brake efficiency problem

[davegeezzer008]

Hi Guys Ive guys disc brakes on all four corners but the braking is crap !!!, Ive got a beachbuggy that weighs in around 700kg with a 2110 lump, it only just scrapes through the MOT test. ive got a Rage hydraulic pedal set with a 7/8 master cylinder

what i need help on is if i was to use a 5/8 cylinder this would create more pressure but push less fluid with the same effort but would it make the brakes more efficient ?

any input appreciated !!!

[Steve Arndt]

What brakes do you have? Certain of no air in the lines? Residual pressure valves? The Latest Rage master doesn't have a front valve like the stock master. Also 7/8 bore is ~22mm. That is much bigger than the stock 19mm.

[Ol'fogasaurus]

Plus an (adjustable?) proportioning valve. If you have a glass buggy (beach buggy is usually an east coast or off shore term. Tub buggy is common in the mid-west and on the left coast it is usually the generic use of Manx or dune buggy) then there is going to be less weight differential and it will be balanced out differently. You probably less brake bias up front as compared to a stock bug and with more weight being in the rear. Are you running "cans" (drum) brakes up front?

Lee

[davegeezzer008]

What brakes do you have? Certain of no air in the lines? Residual pressure valves? The Latest Rage master doesn't have a front valve like the stock master. Also 7/8 bore is ~22mm. That is much bigger than the stock 19mm.

the brakes are an EMPI kit, and they have been on the bug for around 5yrs there all bled and no there is no pressure valves fitted, thought i need to get them sorted as i want to fit a turbo

when i put it on the test rollers i can put all my weight on the pedal and i barely can stop the rollers !!, The tester guy said if he was testing my buggy as a 1964 beetle( original donor vehicle ) then it would definetly fail the test.

[davegeezzer008]

Plus an (adjustable?) proportioning valve. If you have a glass buggy (beach buggy is usually an east coast or off shore term. Tub buggy is common in the mid-west and on the left coast it is usually the generic use of Manx or dune buggy) then there is going to be less weight differential and it will be balanced out differently. You probably less brake bias up front as compared to a stock bug and with more weight being in the rear. Are you running "cans" (drum) brakes up front?

Lee

Sorry forgot about our slang difference !! , Yes its a fibreglass beachbuggy/dunebuggy i havent any bias valves fitted and ive got discs or rotors !! all round, years back i used to have a vw beetle dual circuit master cylinder that i had to use a proportion valve but since upgrading my pedals to the RAGE ones i havent needed the valve

[Steve Arndt]

I would try a stock size master. I run four wheel CB (stock style) brakes on my bug with a standard 19mm master and rear RPV. It is a great setup, basic but works very nice.

[Steve Arndt]

Residual pressure valve is just to help keep a high and hard pedal. It doesn't change pedal force.

Adjustable proportioning valve can change bias front to rear. That has nothing to do with pedal force.

Try the proper size master cylinder.

[davegeezzer008]

Residual pressure valve is just to help keep a high and hard pedal. It doesn't change pedal force.

Adjustable proportioning valve can change bias front to rear. That has nothing to do with pedal force.

Try the proper size master cylinder.

I understand the RPV is just a one way valve and im trying to work out what size bore cylinder will work best. If i go back to a standard vw cylinder it wont fit the rage pedal cluster as the Rage mc has the bolting flanges top and bottom and the vw are either side .

[Ol'fogasaurus]

Steve is correct about proper MC size. I suspect that has a lot to do with your problem.



I run a glass buggy myself; not on the street but on the sand. I only use rear brakes (remove some weight off the front of the buggy plus, when the brakes are applied, the front tires want to lock up on the sand and dig in which can pull the steering wheel out of you hands) and they are probably the same Latest Rage (LR) design brakes you are using; based on the type III design. I suspect that I have had them for close to 15+ years now.

VW went away from the single cylinder MC as a safety thing (as I remember, the US mandated it) as if one chamber goes TU then the other chamber still should give you some stopping power. With a single chamber you have to put a Tee in place and control all four wheels from it. I use the common Bus MC but one of the bad things around the aftermarket pedal assemblies is they use a MC with mounting holes top and bottom while VW uses horizontal mounting bolts through the Napoleon's hat (front fire wall so-to-speak). I think it is the Super Beetle (I don't remember which year) has/had a MC with the mounting holes on the diagonal which, when mounted on the aftermarket pedal assembly, the reservoir, if it was attached to the MC, would be tipped; you use a remote reservoir in this case. I have one somewhere and if you want I can see if I can find it and take a pix for your. I have been told it works w/o putting bubbles in the MC but I have not tried it yet.

Lee

[Steve Arndt]

3/4" bore would be close to stock 19mm size and should give you reasonable pedal effort.

[Ol'fogasaurus]

davegeezzer008 My memory is poo-poo! When I did find the MC it wasn't what I remembered; it had conventional VW horizontal mounting. I just checked with a local VW shop and all bug is horizontal mounting and all super beetle ('71 to '79) is diagonal mounting. I hope this can get verified by a SB expert here.

If you are going to use the LR pedal assembly (I have a couple of them here myself) you are either going to have to live with the vertical mounting locations and find the proper sized MC (not a problem and the easiest and cheapest way most likely) unless you want a dual chambered MC.

If that is the case you should be able to make an adapter to mount the horizontal or diagonal hole'd VW MC to the vertical hole'd MC the LR design is designed for plus you may have to use/find/make a longer push rod. As I remember, the LR MC's push rod is captured in the back of the MC.

I did a conversion of a LR pedal assembly into a VW pan but I sure wouldn't recommend it... at least the way I approached it that is.

Lee

[FJCamper]

Hi davegeezzer008,

Let's see, 4-wheel disks but poor braking, and the boys are arguing different m/c diameters and residual valving.

Do you have rubber brake lines? I'd replace them for sure just to make the next step accurate.

Get a brake pressure gauge. It will tell you exactly what hydraulic pressure is going to your brake calipers.

http://www.summitracing.com/parts/str-p ... fgodUQYABg

You'll know exactly where the problem is.

FJC

[Ol'fogasaurus]

Checking the soft lines is a good point FJC. After just replacing mine on line that caused a similar problem I should have thought about them too.

[davegeezzer008]

Hi Guys thanks for all your replys, I had a chat with my tester guy and i need a minimum of 50% brake efficency this is calculated from the weight of the vehicle, my buggy weighs around 700-750KG a brake efficency of 350-375KG this is the load applied on the rollers on the test ramp.my calipers are single pot, my brake lines are Teflon with stainless overbraid from the MC to the calipers with aero fittings.

whatever the pressure is i need more !!!, I think ive found the scientific answer on the internet how to work it out !!!

the recommended pedal ratios are based on a maximum force of 150lbs on the pedal to attain the maximum rated pressure of a master cylinder.if the bore size of the master cylinder is decreased and the mechanical advantage ( pedal ratio ) and push on the pedal remain the same the fluid pressure and the stroke both increase.

E.G 100lbs push on the pedal and a 4;1 mechanical advantage ( pedal ratio ) gives a 400lbs push on the master cylinder.

my 7/8 master cylinder has a piston area of 0.60 sq inch and the pressure developed is 400/0.60= 667psi.
the stroke to move 0.60 cubic inches of fluid is 0.6/0.6 = 1 inch

with a 3/4 inch bore the piston area is 0.44 sq inch and the pressure developed is 400/0.44 = 909psi
the stroke to move 0.6 cubic inches of fluid is 0.64/0.44 = 1.4 inches.

What do you think ???

[davegeezzer008]

davegeezzer008 My memory is poo-poo! When I did find the MC it wasn't what I remembered; it had conventional VW horizontal mounting. I just checked with a local VW shop and all bug is horizontal mounting and all super beetle ('71 to '79) is diagonal mounting. I hope this can get verified by a SB expert here.

If you are going to use the LR pedal assembly (I have a couple of them here myself) you are either going to have to live with the vertical mounting locations and find the proper sized MC (not a problem and the easiest and cheapest way most likely) unless you want a dual chambered MC.

If that is the case you should be able to make an adapter to mount the horizontal or diagonal hole'd VW MC to the vertical hole'd MC the LR design is designed for plus you may have to use/find/make a longer push rod. As I remember, the LR MC's push rod is captured in the back of the MC.

I did a conversion of a LR pedal assembly into a VW pan but I sure wouldn't recommend it... at least the way I approached it that is.

Lee

Hi Lee i converted my chassis from VW pedals to take the LR pedal set and your right i dont want to touch it to convert it back as it was a lot of work and id have to strip the whole buggy to get to it/carry out the work and respray the area as all the holes through the tunnel were welded up and ive now got a hydraulic clutch , I did contemplate trying to adapt a dual circuit mc to fit the LR pedals but there isnt enough room between the other pedals for the horizontal bolt pattern. Only other thing i could try is fitting a remote servo as these work off a single circuit mc but id have to run a vacuum line from the back to the front. Dave