Cousin Cleotis
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| posted on 22/7/09 at 09:36 PM |
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Why cant you change the pedal ratio?
I dont think more pad area acting on the disc will improve rear braking effort. More pad area with the same force acting on it will reduce the pad
pressure.
It would probaby be best the balance the brakes with line pressure, eg 0.7 front to change balance and change the pedal ratio to increase pressure to
rear. This will leave you with some fine adjustment using your bias bar.
Paul
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RazMan
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| posted on 23/7/09 at 06:14 AM |
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Thanks Paul, that's just about what I have decided to do now. I have already remade the brake pedal to improve the ratio, and this reduced the
pedal pressure and gave better feel, so increasing the size of the front m/c is my next step after trying the new pads. As you rightly say, I should
then use the bias bar to fine tune the balance ..... in theory 
[Edited on 23-7-09 by RazMan]
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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britishtrident
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| posted on 23/7/09 at 07:51 AM |
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Compound levers --- some clever forum bod sugested it yonks ago but it didn't strike me as practical at the time.
Since then I had a close look at the pedal set up on the Rover 75 it uses a bell crank -- the servo and master cylinder centre line runs accross
the car at 90 degres to the usual direction.
[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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ghostrain
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| posted on 23/7/09 at 09:55 PM |
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Razman...lets go back to basics.I assume your front Dynalites have 1.375 pistons and your rear Powerlites have 1.0 pistons.The rears are kept to small
piston sizes and a 4-pot with 1.0 pistons has the same swept area as say single pot VW calipers or Sierra rears...it is so easy to overbrake the rear
of a conventional seven with front engine and rwd.However your mid engine would need some more braking to the rear....this would normally be achieved
by bigger pistons on the rear but you have selected the Powerlites with integral handbrake and they cannot accept bigger pistons.Assuming 1.375
pistons on the front then 0.625 master cylinder is a well proven combination and should stay,if you go up to 0.7 on the front you will have a hard
pedal on the front with no feel.
On the rear you need to achieve a higher velocity ratio ,AP racing have a 0.5 cylinder,it is expensive but would achieve more power to the rear.
At present the front master cylinder needs to move substantially more fluid so the front pushrod length should be longer than the rear,at static.
You are using all round small piston sizes in all your calipers so you need to achieve more power either mechanically or hydraulically....if you up
the pedal ratio to 6:1 and change the rear master cyl to 0.5 that will achieve more power/less effort as economically as possible.
Everybody blames pads when their brakes are rock hard with no feel but pads are not usually the problem it is mostly due to incorrect
hydraulics...your brakes squeal because the lack of power is not cutting the pad against the disc,lack of power causes glazing which agravates
squealing. The Mintex is in my opinion a better all round pad over the Smart pad but will only make minor improvements it is getting the hydraulics
and mechanical advantage correct that will reward the best brakes.
Hope that helps.
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RazMan
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| posted on 29/7/09 at 07:54 PM |
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quote:
Originally posted by ghostrain
Razman...lets go back to basics.I assume your front Dynalites have 1.375 pistons and your rear Powerlites have 1.0 pistons.The rears are kept to small
piston sizes and a 4-pot with 1.0 pistons has the same swept area as say single pot VW calipers or Sierra rears...it is so easy to overbrake the rear
of a conventional seven with front engine and rwd.However your mid engine would need some more braking to the rear....this would normally be achieved
by bigger pistons on the rear but you have selected the Powerlites with integral handbrake and they cannot accept bigger pistons.Assuming 1.375
pistons on the front then 0.625 master cylinder is a well proven combination and should stay,if you go up to 0.7 on the front you will have a hard
pedal on the front with no feel.
On the rear you need to achieve a higher velocity ratio ,AP racing have a 0.5 cylinder,it is expensive but would achieve more power to the rear.
At present the front master cylinder needs to move substantially more fluid so the front pushrod length should be longer than the rear,at static.
You are using all round small piston sizes in all your calipers so you need to achieve more power either mechanically or hydraulically....if you up
the pedal ratio to 6:1 and change the rear master cyl to 0.5 that will achieve more power/less effort as economically as possible.
Everybody blames pads when their brakes are rock hard with no feel but pads are not usually the problem it is mostly due to incorrect
hydraulics...your brakes squeal because the lack of power is not cutting the pad against the disc,lack of power causes glazing which agravates
squealing. The Mintex is in my opinion a better all round pad over the Smart pad but will only make minor improvements it is getting the hydraulics
and mechanical advantage correct that will reward the best brakes.
Hope that helps.
You've been inside my head haven't you! I am thinking on exactly the same lines and I now see my choices as follows:
- Find a 0.5" m/c for the rears (if one exists) *edit* just re-read your post and will seek out an AP jobbie
- Increase the size of the rear disc (£400 for custom bells and rotors
 )
- Increase the size of the front m/c and increase pedal ratio (tricky due to my footwell constraints)
ps. I have now installed Mintex pads front and rear. These have given a big improvement in 'feel' but the front/rear imbalance of course
still remains - brilliant pads though!
BT - compound pedal is a novel idea but would again be very tricky due to footwell design. Thanks for the idea though.
pps. The squealing has now been completely stopped with the anti squeal tape (made by 3M). As this is a road car the brakes are used fairly
conservatively so perhaps they never really get hot enough to completely stop any 'glaze squeal' but the tape is a good compromise and I
can recommend it.
[Edited on 29-7-09 by RazMan]
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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RazMan
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| posted on 29/7/09 at 08:06 PM |
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Just had a look on Demon Tweeks website and found an AP CP2623 Compact Master Cylinder with a 14mm bore (the smallest they do) At £76.65 - £99.26(exc
VAT) they might be expensive, but a whole lot cheaper than new discs. I have requested info  I might even replace both front and rear while
I'm at it.
Hmmm I wonder if a 14mm/15mm combo would work better. Does anyone know how much extra braking force will be given with a 14mm m/c compared with a
0.625" (15.87mm) one?
[Edited on 30-7-09 by RazMan]
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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MautoK
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| posted on 30/7/09 at 04:20 PM |
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Taking the ratio of the diameters ^ 2 you get 196 to 252 (14mm and 5/8" respectively) so you'll get about 20% more fluid pressure with the
14mm bore for the same pedal force.
He's whittling on a piece of wood. I got a feeling that when he stops whittling, something's gonna happen. (OUATITW/Cheyenne)
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RazMan
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| posted on 30/7/09 at 06:20 PM |
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Aha! so it looks like a plan then - a 14mm m/c will be ordered [grits teeth]
I just found a lovely little brake performance calculator created by a guy called Mike Polan. It basically confirms that my combination of brakes
requires the same sizes that this thread has just deduced It should give me a 60/40 front/rear ratio which is about right for a middy.
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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RazMan
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| posted on 1/8/09 at 09:02 AM |
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Update:
After studying the AP drawings it appears that their m/c has a shorter stroke than the Girling so I have decided to buy a pair of APs to avoid any
mismatch on the bias bar - 14mm & 0.625"
That should sort my brakes out once and for all
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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RazMan
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| posted on 10/8/09 at 03:57 PM |
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Final Update:
Well my AP master cylinders arrived from Demon Tweeks and they seem nicely engineered, although I still wince when I look at the invoice - ah well the
price of perfection I suppose
Fitting them was fairly straight forward, in fact they are quite a bit shorter than the Girling units so there was a little more room to play with. I
had to shorten the pushrods by about 10mm or so to get the right pedal position but everything bolted in and it was soon time for a test drive.
As expected the pedal feels a bit 'longer' but the front / rear bias is now much better, although I still need the bias bar to be set
fully to the rear at the moment - I will have to take the car to my local garage's brake test rollers to be certain. The Mintex 1144 pads have
certainly improved the feel and I can predict and control lockups much easier now.
Brakes are now sorted - now where did I put those lumpy cams for the V6? 
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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