using??? Rule out Low Drag yet???? Is the system bled properly??? (just checking)
How much Pedal Stroke do you have? enough to bottom out the m/c at the same time the pedal stops Which calipers are you using??? Rule out Low Drag yet? 71-76 gm a-body Is the system bled properly? no air, and has 10psi valve in the rear, 2psi on the front. braking force doesn't "feel" different with more pedal. it feels like i'm only pressing on the pedal a little, and coming to a slow stop. 1/4 pedal travel or 1/2 pedal travel. I'm also going to make sure nothing is binding in the linkage, I may have to re-engineer the whole thing and use a combination valve.
OK just to rehash a teeny bit - 1" corvette master - I am ***uming this is the one that appears "BLOATED" towards the front (opposite pedal side) - and since it origionally was disc/disc it has no internal RPVs. You plumbed the LARGER reservoir towards the fronts - right? And the rear (smaller) reservoir to the rears. What size are your rear wheel cylinders? - keep in mind that even if your rear wheel cylinders are improperly sized you should STILL be able to get the FRONTS to work so long as the rear brakes are adjusted properly. If they're not adjusted right all bets are off OR!!!!!! IF they are FROZE (seized) that will also impeed the fronts from working right. Have you "blown apart" the rear wheel cylinders to make sure they are fully operational???? If not you NEED to do so. Once they (the rears) are verified to be working, bled, adjusted & inspected THEN you should worry about matching wheel cylinders (IMHO) - I say this because IF the rears are functional (but working like **** - say because the shoes were wet - the fronts should have a TON of stopping power all by themselves!!!! Of course this ***umes that the front are also working right. Not to be a smart *** - but they are mounted with the air bleeds on TOP (pointing at 12:00) right???? You say the pedal will bottom out the master - so you're getting the full travel - probably 1-1/4" right??? I still think the Proportioning valve is a definite step in the RIGHT direction, but if by chance that doesn't resolve this then I would question that "NEW" master cylinder of yours - an internal seal might be leaking not allowing full pressure to the front system. You might FAST FORWARD to your answer if you could rig a pressure guage to your brake lines - do you have any roundy round friends - thay are often sensitive to brake pressures and often have a guage you could temporarily rig in to be sure it is actually coming up to pressure. If I were you I might be tempted to make a list and go through it point by point - hitting everything startign with the basics - both M/C ports are uncovered (pedal adjustment) junk like that. Here's another test for "goofy" problems - pump the **** out of your brakes and hold the pedal down- have a helper pop off the master cover and carefully look in there while you let off teh pedal - if you get a big gyser from the ports it suggests that you have AIR in the line somewhere. Since brake fluid is incompressible you shouldn't get a gyser - of course that's perfect world stuff - in reality you do get a little brake hose and seal flex so you should see a little gyser as these return to a relaxed state. But it there's AIR in there you will see a WHOLE bunch of fluid movement as the air expands back to it's "relaxed" volume. Bottom line - there are a LOT of possibilities - if I were you I would start by FULLY emulating a "factory" type getup = proportiong valve and all. If THAT surprises you then go to the trouble shooting stage. This should have been my FIRST response - hey what can I say - it's tough to get good help. Oh BTW '71-'76 - shouldn't be any low drag junk there!!!!
the corvette m/c has the rear chamber to the rear and front to the front? (as it sits originally)? I have the rear(closer to the bolts) going to the fronts and the front (further away from the mount) to the back brakes. If thats all the problem is, I'm going to be mad. I thought all chevy disc m/c were *** backwards.
On the "Corvette" master - larger goitered side towards front (opposite mtg bolts) goes to your front brakes. Not sure if having this backwards will cause your problem or not, but it does sometimes result in issues. For instance, on an "old car" with single servo rear brakes the size/fitting of the line may act as a restriction resulting in a SLOW pedal return. Your problem sounds like it is mainly NOT building pressure in the FRONT system -- since we have ruled out LOW DRAG calipers as a possible result we need to look elsewhere (like verifying the M/C is GOOD) - we also need to know if you pedal ratio is resonable or not. And we can't forget basics - like bleeding - I know you said it was bled out, but you wouldn;t be th efiorst person to think they had it bled properly whenit wasn't (myself included of course) - bleeder position actually does matter - regardless what some people think (we can't redefine physics - no matter how much experience we think we might have - nyuk nyuk nyuk) seriously though - setting up a new brake system has to take alot of stuff into consideration. ***uming all parts are good is a mistake - we must verify each one. making a list might sound goofy but it sure does make trouble shooting easier!!
you were saying that disks need more line pressure than drums,which is right,but no one has said that you need to run 3/16" lines on disks and 1/4" on drum.if you look at a factory built car with disk/drum combo they have 3/16 on the front and 1/4 on the rear(feeding the rear axle,then 3/16 on the rearend feeding the wheel cyclinders). -danny
The problem here is MAKING enough pressure to the fronts - right?? If so the line size bears nothing in preventing this - like I hinted earlier - if a line was undersized you might experience a slow pedal return or slow pedal application, but ultimately you WILL make pressure - you're not - so your "big" problem is elsewhere.
If you aren't making pressure enough to lock the fronts OR the rears - then you need to evaluate your M/C bore size & pedal ratio to make sure it's compatible with your calipers/wheel cylinders. When you had the smaller M/C bore size how did the rears work compared to now??? Since you ENLARGED the M/C bore you will now require HIGHER pedal effort than before. By changing the bore size you will effectively trade off pedal effort for volume (distance you move the piston). Makes sense right? A smaller M/C bore will require LESS EFFORT but will require MORE TRAVEL to get the same volume.
If your pedal ratio is reasonable and wheel cylinders caliper etc are all reasonable then you need to determine what isn't working as designed. Caliper Brackets that flex (or are twisted)- can cause excessive volume to be used preventing what is needed to build pressure - and we still haven't totally ***ured ourselves that the M/C is even any good, but ***uming it is (never ***ume) are the front rotors mounted correctly - bearings adjusted right - anything here that might "waste" fluid volume will possibly result in "wasting" just enough fluid volume to make things og whacky and might be a cause for not having enough volume to build pressure. Pads contacting squarely etc etc. Can you have a helper pump the brake swhile you watch the calipers/pads? Do the same for the rears. If your system isn't designed "right" (pedal ratio not so good) you're gonna have a tough time regardless. Just not enough mechanical advantage.
I made sure the pedal didn't stop until the m/c was bottomed out in mock-up, so I should have plenty of travel. I'm going to switch the lines tonight and mity-vac it to get all the bubbles out. stay tuned...
I have the same issue, I used the eci disc set up with a 1inch bore manual disc/drum corvette master that eci recomended, my brakes have never felt really strong, ok to drive in traffic but a little less stopping power than what I had expected. It has gotten a little better over time as the pads and rotors wear in and Ive bled it 4 times after I did all the initial setup. It sounds like we are having the same problem. I was thinking of goind to a 7/8 master to get a little more presure. I am running stock mustang drums that came on the 8.8 ford rear end and I also have the 2 and 10lb presure valves and a proporting valve set to max presure on the fronts. Id really like to either decide if this is just the way it is or if there is a problem. Im also wondering if I have a leak of some sort, I never have any fluid loss on the ground and nothing looks wet but I normally have to give a quick pump then push the pedal in to stop, after I bleed it the pedal was firm on the entire stroke but after a few miles I was back to the short pump before I would brake.
the rear port is 1/2" and the front is 3/8. the front reservoir is larger. which one goes to which? i am going to the store to get new adapters. this is really aggravating now.
Don't let the sizes confuse you - the factory used fittings that had nothing to do with the actual size - I imagine it was merely to prevent some *********** from inadvertantly switching fronts for rears. There used to be a really good illustration at one of the high end brake websites - but I can't find it. I did a quick search and did find this: http://www.mpbrakes.com/troubleshooting.htm Notice on the left side they show a "corvette" type master cylinder - notice that the LARGE - front reservoir goes to the Front brakes while the smaller rear (closer to the mtg bolts) goes to the rears. I'm not sure if this will solve your problems - but you gotta eventually get EVERYTHING right so I definitely reccomend changing it. mpbrakes does have a bunch of information - some of it doesn't make sense (to me) but all in all - it's definitely worth reading.
Stupid thought, but i always have a hard time with bench bleeding the master. When not bled well enough it seems to cause the same type of problem. Now I do masters on the car. Might help, no clue. .
OK! I put the front (further from mount) to the front, ran 3/16 to both ends, checked all fittings for leaks, had mom help with bleeding. I want to re-do the lines in the future to clean it up, but for now its working. Now it stops really well, but nose dives hard once the pedal firms up, 1/2 way down. I'll be putting a combination valve on from the same donor car. that should balance it out some, right? should I bother with the adjustable prop valve? It seems the rears need to "catch up" not be slowed down. would it be terrible to have the combination valve level with the m/c? there is only inches of space underneath and just enough in between the frame. they have rpv's built in so, it should work. side note, casey's e85 gas has finally flushed out the rust that was hiding in the tank. good thing i carry a spare filter. Thanks everyone, esp. hemirambler, for your help. this is going to make a good tech week entry once I get pictures of each process and make it look better.
Aren't Mom's the best!!!! Gotta love it when they help you with your Hot Rod!!! Good to hear you are making progress!!!! Nose diving HARD suggests that you don't have enough pressure to the rears now (and since you previously didn't have enough to the fronts prior to switching - it sounds like maybe the M/C may not yet be bled completely - switching your problem from front to rear possibly?) but ***uming (never ***ume ) it is bled completely and working right- your rear wheel cylinders may be under sized - as you increase the wheel cylinder size you should get MORE pressure to the rears. The proportioning valve won't help JUST YET as it's function is to REDUCE pressure rise to the rears - the harder you brake the less pressure you get to the rears -with a proportioning valve installed. BTW a proportioning valve should be added in ONCE you get everything else sorted out (and CLOSE to right) then the proportioning valve is used as a fine tuning tool - otherwise it won't perform properly. What teh proportioning valve WILL do NOW is to "hold off" your fronts from applying UNTIL a preset pressure is reached in the rears - this might reduce some of your diving issue. Proportioning valve placement doesn't matter - since it's a sealed system. Here's one "sticky" - if your donor car had DUAL SERVO rear brakes and your present car has SINGLE SERVO rear brakes you might end up needing to change the wheel cylinder bore size - maybe. I say this because DUAL SERVO requires LESS PRESSURE to operate than SINGLE SERVO. Complicated sometimes ain't it?? On the positive side - ain't NO ONE gonna understand your car's brakes better than you do once you get all this figured out!! Keep pluggin' away!!!
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