11 replies to this topic

[Bazza]

Hi all

 

I have never come across this phenomenon before and it has me stumped.

 

Newly reconditioned big nut master.

New pistons and seals in calipers in original Girlocks.

New flexible hoses.

Measured booster pushrod length using 3 diffiernt methods - always results at around 25mm protrusion.

 

The problem is the system won't bleed properly. Tried 4 different methods. I reinstalled a known good after-market master but it made no difference.

 

If I pinch off just the rear flex hose - no pedal.

If I pinch off just the front right hand flex hose - no pedal.

If I pinch off the rear and front right flex hoses - no pedal.

If I pinch off just the left front flex hose - good pedal.

 

This points to a problem with the left front caliper. I have pulled it apart numerous times and the bores are still whistle clean and the pistons move well. Good flow of fluid when bleeding by different methods.

As a last resort I split the caliper looking for trapped grease (I used the grease gun method when I popped the pistons) - whistle clean.

No fluid leaks anywhere.

 

Any clues folks?

 

Bazza

 

 

 

[RallyRed]

hmm......calipers on right way up? ( I reckon they would be)

Can you take the hose off the suspect caliper and plug it? to 100% confirm that the caliper is the problem

[S pack]

Does sound every bit like a caliper installed upside down preventing all the air from being bled out.

[Bazza]

Hi

 

Re upside down caliper. Nope - I removed, rebuilt, and replaced them one at a time. Besides, this isn't my first rodeo and the right hand side wouldn't be working correctly either would it?

 

Bazza

[S pack]

OK then caliper bleeder nipple orientation isn't the issue so does the pedal pump up at all to give at least some resemblance of a brake pedal.

[rodomo]

Drawing air back in through either end of the short pipe between the hose and the caliper?

[Bazza]

OK then caliper bleeder nipple orientation isn't the issue so does the pedal pump up at all to give at least some resemblance of a brake pedal.

With the right front and rear brakes flexible lines clamped off, it feels exactly like there is air in the left caliper. There is some slight build up of pressure but it can't be maintained even when the bleeder is closed.

You would think that if air is getting in, then fluid should be leaking out, but it's not. I might try putting the old seal and pistons back in.

[S pack]

With the right front and rear brakes flexible lines clamped off, it feels exactly like there is air in the left caliper. There is some slight build up of pressure but it can't be maintained even when the bleeder is closed.

You would think that if air is getting in, then fluid should be leaking out, but it's not. I might try putting the old seal and pistons back in.

I was going to suggest another caliper if you can get hold of one.

Have you had an assistant work the brake pedal whilst you observe the movement of the brake pads in the left front caliper?

Edited by S pack, 03 February 2023 - 09:44 PM.

[Bazza]

I was going to suggest another caliper if you can get hold of one.

Have you had an assistant work the brake pedal whilst you observe the movement of the brake pads in the left front caliper?

Yes, but not since I stripped it down for about the 4th time. I will try to bleed it with the right front clamped off.

 

Thanks

Bazza

[RallyRed]

Not a dodgy new hose, that balloons up when pedal is pressed?

[Bazza]

Not a dodgy new hose, that balloons up when pedal is pressed?

Hi Col. I had thought of that but haven't checked yet.

 

Bazza

[IanC]

When pumping the brake pedal, can you see air bubbles in the brake fluid reservoir?.