Rear pads not clearing rust of brake discs

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ONE LIFE LIVE IT. D90

ONE LIFE LIVE IT. D90

Active Member
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953
Hi all

Ive had a couple of opinions on this, but realise you can never have too many thoughts.
Ive carried out a lot of work on my 1995 300tdi defender braking system as some of you may know. And its hugely improved from when i purchased it. It actually stops now haha.

6-7months ago i replaced the calipers all round and new mintex discs and pads on the rear.

Couple of months ago changed the flexis hose for braided.

And then a few weeks ago, replaced front discs and pads, and rebuilt the master cylinder.
The reason for rebuilding the master cylinder, was because the brake pedal felt poor and spongy.

Anyway, the brakes seem a big improvement, however i cant work out why the rear discs are not being cleared of their rust. The pads are lightly skimming the disc, and clearing the surface rust, but not properly sweeping the disc and polishing it as they should, as good working brakes do (like the fronts do infact). Theyve only been on six months, so arent heavily corroded, i just notice they are starting to Pitt.

The reason i replaced them was because they were excessively rusty on the rear. Not due to being worn. This led me to replace the calipers.

Has anyone got any ideas please? Could i have messed up the master cylinder rebuild?

Ive had someone pump the pedal while i view the calipers, there isnt much action, but the pistons are moving in, not much difference between engine on and off though.

5acde663b0fc3ef5b044cad22377da96.jpg
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The photos make the discs look better than they are really. Its not orange surface rust, its like more deep permanent rust, that with a good brake, should clear. But it isnt. The lines on the discs arent scoring, its rust lines that havent rubbed off by the pads. Surface rust from washing (kind of) last ages on the rear discs too.

Any thoughts guys? Thankyou in advance
 
I know that photos can lie but that looks to be a heck of a lip on discs that are only 7 months old.
As for your problem is there a load distribution valve in the system?
 
dogsbody said:
I know that photos can lie but that looks to be a heck of a lip on discs that are only 7 months old.
As for your problem is there a load distribution valve in the system?
Click to expand...


Sorry for the poor pictures. I'll try and get some better ones tomorrow

Theres no lip on them at all. They arent beig used enough

I beleive there is yes, its that valve near the bottom of the bulkhead on one of the chassis rails. Intake pipe is fastened to it i think.
 
If the front brakes are working then you can't have made too much of a mess of the master cylinder.
So you've got pressure but it's not getting to the rear wheels.
1 - You've plumbed the rear calipers upside down so that the bleed valve/valves are at the bottom and you haven't got all of the air out.
2 - there's another flexi from the body down to the back axle and it's gone weak and is bulging under pressure
3 - there's a pinhole leak in the rear pipework only leaking under pressure
4 - there's a load sensing valve and it's not allowing enough pressure through to the rear
5 - there's a shuttle valve that shuts one axle off in the event of a leak leaving the other to take the load and you've triggered it whilst working on the brakes

and breathe
 
Have you had it MOT'd since you completed all the brake work, if you have then they must be working to the legal minimum effort at least. That brake test is normally the one I watch like a hawk on the MOT so I can look for imbalances etc.
 
dogsbody said:
If the front brakes are working then you can't have made too much of a mess of the master cylinder.
So you've got pressure but it's not getting to the rear wheels.
1 - You've plumbed the rear calipers upside down so that the bleed valve/valves are at the bottom and you haven't got all of the air out.

A: Bleed nipples are at the top

2 - there's another flexi from the body down to the back axle and it's gone weak and is bulging under pressure

A: Replaced for braided, as are the rest

3 - there's a pinhole leak in the rear pipework only leaking under pressure

Checked all over whole system, pedal feels decent too

4 - there's a load sensing valve and it's not allowing enough pressure through to the rear

Is this the bias valve on bulkhead?

5 - there's a shuttle valve that shuts one axle off in the event of a leak leaving the other to take the load and you've triggered it whilst working on the brakes

Where would i find this? Mines a 1995 300tdi defender.

and breathe
Click to expand...


Ive answered questions above. Thankyou
 
Kwakerman said:
Have you had it MOT'd since you completed all the brake work, if you have then they must be working to the legal minimum effort at least. That brake test is normally the one I watch like a hawk on the MOT so I can look for imbalances etc.
Click to expand...


Sorry guys. Im useless at quoting!

It hasnt been MOT'd since no. However im pretty sure it would pass on brake efficiency. Why the rears arent working properly i spose i could be guessing.
 
ONE LIFE LIVE IT. D90 said:
Ive answered questions above. Thankyou
Click to expand...

Sorry I'm not a 'fender man so can't be more specific. I was just running down what I would do as a fault finding list.
Yes, it's the bias valve that I'd be investigating, it could also contain a shuttle. Also don't blindly trust your new flexis. I have had a faulty, brand new one. It was weeping inside the braiding. It was a b****r to find, all that I knew was that my brakes started out very good but lost their 'edge' over the next few weeks.
 
dogsbody said:
Sorry I'm not a 'fender man so can't be more specific. I was just running down what I would do as a fault finding list.

Yes, it's the bias valve that I'd be investigating, it could also contain a shuttle. Also don't blindly trust your new flexis. I have had a faulty, brand new one. It was weeping inside the braiding. It was a b****r to find, all that I knew was that my brakes started out very good but lost their 'edge' over the next few weeks.
Click to expand...


Thankyou again. How can i tell if its the bias valve without swapping out parts?

Is there anyway i can tell its not a fault with my aster cylinder rebuild ?
 
As a side note is master cylinder fully returning and do you get good flow to rear when bleeding?
Several vauxhalls i had to tap master cylinder every time to get them to return as further than normal travel during bleeding.
 
just to confirm the discs are smooth to the touch and no lip/scoring?

is the pedal still spongy? and you've setup the mc properly?

do you have a gvalve plumbed into the rear line? usually on the chassis leg. is it nosed slightly upward? maybe this is partially stuck?

also if you take it to a garage who can test all wheels individually on a 4x4 roller you can see actually see how they are performing.
 
fanatic said:
As a side note is master cylinder fully returning and do you get good flow to rear when bleeding?
Several vauxhalls i had to tap master cylinder every time to get them to return as further than normal travel during bleeding.
Click to expand...
I only used eezi bleed mate. Cant really remember to tell the truth
 
trax said:
just to confirm the discs are smooth to the touch and no lip/scoring?

is the pedal still spongy? and you've setup the mc properly?

do you have a gvalve plumbed into the rear line? usually on the chassis leg. is it nosed slightly upward? maybe this is partially stuck?

also if you take it to a garage who can test all wheels individually on a 4x4 roller you can see actually see how they are performing.
Click to expand...
The discs are smooth, the lines on the discs are just rust lines from the pads not cleaning the discs properly. Theres no lips on the discs either.

The pedal isnt half as spongy ad it was, quite good infact. Its spongy when reversing oddly enough though.

what do you guys recommend i do next, as the money pot for these brakes is running dry.

Thsnkyou all
 
ONE LIFE LIVE IT. D90 said:
The discs are smooth, the lines on the discs are just rust lines from the pads not cleaning the discs properly. Theres no lips on the discs either.

The pedal isnt half as spongy ad it was, quite good infact. Its spongy when reversing oddly enough though.

what do you guys recommend i do next, as the money pot for these brakes is running dry.

Thsnkyou all
Click to expand...

i'd knock up a lil pipe to bypass the gvalve and see if it fixes it. if so, buy a new gvalve.
 
trax said:
i'd knock up a lil pipe to bypass the gvalve and see if it fixes it. if so, buy a new gvalve.
Click to expand...
Cheers tax, is that the part that is on the chassis leg in front of the bulkhead, and the intake system (the piece drain) is fixed to it via a metal bracket?

You guys don't think it's my master cylinder error then?
 
ONE LIFE LIVE IT. D90 said:
Cheers tax, is that the part that is on the chassis leg in front of the bulkhead, and the intake system (the piece drain) is fixed to it via a metal bracket?

You guys don't think it's my master cylinder error then?
Click to expand...

not sure, my 110 doesn't have one, think it's from 300 90's on.

wouldn't be able to say about the mc unless i was in person.. even then i can get it wrong :D
 
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