pdapaul's YellowSpeed Time Attack EKK24 on ITBS


I have removed my post as John is right and I'm a knob!!! :)
 
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Not so. For the slave cylinder yes, but pressure is force over area. Moving to a smaller cylinder, area goes down, pressure is constant (foot), thus pressure increases.

This is 'my' area as it were. :)
 
If you had all rears you'd have spun off on the first corner. ^^

You alway need to check what an "expert" says. Mr Flook thinks a spoiler makes more downforce if he connects it to his diff rather than his boot. No amount of arguing physics and maths will convince him otherwise because an aero expert told him.
 
80-20 front/rear is typical for a fwd car btw. And at 100% front you could drive it, buy 100% rear and you simply would lock up or hardly slow at all.

I do hope my tone is that of "helpful". I am trying to say what you have been told does not add up, and this is one area I am useful in.
 
See this is why I got confused.

My apologies John, of course your right, as the larger mc is on the rear not the front!!!

Despite my feeble attempts at explains the issue though my setting the balance bar straight was definitely the issue. The only reason it didn't cause many issues the first time out I think was the massive wing on the rear. When I took it off at Oulton my first drive into the chicane was backwards ha ha. Braking in anything other than a straight line and it just wanted to swap ends
 
JohnTurbo said:
80-20 front/rear is typical for a fwd car btw. And at 100% front you could drive it, buy 100% rear and you simply would lock up or hardly slow at all.

I do hope my tone is that of "helpful". I am trying to say what you have been told does not add up, and this is one area I am useful in.
Click to expand...
I'm always grateful for help! I just wish I'd ask for it more before I start projects !!!

Maybe my % assessment of fr/rr bias was a little exaggerated, but if you had felt the pedal how it was and now how it is I think that most of the things I've read, and implemented are somewhere near.
 
Ha ha..thankfully it's a lot easier to rectify when you have it in front of you rather than try and articulate it!!
I shall now go back and change my earlier posts so I look less of a numpty :-(

Does the way I've described it now make sense john? Now I've adjusted the balance bar 45 degrees so the front mc rod is longer than the rear. So when I press the brake I get predominantly front mc rod movement. My initial testings seem to have alleviated my issues, but if there are any other little adjustments you can suggest I'd be grateful
 
Right, I'm getting nowhere fast with the brakes, and could really go with some input. I've taken done videos to try and show the issues.
Problems I can see:
the balance bar doesn't seem to be moving as I need. It pretty much just goes back and forwards at the same angle.
The rear m/c literally needs 5mm to be fully on. The front needs at least 20 to be fully activated.

Video 1-
Everything is connected. The balance bar is approx 45 degrees as it should be and the rear mc rod is shortened. This is with the pedal pressed as hard as possible. As you can see the rear m/c throw is so short that the front barely moves.


Video 2
This is with the rear m/c removed. As you can see it literally barely moves. But it does work the rear brake even at this small movement.


Video 3
This is with the rear m/c removed from the pedal box. As you can see the rod travel is quite long. At its fullest extension the brake pedal is nearly touching the floor and there is very little pedal pressure.


My thoughts:

I think that my issues are 2 fold. I think there is an issue with the rear m/c as I don't believe that the throw can possibly be supposed to be that short. Secondly I think that the fronts are bled properly. It was all bled with both m/c in place. This would mean that when the front calipers were being bled that the rod was hardly being moved at all, this leaving air in the system.

When the box was put together the rear calipers didn't bleed as no fluid was getting to them. I tested the m/c..seemed fine..put it on the car ..no output. Eventually it just suddenly started flowing fluid, and seemed to bleed fine.

Any help would be appreciated, otherwise I'm going back to OEM.
Cheers
 
I've just looked at the last video, and I think I might have noticed another issue.

To get the fronts to activate more I screwed the balance bar towards that m/c. Should it be the other way?
 
Paul...where do live by the way. Nowhere near manchester?

As long as the spherical bearing is free the forces in the cylinders should look after themselves.

The nearer to a master cylinder your pedal actuates the bar, the more bias you are giving it.
 
I take it you meant to say the fronts didn't bleed properly? I'm by no means an expert I've never even seen these but I'm just going to give some thoughts I have - they could all be utter rubbish so don't shout at me please :D First - do you think you could have damaged the rear MC when you shut off the rear using the in car bias adjuster and stepped hard on it? I can imagine it should be able to take quite some pressure but I guess it is a possibility? Have you tried to remove both MCs and compare how much are the two piston shafts sticking out? If they were the same to begin with and one is now shorter you know it's buggered. As for the balance bar - is it attached to the pedal bang on in the middle? Or is it offset? Also, are you sure both MCs are fully relaxed when the pedal is off?
 
Also, sorry if I missed it somewhere, but are you using the larger one fro the front and the smaller one for the rear?
 
I don't think there is much wrong here.

What gives you your throw is purely the stiffness in the system. The rear looks right. If the front has massive throw that will be due (most likely) to trapped air.

Don't set it up with such an angle on the bar. The angle would ideally be around the horizontal position.
The ability it has to move is just because the movement will be a little different on each M/C due to variation in your bias on that cylinder, its diameter and the flexibilty of your braking system.

As I said...its the relative distances from the actuation of the pedal bar to each cylinder that gives your bias.

Ideally You would set it so that the bar is horizontal with light pedal pressure, and the actauation point is central, then adjust from there.

Remember the relative diameters of the master cylinders will be doing most of the biasing job by themselves. If I knew the full specs of all your brakes I could tell you precisely.
 
Hi , sorry yes I meant not bled properly!

i think the issue with the rear m/c (if there is one) has always been there since I bought it.

Before I trimmed the rear rod they were exactly the same, and when I've removed them I've endured that they are able to move to full rest.

I've checked the pedal rod, and it seems to be aligned. I've also pushed it whilst laid on underneath, and it seems to move in a linear fashion.
Yes, I believe they are fully relaxed, and all the wheels turn freely.
No I've got the 0.75 on the rear and the 0.625 on the front.
 
There is an expectation that the travel will be different, thats the purpose of the rod moving.

You may have to bleed front and back at the same time in order to get the air out. Its impossible to say without seeing, but your bar might reach the maximum angle and lock out otherwise.
 
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