ashg
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| posted on 5/2/10 at 01:05 PM |
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Brake Calculations
Ok Guys im tring to get my head around some brake calculations.
my brake set-up was this below
master cylinder 22.2mm
front calipers 2x 53.9
rear cylinders 2x 20.6
I have since changed the setup to
master cylinder 20.6mm
front calipers 2x 53.9
rear cylinders 2x 20.6
since the change i have noticed that the pedal has quite a bit more travel. the problem is if i push with all my strength i can almost get the brake
pedal to hit the bulk head.
there is no air in the system and the wheels will lock at about half way towards the bulk head. im just worried that i can push the pedal well beyond
the point where the wheels lock up.
my iva is approaching soon and i wouldn't want to fail because of this.
should i just get a longer push rod or should i be looking for a different solution?
[Edited on 5/2/10 by ashg]
Anything With Tits or Wheels Will cost you MONEY!!
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mookaloid
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| posted on 5/2/10 at 01:15 PM |
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are the brakes bedded in yet? the pedal should improve as they do.
you would expect more pedal travel with a smaller bore M/C but it will be easier to press.
check that none of the brake hoses are ballooning too.
Cheers
Mark
"That thing you're thinking - it wont be that."
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ashg
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| posted on 5/2/10 at 01:19 PM |
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no they are not really bedded in other than using the rears to slow down the rollers at the rolling road and a couple of short test drives round show
grounds.
im confident that the car will stop im just worried it will fail on to much pedal travel.
the brake hoses are all brand new braided items. i have checked everything 10 times over as i thought i could have a bad flair or something silly
but everything is fine.
[Edited on 5/2/10 by ashg]
Anything With Tits or Wheels Will cost you MONEY!!
Haynes Roadster (Finished)
Exocet (Finished & Sold)
New Project (Started)
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Angel Acevedo
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| posted on 5/2/10 at 01:24 PM |
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KB58 reported his calipers flexing, may that be your case?
As you have more pressure in the system, theyre subject to more pressure than theyé designed to.
Beware of what you wish.. for it may come true....
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Bluemoon
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| posted on 5/2/10 at 01:31 PM |
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Are you sure you've not got air in there.. A the diameter change is small so the travel should not be all that different (~16% longer)
Dan
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ashg
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| posted on 5/2/10 at 01:35 PM |
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could be a possibility .
what i really need to work out is how much more the pedal should travel with the new master cylinder. i have been trying to find a tool on the net to
work it out but they all want silly money.
[Edited on 5/2/10 by ashg]
Anything With Tits or Wheels Will cost you MONEY!!
Haynes Roadster (Finished)
Exocet (Finished & Sold)
New Project (Started)
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Ivan
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| posted on 5/2/10 at 01:39 PM |
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I definitely wouldn't be happy with this - never mind the test - sounds like you have no margin for lost efficiency at all in the future.
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ashg
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| posted on 5/2/10 at 01:43 PM |
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the thing is the car will stop at the lightest touch of the pedal. it doesn't feel spongy, its nice and progressive and will lock the wheels
quite easily.
Anything With Tits or Wheels Will cost you MONEY!!
Haynes Roadster (Finished)
Exocet (Finished & Sold)
New Project (Started)
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Ivan
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| posted on 5/2/10 at 01:47 PM |
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quote:
Originally posted by ashg
could be a possibility .
what i really need to work out is how much more the pedal should travel with the new master cylinder. i have been trying to find a tool on the net to
work it out but they all want silly money.
[Edited on 5/2/10 by ashg]
I think that the pedal travel is an inverse of the area of the MC against original MC area. i.e. reducing the area of the MC by half will double the
travel
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bodger
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| posted on 5/2/10 at 01:48 PM |
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I think this came up on here not long ago. They failed IVA. I think they eventually discovered a slight leak to be the cause. Once the calipers have
clamped around the discs the pedal should be rock solid, you can't compress a fluid so i'd suspect a leak in the pipework or internally in
the master cylinder.
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brianthemagical
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| posted on 5/2/10 at 02:16 PM |
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Why did you change the MC. Sounds like you could use a larger MC and still have adequate power.
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ashg
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| posted on 5/2/10 at 02:22 PM |
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the seals blew out on the old master cylinder so when changing it I decided too get a smaller one as others had recommended it as as an improvement
Anything With Tits or Wheels Will cost you MONEY!!
Haynes Roadster (Finished)
Exocet (Finished & Sold)
New Project (Started)
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Horizenjob
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| posted on 5/2/10 at 02:59 PM |
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As said above the difference is 16%. You may never have pushed as hard on the old brake setup. Something is flexing or there is air.
If the pads are old they may have a taper. If they are new and the disks have a little wear, you must wear the pads a bit to conform. You could likely
see this or bending of the calipers if you have someone else do the pedal while you watch each brake carefully.
I find bleeding after driving a distance gets a little more air out, it shakes some bubbles lose.
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RAYLEE29
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| posted on 5/2/10 at 03:06 PM |
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If i were you id look at the rears take it theyre drums?
if you have old drums and new shoes they could quite easily work ok but flex out to fit as more pressure is applied.
check the drum diameter is not at or over max size. you used to be able to buy oversize shoes years ago but not these days.
when you take off the drums look to see how the shoes are wearing if its not even all round then theyre definately not the same rad as the drums and
will be flexing
Ray
[Edited on 5/2/10 by RAYLEE29]
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RAYLEE29
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| posted on 5/2/10 at 03:12 PM |
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if you get desperate to find where the prob lies use g cramps to stop your pistons moving. do the rears and try then the fronts. you should be able to
tell where the problem is and concentrate on that area
Ray
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Bluemoon
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| posted on 5/2/10 at 04:01 PM |
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ashg, The master cylinder you choose is little different from the original, you will get as said about 16% more travel and 16% more breaking effort
for foot effort, not a big difference (not to say it's not noticeable, or worthwhile!). Might do this myself one day (but have new old stock
master cylinder that's good at the moment).
Once properly sorted it should go solid quite quickly the movement required by the slave cylinders is very small and should not use much fluid..
Dan
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