problems with soft brake pedal and weak brakes.

Rune

Supporter
I bleed and bleed , use 2psi valves to prevent backflow , but the brakes did not pass SVA . I use 4 pot calipers all around and 3/4 master cyl. I am about to change the master cyl for rear brakes to 5/8" due to the brakes was better than the front. I have moved the bias toward the front brake. This is more and less situation now.

How to get rid of the soft pedal? there must be air locked in somewhere. I was told to move the calipers down to lower level than the master cyl and bleed. Is this a idea?
I maked a cyl . hold 2 liter brake fluid and will connect to the suction side of master cyl. and it will be pressurised to 10-15 psi. Than easy to bleed alone.
But first of all I need good tips how to deal with the soft pedal.
 

Ian Anderson

Lifetime Supporter
Hi Bune
The smaller master cylinder will generate a higher pressure in the pipe and increase the brake force on that circuit, I presume you say you will change the front cylinder for the smaller one.

if bleeding the rear brakes I would raise the rear, so any bubbles in the chassis length would naturally try to move to the rear.

have you got air inside the calipers? Some people remove them and hold them with the bleed nipple at the highest point to ensure no air inside.

But yes initial bleeding took a lot of fluid!

ian
 
If you can rig a vacuum line onto the bleed nipple at the caliper, and stop in from pulling fluid from the master reservoir by slightly depressing the brake pedal to close the port to the reservoir, the vacuum will cause any bubbles in the line to expand. with the bleed port positioned at the highest point in the system, the bubble should flow towards the bleed nipple. You may need to cycle the vacuum on the bleed nipple.

on my bike i do this by attaching at syringe full of brake fluid to the bleed nipple (use a short silicon hose and cable ties) and then pulling on the syringe. you should see a rush of bubbles in the fluid as the pressure drops. Then push the fluid back into the system and presurerise it with the syringe then pull vacuum again.

if the port to the main reservoir is blocked at the master cylinder you should not be able to pull or push fluid from the system. you should just get the bubbles accumulating in your syringe.

I will try and find a link that shows it on the bike.
 

Randy V

Admin
Lifetime Supporter
Light tapping on each caliper with a small hammer will dislodge air bubbles so they can be purged from the system. It works every time for me whether using pressure/vacuum bleeder systems or the old fashioned way...
 

Rune

Supporter
Many good tips here, I may try them all. will come back when the brakes are free of air.
 

Cliff Beer

Supporter
Perhaps try a pressure bleeder at the MC. The pressure bleeder can work very well to clear air in the lines.

Make sure your pedals and pedal box is secure, stiff/strong, and properly bolted in.

Check your soft brake lines. If they’re old then consider new lines. The stainless sleeve type can be helpful in promoting a firm pedal.

just a few suggestions.....
 

Howard Jones

Supporter
Do a combination of Cliff's pressure bleeder, Morten's bleed all bleed ports at each caliper one at a time, and Randy's light tap on caliper body while the caliper in process is bleeding.

I have one of these: works perfect every time and you will not need any help.

 
Is anybody aware of a way to incorporate a residual pressure valve between the MC and banjo fitting? My calipers are slightly higher than the MC, and are plumbed with soft lines and banjo fittings. Only way I can fit an in-line RPV is at the caliper, or, for the rear circuit, all the way at the back of the car next to the brake pressure sensor switch. If I could sandwich mount one between the MC and the banjo fitting, that would be the cleanest and most effective position I think.
 
had a further think on this - using remote reservoirs, mounted higher than the MC and calipers, should reduce or eliminate the issue, along with no fitting issues.
 
Pressure bleeding sometimes helps, Get someone to pump the pedal a few times then when the pedal is being pressed down, open the nipples on the caliper when the pedal hits the floor close the nipple, repeat a few times on each corner
 

Rune

Supporter
I have now done lots of bleeding with pressure with vacuum and with help of my friend. And the pedal seems harder now. I also had a problem with my hand brake, the construction was not good enough. So I contacted HiSpec motorsport in UK and ordered electric handbrakes from them. Took long delivery time and a week to fit to the car. But now the hand brake are excellent. will put all covers on and try the car soon.
 

Rune

Supporter
Is there someone that know the effect of the bias. I have turned so that the front brake is most powerfull. but if I turn it two turn back, will I see any change when braking. Some of you out there have done this work before and know how much or little nedded to see a change in brake eff.
Also I feel that I need to do a lot of hard braking to let the pads be good. The brakes was better after some hard brakings. But can I get the wheels(all4) to lock on hard braking? I need some answers from you uot there.
 

Morten

Mortified GT
Supporter
Hi Rune, I’ve set my APs to 1000psi front 600psi rear on pedalpressure with pressure gauges on calipers. But I’ve got the same calipers on all 4 corners.
Needs three people, or phones live feed video of gauges to yours in cockpit for bias adjustment.

Best of luck Rune.

Morten
 

Ian Clark

Supporter
About the brake bias, when they are properly bedded in and bias adjusted for optimum braking on smooth flat clean pavement you should have all four brakes on the verge of locking simultaneously, however in extreme braking the front brakes should lock first.

The suspension must be properly set up for corner weights, shock absorber settings, ride height, caster, camber and toe, both front and rear before you can begin to adjust the brakes. Watch your tire pressures too, lot's of ways to screw up dialing in a brand new car.

You won't know if it's spot on without track testing by an experienced driver who can give you his opinion of brake balance and adjust again if necessary.

On public roads it's equally important the rear brakes do not lock first in a panic stop, good chance of spinning the car as if your heart wasn't beating fast enough already.

AP Racing recommends about 5% maximum offset in the bias bar in the pedal set by the way, there is technical advice on the AP website that will shed more light on the topic.

Hope this helps

Cheers
Ian
 
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