soft/low brake pedal

[pete30nz]

OK. Can we confirm exactly what booster, Master cylinder and brake calipers you are running. I'm wondering if there is a miss-match of parts possibly?

I'm not 100% sure but I believe the plug with the hex fitting is possibly to adjust the bias between front/rear?

IF you have little to no movement with the brake lines clamped at the caliper it would suggest the issue lies with the Booster/MC.

Hi Immortality,

The brake master is a PBR 15/16, the booster is a PBR VH512 . And unsure of brand calipers, but I'm sure they are standard because when I buy pads for the calipers they go by the year and model of the car.

The boozer could be making a good point, about the reaction disc in or near the booster going missing when pressing the pedal with out the master cylinder in place??

Cheers Pete

 

[greenacc]

Sounds a bit dicey to me. If vacuum has built up with engine running it should hold the vacuum when you turn engine off until you pump the pedal 1 or 2 times.

I meant if the engine runs for a while then you switch it off without touching the pedal, come back half hour later and flex the vacuum hose to booster at the booster fitting and see if you hear Hissing of air being sucked in showing there is still vacuum in the booster.

 

[pete30nz]

Here are the photos of the original booster, I swapped it with another spare one.
As far as I can remember when I took it apart, what you see in the photos is what I saw.
I have not put a photo of the diafram.

So where should the reaction disc sit.
I do have a diagram to look at, but am wondering if photos can tell a story

Cheers Pete.

 

[pete30nz]

Sounds a bit dicey to me. If vacuum has built up with engine running it should hold the vacuum when you turn engine off until you pump the pedal 1 or 2 times.

I meant if the engine runs for a while then you switch it off without touching the pedal, come back half hour later and flex the vacuum hose to booster at the booster fitting and see if you hear Hissing of air being sucked in showing there is still vacuum in the booster.

Hi Greenacc,

I'll hopfully get around to checking the booster after turning engine off in the next few days. I think we may have checked it, won't hurt to check it again.

Cheers Pete

 

[pete30nz]

Hi,

So I have tried another booster to no fix yet. Hopfully tomorrow I'm lending a brake booster and master cylinder of another VR V6, which has recently been driven, and brakes were working fine.
I'm really hoping my brake issue is to do with the master cylinder bypassing inside it self.

I'll let yous know once I try this booster and matching brake master.

Pete

 

[Brisbarnz]

My thought was air trapped in the abs unit, I had a doughy pedal after a fluid change one day and wouldn't come good after several bleeds. I learnt a way to do a trick via this site, go for a drive in a safe area an smash ya brakes on a few times. The goal here is to get the abs unit working which will release any trapped air. Head home n rebleed brakes again, I repeated that process twice an pedal has never been so firm, it worked for me. But I have read that your car went to a shop, did they cycle the abs unit?

 

[pete30nz]

My thought was air trapped in the abs unit, I had a doughy pedal after a fluid change one day and wouldn't come good after several bleeds. I learnt a way to do a trick via this site, go for a drive in a safe area an smash ya brakes on a few times. The goal here is to get the abs unit working which will release any trapped air. Head home n rebleed brakes again, I repeated that process twice an pedal has never been so firm, it worked for me. But I have read that your car went to a shop, did they cycle the abs unit?

Hi Brisbarnz,
I do not know if they cycled the abs unit, I never asked if they would, and the guy who took the car to shop for me, didn't see what they were doing.
I have driven the car and made the abs kick in, and then bled them a day or 2 later.
But still no different

Pete

 

[ephect]

ok couple of things, clamping the fronts the rear is spongy. So lets focus on the rear.

hoses are my first thought, they're prolly stuffed and bulging.

only other thing it could be is the calipers are installed upside down, where the bleeder screw is pointing down and not up. That's about the only thing left to check.
check the fronts while your at it.

 

[pete30nz]

ok couple of things, clamping the fronts the rear is spongy. So lets focus on the rear.

hoses are my first thought, they're prolly stuffed and bulging.

only other thing it could be is the calipers are installed upside down, where the bleeder screw is pointing down and not up. That's about the only thing left to check.
check the fronts while your at it.

Hi Ephect,

I'm pretty sure the bleeder nipples are facing at the top.
I haven't replaced the rear hoses yet, actually I haven't had a great look at the rear hoses. I should do that.

Clamping the front hoses made pedal firm, clamping the rear, the pedal was not as firm.

Pete

 

[ephect]

sorry I read it wrong, rears sound ok, front hoses could be stuffed if its soft when the rears are clamped. It's all pointing to the front components.