Brake pedal goes to the floor

v8viva · Post by **v8viva** » Mon Feb 12, 2007 6:38 pm

Hi..just finishing off my HB Viva V8 project and have a problem with too much travel on the brake pedal.I am using calipers all round(scorpio on the front with focus discs and sierra discs and calipers rear) and have an oldy worldy single line girling master cylinder.If i clamp the rear brake hose off ever so slightly the pedal is ok and the same with the front flexi's....clamp them off slightly and the pedal is at the top and rock solid,but without a clamp the pedal is somewhere near the floor.
Does it seem like the master cylinder isnt man enuff to shift enuff fluid for 4 calipers or does it seem like i need brake reducing valves to the rear to limit the amount of fluid travel to the rear calipers?
I read a bit on risidual pressure valves but these are only really used if the master cylinder is mounted lower in the system than the calipers.
I have a remote servo plumbed in under the dash if this should make any difference?
Just wondering really if anyone is using a girling master cylinder with caliper front and rear set up

Post by **Coops** » Mon Feb 12, 2007 6:47 pm

i would say master cylinder,
as it was designed for smaller pistoned front calipers and wheel cylinders on the rear.
and not the big scorpio front pistons and sierra rear pistons,

Post by **katanaman** » Mon Feb 12, 2007 7:20 pm

I would second what Tony has just said, your master cylinder will be too small.

ian.stewart · Post by **ian.stewart** » Mon Feb 12, 2007 7:48 pm

Master cylinders, my favorate

Lets get this right,
You are using Scorpio front callipers, and Sierra rear callipers,
the thing you have to look at is the master cyl volume compared to the volume needed for the calipers, if you go around the breakers yard and look for a car with a similar system to what you are using, IE single floating caliper on the front, and single on the rear, I did the walk around the breaker thing, and selected a master cyl from a BMW for my Cortina with 4 pots on the front and single calipers on the rear, which was almost identical to the BMW set up,
For You, I would probably be looking at somthing like a 4WD disked Seirra, Mk6 RS2000 or Mundano, If you use the master cyl from one of these cars, they will be in the area of what you need, What you will need to do is remove the cylinder from the servo and make an adaptor to fit your bulkhead and pedal, you may also need to convert the master cyl to remote bottles if the cylinder is at an angle in the original car.

v8viva · Post by **v8viva** » Mon Feb 12, 2007 9:00 pm

Cheers for all that and it does all make sense.Not really overjoyed at the prospect of chopping it all about but needs must and all that.
If it was easy everyone would be doing it!!

ian.stewart · Post by **ian.stewart** » Mon Feb 12, 2007 9:33 pm

fitting the master cyl is probably only a plate to turn the bolt pattern around from the vertical to the horizontal, and you may be lucky with the resovior which may pull out and leave rubber bungs behind, so all you need to do is get some push fit pipe tails made, so you can plumb in a remote.

v8viva · Post by **v8viva** » Mon Feb 12, 2007 10:07 pm

Plus if i go down that route i can run a dual line system rather than single line.Servo would get binned but i have size 12's so shouldnt struggle!

Post by **katanaman** » Mon Feb 12, 2007 11:38 pm

If you insist on not using a servo then you have even more problems. You will have to get the ratio perfect or you will easy end up with a brake peddle that is rock hard and absolutely no feel to it. And that's assuming you can even get the car to stop. Disk brakes need a servo as the have no self servo effect like drums do. It can be done without but your going to have to do the maths to get it right.

JSF55 · Post by **JSF55** » Tue Feb 13, 2007 12:04 am

Theres a good right up here in the tech pages, unfortunatley the site is down at the moment, but don't worry i've pm the server guy, and if it's not up and running tmrw i'm not buying him any beer !!
http://www.uk-hotrods.co.uk/v2/contents.php

ian.stewart · Post by **ian.stewart** » Tue Feb 13, 2007 12:17 am

Marki, perhaps I have been lucky, but, I have had no problems like you describe, I think the only problem that may occour is the pedal ratio may need adjusting, and I think the car being a Viva it probably has a pedal ratio more suited to a non servo set-up
I have superb brakes using a non-servo system and discs all round, quite a few people have commented more on the stopping power my the car rather than the accelleration

The other way I look at it is you dont see many Race cars with servos, All servos do is lessen the pedal pressure at the detriment to the feel of the brakes, Servos are for GIRLS
The other thing with servos with tuned engines with lumpy cams is the lack of vacuum to power the servo.

Post by **katanaman** » Tue Feb 13, 2007 12:25 am

I agree with you Ian it can be done but given the member threw a load of brake parts onto a car and didn't even think about the master cylinder I think in this case it would be very unwise. No offence meant v8viva I am just trying to keep you in one piece and make you realise you have some working out to do. If you went the route Ian originally suggested it would be a lot easier and safer.

ian.stewart · Post by **ian.stewart** » Tue Feb 13, 2007 1:00 am

The way I described will probably work as the set up used is a standard ford set up, may even be worth a look at the Scorpio,[the only reason I never mentioned the Scorpio is it may be hard to get the cylinder to work due to the ABS] as the front brake calipers are from a Scorpio and the rears are from a sierra, which are the same calipers as used on the Scorpio, other than some being capable of using vented discs. I am fairly sure all RWD disc braked fords used the same caliper on the rear, apart from the vents, and I also think the Mk6 RS2000 used the same callipers, so all is not lost. and even the hand brake cable from the Escort could probably be used, abiet with a suitable handbrake lever with the correct ratio for disc brakes,
Ian

kiwicar · Post by **kiwicar** » Tue Feb 13, 2007 2:11 pm

Hi v8viva
If you are going to have to go to the effort of building a set up to adapt a non standard master cylinder into the Viva it may be of little more effort to use a dual master cylinder pedle box for a seven replica, or similar(robin hook, MK, sports, SSC, etc) this would give you the ability to ballance the front to rear breaks and someone will have already worked out the pedel ratio. This is a common set up on Sevens so will be mostly sorted.

here I go again

Best regards
Mike

v8viva · Post by **v8viva** » Tue Feb 13, 2007 6:54 pm

cheers again for all that.My mate is running a lotus powered viva using calipers front and back and still has the standard girling master cylinder albeit without a servo which works ok ,so i guess its not all doom and gloom.
Out of interest ian....what master cylinder do you use on your mk2 tina?

ian.stewart · Post by **ian.stewart** » Tue Feb 13, 2007 8:10 pm

The cylinder is from a 5 Series BMW, 525 I think, the reason I used that one over the later one was the master cyl has a remote resovior but still uses a similar set up to what I am using, Porsche 968 calipers on the front and Scorpio non vents on the back, originally I had Princess callipers but later went for the Porsche just because they are lighter,