Excessive brake travel ?

[hissing sid]

I have an XR4i pedal box, servo and new master cylinder, with jag XJ 6 brakes, all with new pistons and seals. I've bled them twice and the pedal is very firm ... eventually ... That's the problem, I have about 40mm of free travel before the brakes operate. Is this because I'm driving 12 pistons with a master designed for 4, so no solution, or is there something I can do ?

[TINKA]

Sometimes thees brakes take a lot of bleeding, I would suggest trying it again. I have a Marina setup which operates perfectly with hardly any free play at all, so just keep bleeding. I had trouble when I first built my car and did find in the end that despite all these quick and easy bleed accessories the only way to do it properly is one person pumping the pedal and another with a spanner on the bleed nipple doing it the old fashioned way.

[neil still building it]

hi

if you can ...use hose clamps (that temporarily clamp the hose ) and isolate each corner ,to highlight which wheels the problem.then when you bleed, if you can also push all pistons fully home ie evacuate all the gaps available for air to get trapped in.
so wedge caliper pistons -be carefull of your dust seals.
and clamp brake shoes together to do the same with these pistons(you can put a sdrew driver between the piston and shoe , rotate the piston 90 degrees to stop the shoe going in the slot,maybe even wedging to help.
all this stops air getting trapped where it can't get 'out'
it helps!!!
this may or may not be your problem.......
now is your master cylinder returning fully home?? if not you won't uncover the 'port' that leads to the reservoir...also not good.....
so a few things to check??
good luck
NEIL

[mikey]

I guess I get around 30 to 40 mm at the pedal, but they are firm and it will lock the wheels evenly without pumping. If it dosent feel spongy and you dont need to pump them up then I'd leave them alone unless it bothers you.
If you want to check if its OK take it to a tyre place and get the efficiency tested on each wheel and see if they are even.
Mike

[neil still building it]

hi guys
sorry i just reread the post ...of course you'll be needing to push all the pistons in ...then bleed it of course...DOH!! but some still applies..clamp each wheels' hose to identify the culprit..then you can concentrate on the worst /only bad one instead of wasting time....
NEIL

[Purple AK]

Hi Sid.

I guess it was you I spoke to at Brands on Saturday Sorry if I seemed a bit vague (It's normal) but it had been a long couple of days
I don't think it's a 4 piston 12 piston thing, as many manufacturers use a similar setup (AK - Escort/Marina. Dax - Escort, Etc) all with Jag calipers. You may find that it is just that the pads are not yet bedded in My pedal improved alot after a few miles :thumb:

[Alaska Gray]

Clamp each flexable pipe then bleed one at a time starting furthest away fron the master cyl useualy works:thumb: :thumb:

Graham

[mikey]

I am still a bit confused. I had a check last night after the post.

By Beamer gives about 40 mm before the brakes bite and my brother in-laws Mondeo is over 50 mm. These are all at the pedal.

Does the pedal feel spongy. Engine on tickover push the brake hard - does the pedal want to dissapear to the floor. Also can you pump it up or not.

Sorry but if you have a good pedal I think you could be barking up the wrong tree unless I have misunderstood you.

Dave Brooks build a lot of Cobras and as I dont think it gives a monkeys how many pistons you have I would ask him for a general view
Mike