Brake issue at mot...

hi all

Il try to keep this simple. I took the old girl for her mot and all was good apart from we had a bit of an issue with rear brake effort being close to too low. It went thru but the tester knows me and the vehicle and commented that it usually sails thru no probs. It had new discs and pads and 2 new rear callipers before the last mot (not cheap junk) and was fine last year but I’ve noticed them not as good as they used to be. The rear callipers were seized but I’m wondering if there could be an issue with the bias valve or master cylinder or...? I’m not really up on the workings of the brake system so any advice or experiences would be gratefully received.

Vehicle is a 98MY d1 non abs

Many thanks in advance

Towsey

towsey956 said:

The rear callipers were seized

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And it still passed!?
There is your answer!
Take the pads out, use pedal pressure to push them both out against the disc, lube the pistons with caliper grease, obtainable from morobike shops as most car blokes don't know about it, push em back in. Work em in-out-in-out, until they move freely.
Or if you are more bothered, strip em down and rebuild them with new pistons and seals.
Or if you like spending money, buy new calipers.

Sorry, I was rushing my first post because my tea was ready


The original callipers were seized and had had the exact treatment you described with some nice wurth brake grease before it got new discs and pads right round and new rear callipers that a mate bought but never used.
What I meant was I was wondering if, although seized callipers a common enough, the original callipers were maybe being hindered by lack of pressure and the same lack of pressure is why they don’t feel as good as they used to and why the effort was down some on the mot. It was still over the required amount but not by loads but even since the new brakes were fitted the rear discs do like to rust up. Basically I’m wondering if lack of effort on the rear is common and what can cause it

Thanks

Towsey

Depends how you drive it. If you are gentle, it is the front brakes that do most of the braking. If you hammer up to every bend then stand on the brakes, the rears will get exercise.
How long is it since you changed the brake fluid? If it is a while then the fluid will have absorbed water from the vapour in the reservoir and the rears having the longest pipe runs will have fractionally more compression in the water brake fluid mix, which means that the application of pressure to the brake pedal will result in slightly less pressure at the rear pads.
So simplest answer, change the brake fluid and wait a while while driving normally to see if it reoccurs.
Let's face it, you've changed everything else!.

Thanks for the reply

The fluid was changed (all of it) just before Xmas when I fitted braided hoses, before that it was about 18 months ago when I did the discs/pads/callipers but thanks for the idea. Like you say a lot of it’s new, only front callipers, bias valve, master cylinder and servo left which are the bits I know least about

Cheers

Towsey

towsey956 said:

Thanks for the reply

The fluid was changed (all of it) just before Xmas when I fitted braided hoses, before that it was about 18 months ago when I did the discs/pads/callipers but thanks for the idea. Like you say a lot of it’s new, only front callipers, bias valve, master cylinder and servo left which are the bits I know least about

Cheers

Towsey

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Really getting into it now aren't we?!

Maybe the split in the dual circuit is the answer. Maybe and don't know, but if it is split into fore and aft, then the aft bit of the master cylinder needs a rebuild, or even just a bleed, although when changing the fluid that should have got rid of the air, BUT you could have a slight airlock in the rear pipe(s).
Servo feeds all of system so shouldn't be that I'da thought. Only what i said and bias valve left i think.

98 tdi or td5?
Fixed calipers or sliding type?

Yeah that’s about where I had got it down to as in first post but should of made first post more informative, my bad, it was the Sunday lunch/tea sat waiting for me that made me do it ha

She’s a T reg tdi on the fixed callipers

Thanks again

Towsey

towsey956 said:

Yeah that’s about where I had got it down to as in first post but should of made first post more informative, my bad, it was the Sunday lunch/tea sat waiting for me that made me do it ha

She’s a T reg tdi on the fixed callipers

Thanks again

Towsey

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You explained correctly in your first post what model u have, some need a hand in under standing difference in the two model years available in late 1998
The T registration doesn’t mean much, it the model year that does, so u may have a 1998MY or maybe not, do u know the difference between 1996-1997 and 1998MY D1s ?

So back to your iffy brakes, I would assume the the hydraulic side I’d ok when the system was filled with new fluid following the disc replacements, I would go straight to the vacuum and check the one way valve is fully functioning just by removing it from the servo cleaning and refitting.

My disco being petrol has two valves so when I had similar issues I remove both dropped them into some solvent for a couple of minutes and refitted braking backed to normal, also if as I do don’t use the vehicle a lot, I use the brake for the first couple of miles to clean up the discs/pads... take it up to 30mph and do a emergency brake as u would in bedding in new pads

towsey956 said:

Yeah that’s about where I had got it down to as in first post but should of made first post more informative, my bad, it was the Sunday lunch/tea sat waiting for me that made me do it ha

She’s a T reg tdi on the fixed callipers

Thanks again

Towsey

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Must be one of the last? hence the reason I asked as td5 has sliding type.
What you need to do is remove one pad at a time, get an assistant to press pedal until piston is out approx 1/2 an inch, then watch the pad as they release the pedal, does the piston go back a knatts cock or a couple of mm?
Try this one pad at a time on all 4 pads, if all the same most likely good, I have had new pads where the piston seals were dry and when pedal released the seal which being dry has rolled rather than slid over the piston, this then pulls the piston back to far, a little brake fluid dripped onto each piston as a lube cured that.
Anyway good luck, got to shoot off.

towsey956 said:

Yeah that’s about where I had got it down to as in first post but should of made first post more informative, my bad, it was the Sunday lunch/tea sat waiting for me that made me do it ha

She’s a T reg tdi on the fixed callipers

Thanks again

Towsey

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T reg? !998? My1998, easy to remember as it is a Anniversary and says so on the V5, is on R plate and the V5 says the number cannot be changed. Yet the year letter for 98 is S. So I have no idea how that happened. Mk1s did go on to T as my other mk1 is a T I think, will just go and check. Yup ,it is a T although it's a V8. So yours, hate to contradict you, I think must be a T on a 1999. Not that it matters about your brakes!

Thanks for all the replies

She’s a 1998MY as said in first post but was registered in 99 so T reg, it’s a safari so one of the last 300’s and the colour is highland green which I believe was carried on to d2 aswell, I just put t reg in post 8 because some people see the reg and try tell me it’s a td5 especially since I put d2 lights in it, this even happens when I go for engine oil.

I never thought of the one way valve in the vacuum pipe so will check that thank you

As for the pads, I have never checked them in that way but I have noticed they are wearing evenly, but will when I get chance

Cheers

Towsey

Well I eventually got round to spending a bit more time on this

All vacuum side is ok, pump, pipe, one way valve and servo ok giving about 25hg of vacuum and holding it after turned off till I got bored of waiting

Been told that sometimes the pressure reducing valve can have a dicky fit when bleeding the brakes so I had my lass stabbing at the pedal while tapping the valve in case it was stuck one way but to no avail, maybe a load of rubbish anyway but it was free to try it!

If I’m honest I’m still wondering about either the master cylinder or PRV but with the current situation I don’t want to be spending money on the wrong part. Although the pedal starts to work lower down than it used to it doesn’t carry on sinking to the floor so I don’t know if it’s the master cylinder or not but I’d be glad of any advice or experiences shared

Also, which parts are you finding work well and last

Thanks again

Towsey

Thinking dead simple, if front brakes are working okay and showing signs they are working, then the valve in the rear brake lines has to be the logical first port of call?

Rear flex hose not collapsed internally?

Are you sure the rear caliper pistons are moving freely? ie one pad at a time out, pres pedal out a couple of pedal pumps, then push piston back in with a screwdriver, pad back in and repeat on the other three pads?

Yeah front brakes fine.

Can the PRV be stripped and freed off?

On very gentle braking the rear callipers do favour the inside pads first then once the bit of slack is taken up against the discs the outer ones kick in more but this is when just touching the pedal and prob due to the pipe entering on the inside? The discs, pads, callipers and flexis have all been changed since this problem began and none of it has made a difference, it does seem that the pedal working lower down and lack of rear effort are related, could this be the seal in the rear brake half of the master???

Cheers

Towsey

towsey956 said:

Yeah front brakes fine.

Can the PRV be stripped and freed off?

On very gentle braking the rear callipers do favour the inside pads first then once the bit of slack is taken up against the discs the outer ones kick in more but this is when just touching the pedal and prob due to the pipe entering on the inside? The discs, pads, callipers and flexis have all been changed since this problem began and none of it has made a difference, it does seem that the pedal working lower down and lack of rear effort are related, could this be the seal in the rear brake half of the master???

Cheers

Towsey

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Could well be the master seal, never had it on one of my cars, but that does not mean it cannot happen, after all they are old cars now.
Had masters seize from lack of use.

I can remember the early 200 discos had an adjustable/eccentric master pushrod which was adjustable from inside the car at the top of the pedal, not sure if later models still had that fitted?

I would replace the pressure reducing valve (NTC3059) on mine, had similar problems with mine so change it and bleed system and it’s now fine, they are not a serviceable item unfortunately,
Mines a early MK 1 200tdi so not entirely sure it’s the same as yours but the symptoms were the same,

Thanks

Yeah I’ve wondered about the adjustable pushrod thing, old fords and some others had it but to be honest I didn’t think of looking from inside cos ya used to take master off to do ones I’ve done before but il have a look see

I just can’t decide which to buy first haha, But sumats gonna have to be bought and people with same experience is helpful

Cheers

Towsey