I need a small master cylinder with 7/8" bore

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Not sure what to say here, other than your parts selection is very questionable.
On top of that, not sure why you would mess with the original brake rod, when it should be a bolt in process.
I get it, hot rodding is cool. But when it comes to stopping, I like to keep it real.

I would have gone with a rear wheel drive aluminum MC from a Dakota.
Used the stock, unaltered brake rod, and bolted it all in.
Plus, it is imperative that you use the small rubber brake rod bushing, that some mentioned.
It does a couple things. It helps secure the rod into the MC.
And it keeps the rod positioned in the MC, where it should be. Also keeps it from rattling.

Hope this helps.
 
rmchrgr said:
FWD cars generally have a diagonally split system so the proportioning would likely be incorrect. I guess you could get away with it but that's the reason not to use a FWD master cylinder on a front/rear split car.
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I don't think the front wheel drive MC has anything to do with the braking problems I'm having. There is absolutely none of the original brake system left on the car. The front reservoir goes to a line lock then to a tee fitting then to the front wheels and the rear reservoir goes to an adjustable proportioning valve, then to the rear brakes. This K car MC has a 7/8" bore, which is the same as the Wilwood one it replaced and it performs exactly the same as the Wilwood one did. I believe the problem is with the pads and/or rotors. I either have the wrong pads or I failed to properly burnish the new pads even though I followed Wilwoods instructions on how to do that. There is a third possibility and that is that the Wilwood brakes simply do not perform up to par, which is something I have heard other guys say. No matter what, I have to solve the problem and I'm going to do whatever it takes to do it, even if it means ditching the Wilwood brakes.
 
Doosterfy said:
I don't think the front wheel drive MC has anything to do with the braking problems I'm having. There is absolutely none of the original brake system left on the car.

This K car MC has a 7/8" bore, which is the same as the Wilwood one it replaced and it performs exactly the same as the Wilwood one did.
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I was just making a point as to why you wouldn't choose a FWD master if you were theoretically starting from scratch. A MC designed for a diagonally split system may work but also may not. Like I said the proportioning may be off since in a diagonal system, one reservoir handles one front and one rear wheel as opposed to a front/rear split master that supplies front and rear with individual reservoirs. In most braking systems, especially disc, the fronts do the majority of the braking so if you have a master designed for something different, then well, that could be your problem. Just food for thought. Get in touch with Ehrenberg or call Wilwood.

Doosterfy said:
The front reservoir goes to a line lock then to a tee fitting then to the front wheels and the rear reservoir goes to an adjustable proportioning valve, then to the rear brakes.
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Are you saying you don't have a distribution block? Might need one of those.

About the line lock - some will argue and say they did it the way you did it for years but you have it plumbed wrong. The line lock should be installed after the distribution block in the front lines. You are creating a situation where there is unequal pressure on both sides of the line lock. ((not enough where it needs to be) They way you know that this is a problem is if you get a brake warning light on when you activate the solenoid because the brake system is losing pressure on one side of the solenoid.

The prop valve in the rear line is also redundant and unnecessary. What size/type of brakes in the rear? If they are drums, are they adjusted correctly? Sometimes you need to have a smaller rear wheel cylinder to compensate for bigger brakes up front.

Doosterfy said:
I believe the problem is with the pads and/or rotors. I either have the wrong pads or I failed to properly burnish the new pads even though I followed Wilwoods instructions on how to do that.
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It's not the pads or burnishing them in. Unless you see that they are totally glazed over then I wouldn't be concerned with it. You have a pressure problem caused by an incompatible mix of parts and plumbing errors.

Doosterfy said:
There is a third possibility and that is that the Wilwood brakes simply do not perform up to par, which is something I have heard other guys say. No matter what, I have to solve the problem and I'm going to do whatever it takes to do it, even if it means ditching the Wilwood brakes.
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Never heard of anyone having a problem with Wilwood stuff. In regards to the other stuff, I am speaking from experience here because I went through a similar situation a few years ago. I have SSBC aluminum calipers, aluminum MC, Line Loc, adjustable prop valve in the rear line, stainless braided front lines and brand new 10 x 2 1/2" rear drums with 7/8 rear wheel cylinders. I bled them what seemed like 40 times but the brakes sucked. Hauling it down at the end of a run was downright scary. The line Lock would not hold either and it was plumbed correctly after the distribution block. I went to a smaller bore master and still not good. After that I yanked out the extra crap (Line Lock/prop valve) and things were better.
 
Its become apparent to me that I am wasting my time here. I can see that some people don't know their *** from their elbow.
 
Gentlemen, I'm sorry for the angry comment. My mistake was mentioning a problem I was not seeking advice on. The original post was to find a MC that met my requirements. The performance issue was there with the Wilwood MC the new one replaced. The reason I went to a different MC was not to try and correct the problem, it was a space/packaging issue because of the new, bigger (much bigger) headers. This MC performs exactly the same as the Wilwood one it replaced as I expected it would because they both have a 7/8" bore. I realize you are trying to help and I appreciate that. This problem is going to require a methodical diagnosis with pressure gauges on both the front and rear lines to see what's going on. I strongly suspect that Wilwood sent me the wrong pads. The reason I think that is because the hotter they get, the better they work. After I burnished them the first time and they were ripping hot they worked pretty decent but once they cool off they do not perform well. Also when I make runs at the track I like to make the first turnoff so I stand on them hard at 121 mph at the end and I can feel them grab harder and harder as I'm doing it. Then on the return road I tried them and they work fairly good. Once they cool off again they are weak. I have worked in the automotive performance racing industry for ten years at two different manufactures and I can tell you that more than half the people at the companies I worked at were not car people and knew very little about the products they were making or selling screw ups in all the departments happened. Packaging was one of them. Again, thank you for your input and I do apologise for being a jerk. The car is going into storage now because my wife and I are about to sell our house and relocate from Connecticut to North Carolina so I will not do anything with the car until we purchase another house. When I resolve the problem I will share what I found and did. Thanks again and have a good evening!
 
Doosterfy,
I agree w/ your analysis. I also doubt the MC has anything to do with the problem. Even if it were originally used in an X-split car (not K-cars), that would only affect the car's plumbing, not the MC itself (save for reservoir sizes which only matters over the long term). Glad you apologized for your frustration and are learning to filter and weigh each response. Many OP's here never man-up. Most replies on this site are spot-on, but some are just vague speculation, though all can be useful in solving a problem. I can't even count the number of times I have said "can't be that", but turned out to be. My wife (knows little of cars) once mentioned I should try new spark plugs when I had a mis-fire. After discounting that and swapping many other ignition parts that turned out to be the fix (sort of, needed smaller gap too).
 
I have an update. I took the car out of storage a few weeks ago and got back on the problem. Bought a brake pressure gauge that screws into the bleeders and checked the pressure. Turns out there was still air in the lines despite repeated bleeding. I was getting 500 psi at the calipers and if I pumped them up and applied heavy foot power it would go up to 1000 psi. So I bought a power bleeder by Motion products and it took about 15 minutes to get all the air out of the system. I now get 1000 psi to the calipers with firm but not excessive foot pressure on the pedal and the pedal feels nice and firm. It did improve the performance but still not as good as a want or expected. I pulled out the Wilwood paperwork and receipt and checked the part number of the pads they sent me and they are the correct pads for street and drag racing. I called Wilwood and spoke to a tech guy and he says to pull the calipers and scuff the rotors and pads with 100 grit sand paper. That's my next move and if that does not solve the performance issue I'm going to install a hydroboost sytem to simply get more pressure to the calipers. I can lock up the wheels with high foot pressure but these brakes simply don't have a nice immediate grabbing feel when I apply the brakes. I have the adjustable proportioning valve (it limits the pressure to the rear brakes) set so its not limiting any pressure and am getting 1000 psi at all four calipers now. My opinion is that the brakes are too small. The car weighs 3500# with me in it.
 
rmchrgr said:
FWD cars generally have a diagonally split system so the proportioning would likely be incorrect. I guess you could get away with it but that's the reason not to use a FWD master cylinder on a front/rear split car.
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I`ve got 4 wheel disc brakes on my 68 fastback. used the stock splitter, and an 86 diplomat- Chrysler alum master cyl. 7/8 bore, works perfect . (willwoods on the front)
 
famous bob said:
I`ve got 4 wheel disc brakes on my 68 fastback. used the stock splitter, and an 86 diplomat- Chrysler alum master cyl. 7/8 bore, works perfect . (willwoods on the front)
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At this point I'd say for certain using the fwd mc is not a problem, at least the one I have. Mine is a K car mc.
 
rmchrgr said:
86 fifth ave is RWD.
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Yeah I forgot about those cars. That's those mid sized boxy looking luxury cars with the super fragile rear axle. Well anyway I know the fwd K car mc in my car is not a problem. I've seen plenty of other rwd cars with mc out of Daytonas and other fwd Mopars too. Could be that some fwd mc will not work.
 
Every MC for disc brakes I have seen, the rear Res. goes to the front brakes and the front Res. goes to the rear brakes. I think it matters.
 
Since you quoted my post about FWD mcs, I was just pointing out the distinction, seemed like you were implying they were the same as the fwd cars.
 
Mopar Tim said:
Every MC for disc brakes I have seen, the rear Res. goes to the front brakes and the front Res. goes to the rear brakes. I think it matters.
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That may be true on most OEM brake systems but I'd say at this point that its not an issue with the hydraulic portion of the brake system. Remember, I started out using two different Wilwood master cylinders. The first one was a 1" bore and it was so bad the car was not drivable. The next one was a 7/8" bore and it made an improvement but still not good. The two reasons I went to the K car mc was space (the Wilwood cylinders were large) and I did not like the lid that was held on with four tiny socket head screws. The air in the system was a problem for sure but now that I have gotten all the air out and am getting equal (1000 psi) at all four calipers, I'd say the plumbing is not the problem. Also worth noting the way its plumbed is exactly the way Wilwood says to do it. All four calipers are identical and the front and rear rotors are the same diameter. I'll be doing the scuffing with sandpaper later today but to be frank, I doubt it will work. If I were starting from scratch I'd be opting for much larger rotors and calipers. There's a reason why the auto manufacturers went to larger brakes, they work much better.
 
Mopar Tim said:
Every MC for disc brakes I have seen, the rear Res. goes to the front brakes and the front Res. goes to the rear brakes. I think it matters.
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Also I forgot to mention when I swapped from the Wilwood 7/8" bore cylinder to the K car 7/8" bore cylinder it performed exactly the same.
 
Adding a hydra-boost, or any brake booster isn't going to increase the pressure to the calipers. All that a booster does is reduce the amount of pedal effort the driver has to exert.
What is important is the amount of pressure applied against the rotor vs the amount of pedal travel. Also the pressure reading at the bleeder screw is only telling you the hydraulic pressure in the system. What you need to verify is that you have enough pressure being applied to the brake pads themselves & ultimately the rotors. In other words; you may have 1000 psi at the bleeders indicating 1000psi of hydraulic pressure in the system but if the pistons are not moving enough to press against pads to stop the rotors it's not going to matter. So you need to check the actual pressure being squeezed against the rotor by the caliper/pads. They make gauges to do this. Maybe you can rent one from a parts store in your area, Idk. If you can't get the brake pressure(force) tool I mentioned then you can try measuring the temperature of each rotor from both sides immediately after a few hard stops with an infrared temp gun and compare the differences. They can be bought pretty cheap at Sears or Harbor Freight.
I know you have said you had a larger diameter bore M/C on the car & it didn't stop well with that either but I would not rule out the possibility that a 7/8" M/C is too small. What you have to understand is the volume of the master cylinder to the volume of the caliper pistons. A smaller piston M/C has to move a greater distance to move the same amount of fluid against a larger total area of the caliper pistons to create enough force to stop the car. People who convert to manual disc brakes often go to a smaller M/C bore to reduce pedal effort because they don't like the rock hard pedal & higher effort required to stop the car with the larger M/C. And that's fine as long as the smaller M/C can move enough fluid to fill the caliper piston chambers in a relatively short amount of pedal travel.
Now take into consideration that you have 4 pistons in each caliper to move to apply the braking force. That's a lot more area to fill and now it's with a smaller M/C. I think of it like trying to fill a bucket using a smaller bucket then switching to an even smaller bucket. The smaller bucket takes less effort to lift the water but a lot more movement to move the same amount of water.
Also I would re-plumb the lines so that the rear M/C chamber operates the front brakes & the front chamber operates the rear. Also there are mechanical differences in FWD M/Cs from RWD ones beyond bore sizing. There are springs inside on the pistons that are calibrated accordingly. If it was just about bore size then they'd all share a similar part # with the same bore sizes.
 
Lonewolf3165 said:
Adding a hydra-boost, or any brake booster isn't going to increase the pressure to the calipers. All that a booster does is reduce the amount of pedal effort the driver has to exert.
What is important is the amount of pressure applied against the rotor vs the amount of pedal travel. Also the pressure reading at the bleeder screw is only telling you the hydraulic pressure in the system. What you need to verify is that you have enough pressure being applied to the brake pads themselves & ultimately the rotors. In other words; you may have 1000 psi at the bleeders indicating 1000psi of hydraulic pressure in the system but if the pistons are not moving enough to press against pads to stop the rotors it's not going to matter. So you need to check the actual pressure being squeezed against the rotor by the caliper/pads. They make gauges to do this. Maybe you can rent one from a parts store in your area, Idk. If you can't get the brake pressure(force) tool I mentioned then you can try measuring the temperature of each rotor from both sides immediately after a few hard stops with an infrared temp gun and compare the differences. They can be bought pretty cheap at Sears or Harbor Freight.
I know you have said you had a larger diameter bore M/C on the car & it didn't stop well with that either but I would not rule out the possibility that a 7/8" M/C is too small. What you have to understand is the volume of the master cylinder to the volume of the caliper pistons. A smaller piston M/C has to move a greater distance to move the same amount of fluid against a larger total area of the caliper pistons to create enough force to stop the car. People who convert to manual disc brakes often go to a smaller M/C bore to reduce pedal effort because they don't like the rock hard pedal & higher effort required to stop the car with the larger M/C. And that's fine as long as the smaller M/C can move enough fluid to fill the caliper piston chambers in a relatively short amount of pedal travel.
Now take into consideration that you have 4 pistons in each caliper to move to apply the braking force. That's a lot more area to fill and now it's with a smaller M/C. I think of it like trying to fill a bucket using a smaller bucket then switching to an even smaller bucket. The smaller bucket takes less effort to lift the water but a lot more movement to move the same amount of water.
Also I would re-plumb the lines so that the rear M/C chamber operates the front brakes & the front chamber operates the rear. Also there are mechanical differences in FWD M/Cs from RWD ones beyond bore sizing. There are springs inside on the pistons that are calibrated accordingly. If it was just about bore size then they'd all share a similar part # with the same bore sizes.
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That's good helpful info. I will try to locate the tool to measure the actual clamping pressure exerted by the calipers. About the 7/8 bore not having enough volume to fill all those pistons at the calipers; Wilwood recommended going to the 7/8 bore to get more pressure to the calipers with less pedal effort. If I did have a case of not enough volume would it not show up with a very low pedal? My pedal goes down about half way and is no where near bottoming on the floor. I will try swapping the lines so the rear piston powers the fronts and vice versa, that will be very easy to do. Now the hydroboost. Heres why I think it would help a lot; when testing with the pressure gauge I'm getting 1000 psi with normal firm pressure on the pedal. I also got it to 1300 with very high pedal effort and when I road test it I can lock the wheels with the same very high pedal effort. My thinking with the hydroboost is that I would be able to get the higher pressure to the calipers without having to exert very high effort on the pedal. Vacuum boost is not an option because the cam is too big so I only have 5hg of vacuum. Thanks for the input.
 
Doosterfy said:
That's good helpful info. I will try to locate the tool to measure the actual clamping pressure exerted by the calipers. About the 7/8 bore not having enough volume to fill all those pistons at the calipers; Wilwood recommended going to the 7/8 bore to get more pressure to the calipers with less pedal effort. If I did have a case of not enough volume would it not show up with a very low pedal? My pedal goes down about half way and is no where near bottoming on the floor. I will try swapping the lines so the rear piston powers the fronts and vice versa, that will be very easy to do. Now the hydroboost. Heres why I think it would help a lot; when testing with the pressure gauge I'm getting 1000 psi with normal firm pressure on the pedal. I also got it to 1300 with very high pedal effort and when I road test it I can lock the wheels with the same very high pedal effort. My thinking with the hydroboost is that I would be able to get the higher pressure to the calipers without having to exert very high effort on the pedal. Vacuum boost is not an option because the cam is too big so I only have 5hg of vacuum. Thanks for the input.
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You have to remember that a booster of any kind is operating outside of the hydraulic braking system. It essentially is like just giving you a heavier foot to push the pedal. It's not changing the amount of hydraulic pressure being made by the master cylinder. Again I go back to what matters is the amount of force applied to the pads/rotor vs the amount of pedal travel.
To answer your other question about whether too small of a M/C piston would make the pedal low, I'm going to assume you mean it travels farther toward the floor, yes a smaller bore would increase the travel and make it closer to the floor but you would still feel a firm pedal as long as it were bled correctly and there were no air in the system. However there is a certain amount of limitation to the smaller M/C's leverage, if you will, so you would get to a point where your foot would feel a hard pedal but you wouldn't be able to make enough pressure. As the pressure you do make increases the more difficult it becomes to continue to increase it more. It goes back to the ratio of the M/C vs the Caliper piston.
I hope this is helpful & that I'm not confusing in my explanation. Please post what happens with the changes as you go. Good luck! -LW
 
Lonewolf3165 said:
You have to remember that a booster of any kind is operating outside of the hydraulic braking system. It essentially is like just giving you a heavier foot to push the pedal. It's not changing the amount of hydraulic pressure being made by the master cylinder. Again I go back to what matters is the amount of force applied to the pads/rotor vs the amount of pedal travel.
To answer your other question about whether too small of a M/C piston would make the pedal low, I'm going to assume you mean it travels farther toward the floor, yes a smaller bore would increase the travel and make it closer to the floor but you would still feel a firm pedal as long as it were bled correctly and there were no air in the system. However there is a certain amount of limitation to the smaller M/C's leverage, if you will, so you would get to a point where your foot would feel a hard pedal but you wouldn't be able to make enough pressure. As the pressure you do make increases the more difficult it becomes to continue to increase it more. It goes back to the ratio of the M/C vs the Caliper piston.
I hope this is helpful & that I'm not confusing in my explanation. Please post what happens with the changes as you go. Good luck! -LW
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I'll post what happens. I have to see it through, these brakes were not cheap, altogether they were $1200 not including all the lines, fittings and other small parts I had to buy to get the system in. I have to say I'm disappointed with the tech support I've gotten from Wilwood. I've talked to a bunch of their tech guys and gotten steered in all sorts of directions. One of them even recommended going to a longer brake pedal arm to get more leverage. That stunned me, I understand the logic but there's no way I'm going to have some stupid looking setup with the brake pedal extended towards the floor. To put it in a nutshell what they're saying is that I need to get more pressure to the calipers.
 
Doosterfy said:
... these brakes were not cheap, altogether they were $1200 not including all the lines, fittings and other small parts I had to buy to get the system in. I have to say I'm disappointed with the tech support I've gotten from Wilwood ...
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Ditto w/ the after-market Holley 2-D Pro-jection TBI kit I put on my 65 Newport in 1996 at $600 retail price. I never realized improved mileage or performance over the carburetor and it had many quirks that I never worked out, mainly from a bad fuel controls concept (no MAP or MAF sensor). Many people find it better to retro-mod w/ factory parts. In front brakes, those are advantages of using the 1973+ A-body setup (spindles, hub-rotor, calipers) or Scarebird's kit (custom mounting plate w/ GM caliper & Toyota rotor).
 
BillGrissom said:
Ditto w/ the after-market Holley 2-D Pro-jection TBI kit I put on my 65 Newport in 1996 at $600 retail price. I never realized improved mileage or performance over the carburetor and it had many quirks that I never worked out, mainly from a bad fuel controls concept (no MAP or MAF sensor). Many people find it better to retro-mod w/ factory parts. In front brakes, those are advantages of using the 1973+ A-body setup (spindles, hub-rotor, calipers) or Scarebird's kit (custom mounting plate w/ GM caliper & Toyota rotor).
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Yup, I've been involved with the automotive hobby for 40 years and have worked at three different performance/racing parts manufacturers. Nothing beats OEM parts for quality and fit. I had considered using a factory front disc setup. The only reason I did not was because I don't like the wider track width they have on A bodies. My brother is currently building a 71 Dart Swinger. It was a /6 car with the same puny drum brakes mine had. He purchased a front disc setup from a vendor off ebay. It uses Toyota rotors and GM single piston calipers. All the kit is, is bearings that enable the Toyota rotors to mate to the original spindles and brackets that mount the calipers. He purchased the rotors and calipers from Rockauto. I forget how much he spent but I do know it was far less expensive than the $600 I spent for the setup on the front of mine. It will be interesting to see how well they perform. He's using factory 11 inch drum brakes in the rear.
 
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