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Hey guys- I'd like your thoughts on my latest plan to 'fix' my brakes.. Big picture: there's no room at the firewall for a booster, so I've currently plumbed in the brakes as non-power brakes (old-school, no vacuum boost).. I've tweaked on them a bit, and I just don't like them (I'm running 4-wheel discs).. They aren't 'grabby'/ 'positive' enough for me.. I've nearly tripled the car's HP, but the brakes still make it stop like an old car- I can get them to stop and even lock up, but I have to REALLY stomp on them, and I don't like it.. So, I'm going to bite the bullet and install a remote power assist unit, but it comes with it's own issues...

Here's what I believe I need: A 'single circuit' master cylinder at the firewall.. Plumb that back to the remote vacuum power assist unit (located in the trunk) *pic is just a generic unit, then plumb brake lines from the power assist unit out to each wheel.. the rear wheels will need an inline adjustable proportioning valve to choke off some of the power assist and avoid early lock up in the rear..

All of this make sense, yes? My issue as I see it is I need a single circuit Brake Master Cylinder that will move enough fluid for 4 disc brake calipers.. Any idea where to source such a MC? Looking for a 7/8" bore..

**btw, I know it's not ideal to run a 'one circuit' MC, as in the event of a MC failure it's a 100% loss of brakes... The issue I have is I'd like to avoid running 2 remote power units... -also, I can't go hydroboost because I have no PS pump option on this engine that will fit my engine bay..

A sound plan? Am I missing something in my quest to get the Power in my power brakes?

As always, thanks for your thoughts

--ccrunner

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Dean

1972 Honda N600 Restomod "ccrunner's N600 VFR800 repower"

1963 Volvo P1800 Restomod
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1959 Berkeley SE492 Restomod...
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"ccrunner's 1960 MGA coupe Restomod" found on MGExp.com

Just as a data point, my '78 Ford Fiesta did not have a vacuum booster and it stopped just fine. I put bigger wheels and tires on the car and it still stopped fine. I could over heat them when I drove it on a track, but that's a different issue.

Maybe newer or softer pads would help or go to a smaller master cylinder. If it's easier or cheaper to go with a booster that's OK, but it seems more complicated and has it's own issues. You should be able to lock them up with reasonable effort.

Someone else on this site recently fixed their problem just with new pads.
Sorry your having trouble with this. Can you remind us wht you're using for calipers and size of master cylinder?

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Marcus Barrow - Car9 an open design community supported sports car for home builders!
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I do believe it is not only unwise to run a single circuit, but afik, it is also illegal, at least on the streets.. Depends on how your state titles / registers these cars, and if it would be "Grandfathered" under certain circumstances.

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Dismantalus, Fabricatus, Assemblus.....
Certified Welder, Certified Welding Inspector, Full Time Car Freak...In New Jersey no less!

I would suggest if you don't already have them, throw some performance street pads in and re-assess. Also, are you able to go down a M/C bore size or two?

I get the idea: I go from my daily Yaris (2300lbs w/ street/track pads, semi slicks and power brakes) which takes zero pedal effort to be in the windshield to my Seven with manual brakes and, even though the Seven probably outbrakes the Yaris, it's less confidence-inspiring due to the higher pedal effort. I'd like less pedal effort on the Seven but it's not worth risking people's lives over.

Cheers.

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It sounds like all you have to do is change the brake pedal lever ratio. Try a ratio of 6 to 1. Move the push rod clevis on the brake pedal lever or the pivot point on the hanger bracket. [try to keep the push rod angle under 7* or move the M/C.]
I have 4 wheel disc and a lever ratio around 5 to 1 and can stop on a dime using a larger M/C dia.
Dave W

I appreciate your thoughts guys... The more I think about it, the more I think I MUST have air in the MC/lines.. it just doesn't feel or act 'right'...

I take the brakes pretty seriously, given the safety concerns involved.. It just struck me to go (back) to the single circuit/ remote booster as this car came with a single circuit stock, and the booster would be a driver preference..

I think I'll go back after the brakes in a few months when I have time off and a chance to have the system down for awhile (as opposed to having to drive it to work on Monday morning)..

thanks guys-

--ccrunner

_________________
Dean

1972 Honda N600 Restomod "ccrunner's N600 VFR800 repower"

1963 Volvo P1800 Restomod
http://locostusa.com/forums/viewtopic.php?f=36&t=16309

1959 Berkeley SE492 Restomod...
viewtopic.php?f=36&t=19397

"ccrunner's 1960 MGA coupe Restomod" found on MGExp.com

Air in the brakes will make for a spongy pedal. Sounds like yours is pretty firm if you are able to "REALLY stomp on them". To see if there is any air, pump the brake pedal while stopped. Note the pedal height and then take your foot off and wait 10seconds or so. Then apply the brake with the same amount of force as before: Does the height change? If so, you have air or some other factor. You can also just pump the pedal after sitting for a bit and see if each pump gets the pedal higher.

How old are the brake pads? Reason I ask is they can go bad over time. My car had poor brakes (rock hard pedal and huge pedal force required to stop). New pads and instant lockup under normal effort at 100kph.

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Build log: viewtopic.php?t=9291

I've been here. I put Volvo 220 (122 wagon) front discs on my Volvo 544 to replace the perfectly good drums... and utterly ruined my braking ability. Heavy heavy pedal and radical rear lock up that no adjustable balance valve could stop. I went to smaller rear wheel cylinders to try to make it safe, but it never was.

The 65-to-67 122/220 & 1800s Volvo's from which I scavenged my front brakes used a single circuit master which then split into front and rear circuits, and boosted only the fronts using that exact type of remote booster shown above. The rears were drums, and thus somewhat self energizing due to "wrap" of the shoes within the drums jamming them on. Not very linear, where the fronts were more or less purely linear. My 544 didn't take the booster and could never actuate the front discs proportionately. To me that linear front/non linear rear was the biggest fault. Not that it isn't common but doing a balance valve set up on that where do you even start when you have a graph of brake force that is a straight line that overlays one that is almost exponential?

Anyway...
So yes you can and should use a double circuit master- and try boosting just the fronts.
Dual circuit master are (more or less inherently) stepped. So can you use the differing front and rear bores on such a mast cyl to help your balance set up? Many cars run the front brakes off the back port (that is to say the master cyl outlet closest to the firewall).

One last thing- the Volvo calipers/spindles have 3.5" mount ears. So do many Wilwood calipers (and I think other brands).
With the common 5x4.5" wheels, you should be able to come up with a hat dimension that would allow everything to bolt together. One problem is Wilwood has decimated their under-12" rotor offerings.

**Wanted to check in with a result.. I thought awhile ago that I may have glazed the pads (I got things VERY!! hot during initial install/ testing), creating my own problems (hard to see in the pic, but the pads I took out were 'shiny' for lack of a better term).. that does in fact seem to be the case ... I swapped out the pads all-around, and what do you know? Now she stops just as she should, and the pedal 'feel' is just as it should be ....SO nice to have this figured out- I now have total confidence in the car's ability to panic stop..

Thank you for your thoughts and help on this one-- brakes are nothing to mess with..

--ccrunner

_________________
Dean

1972 Honda N600 Restomod "ccrunner's N600 VFR800 repower"

1963 Volvo P1800 Restomod
http://locostusa.com/forums/viewtopic.php?f=36&t=16309

1959 Berkeley SE492 Restomod...
viewtopic.php?f=36&t=19397

"ccrunner's 1960 MGA coupe Restomod" found on MGExp.com