Technical Booster

[Stanley Searra]

A Question

Can i have a brake booster fitted to my X. I feel that the current stopping power is not enough. I have done the Brake disc upgrade but i feel the car has no stopping power. Is this a general that the X1/9 has.

 

[jimbro1000]

A brake booster isn't going to increase the stopping power, just reduce the pressure you apply with your legs. The stopping power is ultimately limited by the grip of the tyres, not the brakes.

If you find the stopping power is inadequate it is more likely to be the brakes starting to seize in the carriers or the flexible lines ballooning under the pressure - both of which are very common and scary enough at normal speeds but with the sort of speed you are carrying (I have a similar potential problem) you need more confidence.

If you haven't already - start with trying to get Mk1 Uno Turbo brakes on the front (I think this is what you are referring to so ignore me if you've already done it).

You also need externally braided flexible brake lines to remove the old parts from the equation (again assuming you still have them).

After that (or perhaps before all that) is a check of the master cylinder to make sure it is up to scratch - after 30 years the odds are that the internal seals are failing and a lot of pressure is being wasted.

Failing all of the above something like a tilton pedal box which can replace the brake and clutch master cylinders and even offer a brake bias control.

 

[Stanley Searra]

Ok thank you. The reason that i asked the question is a mate of mine also has the X but it's fitted with the palio 16V motor and is running a T66 on it..This car is quick and stops like hell.. But it was fitted with brake booster.

Thank you for the advice:devil:

 

[littlephil]

just to add, i was talking to a bloke that used to race old escorts. what he used to do to chuck the servo (if fitted) then bore out both circuits in the master cylinder then spin some oversized pistons and take them to the factors to find seals to fit. 'This boosted the braking pressure, retained brake bias and improved brake feel dramatically over servo assisted systems.'


sounds plausible to me?

 

[ppalma]

Weird. I could swear that boring out the master cylinder would decrease the braking pressure. Not really sure what that means, but my point of view is that for a given force applied to the pedal, the pressure inside the system will be force/piston area, and therefore bigger piston, smaller pressure. It may improve the brake feel, though...

 

[jimbro1000]

Weird. I could swear that boring out the master cylinder would decrease the braking pressure. Not really sure what that means, but my point of view is that for a given force applied to the pedal, the pressure inside the system will be force/piston area, and therefore bigger piston, smaller pressure. It may improve the brake feel, though...

Yep:

Pressure = (Leg force on the pedal) x (Pedal Ratio) / (Master Cylinder Piston Area)

A larger bore master cylinder will take up slack faster, will feel less spongy but will require more force to achieve the same braking effect which is what I think was the idea.

For racing and rallying I think this would actually be desirable (for a non-servo system), it gives much more control and feels like a solid pedal but you need serious thigh muscles to get the braking effect you would typically expect. That said I've had a brake servo fail on a race car in mid-race (at Rockingham of all places where you have to brake from high speed into a chicane at the end of the banked section of the infield circuit layout - not the best place to start practising) and getting the car to stop was brute force and guess work. The pedal felt rock solid to start with so why anyone would want to overbore a master cylinder intended for a servo system but without the servo is beyond comprehension.

 

[littlephil]

he is a fell-running brickie. He told me the reason why he did it was he also had servo fail and it put him into a tyre wall at knock hill. He described to me today that in his 'development' stage he bored out and sleeved the master cylinder to add more braking pressure but it just felt spongy as hell and kept locking the brakes. so he bored it out to where he could feel the road through the brake pedal. Oh yeah he was a left foot braker which answers a lot. He did say he tried to bore out the brake calipers and rear slaves to adjust something (i couldn't hear him so i nodded politely) but it didn't work out and f*cked up the bias.

 

[jimbro1000]

What you've described pretty much sums up what I said before.

The key to getting it all to work is to match the components together appropriately. There are plenty of sources on the internet for the equations to sort out balance and bias.

I just opted to use a tilton pedal box instead which gave me two separate brake master cylinders with a bias bar between them plus I can swap the cylinders around to get the ideal bore without having to replace anything else. It also replaced the clutch master cylinder making that significantly easier to work on.

Now I have an access panel above the pedals to stop all the stupid messing around upside down in the footwell and I can just drop the pedals out if need be without messing with anything else - supremely easy and with a huge range of options for adjustment.

 

[ppalma]

I do recall that the standard Uno comes with a pressure regulating valve for the rear brakes, a sort of cheap "ABS" that reduces the braking pressure to the rear when there is weight transfer to the front. You could theoretically fit one and modify it to adjust brake bias. Just an idea, I personally don't like to mess with the braking system.

 

[jimbro1000]

Regulator valves do not make for good brake bias control, all they do is limit the maximum pressure so both the front and rear build pressure at the same rate until the pressure limit is reached, then the rear stops while the front pressure continues to build.

A proper brake bias requires a split circuit and a proper balance bar. Even the inline bias controls are far from ideal (just a user controllable version of the regulator valve).