mainlandboy
|
| posted on 30/3/04 at 01:04 AM |
|
|
No brake booster = hard pedal?
Hi all,
Quick question. I noticed that no one building a locost uses a brake booster (I think over there you call them a servo). Either way, I mean the
vaccuum operated assist chamber usually mounted in front of the master cylinder.
How heavy is the pedal effort without using the brake booster? Is the weight of the Locost low enough that the pedal effort is not too bad without
it?
Thanks!!
Mark.
|
|
|
|
|
Jon Ison
|
| posted on 30/3/04 at 06:06 AM |
|
|
yup, nice "firm" pedal, gives a better (IMO) feel to braking too.........
|
|
|
theconrodkid
|
| posted on 30/3/04 at 07:55 AM |
|
|
you wil need a long pedal tho,to give you about 5-1 leverage or its hard work stopping 
who cares who wins
pass the pork pies
|
|
|
Hellfire
|
| posted on 30/3/04 at 08:56 AM |
|
|
You may have to go to the Gym to give the left leg a work out ~ if you don't want odd legs that is 
Unless you're trained in the left foot braking technique! Eh Jon?
|
|
|
steve m
|
| posted on 30/3/04 at 09:14 PM |
|
|
My brakes wer not very good as I had shortened the peddle to much
so by using 4 pot calipers improved them
also by moving the fulcrum point up the peddle by 1/2" , gave me a much better feel and brakes
|
|
|
stephen_gusterson
|
| posted on 30/3/04 at 09:34 PM |
|
|
i think most dont use them cos the servo part is big and takes up a lot of space.
I have used an ABS system thats pretty huge on my car. I fitted the abs cylinder transversely on the passenger side, and operated it via a crank and
rod system. A lot of UK cars have a remote system to operate the brakes as many cars are designed RHD and the mfr keeps the cyl in the original
position, using the linkage.
atb
steve
[Edited on 30/3/04 by stephen_gusterson]
|
|
|
britishtrident
|
| posted on 1/4/04 at 07:52 AM |
|
|
quote:
Originally posted by mainlandboy
Hi all,
Quick question. I noticed that no one building a locost uses a brake booster (I think over there you call them a servo). Either way, I mean the
vaccuum operated assist chamber usually mounted in front of the master cylinder.
How heavy is the pedal effort without using the brake booster? Is the weight of the Locost low enough that the pedal effort is not too bad without
it?
Thanks!!
Mark.
Use a mastercylinder size that is suitable for non servo use and a pedal ratio of between 4.5 to 1 and 5.0 to 1 and everthing is fine. No need to
change the caliper (they were oversized for the book donnor Escort).
An easy to find mastercylinder design for use without a servo is one from a base model 1980s VW Polo or Golf it is a 19mm (3/4" bore., cars
with servos use mastercylinders with a bore 22.2mm (7/8" or bigger.
Using a smaller mastercylinder bore reduces pedal effort.
If you do build the car and still find the pedal too heavy then Green Stuff brake pads give a 10% increase in braking effort for the same pedal
effort.
[Edited on 1/4/04 by britishtrident]
[Edited on 1/4/04 by britishtrident]
|
|
|
Marcus
|
| posted on 3/4/04 at 03:14 PM |
|
|
On car 1 we used a servo with no problems at all - if you go for a floor mounted pedal box, there's plenty of room.
Car 2 (avatar) has no servo and a similar floor mounted pedal box, albeit with slightly longer pedals, there appears to be little or no difference in
pedal effort. Both cars stop very quickly even with stabdard calipers / pads.
Marcus
Marcus
Because kits are for girls!!
|
|
|
madforfishing
|
| posted on 4/4/04 at 06:04 AM |
|
|
After much consideration and the fact that having a long pedal to conpensate for lack of servo assistance would really mess things up with my UK size
12 feet, I decided to use a servo. Space is a problem as the reservoir sits on the master cylinder and clashes with the steering column
extension. The solution was to remote the reservoir up to the scuttle using appropriate pipe. I just made a bracket to mount it out of folded Ali
and bolted it up. It makes for a P.I.T.A** when removing the scuttle, but hey, there's loads of other stuff to remove if it comes to that, so
why not.
|
|
|
britishtrident
|
| posted on 5/4/04 at 02:31 PM |
|
|
quote:
Originally posted by madforfishing
with my UK size 12 feet, I decided to use a servo. Space is a problem as the snip
o that, so why not.
Even with a size 9 its cramped
If starting a new chassis I think would increase the height of the chassis sides by a 1 inch perhaps even 2 inches and have sloping sides in the
cockpit Lotus 7 style.
|
|
|
Jasper
|
| posted on 5/4/04 at 03:18 PM |
|
|
No servo, pendulum pedals, 4 pot calipers, seems just perfect to me, good feel to the brakes without too much effort.
|
|
|
andkilde
|
| posted on 5/4/04 at 03:52 PM |
|
|
Hi there, Ted from Ontario. It's worth spending a bit of time researching how to size braking components, you get a good understanding of the
forces involved. The racing brake folks have formulas and selection guides on their websites -- very informative.
The basic parameters are master cylinder bore size, caliper bore size*, pedal ratio, diameter of brake disc/drum and coefficient of friction (µ) of
your pad/rotor combo.
*Some caveats for calculating caliper size, you need to add up the total amount of piston area (either, single piston sliding, double opposed pistons,
two piston sliding, four opposed pistons, etc depending on donor), for sliding calipers you double it.
The system pressures and such can all be calculated using simple math.
ie. assuming the following
5:1 pedal ratio, 1 sq" master cylinder bore, µ=1, 12" rotor, 4 sq" caliper, 100lb foot pressure.
Stopping power at wheel= 5(pedal ratio) x 100lb(foot pressure) x 4 sq" (caliper) / 1 sq" (master) x 12" (rotor dia) x 1 (µ)
=24,000 inch pounds (2000 foot pounds) of stopping force at wheel
Actual numbers wil vary a bit µ is usually closer to 0.4 or 0.5 (number usually provided by the pad supplier), and if you go to the gym you'll
discover that you can probably do a 300lb leg lift (with one leg).
Or to get back to your original question -- you can get excellent stopping power out of an un-servoed system, particularly on a light car such as a
locost. Look up some of the boys from the Vancouver Mini club and take an old Mini out for a drive, they're about 1500 pounds and use a simple,
unservoed brake system, very progressive and not too much pedal effort -- I always have a difficult time getting used to power brakes after driving a
"proper" car, find them spongy and unpredictable by comparison.
Cheers, Ted
|
|
|
dblissett
|
| posted on 5/4/04 at 09:33 PM |
|
|
pedals from sierra
i was planing to use the sierra pedal box and standard pedals without the servo
but this seems to have about 4.5 /1 ratio
if all the other coments are true does this mean i will have crap brakes not good for a sports car
has anyone else used standard length sierra pedals and what are your brakes like
cheers dave
|
|
|
britishtrident
|
| posted on 6/4/04 at 06:01 AM |
|
|
quote:
Originally posted by dblissett
i was planing to use the sierra pedal box and standard pedals without the servo
but this seems to have about 4.5 /1 ratio
if all the other coments are true does this mean i will have crap brakes not good for a sports car
has anyone else used standard length sierra pedals and what are your brakes like
cheers dave
A servo dosen't give you better brakes just a lighter pedal with less control of the brakes.
The OP was asking if he could have light pedal effort to suit his damaged knee without using a servo the answer was yes.
|
|
|
dblissett
|
| posted on 6/4/04 at 11:31 AM |
|
|
pedal effort
does this mean that with no servo the effort needed on the brake pedal is much higher to get the same level of braking
therefore no servo and standard pedals = lots of force needed at the brake pedal
which to my thinking means crap brakes
i used to have an old transit van without a servo it took a good stamp on the brakes to get it to stop and i am trying to avoid that
cheers dave
|
|
|
britishtrident
|
| posted on 6/4/04 at 11:45 AM |
|
|
Never had any problem stopping with Transit brakes --
Do you mean a Transit van without a servo or a Transit with a non-working servo --- Having been asround Transits since 1967 I can't remember
one without a servo certainly not one with disc front brakes which came in when the V4 was ditched in 1976, prior to that they had drums on the front
which work better without a servo..
|
|
|
dblissett
|
| posted on 6/4/04 at 11:51 AM |
|
|
transit
it was a very old transit van which never had a servo to start with
i ran it for motor bike racing in the early 80's it was a banger then but i cant remember how old
it carried the bike so thats all i was botherd about at the time
dave
|
|
|
mackie
|
| posted on 6/4/04 at 12:26 PM |
|
|
It can be a bit disconcerting when driving an unservoed car after being used to servos
However if it's designed properly (and it really needs to be!) then it's still quite possible to exert maximum braking effort (ie locking
the wheels) and you get a whole lot nicer feel and a much firmer pedal.
We are going to not use a servo i think, primarily because I don't think it's needed and secondly because a servo probably won't fit
with the big engine.
|
|
|
