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Requesting manual brake setup advice

Posted by Pete 
Robert Culbertson
Robert Culbertson
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Re: Requesting manual brake setup advice
September 06, 2017 05:53PM
Quote
Pete
Allegedly the booster provides 4:1 assist. No idea at what vacuum though. Certainly with the bridge port I can run out of assist in less than one brake application. The car getting converted to manual is getting a 48mm side draft so I'm expecting it to also not do much for vacuum. Plus I don't like the idea of sourcing vacuum from half the engine, seems like it would cause odd running sometimes.

Key to using the four pots is because they are 1 3/8" bore. The same castings were available with 1 3/4" bore, and I need that extra 3/16" of meat to machine away. Convert some of the caliper to aluminum shavings and it will fit on the 9" rotor just fine and clear the OE 13" wheels. I figure that there's enough pads available for Dynalite calipers that in the off chance that I end up wanting more front braking, I can go to a grippier pad.

What's the diameter of the rotor going to be?

I think that even a 5/8 MC is going to be to big with that setup.

The Volvo is a 1.5in 4-piston in the front (as John mentioned) with a 10.4in rotor. Un-boosted, it's doable, but not ideal (5/8in MC and 4-4.5 pedal ratio). Like you have to really stomp on it, but that's just from personal experience DD'ing a car with a blown out booster for a few months...
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Pete
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Re: Requesting manual brake setup advice
September 06, 2017 07:12PM
9". It's a goofy rotor where the ID of the friction surface is smaller than the OD of the hub. It's real close to full pad contact if I just set the caliper down until it barely cleared the hub, maybe 8mm of overhang, but if I cut a little bit out of the bottom/outer face it will clear the hub even better and only leave a couple mm of overhang, which I'd prefer since then you get no lip on the outside of the rotor. Clearing wheel is no problem, heck it would clear even if I didn't sit the caliper down more, and the 4-pot barely sticks out past the hub face so clearing spokes is also a non issue.

That's off in the distant future, though, after we get our machine shop setup again. I'd like to flycut the calipers rather than hand-booger them, and I'm patient.

Note that I've already modified the brake pedal for 7:1. I *get* that leverage and hydraulic multiplication have two separate feel effects, more leverage over the master gives you more control even if the end multiplication from pedal to brake pad ends up being the same. (Kind of like a quick rack and a 350mm steering wheel vs. 6 turns lock to lock and as doorknob, I guess)

The other thing I consider, is I've customers with manual brakes, 1" bore masters, and 1.75" 4-pots over little 10" drag rotors, and the braking feels better than my power brakes. So I do have some faith that pad composition and proper leverage are worth a lot.

Or I could say fark it, and blow another $400 and get one of these things:

http://www.ebay.com/itm/MAZDA-MX5-HYDRAULIC-BIAS-BOX-KIT-B-WITH-LINES-CMB6331-KIT-LINES-/282084767188?hash=item41ad8ff5d4:g:nooAAOSwwo1XdRzb&vxp=mtr



which I'm considering for the bridge ported RX-7 because it kind of IS "that kind" of car...



Pete Remner
Cleveland, Ohio

1984 RX-7 (rallycross thing)
1978
Silence is golden, but duct tape is silver.



Edited 3 time(s). Last edit at 09/06/2017 07:19PM by Pete.
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john vanlandingham
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Re: Requesting manual brake setup advice
September 06, 2017 07:43PM
Quote
Robert Culbertson
Quote
john vanlandingham

Give you an idea..240 Volvo have 4 x 1.5" pistons front, 2 x 1.5" per caliper back..a delightful size on cars around 2050--2300lbs...That worked,,,but using the lurv-erly Sumitomo RX7 4 piston things without a booster didn't work.. and they 4 x 36mm..turns out that's nearly 19% reduction..

Just an FYI:
The Rx7 calipers work just fine with a larger diameter rotor, like a 9-series volvo. Using the 9-series rotor results in brake torque that's withing 1% of a stock volvo setup (clamping force and radius, easy things to calculate). The added benefit is the pad selection (WAY cheaper) and better heat dissipation.

That's the current setup on the rally Volvo, and there's no issues with locking up the tires at any speed...

Other readers..I invented the RX7 caliper and big 740 rotors on 240 spindle 13 years ago and it is a reduction of 19, sumpin percent in hydraulic are versus stock Volvo calipers..
ALL the drivers I know who actually have driven rallies--in contrast to those who haven't driven rallies, ALL agree its insuffient force to lock even at Grass-o-cross speeds..

Believe them or believe Cult-person, your choice. But we tried it cause it cost us under $15 and it was not good.


Guys, this brake sizing shit is one of those horses that hets pounded to death again and again..

If you're not like some people who even though they have never driven a single event or maybe done 4 over 15 years and yet you feel compelled to offer advice on how well things work, fine go discuss and figure out with your favorite on-line calculator....and fap to your hearts content.

But there is an alternate method and that called empirical engineering..
What is the "industry standard" for car this (or that weight) and use and surface?

We can look things up...So a 2080lb for Escort in Group 4 spec---which is a good enough car to win overall today used Nice 4 piston AP calipers with 4 x 1.5" or 38mm pistons..front and 2 x 1.5" pistons rear..
Thats with front pads about 100mm long..

Now Pete's looking at some junk that is significantly smaller--because second hand?---so that makes for problems...
But at least knowing the "industry standard" one can do some areas and juggle some per centages and make a better stab--a half educated guess.


Pete you have some second hand calipers lined up for cheep cheep?



John Vanlandingham
Sleezattle, WA, USA

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Pete
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Re: Requesting manual brake setup advice
September 06, 2017 08:28PM
No, I have some calipers I was going to run on something else and now they're just laying around. Brand new, marked down from $125ea to $25ea at Summit. Buy first, ask questions later, you know? Like the RCI camlock 6-points that I grabbed for $50 each...

I'm not worried about braking at rallycrosses, I don't hardly ever use the brakes at those except for a little weight transfer, it's faster to just pitch sideways and let sliding slow you down, which also conveniently gets you pointed in the right direction to power out of a corner. Slow down from 60 to 30 real quick when you pitch sideways on dirt/clay, and if you're going slower than that then you don't need to slow down anyway... 'Sides, this car probably won't ever really get used for that, it seems like to be successful in the classes it's legal for, you need way more power and fresh tires all the time. Not 160hp and 15 year old Silverstones. So, just a street toy, something fun to drive that isn't a pain in the ass to live with.



Pete Remner
Cleveland, Ohio

1984 RX-7 (rallycross thing)
1978
Silence is golden, but duct tape is silver.



Edited 1 time(s). Last edit at 09/06/2017 08:31PM by Pete.
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DanielSL
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Re: Requesting manual brake setup advice
September 07, 2017 09:21PM
Quote
Pete
No, I have some calipers I was going to run on something else and now they're just laying around. Brand new, marked down from $125ea to $25ea at Summit. Buy first, ask questions later, you know? Like the RCI camlock 6-points that I grabbed for $50 each...

I'm not worried about braking at rallycrosses, I don't hardly ever use the brakes at those except for a little weight transfer, it's faster to just pitch sideways and let sliding slow you down, which also conveniently gets you pointed in the right direction to power out of a corner. Slow down from 60 to 30 real quick when you pitch sideways on dirt/clay, and if you're going slower than that then you don't need to slow down anyway... 'Sides, this car probably won't ever really get used for that, it seems like to be successful in the classes it's legal for, you need way more power and fresh tires all the time. Not 160hp and 15 year old Silverstones. So, just a street toy, something fun to drive that isn't a pain in the ass to live with.

Be careful Pete. Buying first and asking questions later is my usual way of doing things. And we all know how that turns out around here. But hey... I've learned to stop doing that, so I guess my wife is right. I am trainable... on some things.
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Pete
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Re: Requesting manual brake setup advice
September 08, 2017 06:49PM
I have a garage and a basement and a storage locker full of buy first ask questions later. When a deal comes up, grab it!

My Volvo is now riding on springs I grabbed over ten years ago that were new takeoffs from an '04 Camry. Somehow they fit just right and have the right rate and ride height I want. This is a bad precedent for hoarders.

Anyway, I know this is for a street car and not a stage rally car, but I ask these questions here because there seems to be a lot more practical knowledge regarding braking *here* than at any other site I frequent... more builders and did-ers (it's like do-ers, but with more experience).



Pete Remner
Cleveland, Ohio

1984 RX-7 (rallycross thing)
1978
Silence is golden, but duct tape is silver.
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Pete
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Re: Requesting manual brake setup advice
11 days ago
Then I discover that this exists:



http://www.wilwood.com/Pedals/PedalProd.aspx?itemno=340-4630

Neeeet. Balance bar attached to a remote mountable bracket with a built in 1.48:1 ratio lever. That will turn a 4.5:1 pedal into a 6.66:1 pedal. Be simple to knock up a strong bracket that attaches this to the firewall. Already have a .700 and a .750 master, as well as a .625 for the handbrake, to replace the .700 already there.



Pete Remner
Cleveland, Ohio

1984 RX-7 (rallycross thing)
1978
Silence is golden, but duct tape is silver.
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john vanlandingham
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Re: Requesting manual brake setup advice
11 days ago
Quote
Pete
Then I discover that this exists:



http://www.wilwood.com/Pedals/PedalProd.aspx?itemno=340-4630

Neeeet. Balance bar attached to a remote mountable bracket with a built in 1.48:1 ratio lever. That will turn a 4.5:1 pedal into a 6.66:1 pedal. Be simple to knock up a strong bracket that attaches this to the firewall. Already have a .700 and a .750 master, as well as a .625 for the handbrake, to replace the .700 already there.

Niice



John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.
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