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

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Doosterfy

Doosterfy

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I have a 70 duster with a 440. Running Wilwood discs front and rear with a Wilwood 7/8" bore MC. I'm now installing Proparts headers and the Wilwwod MC is much too large to clear them. I'm thinking about going to an original non power/four wheel drum style MC but don't know the bore size. Does anyone know what the bore size is on these? I prefer to stay at 7/8" bore because I tried 1" bore and was not happy with the performance compared to the 7/8" bore. I would also be willing to use an MC from a different make but it must be small, have equal size reservoirs and have no larger than a 15/16" bore and preferably a 7/8" bore. Thanks!
 
OK, I found what I needed. After some research I found out that K cars came with a nice small MC with a 7/8" bore. Perfect for what I want. I bought a brand new, NOT remanufactured one off Rockauto for $42 including shipping. Done deal.
 
I'm surprised a K cylinder is that large. What did you have to do to mount it?
 
67Dart273 said:
I'm surprised a K cylinder is that large. What did you have to do to mount it?
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I don't have it yet, waiting for delivery from Rock auto. It's a two bolt flange mount. The Wilwood I have now is also two bolt and I have relocated it four inches away from the engine to gain clearance for the valve cover so removing it to lash the valves is easy. You can see how I did the relocation by going to my photo gallery on here. Going to install the new headers and choose the location I want with the new MC and do whatever fabrication is needed. On another subject, the electrical system worked 100% flawless, your advice on the four pole battery disconnect helped tremendously!, thanks!
 
Doosterfy said:
I don't have it yet, waiting for delivery from Rock auto. It's a two bolt flange mount. The Wilwood I have now is also two bolt and I have relocated it four inches away from the engine to gain clearance for the valve cover so removing it to lash the valves is easy. You can see how I did the relocation by going to my photo gallery on here. Going to install the new headers and choose the location I want with the new MC and do whatever fabrication is needed. On another subject, the electrical system worked 100% flawless, your advice on the four pole battery disconnect helped tremendously!, thanks!
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let me know if that shows up with an aluminum base and plastic tank if you don't mind. i dug forever to find one still being made with an aluminum base, and ended up with one from a 89 dodge daytona. best thing about it was it was 3/16, normal brake fittings on both ports. only thing i dont care for is the reservoir is on a slight slant.
 
johnnymac2k6 said:
let me know if that shows up with an aluminum base and plastic tank if you don't mind. i dug forever to find one still being made with an aluminum base, and ended up with one from a 89 dodge daytona. best thing about it was it was 3/16, normal brake fittings on both ports. only thing i dont care for is the reservoir is on a slight slant.
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Will do when I get it. Should be here Monday 8-24 or Tuesday.
 
I put a 7/8"D bore MC from a 95-99 Breeze (w/ ABS) on all my 60's Mopars. One is a manual setup. I used a 2-4 bolt adapter plate, except on my 65 Dart since that has a Breeze booster too (on Dart brackets) so direct 2 hole bolt-up. The manual MC rod fit into the MC piston, and the pedal wound up in the same place.
 
Mine got me stopped from 127 mph in the 1/4 the other day. My only annoyance is the reservoir is on a downhill slant, so it can leak out the front cap if overfilled. Again 89 daytona/spirit was the one I bought. Dart drag car
 
70Duster440 said:
I don't recall the exact reason (or if Ehrenberg even says why), but he recommends not using an MC from a FWD application. ...
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He even says it with an exclamation point, but doesn't clearly state why. Perhaps it is because all FWD cars had power brakes and the MC piston thus won't have the internal step to capture the rubber bushing and secure the brake rod. But, he says a later truck MC is OK, and most of those came w/ power brakes.

I used an MC for a FWD car. My brake rod is well captured. Indeed, I did a test-fit and couldn't get the rod out without destroying the rubber bushing. I was removing it to add the dust bellows. If I die from this, write on my tombstone, "Bill said it would work".
 
BillGrissom said:
He even says it with an exclamation point, but doesn't clearly state why. Perhaps it is because all FWD cars had power brakes and the MC piston thus won't have the internal step to capture the rubber bushing and secure the brake rod. But, he says a later truck MC is OK, and most of those came w/ power brakes.

I used an MC for a FWD car. My brake rod is well captured. Indeed, I did a test-fit and couldn't get the rod out without destroying the rubber bushing. I was removing it to add the dust bellows. If I die from this, write on my tombstone, "Bill said it would work".
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The rubber boot is not there to "capture" the brake pushrod. The brake rod should be captured by the brake pedal being against the stop when the brake pedal is all the way up. I.E. the rod goes into the hole on the piston and when the brake pedal is all the way up (not depressed at all) the rod is still sufficiently into the MC piston far enough where its not possible for it to come out.
 
johnnymac2k6 said:
let me know if that shows up with an aluminum base and plastic tank if you don't mind. i dug forever to find one still being made with an aluminum base, and ended up with one from a 89 dodge daytona. best thing about it was it was 3/16, normal brake fittings on both ports. only thing i dont care for is the reservoir is on a slight slant.
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I got it. Its cast iron with a level plastic tank and has the good old standard ports for 3/16" lines with 3/8"x24 flair nuts. Its Raybestos MC39327 and its on closeout so I assume they're not being made anymore.
 
70Duster440 said:
I don't recall the exact reason (or if Ehrenberg even says why), but he recommends not using an MC from a FWD application. Not saying you can't - just bringing it up. I got a smaller one from Dr. Diff (with adaptor) but not cheap.

http://www.moparaction.com/Tech/archive/disc-main.html
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I took a look at the link and saw it. Like you said, no reason given. This cylinder meets my requirements for what I need so I will proceed with the install and ignore a warning without explanation. I've been at the car hobby since the 70s and have learned that a lot of so called experts are not as expert as they say or think they are. If there is a problem (and I'm still alive, LOL) I'll share it. Thanks. Love your car BTW!
 
Doosterfy said:
The rubber boot is not there to "capture" the brake pushrod. The brake rod should be captured by the brake pedal being against the stop when the brake pedal is all the way up. ...
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You mis-read. I didn't say the rubber boot had anything to do with capturing the rod (just keeps dust out). On manual brake rods, a stiff rubber bushing fits on a groove at the end of the rod. When you insert the bushing into the MC piston, the bushing locks it in the piston. People say that manual MC's have an internal step in the piston's hole to help grab the bushing (I never checked). My point is that in the "power MC" I used, the bushing still locked in very tight, so "should work".

You are correct that the brake rod won't pop out if there is no such rubber bushing and if as the pedal returns to its high stop, the MC piston follows it (due to its internal spring). But, what if the piston hangs up due to rust? I think the brake rod could get enough clearance to come loose. Unlikely, but one guy said it happened to his son. If so, next time you try to apply the brakes the rod might be pushing on a fixed surface, thus no brakes. My MC bores will never get rusty since I use silicone fluid, but what of the poor souls here who are not so enlightened?
 
BillGrissom said:
You mis-read. I didn't say the rubber boot had anything to do with capturing the rod (just keeps dust out). On manual brake rods, a stiff rubber bushing fits on a groove at the end of the rod. When you insert the bushing into the MC piston, the bushing locks it in the piston. People say that manual MC's have an internal step in the piston's hole to help grab the bushing (I never checked). My point is that in the "power MC" I used, the bushing still locked in very tight, so "should work".

You are correct that the brake rod won't pop out if there is no such rubber bushing and if as the pedal returns to its high stop, the MC piston follows it (due to its internal spring). But, what if the piston hangs up due to rust? I think the brake rod could get enough clearance to come loose. Unlikely, but one guy said it happened to his son. If so, next time you try to apply the brakes the rod might be pushing on a fixed surface, thus no brakes. My MC bores will never get rusty since I use silicone fluid, but what of the poor souls here who are not so enlightened?
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Yes I mis-read that. Sorry. A friend of mine had an incident after he finished building his race car. He had neglected to have any method to positively capture the brake rod and on the very first pass when he launched the G force pushed the pedal up far enough for the rod to fall out and he did not discover it till he went through the traps at about 140 mph. He was lucky but the engine was just about ruined because he had to put his powerglide into low gear to slow it down and the car itself was damaged when he hit the sand trap at the very end of the track.
 
I installed it. It fits perfect I like the no bling look much better than the Wilwood cylinder I had. I custom fabbed an adjustable pushrod. The bore on the piston where the rod goes in is about one inch deep so the rod is retained by the brake pedal coming up against the brake light switch at the top of its travel. I'm going to add a positive stop for the pedal for added safety. The rubber boot that came with the cylinder fits great too. It has a shoulder on top so it fits into the hole in the firewall and the shoulder is big enough where it seats up against the firewall and the MC has a register machined into it that fits over the shoulder on the boot and captures it perfectly so it can't fall off. The boot on the Wilwood cylinder did not have this, it only slid over the cylinder so I had issues with that one slipping off. I'll have the car up and running in a few weeks so I'll let everyone know how it works out.
 
Does the piston have the recess for the rod retaining bushing as well?
 
mguner said:
Does the piston have the recess for the rod retaining bushing as well?
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I'm not sure what that would look like. The hole is aprox 5/16" and has a concave seat at the bottom of the hole. I simply used 3/8" rod and turned down the end where it goes into the piston and carefully ground the end of the rod round to fit into the seat of the bore. I ran the brake pedal through it travel to make sure there is no binding.
 
Sounds like you don't have a rubber bushing at the tip of the brake rod to secure it in the MC piston. It will work as long as the piston always quickly returns (due to spring in MC). But, (to repeat) what if the piston hangs up in the bore?
 
BillGrissom said:
Sounds like you don't have a rubber bushing at the tip of the brake rod to secure it in the MC piston. It will work as long as the piston always quickly returns (due to spring in MC). But, (to repeat) what if the piston hangs up in the bore?
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I've never seen a MC piston bind in the bore. Unless I'm not aware of something, the only way I can see rust forming in the bore would be if water somehow got into the MC. I do have a small plastic bushing that came with the MC so I assume that's the locking bushing. I'm pretty sure I can get a brake pushrod from a front drive Mopar from a friend of mine. I'll have to see how it's configured and possibly rework my rod to incorporate that for added safety. In the meantime I'm comfortable with the setup I have now.
 
OK, the car is up and running again. I drove it up and back from Lebanon Valley Dragway and made four passes at the track. 220 mile round trip. This master cylinder (the K car one I just installed) performs exactly like the Wilwood one it replaced. Overall the brakes are a big disappointment. I'll be contacting Wilwood to see what they say and recommend. I'm sure I'll wind up installing a pressure gauge as part of the diagnostics. Wilwood discs on all four corners. They simply lack that quick grab that good brakes deliver and the will not even lock up the wheels, so something is wrong. They do work better when they're hot but that's no good for a street strip car.
 
I've got Wilwoods on the front and running their master cylinder and proportion valve on my duster..car stops wayyyyyy better then the stock brakes ever could..race it all the time.
 
Probably depends on the pads. I have read that "race only" pads only grab well when hot, so not good for a daily driver, but have no personal experience.
 
BillGrissom said:
Probably depends on the pads. I have read that "race only" pads only grab well when hot, so not good for a daily driver, but have no personal experience.
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I suspect Wilwood sold me race pads. The tech/sales guy I ordered the parts from didn't seem too bright. I told him its a streetlstrip car. I'll get to the bottom of the problem.
 
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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