Brake brake brake.... another probably bindingly obvious question :-)

[gbmoto]

Afternoon all, me again.

Sorry to be asking what is probably another obvious question again, have had plenty of landys but generally standard, have even done a chassis up rebuild, engine swops etc

But this 3.9 efi 90 is a bit of a mixture, it's now running nicely with a standard air filter arrangement replacing a k&n, interestingly the tickover had been tweaked by tightening the throttle cable 😨

Replaced the manifold gaskets, made a lot more difficult by the tubular headers.....  I sooo like standard!

So now on to the brakes, they are not awful, passed MOT etc but there is way too much pedal travel.

So far have put on a new servo as the original looked dodgy and have fiddled with the pushrod, if I adjust it for a sensible pedal then I get binding after a couple of miles.

Soooo thinking it may be worth a master cylinder swop and bleed etc.

Now the 90 has 24 spline disco axles, discs front and back..... all new and fangled to me!

Have bills for recent replacement callipers  so hoping that excludes those.

The current master cylinder looks nothing like my previous coil landys, which were all drums on the back, but braked well with a good pedal.

Is this one correct?   On my others it was much bigger and alloy

Or should I also look at the proportion valve thingy.

Piccys attached.

Normally I would just find the pn for an mc of the correct year and order it, but would like a bit of advice, I'm sure the combo of parts I have isn't too unusual.

Many thanks. 

[western]

Make sure there is a clearance between servo pushrod end & the master cylinder piston, I had a rear brake binding issue after swapping rear drum for disc on my 110, I had to tweak the servo pushrod, measured the gap with a blob of blutak then pushed the master cylinder back in place, carefully removed the blutak & measured the thickness where the pushrod & piston meet, manage to get it to 0.7mm, & no more binding rear brakes.

Yes that is the correct fluid tank/master cylindr & servo for a 300Tdi onwards

[gbmoto]

Thanks Western, it's good to know I have the correct mc

I'll try the measuring plan, so far has been guesswork!

[miketomcat]

To much pedal travel is quite often a loose wheel bearing. This causes the disc to move pushing the pistons back.

Mike

[gbmoto]

Thanks Mike, pretty sure I am OK there but will check them out.

[Snagger]

As Ralph confirmed, that is the correct MC for 4x discs.

He’s also right in the likely cause of the binding being an overadjusted servo pushrod preventing the brakes from backing off enough. Do also check for stuck pistons that prevent pad retraction, as the discs and pads would expand a little when warm and could then bind.

Take a look at the flexible hoses to check for perishing and for swelling under pressure, as that will allow a lot of pedal travel and efficiency loss.  Goodridge do standard size replacement hoses with braided stainless steel sleeve which prevent expansion of the hoses and also prevent UV (and much other) damage.  I have been very impressed with their results.

[gbmoto]

Thanks Snagger, it already has braided hoses thankfully.   Hopefully will do the blu tak this weekend.

With any luck will come back brimming with stories of success 😃

[gbmoto]

Well, tweaked the servo rod and now have a very slight bind at the rear ( only really noticeable when reversing slowly ) but still too much pedal travel.

Wheel bearings all seem fine, braided hoses look all ok, bills for rear calipers replaced recently by previous owner ( possibly this has been an ongoing issue...hmmm )

Looks like the proportioning valve has been in place for a long time, I am starting to point an accusing finger at this.    

Or am I unfairly maligning it??

I'll probably get friendly mechanic to change that so maybe master cylinder at the same time since it will need a full bleed anyway?

Does this sound the right next move?

[western]

It's not a proportion valve, it just closes off the front or rear circuit if there is a leak & isolates the faulty circuit. 

[gbmoto]

Ah ok, prob not that then!, ta Western.

[western]

This might help 

[Snagger]

On 6/6/2022 at 12:09 PM, western said:

It's not a proportion valve, it just closes off the front or rear circuit if there is a leak & isolates the faulty circuit. 

Close, but PDWA valves don’t close off leaking brake circuits, contrary to the belief of most owners.  They merely activate a dash light to warn the drive of a failed brake circuit.  They are exactly what their name suggests - Pressure Differential Warning Activation/Alert.

[Junglie]

4 hours ago, Snagger said:

Close, but PDWA valves don’t close off leaking brake circuits, contrary to the belief of most owners.  They merely activate a dash light to warn the drive of a failed brake circuit.  They are exactly what their name suggests - Pressure Differential Warning Activation/Alert.

I always thought this was correct, but reading the description in the manual above...I think we may have it wrong. Yes, the PDWA activates a warning light, but it seems that activation is caused by a piston moving and isolating the duff circuit.

[western]

The Pressure Differential Warning Actuator (PDWA) is not a proportioning valve. It measures the relative pressure in the dual brake circuits; if one circuit loses pressure, an electrical circuit is created and the dash warning light illuminates.

more in this post.

[Snagger]

14 hours ago, Junglie said:

I always thought this was correct, but reading the description in the manual above...I think we may have it wrong. Yes, the PDWA activates a warning light, but it seems that activation is caused by a piston moving and isolating the duff circuit.

It does work by pressure differential moving a shuttle valve across to the low pressure side, but it doesn’t isolate anything.  The leak continues.  
 

Prevention of all fluid loss is done by having twin circuit brakes with a dividing wall inside the reservoir and by the driver stopping the vehicle when a low fluid level sensor or PDWA triggers a warning light.

[Junglie]

29 minutes ago, Snagger said:

It does work by pressure differential moving a shuttle valve across to the low pressure side, but it doesn’t isolate anything.  The leak continues.  
 

Prevention of all fluid loss is done by having twin circuit brakes with a dividing wall inside the reservoir and by the driver stopping the vehicle when a low fluid level sensor or PDWA triggers a warning light.

Huh. Every day's a school day. Thanks...but what a bloody silly design!

[western]

It was superseded by the low fluid level float cap on later vehicles, which is a better idea. 

[Snagger]

I agree with both of you.  I fit a level sensing cap on my 109.  That gives a more reliable alert and will warn of slow leaks, not just large ones.

[gbmoto]

Thanks all, sorry for the tardy reply as ever!

The bit I am suspicious of is this    

Land Rover Defender 90 Brake Compensator Valve - 94 onwards - OEM - NTC8836

Doesn't appear to have any electrical connections.

Sorry, as ever I probably didn't explain myself properly 🙄

[western]

The combined PCR

https://www.johnrichardssurplus.co.uk/land-rover-brake-bias-valve-ntc8836.html

 

& PDWA have an electrical connection, the G valve doesn't. 

[chuff]

Clamp the flex pipes off in turn to eliminate each corner / rear. If the travel goes then that corner / axle is your problem. If it doesn't then it's up-stream. 

Personally I would bet that it needs bleeding (don't be afraid to proper RAM the pedal down once or twice when bleeding to get trapped air out) or that britpart servo is shorter inside than the previous one and needs the nipple lengthened. I do not use britpart brake components. 

There's most certanly nothing wrong with the valve, even if it doesn't work it still won't effect braking. 

[Snagger]

15 hours ago, chuff said:

Clamp the flex pipes off in turn to eliminate each corner / rear. If the travel goes then that corner / axle is your problem. If it doesn't then it's up-stream. 

Personally I would bet that it needs bleeding (don't be afraid to proper RAM the pedal down once or twice when bleeding to get trapped air out) or that britpart servo is shorter inside than the previous one and needs the nipple lengthened. I do not use britpart brake components. 

There's most certanly nothing wrong with the valve, even if it doesn't work it still won't effect braking. 

I agree.  In the case of SIII 109s, which have a relatively large volume inside the PDWA unit, I think it is the biggest cause of bleeding problems, not the poorly designed single acting slaves with air traps.  I had a hell of a time bleeding the system after I fit later axles with Discovery callipers front and rear and a Discovery master cylinder.  It was the PDWA  trapping air.

[gbmoto]

Afternoon all, sorry for the long delay, hols and other life things got in the way of Land Rovers 😲

Many thanks for all your responses.

In the end I put on my brave pants and replaced the PRV, obviously had to then do a bleed/renew brake fluid.

The result....... a firm pedal with very little travel and no draggy back brakes.

My wife has just had a knee replacement so I couldn't take the Landy out for a long run but brakes were good on a short run and back at home the drive slopes slightly and it happily rolled backwards.

So longer run next but cautiously optimistic.....

Next off with the inlet manifold to cure a water leak...... 🙄

Hopefully won't need to pester you all on that one.