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Remote brake booster selection


BlownCorona
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Hi all.

I'm at the point in my 18rgeu swap where I need to select a remote brake booster. The options are a 'drum + drum' vh44 booster which puts out something like 850 psi.

Or the 'drum + disk' vh40 which puts out something around 1400psi

Now my car is a disk front drum rear setup, but small single pots and only a single circuit system.

If I can use a vh44 style then I get get decent repro cheaper options, but if I need the big one I have to shell out for a pbr item.

Anyone got personal experience with these things?

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I rolled in boosted brakes in this car for a couple years, till I finally got around to rebuilding the booster (which I'm now tossing :-( ) and it quite sucks.

Also I only just have enough room for the single circuit master so I'm not sure if a dual would fit.

I could be open to running a resized master but boosted brakes are always nice, and it feels wrong to be adding so much more power and again when I fit the supercharger and to then take away braking performance

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Although going from a Mastervac type booster to a Hydrovac type is a step back in time , performance and reliability by the look of your overcrowded engine bay it's your only option.

Both the VH40 and VH44 share the same crack crack pressure of 35 psi and runout pressure of 450 psi so under normal driving conditions there shouldn't be a huge difference in driveability and feel between the two. Early single circuit disc/drum combo's were always a compromise between the low pressure high displacement requirement of the drums and the high pressure low displacement of the disc calipers i.e. they tended to run smaller  diameter wheel cylinders for the drums and bigger caliper pistons (remember with a single piston floating type caliper you need to multiply the piston area x2).

All this considered I'l go for the VH44 option Just remember with a single circuit Hydropower system  there is no 2nd chance; a failure of either the pushrod seal or or a failure of the circlip that holds the assembly in place leaves you with a pedal that goes straight to the floor. Don't take any chances with 2nd hand units unless you strip, inspect, and assemble with a new kit.

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13 hours ago, Fliboi said:

I rolled in boosted brakes in this car for a couple years, till I finally got around to rebuilding the booster (which I'm now tossing :-( ) and it quite sucks.

Also I only just have enough room for the single circuit master so I'm not sure if a dual would fit.

I could be open to running a resized master but boosted brakes are always nice, and it feels wrong to be adding so much more power and again when I fit the supercharger and to then take away braking performance

in my opinion a dual circuit cylinder is more important than having a booster, a booster does not improve brake performance apart from making the pedal easier to push.

un boosted isnt that bad if you get the pedal ratio correct.

have you considered a different pedal box to move the master inside the car out of the way? ie a wilwood or similar

or possibly a van one

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Thanks sr2 for the info regarding which booster to select, if I go down this route now! 

Cletus - I did consider a Wildwood style box, though space is at a premium on this car, and debatabley cost is an equal factor, at the same time I don't want to skimp on brakes. 

How compact can you get a dual circuit master, and does the rest of the car then require rehosing in a different layout? 

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found this excellent video from summit racing which ill slot in here for other brake noobs like me. 

 

im pretty sold in the idea of going to a dual circuit and resized master cylinder (smaller according to summit) as it will be tidier in the bay, and probably also cheaper aswell as safer as you guys have highlighted! 

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Great little video but if I may, a few comments.

I'm not sure where the '900 to 1200 psi' came from, it's a meaningless number unless you're taking into account total swept piston area, pad area and compound, rotor diameter, etc. (I've seen 2,500 plus psi on many occasions). The choice of master-cylinder diameter is not simply one of how hard of soft you want your pedal to be, the critical issue they failed to address is one of pedal travel and in some setups not getting a pedal at all! Bottom line is if you reduce master-cylinder size you increase pedal travel; a soggy feeling pedal that only firms up close to the floor is anything but ideal. There is a good reason why the majority of cars produced 50 plus years have had servo assisted brakes.

Until recently (when we have access to ABS systems that are comfortable in a completion environment) I've always run non assisted brakes in our race cars. It's a very fine line between a firm enough pedal,   minimum pedal travel and sufficient front/rear hydraulic pressure but we achieved it with a lot of track testing, a spares kit with a selection of master-cylinder sizes and a service crew that could swap them out in a 10 minute service stop.

IMO (for a street car) removing the booster from a standard braking system and reducing the master-cylinder bore with the expectation of retaining sufficient braking and pedal firmness will probably end in tears. To put some figures on the equation a VH44 increases boost by an approximate factor of 190%  a VH40 300%, achieving the same amount of unassisted braking would involve 2-3 times the amount of pedal travel.

Yes a tandem master-cylinder is a great way of adding redundancy to a braking system but bear in mind (if running a booster)  if you have no firewall space to run the standard Mastervac you’ll need to fit two VH44 Hydrovacs to retain brake proportionality.

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I think that's the best place to start.

If it was my car I'd find out what bore size the master cylinder is and what bolt spacing the flange is, then call into BnT or Safe R Brakes and see what factory dual circuit cylinders are available with the same measurements. Nissan? ones have a neat clamped on reservoir that can be swapped to a clamp on hose tail to make a remote reservoir easily to help fit under your intake manifold. You could space the drivers side engine mount up slightly to gain a bit more room too?

Some early cars that had a brake booster as an option had two holes on the brake pedal for boosted and non boosted options. Depending on the legality you could drill a new hole slightly up the brake pedal to give a bit more leverage with your un boosted system.

My 2cents.

 

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On 12/28/2016 at 0:18 PM, Valiant said:

I think that's the best place to start.

If it was my car I'd find out what bore size the master cylinder is and what bolt spacing the flange is, then call into BnT or Safe R Brakes and see what factory dual circuit cylinders are available with the same measurements. Nissan? ones have a neat clamped on reservoir that can be swapped to a clamp on hose tail to make a remote reservoir easily to help fit under your intake manifold. You could space the drivers side engine mount up slightly to gain a bit more room too?

Some early cars that had a brake booster as an option had two holes on the brake pedal for boosted and non boosted options. Depending on the legality you could drill a new hole slightly up the brake pedal to give a bit more leverage with your un boosted system.

My 2cents.

 

 

If you are going down the path of unassisted brakes (which is still a viable option) converting to a tandem master-cylinder of the same bore diameter would be a pointless waste of time, money and effort.

I have yet to ever find a standard assisted braking system that didn't verge on being un-driveable with the booster disconnected; try lightly pinching off the booster  vacume supply on  your daily driver (with a pair of vicegrips) and you'll appreciate the point I'm making.

I'd be looking at downsizing your (3/4" or 13/16"?) master-cylinder to either 5/8" or 9/16" as a first attempt; if you're taking that route be prepared for it to  be a trial and error exercise.

Unlike single out put master-cylinders (i.e. the ones we run in Tilton and Willwood pedal boxes) Tandem master-cylinders require a push rod that runs as parallel as possible to their bore. If you are changing pedal ratio's it should only be done by modifying the position of the fulcrum (pivot) point, be very aware of the fact that by increasing pedal leverage you will be decreasing stroke - very easy to paint yourself into a corner. (Believe me I've made that mistake in the past!).

Have to say I agree with Fliboi re: raising the HP while reducing braking efficiency being a potential issue, shame you're at the other end of the country otherwise I'd be offering a hand getting it sorted.

What a fantastic project, cant wait to see how it all works out.

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ive got a 7/8ths master currently. and was all but out the door to buy a 3/4 Tilton master cylinder from Sylvester V8 to replace it with, but then the doubt struck and im not really sure what route to pursue. 

i did drive this car with the brake booster dead for a couple years, and it was annoying because i had to double pump the brakes (not sure why this is) but ultimately i just had to press harder and it worked alright. that said, the new refurbed booster is very nice to drive with. 

for aesthetics and simplicity id love to go with unassisted. 

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zero room. pedal is hard against the steering column on the right and on the left is the throttle lever system, 

engine bay isnt much better at all unfortunately. 

nh2ayyxz.cez.jpg

note - the inlet manifold isnt bolted up in this pic, which is why its drooped down to rest on the master cyl. there is about 1.5" of clearance normally 


m2pg13x0.tya.jpg

 

that 90deg kit is pretty cool. but, and im sure cletus would clarify, i assume it would crack testing and certification as youre modifying the braking system beyond bolt on replacement parts, not that thats an issue if it were to solve a problem

 

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I helped a mate with an e30 BMW build  a few years back.

It had a factory 90deg linkage off the brake pedal going across the dash and another 90deg to have the booster and master on the left side of the engine bay.

He took off the second 90deg and used a charade booster on the stock BMW master. You opened the glove box to top up the fluid. It was certed. 

I will look for a photo.

 

Edit- can't find photo. Look in this thread for photos of another person doing it 

 

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  • 4 years later...

Hi All,

I have sticking brakes in my s-type Everything online suggests it is the booster. So I unplugged it and it doesn't stick anymore. With it plugged in the pedal is like wood. 

I have a VH40. I was wondering what is the consensus with rebuilding vs buying new. I'm not interested in a knock off. Had one in my old V8 commer and was a pain. 

If rebuilding is the way to go, anybody know anywhere that does it? 

edit: Ignore that. Apex up north had them on the shelf for only a small bit more than the rebuild kit. No brainer. 

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