brakes Boosterless setup FYI

[Henrygabs]

Just wanted to provide some information about my boosterless brake set-up, which was recently race-tested worked great.  Hope the info helps others avoid the rabbit hole that consumed a metric $#!+ load of my time.

 

Background: Went boosterless in the lemons race car because we want to free up some space in the engine bay for an air box and have more direct braking feel.  Went with the direct to pedal box mounting approach since it is the most cost-effective and lemony approach.  We also wanted to run a tandem master cylinder.  We’re running Volvo calipers up front and have 320 drums in back.

 

The challenge was finding an MC that:

A. Is a tandem MC. (subby single outlet MC are easy to find: Tilton)

B. Has a vertical flange.  The pedal box has little space next to clutch master to accommodate an MC with a horizontal flange

C. Has side or top outlets.  MCs with bottom outlets (e.g., the willwood tandem master and many others) interfere with the steering arm. Outlets should preferably be on the right side to avoid Clutch MC.

D. Has the right size bore.  Bore sizing was a difficult to ascertain.  Lots of conflicting information and opinions and calculators telling you 17 different sizes.  

 

Ultimately, there is not much that fits the bill.  I ended up using a 7/8” bore MC from a 1978-1980 Dodge Colt/ Plymouth Sapporo / Galant. (yeah, random).  It was mounted slightly higher than the clutch master to avoid interference with steering arm.  Drilled brake pedal arm to connect clevis level with the MC (probably a 4-1 lever ratio, not high).  We also used a Willwood proportioning valve but didn't do much fiddling with that yet.

 

Results:  Great feel.  Takes some effort over the boosted setup but its not excessive.  Even the old timers liked the feel of the brakes.  We ran it on the track for two hour stints all weekend long and brakes worked great.  Never got tired and never doubted whether we could get the car to stop when late braking at the end of the front strait.  

 

One possible alternative is a ¾” bore MC from a 1968-1974.5 MGB (the Non-Servo Dual Line Cylinder version).  Should provide a softer pedal feel, but I did not test this out. (Also has left side outlets, which is not ideal.  Might work with banjo fittings).

 

Other than the two options mentioned, I didn't find any other decent alternatives that met points ABCD above. It was a real PITA to find an MC and I'm lucky to have found something workable at the outset.  It would be helpful to have options ranging from 3/4 up to 1" for alternative brake configurations.  So, if anyone has any additional suggestions, feel free to chime in and drop some knowledge.  Cheers! 

Edited October 26, 2016 by Henrygabs

[72ITB]

Thanks for the info, ofcourse would love to see pics.

 

tim

[FB73tii]

Thanks for posting this, I have been looking for a short dual-circuit master cylinder for direct pedal box mount for quite some time for my '69 track car. I just don't like having a single circuit. Based on your info above I did some searching--the only ones I found for the '78 colt have top outlets. Is this what you ended up with?

 

The part numbers I found for the 7/8" bore (22.2mm) are:

RAYBESTOS MC39081
ProStop M51801
Cardone 11-1801

Most of the cylinders listed are 13/16" bore (0.8125"), or don't list the size.

 

The only issue with proportioning valves is that the rear brakes need to be "oversized" to allow any useful adjustment. I did some calculations on my 2002tii and found that the rear only does 15% of the braking. Makes sense since weight is on front under deceleration, and manufacturers don't want a street car to swap ends in a panic stop. Now with Wilwoods all the way around and Tilton overhung pedal box with balance bar in the '74, I can dial in up to roughly 30% brake at the rear. I only use this much in the wet (less weight transfer forward, rear can do more braking), that much is very twitchy under hard braking in the dry.

 

Thanks again--Fred

[TobyB]

Thanks for that Colt part- there is just about bugger- all room down there.

 

I looked at the big 5er MC, but it's bottom- outlet, as are most.

 

7/8" sounds about right.  One thing I ran into with keeping the stock 4:1 ratio

(and it's just for reference)

is that to keep a decent pedal height, you often run out of M/C travel

before the pedal hits the floor.

It only matters when you cook the brakes- the driver's shouting

"I'm standing on the pedal BUT IT"S NOT STOPPING"

and since the pedal's not on the floor, it takes everyone a while to figure

out that yeah, the fluid boiled and the master bottomed.

 

Like when you try left- foot braking at Mission Raceway...

 

 

Nice. In for pix, too.

 

t

 

Oh, and PS, the other problem with proportioning valves is that

they don't seem to be particularly repeatable.  I tried 3 or 4, and

none was particularly consistent- if you roll into them, they 'knee' differently

than if you jump onto them... and even if you're consistent, they

can vary significantly, brake application to brake application.

 

 

Edited October 24, 2016 by TobyB

[Henrygabs]

Thanks for the feedback Toby and Fred. 

 

We didn't end up fiddling much with the prop valve.  It is a glorified splitter right now.  I used the willwood combination prop valve because it split the single front input into two front outs and 1-1 rear line in/out.  The bias seemed good enough and it was wet all weekend long at NHMS, which made it difficult to reliably evaluate the braking.  At some point we will upgrade to rear VW discs, which should make the valve more useful.  I'm hoping that we wont have to revise the MC selection at that point.

 

Fred, yes the MC from the colt had top outlets.  (I edited the original post to reflect that side or top outlets are preferable).  I searched the ATE catalog extensively looking for a suitable MC that was stubby and had multi-circuits.  I found a few candidates that were stubby multi-circuit MCs (often referred to as the "plunger TMC" style).  Check out this helpful ATE tool to find MCs by length, and # of connections, enjoy! (http://partfinder.ate-classic.de/eng/start#Master-Cylinder/search).  Ultimately, I wasn't comfortable enough with my understanding of the different MC designs to try an MC from a newer model car (e.g., the difference between MCs for boosted cars and non-boosted cars, whats the difference between ABS vs. non-abs MCs, etc.).  I went with the Plymouth/dodge because some classic Datsun guys identified it as a boosterless MC alternative and I figured the 02 application was analogous.  It was also $60 vs. a couple hundred.  Although, there is no price on safety.

 

I will take some pictures the next time I am at my shop, which might be a week or two.

 

 

[NickVyse]

Don't know if they're short enough, but RHD 02s had the MC direct on the pedal box (hanging pedals though) and have top exits. 20.66mm, don't what that is in old money. I used a 20mm MC from an e21 on my NK servoless set up, great feel, not much more effort. 

 

 

[markmac]

Seems like Lee has recently posted up some things on this (and has worked out the bugs for the most part).  Is this essentially what you are trying to achieve?

 

 

[TobyB]

To my eye, that looks too long:

As Henry notes in the op, the steering link

is frustratingly tight to the pedal box.

Like BMW never expected to use tandem

brakes with a 2002.

 

Or realized that floor hinged pedals and a booster

just weren't going to work anyway, without some sort of

monkey-motion.

 

t

[markmac]

It may be for a standard car with steering box and what not, mine has Rack & Pinion and has been changed around quite a bit.

[Fatherof3]

Where can these splitter type fittings be purchased?

 

[Henrygabs]

NickVyse, the only stock Brake MC option that I found that had a vertical flange was off of a 1600/early 2002 that had the mechanical clutch and BMC mounted directly to the pedal box.  It is NLA.  I have that old MC on hand, but I didn't have time to get it rebuilt and possibly re-sized.  The MC you noted had a horizontal flange

 

Another nice mod by Lee... looks like he made the mounting plate a bit wider and/or relocated the clutch MC to provide some additional room.  Its a nice setup (as usual from Lee) and beneficial in that there are many more BMC options with that horizontal flange setup.  I like the banjo fittings too, my guess is they can be found at summit racing.  Interference with steering can be avoided by raising the master slightly.  Raising the MC and corresponding mounting point on the pedal arm is done at the expense of pedal ratio.  However, with many more BMC options to chose from you could size the bore to accommodate the decrease in pedal ratio.  

 

Thanks again for the input.

 

H

 

  

[Henrygabs]

No photos yet, but have demonstration of brakes in action!

(note, not my in-car footage, I'm in the alpina themed 02)

http://www.tubechop.com/watch/8516116

Edited November 4, 2016 by Henrygabs