Front Brakes locking up
 

Hi all,
just got the car back from the engineer today,
he was doing the brake and noise test and checking the rest over. good news first was the list of things to fix up was short, bad news was, brake test failed because the right front keeps locking up in the test and the noise failed also, was 94dp, I have fixed the noise I think but the brake problem I don't know, have you got any ideas.
I have commodore booster and master cylinder and jag 4 spot calipers at the front is there a way to lower the pressure to the front brakes.
Thanks
Chris.

Good to hear that you’re so close Chris,
Brings back memories of the final engineers fix up list I had back in 99.
2 and a half metres of chook wire fixed my noise problem.

Not sure why your drivers side would be locking before the passengers, but I can shed light on the front to rear bias.
You may want to take a drive to ABS Brakes in Ferntree gully.
I think they have a brake dyno.

One guy in the club recently took his 4 spotters off and put on 3 spot front calipers on to great affect for front to rear bias.

I recently changed my front calipers thinking it would be a quick cheap upgrade (but nothing is that simple).

Changing the single piston HQ caliper to a 4 piston BMW caliper greatly increased the braking on the front of the car to the point that the rears just couldn't keep up.

My solution was to change the master cylinder to a model that didn't have a crack point (ie: a pressure switch that stops further pressure being applied to the rear brake during hard braking when weight is transferred to the front of the car).

The master cylinder I used was a ford one tonner. That ute came with an auto adjustable bias depending on the weight you were carrying in the rear of the ute.

Once fitted I had equal brake pressure to both front and rear of the car (very dangerous, because the rears would lock up easily under hard braking).

My understanding of a matercylinders brake bias is:
If you are driving at 80kmh and apply the brakes gently you may be placing 500 - 700 psi of pressure through your brake lines to both front and rear and the car will pull up nicely using all brakes.

But if you are traveling at 80kms and have to emergency stop as soon as you hit the brakes HARD a full 1500psi of pressure is applied. The bias switch will be triggered at around 500-700psi and limit pressure to that amount to the rears. As you slow there's a large weight transfer to the front of the car lifting weight from the rear. Hopefully that 500-700 psi is just the right amount of bias to stop the rears from locking before the fronts.

So when I put the new master cylinder in I had to fit an after market brake bias controller (from Wilwood).
I used the Calder park test day to dial it in and as I mentioned in a previous post, the car has never stopped better.
I'm guessing because it has been set up to be so well balanced in the dry conditions, I will need to adjust it if we have a rainy day out at a race track (but I don't mind).

The only other point that I should bring up is with the better fronts fitted it is easier to lock the fronts before the rears in an intermediate braking situation (this being because the fronts are working better than the rears with the same amount of pressure in the lines before the bias switch cuts in).

May have done it all different in hindsight.
But I'm very happy with the end result.

If you do fit an adjustable bias control it will need to be under bonnet to pass ADRs as it is not considered legal to be able to adjust the brakes from inside the vehicle.

Good luck mate, You're so close.:)

Glad to hear you are so close Chris.
With your exhaust are you running under car or side pipes?

Thanks Jason
I was thinking about a bias control but didn't know where to start looking I didn't want to just go anywhere, did FTG brakes fit the bias adjust valve or just supplied the valve. I made two 1 1/4'' pipe silencers to go into the 2 1/2'' pipe just before the mufflers and this has quietened it down a bit I hope.
I will ring FTG brakes in the morning thanks.

Chris.

Hi Boxhead,
I am running under car 2 1/2'' has been a tight squeeze, side pipes will come later I hope,
Chris.

Chris,

No I didn't go to FTG, I fitted the system myself with help from my mechanic friend in Packenham.

I bought the variable bias controller from performance warehouse (only $80).

If I was you I'd leave this as a last option, talk to the brake guys first.

Main reason being you wouldn't be able to fit it with your current master cylinder
and if you do find a master cylinder that is suitable, it may not mate up to your booster.

I think 3 spotters on the front would be the quickest and most cost effective way to get the balance a little better.

Chris,

Talking about brakes, where do your brake lines sit under the front wheel arch?

I've noticed mine, when on full lock are rubbing (almost) against the shock (that is probably why DRB recommend you remove the top sleeve of the shock).

Looking at ripping mine out and re-positioning in a safer position.

Any pics / suggestions would help.

Chris
I use 3 spot calipers and i have no trouble with brake balance.
I did have trouble with the front passenger side locking; bleed the brakes did not make any diffference. Pulled the drivers side caliper down and found a damaged seal on one of the pistons.So leaking fluid and not enough pressure compared to other side.

Hi Chris,

Nearly there mate...keep at it.

Question for you....if both front brakes were locking up at the same time then would the engineer have passed it ? If so then you just need to get them balanced left-to-right rather than replacing the calipers. I assume you've bled them well. Could be a seal as Brian suggested but a good brakes place should be able to find the problem. Could be the pads bedding in if you haven't worked them out yet ?

Just a thought.

I had a similar brake in-balance on my wifes Nissan Sentras rear drums at the last inspection.

What I had to do to get them all balanced was:
1. swap the drums from left to right
2. sand the shoes on the side that wasnt working as well
3. Bleed all brakes

Sometimes I think some of the inspections are a bit fussy.

As for having to adjust less braking at the front, surely not, I would have thought that the inspection problem is either that the fronts are out of balance side to side, or the rears are not working hard enough? Try bleeding the backs as well.

Another option - put some race pads on the front, and in the tests that they do, the fronts wont work as well when they are cold.

It seems wrong to go backwards in braking power to pass a test.

Chris

Good to hear you are so close.

Good luck with the modifications and the second test. **)

On the road soon **) **)

Bernie

Jason,
I have just got back from FTG ABS and the dyno test wasn't to bad they said to go for a long run and then check pads and calipers, this I have just done and found the left side pads were jamming in caliper after checking wear of both sides I found the right pads were worn more then the left mybe saying the left weren't working as hard, I have changed sides and fixed the left side so they don't jam up so I will go for another run and see.
Thanks for the help.
Chris.

Peter,
I will take a photo of my set up so you can see where my are run. Thats if I can remeber how to load a photo.
Chris.

Evlcob,
I hope I have fixed the problem, sounds very similar to yours thanks,

Adrian,
I was thinking the same thing re both locking up I will ask him next time thanks.

Brian,
It all sounds similar so may be it was just the jamming of the left side but won't know until I go for another run but I have to get to work they already think I spend too much time playing with my cobra Chris.

Bernie.
Thanks I hope it goes ok to.
Chris.

I would try to get more braking for the back before going for less braking at the front!!

If you want to stop, you want to bloody stop. It's hard enough to make these buggers slow down, let alone having lower braking power to fix a problem.

Just my 2 cents

Batman