Brake problem

[johnwill]

My brain has given up

I decided to replace all the brake lines on my 4A, and also replace the front calipers with BCC 4 pots.

Everything went well, but bleeding a few times did not make the pedal hard. Pedal straight to floor with no pressure, then 2nd push got some feel. Changed M/C for new, but it didn't even match the old m/c, so put old one back on.

Bled again a couple of times, and got to the point where 1st push gave no pressure, 2nd push it was firm and held in position.  Released, and braked again (all in the garage)

 and straight to floor again, same thing.

Suspected the calipers were pulling the pistons back too far as the fluid level in the m/c rose a little bit after standing a second or two. (Before fitting pads, I had pushed the pistons beyond their "normal" travel so hopefully were in their optimal position)

So, test drive today, thinking the calipers/pistons might all need "bedding in"

Got good pressure on 2nd push of the pedal, which becam 3rd push of the pedal... but braking well. Continued, but then pushed brake pedal to floor,  and it stayed there..!! No brakes. Pulled off road and checked m/c. No fluid loss. Pedal had come up again, so pressed it again, and it went back to the original 1st press nothing, 2nd press good. Decided to drive home very "gingerly" and brakes contined to give some pressure when needed.

With engine running on tickover, I get some pressure on pedal, raise the engine revs, and pedal goes straight to floor... Again, fluid level is fine.

Tearing my hair out has actually been of benefit this time, it's tidied it up a bit :-)

Any advice welcome.

John

[Hamish]

John

with 2x 4 pot  calipers are you not trying to move a lot of brake fluid compared to the original ?

i see their spec say it’s a direct replacement but perhaps the slave is under size now ?
 

just a thought. 
 

I see pedal feel alters with engine revs do you have a servo ?
 

it could be worth jamming the brake pedal on hard with a wood prop or similar and leave it to settle for 24hrs.

 

thats a serious brake upgrade did you have problem before !

as the standard brakes are Normally  good?

[johnwill]

26 minutes ago, Hamish said:

John

with 2x 4 pot  calipers are you not trying to move a lot of brake fluid compared to the original ?

i see their spec say it’s a direct replacement but perhaps the slave is under size now ?
 

just a thought. 
 

I see pedal feel alters with engine revs do you have a servo ?
 

it could be worth jamming the brake pedal on hard with a wood prop or similar and leave it to settle for 24hrs.

 

thats a serious brake upgrade did you have problem before !

as the standard brakes are Normally  good?

Yes, it has an old motovac servo. I wondered about that, but thought I would ask advice before spending more..

I did the wood prop trick each time after bleeding.

brakes have not been efficient for a while, nowhere near what they used to be, so decided to change, and thought the 4 pots would make it even better. Old callipers would have needed replacing anyway.

[david ferry]

I’m in Southam, not far from you, and can supply a set of full professional refurbished original calipers. No exchange needed.

You really should not need 4 pot calipers and, in any event, will mean that you need to make other changes too.

If you’re interested in my last set of these calipers, do let me know.

David

[Hamish]

I think you need servo advice. I don’t run with one. 
someone with servo knowledge will be along in a bit I’m sure.

Edited June 4, 2020 by Hamish

[Nobbyc]

I changed to toyota 4pot calipers no issues.

I suspect the small valve in your master cyl is not sealing 100% and passing fluid back into the reservior under pressure hence no leaks but no brakes

[ctc77965o]

Calipers on upside down? Bleed nipples should be up

[johnwill]

Callipers are correct position, and new m/c didn’t help at all. 
 

going to try something suggested on another thread, put 10mm “fillers” in place of pads, get full braking and Then use the wood trick for a couple of days. Hopefully it’s the piston seals need “settling” in the correct position.

if that fails, will put refurbished original callipers on.

 

[Andy Moltu]

If the calipers aren't leaking and the fluid isn't going down you don't have an external leak.

It may be you have an air lock somewhere in the pipework but I just wonder if there is a problem with master cylinder as it sounds much like that. i know you've changed it but it could be you have a dud.

 

[Hamish]

On 6/4/2020 at 11:03 AM, johnwill said:

 

With engine running on tickover, I get some pressure on pedal, raise the engine revs, and pedal goes straight to floor...

Any advice welcome.

John

I still think you need advice on how to test the servo or brakes With engine on and off. ?!

[ctc77965o]

I still think inverted caliper explains your symptoms:

• The system will bleed ok, as the fluid will run clear from the bottom of the caliper cylinders.
• There are no external leaks
• On first push of pedal, fluid is pushed into the air void inside the calipers cylinders, given the large air volume no 'hydraulic pressure' is built-up,  on release of pedal the fluid starts to slowly 'blow back' but because of the small bores of the pipes it takes some time to blow back (it doesnt 'burp' because fluid entry point is not oriented opposite bleeder).
• A second quick press of pedal pumps enough fluid into the caliper to gain some hydraulic pressure and then brakes work... but after a few mins of inactivity the air pushes the fluid back again.

you could just unbolt the caliper and try bleeding in different orientations...if any air bubbles are released then that might confirm the situation. 

Beware that some hydraulic cylinders have complex drillings meaning physical position of bleeder does not correlate with vent-point in the cylinder... I have BMW cylinders where the bleed nipple points  down (for accessibility reasons), but the internal drilling connects to the opposite (upper) edge of the cylinder.

[johnwill]

19 hours ago, Hamish said:

I still think you need advice on how to test the servo or brakes With engine on and off. ?!

It seems co-incidental that the servo started to play up after i changed the callipers, but it could be. I intend to bypass it after i've ran a few other tests (no bleeding required) to rule it in or out.

[johnwill]

12 hours ago, ctc77965o said:

I still think inverted caliper explains your symptoms:

• The system will bleed ok, as the fluid will run clear from the bottom of the caliper cylinders.
• There are no external leaks
• On first push of pedal, fluid is pushed into the air void inside the calipers cylinders, given the large air volume no 'hydraulic pressure' is built-up,  on release of pedal the fluid starts to slowly 'blow back' but because of the small bores of the pipes it takes some time to blow back (it doesnt 'burp' because fluid entry point is not oriented opposite bleeder).
• A second quick press of pedal pumps enough fluid into the caliper to gain some hydraulic pressure and then brakes work... but after a few mins of inactivity the air pushes the fluid back again.

you could just unbolt the caliper and try bleeding in different orientations...if any air bubbles are released then that might confirm the situation. 

Beware that some hydraulic cylinders have complex drillings meaning physical position of bleeder does not correlate with vent-point in the cylinder... I have BMW cylinders where the bleed nipple points  down (for accessibility reasons), but the internal drilling connects to the opposite (upper) edge of the cylinder.

Understand your points, and thanks for your suggestions

To confirm, Callipers are definitely correctly fitted.

2nd push on pedal is hard, and a second or two after I release it, the next push is to the floor, not minutes.

I'll get back on it on monday and report back :-)

 

[Andy Moltu]

Unlikely to be explained by the caliper seals and the debate over caliper orientation is simple enough- the need nipples will be at the top.

If the caliper conversion is the correct one you might experience a bit more pedal travel related to having a bigger piston area compared to standard but even with a bit of pull off related to the seals you shouldn’t need to pump the pedal.

I assume that you have the inlet and outlet pipes correctly oriented with servo?

It sounds like there is air remaining in the system. Bleed again starting with the furthest rear wheel cylinder and working until you finish with the nearest front in terms of length of pipe work.

It could be the master cylinder as you kept the original so it might be worth replacing the seals as the repro didn’t fit.

[johnwill]

On 6/6/2020 at 1:59 PM, Andy Moltu said:

Unlikely to be explained by the caliper seals and the debate over caliper orientation is simple enough- the need nipples will be at the top.

If the caliper conversion is the correct one you might experience a bit more pedal travel related to having a bigger piston area compared to standard but even with a bit of pull off related to the seals you shouldn’t need to pump the pedal.

I assume that you have the inlet and outlet pipes correctly oriented with servo?

It sounds like there is air remaining in the system. Bleed again starting with the furthest rear wheel cylinder and working until you finish with the nearest front in terms of length of pipe work.

It could be the master cylinder as you kept the original so it might be worth replacing the seals as the repro didn’t fit.

I've always bled it shortest to longest...

[John L]

I would pump it up with the pedal and jam the pedal down overnight with a wood rod.  That should confirm if its air, if it still goes down after this I would expect it could be the MC.

John

[johnwill]

2 hours ago, John L said:

I would pump it up with the pedal and jam the pedal down overnight with a wood rod.  That should confirm if its air, if it still goes down after this I would expect it could be the MC.

John

I originally did this. It stood for 2 days in that state. When I came to remove the wood, the pedal was still solid half way down. Once removed, it gave the symptoms I first raised. 1st push to the floor, 2nd push solid. 

[John L]

Are you using a remote servo or one in front of the MC like the TR5?

How does the pipework run from the MC to the servo, is it above the reservoir level, so may be difficult to get the air out, might wont to open the pipe at the servo and bleed there first of all.

Do you have the restrictor fitted at the first 5 way connector?

Could you post some pictures it does make it a bit easier to understand,

John

[stuart]

12 hours ago, johnwill said:

I've always bled it shortest to longest...

You should always bleed furthest away first.

Stuart.

[Andy Moltu]

The wheel bearing isn't loose by any chance?

[stillp]

On 6/4/2020 at 11:03 AM, johnwill said:

 

pushed brake pedal to floor,  and it stayed there..!! 

This seems to be the most important symptom. I would guess it's a master cylinder seal problem, but I know nothing about servos so can't ruke that out.

Pete

[johnwill]

16 hours ago, John L said:

Are you using a remote servo or one in front of the MC like the TR5?

How does the pipework run from the MC to the servo, is it above the reservoir level, so may be difficult to get the air out, might wont to open the pipe at the servo and bleed there first of all.

Do you have the restrictor fitted at the first 5 way connector?

Could you post some pictures it does make it a bit easier to understand,

John

Remote servo. Pipe work is the same as it has been for the last 45 years of my ownership, and has always been ok until now, so it should be fine. (I hope) No restrictor fitted. 

Edited June 8, 2020 by johnwill

[johnwill]

14 hours ago, stuart said:

You should always bleed furthest away first.

Stuart.

My manual says the opposite, and I’ve always done it that way, but will re-bleed as suggested. 

Edited June 8, 2020 by johnwill

[johnwill]

14 hours ago, Andy Moltu said:

The wheel bearing isn't loose by any chance?

No, both fine. 

[John L]

Have you bleed the servo?  Does the MC pushrod have the proper clearance, and is there a spring to return the pedal?  There are other pages of the fitting instructions if needed.  A picture of you servo would be helpful.

Edited June 9, 2020 by John L