Brake Balance Bar

[yr51ocw]

Anyone used this product, or have an feedback on similar:

http://www.ebay.co.uk/itm/Peugeot-106-Brake-Balance-Bar-Bias-Pedal-Box-Wilwood-Master-Cylinders-/230699874177

It appears to be an simple solution to enable good control of the front/rear brake bias, with the downfall of removing the servo assistance.

Currently I am struggling with reducing the rear brake effectiveness even with a brake bias valve (which I have also found to be un-reliable due to seal failure in both a wilwood and compbrake valve, which use the same seals)

My initial concern is that is looks quite thin walled steel in the construction which could flex under high forces.

Your thoughts?

[axsaxoman]

I have never had a bias valve fail --so something is wrong
plumbed in wrong direction?
connected to wrong half of master cylinder?
Is this an ABS car ?
what size front caliper(piston dia)
I have tried 3 different types of bias pedal boxs and none of them work very well due to lack of mechanical advantage on the leverage ratios from the cross shaft set-up.
that unit you show works fine on LHD as its direct onto the pedal

[yr51ocw]

The compbrake one failed due to brass swarf being inside the valve damaging the seal, poor quaility standard in the manufacturing of the valve, they had also used PTFE tape on the hydraulic sealing threads which is a no no. When I tried to raise my concerns with them, they did not want to know.

The wilwood failed due to a seal ageing.

Just because you have not had one fail, does not mean that it does not happen, although I would agree that it should be very rare.

Direction is as specified, two port ABS master cylinder, with ABS removed. Front lines are from rear port of MC and rear lines are from front port.

Front piston diameter is 34.6mm (4 opposing piston type), about 19% larger area than OEM caliper, acting on a 266mm rotor. I have done a few calcs, and with the set up I have will increase the front bias by approx 2% over a regular saxo vts.

Front to rear static weight bias is 65/35% total vehicle weight (no driver) = 652kg. (citroen ax, not a saxo)

Have you tried a balance bar being actuated from the end of the cross bar? I couldnt quite understand from your post, or have you only tried the floor mounted pedal boxes?

[axsaxoman]

The compbrake one failed due to brass swarf being inside the valve damaging the seal, poor quaility standard in the manufacturing of the valve, they had also used PTFE tape on the hydraulic sealing threads which is a no no. When I tried to raise my concerns with them, they did not want to know.

The wilwood failed due to a seal ageing.

Just because you have not had one fail, does not mean that it does not happen, although I would agree that it should be very rare.

Direction is as specified, two port ABS master cylinder, with ABS removed. Front lines are from rear port of MC and rear lines are from front port.



Front piston diameter is 34.6mm (4 opposing piston type), about 19% larger area than OEM caliper, acting on a 266mm rotor. I have done a few calcs, and with the set up I have will increase the front bias by approx 2% over a regular saxo vts.

Front to rear static weight bias is 65/35% total vehicle weight (no driver) = 652kg. (citroen ax, not a saxo)

Have you tried a balance bar being actuated from the end of the cross bar? I couldnt quite understand from your post, or have you only tried the floor mounted pedal boxes?

yes I have used both the type you show and the floor mounted type .
you really need to connect both the ports together from the m/c then split it to one line to fronts +one to back ,then use the bias on the rear line .
the way the m/c works the twin pistons have a spring gadget between them which will limit the travel to the one having most restsitance --and the bias only restricts pressure after the valve ,so too much up line pressure relative to piston area will not allow the fronts to move enough to get the pressure you need,so you will get lots of rear relative to front, because you have 19% more area you will get more pedal travel to get same braking pressure

with a four port you just link front to back on the m/c and then use the other sides to go to front and back .
you need a minimum of 80-100bar at the frontcalipers to get proper braking and you just can,t get those numbers with a bias box you show ,and have a nice short pedal

the right answer is a larger m/c something a like 25/26mm --there isn,t one made that fits .
I suggested i could get them made years ago ,but everyone seemed to think that £120 for the right cylinder was too expensive --so i never got them made
that would have given a good solid pedal with much less travel --and would have suited any saxo /106

our AX race car was a LHD -and even the std brakes were dramtically better than a rhd axct or ax gti -the cross linkage was never a good design and they didn,t make it any better when the saxo came out --same thing to all intent

[yr51ocw]

you really need to connect both the ports together from the m/c then split it to one line to fronts +one to back ,then use the bias on the rear line .
the way the m/c works the twin pistons have a spring gadget between them which will limit the travel to the one having most restsitance

Thats interesting, I was under the impression that the spring between the two ports gave a delay and reduced actuation to the front port. (hence why fitting the rear hydraulic system to the front port)

I have tried to take a OEM M/C apart, but there is a ball bearing holding the internals in as opposed to a circlip, and I can not seem to get the ball bearing to move. Another option would be to change the spring stiffness between the two cylinders to change the effectiveness of each. Any experience of trying that?

[yr51ocw]

Just been through the front caliper piston area calcs again, OEM calipers are 48mm diameter therefore 1809mm2 area. My current caliper are 2x34.6mm which is an area of 1880, so only a 4% increase in area. Not 19% like I thought.

[axsaxoman]

but if you are using 4 pot caliper ,then you need to double that number =3761
which is nearly twice the area , so twice as much m/c piston travel
the spring pressure is so little it will not make any difference --just link both ports together --

[yr51ocw]

but if you are using 4 pot caliper ,then you need to double that number =3761
which is nearly twice the area , so twice as much m/c piston travel
the spring pressure is so little it will not make any difference --just link both ports together --

Already doubled that number, 34.6mm diameter on two pistons = 1880mm2

Linking both ports together is a bad idea, it means that if there is a leak in any line then ALL braking effort will be lost, at least keeping the lines separate you will loose only the front or the rear, the less of two evils.

Currently looking at differential piston tandem master cylinder with a 23 and a 20mm piston. Doubtful if it can be made to fit though.

[axsaxoman]

I understand what you are saying
BUT
the only usual way you are going to get such a major leak that you won,t have any brakes is if you have an accident and rip a strut off -- in that case you,ve already come to a stop
and you still have a h/brake --or emergency brake as its referred to in the mot manual

what are these calipers from ,as I have never seen a 4 pot caliper with 17.3mm x 4 pistons
or are you saying the caliper only has two pistons --one each side of the disc
we are talking about the front calipers?

[yr51ocw]

front calipers, 4 opposing pistons each with 34.6mm diameter. (therefor the total area of one half of the caliper is 1880mm2)

I would not agree with you in regards to the major leak being only from a crash. I have melted the seals (bridge seals between two half of caliper, unfortunate they are not a race caliper with a hard pipe between the two halfs) which caused a substantial leak.

I have recently tried a pressure gauge on the brake lines, without servo assistance, about 60bar is all that could comfortably be produced (and I guess repeatedly produced for 15-20minutes lapping a circuit), so the standard pedal ratio is not adequate, called the supplier of the product linked to in the first post and the confirmed that is is a 1:1 rocker ratio, so the total pedal ratio would remain as per the standard configuration which is not good to me.

I have also tried to contact wilwood and find out the response curves of their bias valve, as with a differential bore tandem MC I could be under the knee point of the valve for a large proportion of the braking time.

[axsaxoman]

OK but as far as movement of fluid and pedal travel all pistons move back so on first application you are moving 4 pistons per claiper and thats what gives you a long pedal --this is why you see some cars fitted with residual vlaves in the brake lines to stop the pistons moving back to much lsightly out of true discs will cause more piston knock back .
the other suggestion if you wont, accept a coupled m/c is to use the bias twin cylinder unit that can be fitted direct on to the servo unit
even with yuor substntial leak you would feel the pedal going soft ,so you always get a warning ,you never get total brake failure with a leak .
what disc size are you using ?

[yr51ocw]

the other suggestion if you wont, accept a coupled m/c is to use the bias twin cylinder unit that can be fitted direct on to the servo unit
even with your substantial leak you would feel the pedal going soft ,so you always get a warning ,you never get total brake failure with a leak .
what disc size are you using ?

I was thinking that a twin MC unit could be fitted with the standard servo in place, however I am not aware of one being off the shelf, and my I do not have the free time and fabrication skill/tools to be able to manufacture one myself.

Using 266mm disks, under 13" wheels.

[axsaxoman]

compbrake do a universal one --bias unit fitted to a lump of alloy which you machine to fit the servo
the disc+ wheels size will be the main reason for overheating
I am guessing you are wanting to keep 13" rims for the gear ratios/tyre size

[yr51ocw]

just encase anyone searches for this in the future....

the original saxo MC was replaced with one from a Volvo 740 which has two different pistons sizes, 23.8 & 19.04. This has improved the brake balance no end. At the same time a smaller servo was fitted but that was probably a mistake as excessive pedal force was required. So back to the original servo size is the next step

[scottie_436]

Interesting :)

[scottie_436]

Marc...

You still have to use bias valve..yes? And im guessing the bigger piston for the front?

What size servo did you run and what size was the "smaller"?

Ash

[yr51ocw]

Hi Ash,

Yes larger piston for the front calipers, I still have the bias valve but once the larger servo is fitted it will need a little fine tuning, at the minute it is set to minimum rear pressure.

I dont know the servo size that is on it, it was one from a 1.1 AX. I should measure it up at some point.

How was your day at cadwell?

[scottie_436]

Good info there. I really need to sort my brake balance out!

Yeah it was good... Couple of minor issues... Misfire on sighting laps due to water sat in no4 plug hole (doh.. Wont be washing it off again before a trackday lol) ... And a weird over reving problem, refused to idle below 4k revs. Not sure if throttle was jamming or it was a vac leak. Removed the small vac hose from cam cover to tb and blanked it. Seamed to behave after that!

Ian had fun too lol