dan-g
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| posted on 7/4/12 at 10:51 PM |
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rock solid brakes
hi all, new here but i'l not lie, i'l be asking a fair few questions!!
i'm a 3rd year mechanical engineering student and as part of a 4 man team we decided to build a locost style car,we followed the haynes roadster
as our base.
we'r nearing the end now and are running into a problem or 2, main 1 being that theres near no brakes! we have the original set up from out
sierra donor(1988 1.8 cvh, vented front, drums rear) the master cylinder is the original minus the servo. we managed to bleed the brakes but once all
4 were bled the pedal became rock solid, its turned the pedal into a switch, full force locks up the rears or no brakes at all! theres literally 3-4mm
of travel in the pedal so something is obviously wrong!
soooo, kind people of locost, any chance of some guidance?!!! is the mc ok without its servo or do we need something else or is it something else
we'v neglected??
thanks in advance 
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owelly
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| posted on 7/4/12 at 11:00 PM |
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I'd say you'll need a different master cylinder or refit the servo. You could also alter the pivot on the brake pedal to change the
mechanical advantage but for the price of a non-servo m/c, its not worth the grief.
http://www.ppcmag.co.uk
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dan-g
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| posted on 7/4/12 at 11:08 PM |
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thinking the same alright, the servo is eh, kinda gone!
any recommendations on master cylinder?? non servo preferably
cheers owelly
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AdrianH
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| posted on 7/4/12 at 11:11 PM |
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My first thought on this is that you may have no play in the pedal movement. The master cylinder needs to fully return to the end of the cylinder to
allow for fluid to either go back into the reservoir or take from it. If it does not return you can end up with an excess of fluid in the lines and
virtual locked brakes.
So just give yourself a few mm of free play when at rest.
My roadster has the same set up vented disks at the front and drums at the rear, what size drums 8" or 9 ". do you have the sierra brake
valve in the rear line and if so is it the correct way around, do you have a proportioning valve fitted etc.
If you have the 9 inch drums fitted and no valve you may need to fit smaller rear brake cylinders, such as the 19mm ones from an escort.
See this page of my build diary, there is a reasoning behind it. I had very close to 50:50 split of brakes which would have meant the backs would
lock up as the weight transferred to the front. http://www.tamarisktechnicals.com/pages/iva.html
Have you assembled the rear drums correctly shoes have a leading and trailing edge so with some it makes a difference and lastly for now, if turning
the brakes by hand it always appears to me easier to lock the backs then the fronts.
Put up a location for yourselves and you could possibly get local help from other builders.
Have fun
Adrian
Just had another thought, is it the feel of the brakes that you are not used to without the servo there is certainly no compression of the pedal
before you are applying the brakes. Are you driving it around yet or just stationary?
[Edited on 7-4-12 by AdrianH]
Why do I have to make the tools to finish the job? More time then money.
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dan-g
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| posted on 7/4/12 at 11:34 PM |
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the master cylinder is fully returned and when the pedal is depressed theres the 3-4mm of travel and the rears lock up. although there did seem to be
a bit of a hesitation of the cylinder to return through the last 3mm or so, could be onto something there!
the drums are 9" and the valve is not in the circuit, its master cylinder to T piece to rears and master cylinder to fronts
shoes are definitely right, leading edge in relation to rotation n all that!
good thread, unfortunately i fear that'l be another problem a lil down the line, our brakes are either on or off so i'm thinking its
master cylinder causing the trouble
thanks adrian
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AdrianH
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| posted on 7/4/12 at 11:59 PM |
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If its an original MC then replace it as it will be at least 18 or 19 years old, watch out there are a few variants which could mean different hole
sizes in the plate. I have used both so not a major changing from one or the other.
As I said just check you have a few mm of slop before you have your 3 mm of travel to the brakes locking any resistance to the cylinder returning
fully home could cause this.
Have fun
Cheers
Adrian
Why do I have to make the tools to finish the job? More time then money.
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dan-g
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| posted on 8/4/12 at 12:03 AM |
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cheers, i'l give it a check in the morning
thanks, i'm sure i'l be back tomorrow with another question or 2!!
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Macbeast
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| posted on 8/4/12 at 06:48 AM |
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I have original Sierra master cylinder, discs, rear drums etc just as came off the Sierra but no servo.. Brakes work pretty well so you should get
good braking without changing anything. But yes, maybe fit new seals to the master cylinder.
[Edited on 8/4/12 by Macbeast]
I'm addicted to brake fluid, but I can stop anytime.
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whitestu
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| posted on 8/4/12 at 07:09 AM |
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The standard Sierra set up will work fine if in good condition. If you need a new MC get a smaller bore one - you can get a Fiat 19mm MC desigbed for
use without a servo for about £20, or for a bit more a Fiesta one.
Brakes International do them pretty cheap.
Stu
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mookaloid
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| posted on 8/4/12 at 08:06 AM |
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People on here spend ages trying to get a good solid brake pedal. I wonder if you just aren't used to non servo assisted brakes? This is normal
with the sierra MC without the servo. The brakes need a really good shove but they work ok with that MC.
Assuming you are getting braking at the front - you don't say if you are - then the MC might be doing it's job. (although I would follow
the advice above and fit a new one anyway.)
I think you do have a problem with locking up the rears before the front and this needs addressing. either you need a balance valve or the front
brakes are not working.
"That thing you're thinking - it wont be that."
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ChrisL
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| posted on 8/4/12 at 11:52 AM |
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You've not connected them the wrong way around, so rear brakes connected to front's MC connector?
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dan-g
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| posted on 8/4/12 at 12:24 PM |
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quote:
Originally posted by ChrisL
You've not connected them the wrong way around, so rear brakes connected to front's MC connector?
just for clarity what is the right way??!!
the brakes are working up front but no matter how hard the pedal is pushed there is no lock on the front at all!
what year fiesta??
would fitting 1 of Adjustable Brake Bias Valve | eBay to the rear line suit the job??
cheers lads
[Edited on 8/4/12 by dan-g]
[Edited on 8/4/12 by dan-g]
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ChrisL
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| posted on 8/4/12 at 12:48 PM |
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On mine the TWO front ports go to the front brake, one each sine and the ONE rear port goes to the back via a splitter somewhere inline.
Like this:
 
Description
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dan-g
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| posted on 8/4/12 at 01:46 PM |
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quote:
Originally posted by ChrisL
On mine the TWO front ports go to the front brake, one each sine and the ONE rear port goes to the back via a splitter somewhere inline.
Like this:
Description
thats similar to what we'v got, 1 port on the end of the M/C going to the passenger side, 1 port on the bottom slightly closer to the driver
going to the drivers side and 1 port on the side closest to the driver going to the rear with a T piece just behind the diff
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mookaloid
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| posted on 8/4/12 at 02:22 PM |
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the connections look fine.
when you say there is no lock up at the front - do you mean when driving? if so have your brakes been bedded in?
if they are new pads then they will need bedding in.
"That thing you're thinking - it wont be that."
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AdrianH
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| posted on 8/4/12 at 02:22 PM |
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Your set-up seems to be correct. It sounds like standard Sierra set up. I did have problems with my brake switch it is the pressure type in one of
the lines and i could not bleed the air from the line because of it until I made a modified mounting for it.
I assume that the callipers are OK and not sticking, that there is no air in the line, (love the Gunson easybleed for this), and the pads are not
contaminated all teaching you to suck eggs I am sure.
It will be something simple, it has to be.
I friend had issues not being able to bleed and apply the brakes properly because the push rod was not long enough to push the piston before the pedal
hit the bulkhead.
He lengthened the push rod and was able tosort things out from there.
main thing is not to get disillusioned and to give it a rest and then try again with a clear mind, we have all been there, stratched heads and then
kicked ourselves because it should have been obvious, well I have at least.
Adrian
Not sure if adjustable brake valves are allowed or not for IVA they were not allowed when I did mine, but it might have changed since.
[Edited on 8-4-12 by AdrianH]
Why do I have to make the tools to finish the job? More time then money.
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dan-g
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| posted on 8/4/12 at 02:38 PM |
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there the original drums, shoes, discs and pads as they were virtually brand new. the fronts are doing very very little braking, just about cleaning
off the disc and making it shiny again.
the worry is the shear force we have to put into making the brakes work, its an unsafe force needed to do any form of stopping! theres is no gradual
braking at all, no way of just slowing down
it really cant be anything other than simple,
master cylinder, copper lines, flexi hoses, rear cylinders/front calipers
all worked on the donor car with the servo but i cant see, (other than the servo making braking easier) why the M/C cant be used without the servo
we'r not worried about iva's or any testing like that, we just want a fun toy so theres no rules to worry about!!
thanks for the help lads, think i'l go hit it with a hammer or something!!
[Edited on 8/4/12 by dan-g]
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dan-g
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| posted on 11/4/12 at 02:25 PM |
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well after all that we put in a mk2 fiesta non servo M/C and guess what.....solid brakes!! and they're not even bled fully!
the fiesta has 4 ports, a aig and small at the front of the M/C and the same at the back of it, i'v the 2 front ports to the front brakes, the
small rear 1 to the rear brakes, and the big back 1 blocked off is that right??
are the rear shoes self adjusting?? the lil ratchet thingy??!
thanks again
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britishtrident
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| posted on 11/4/12 at 05:46 PM |
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If you have no servo the brakes should be almost solid.
Make sure the handbrake cable isn't over tensioned but my bet would be still on the master cylinder push-rod not allowing the rear master
cylinder piston fully back.
What need to be 100% sure is the rear piston in the master cylinder is by the stop wash not by mushroomed end of the push-rod, you may need to
grind metal off the mushroom to be sure this happens, the rough and ready method of doing this to put the push-rod in the chuck of a hand drill
and grind it against the wheel of a bench grinder.
You should also find you need a return spring on the brake pedal.
It should not matter which brake circuit is connected to which outlet port.
[Edited on 11/4/12 by britishtrident]
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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