Brake upgrades

[Warb]

I've been investigating the options to upgrade the brakes on an 88". The best approach seems to be a straight swap to 109" drums front and rear, using a servo boosted master cylinder.

However I've also considered moving to dual circuit brakes, because like Peter G I've experienced a single circuit failure, by coincidence also in the UK and in a Mini!. There seems to be some confusion about the requirement for a PDWA in such a setup, with several people (on other LR forums) saying the PDWA is more trouble than it's worth. However those comments seem to be based on the assumption that the PDWA is "only a warning light switch", but from what I can see that is not accurate. It appears that the Land Rover dual circuit master cylinders (at least the 109" variant) have no physical link between the pistons for the two circuits, such that if one circuit fails the master cylinder will not provide pressure to the other circuit. The second piston is moved only by fluid pressure from the first piston, so a lack of pressure in the first piston means none in the second either! To overcome this, the PDWA cuts fluid to the failed circuit and in so doing it activates the warning switch.

If that is true, then replacing the PWDA with a couple of T's, as recommended on several Land Rover sites, removes all the advantages of dual circuit brakes and effectively reduces the system to a single circuit.

Can anyone confirm this is the case?

[Johnno1969]

I can't answer this, but the same question bothers me.....

[Lotz-A-Landies]

In a dual circuit syctem, the brake shuttle valve detects a pressure differential between the two circuits moving a piston which illuminates some form of warning usually a lamp on the dash. In some systems it also closes off the part of the circuit with the low pressure.

The last thing you want to do when you have a hydraulic system failure in one circuit is to bypass fluid from the functional circuit to the dysfunctional system. This is because the hydraulic failure may be a ruptured brake line, in which case no matter how much fluid you bypass from the intact circuit to the failed circuit, you will never, ever, have sufficient fluid to make the ruptured system work.

It is far better to have only one circuit working on half the wheels and be able to bring the vehicle to a stop, all be it somewhat delayed, than have no brakes at all.

That's my take on it.

[peterg1001]

There are some variant opinins about what the bloody thing actually does Brake shuttle valve or failure valve on Chassis how do I reset it? (http://forum.landrovernet.com/showthread.php/79467-Brake-shuttle-valve-or-failure-valve-on-Chassis-how-do-I-reset-it).

Diana, if anyone has taken one apart and looked at it's you.

Does the valve seal off the leaking circuit, or not?

Peter

[Lotz-A-Landies]

Peter

In a series and in most other systems AFAIK the shuttle is only a switch to operate the on dash warning. Yes I have held the beastie in my hand.

The way I read the thread, the people are talking of replacing the shuttle with "T" pieces for the front and an end to end connector for the rear only to remove shuttle from the system and not connect the two systems together.

You can do it in an 88" SIIa, you just need to acquire the pedal box from a SIII 6cyl or Stage 1 with the two circuit master cylinder. You will also need to acquire a "T" piece and either an elbow or end to end 3/16" brake pipe connectors, some 3/16" brake pipe and a flare nut for the connector and the master cylinder. Or you can use the brake shuttle and IIRC the shuttle has the ability to either connect 2 pipes ( with a blanking plug) or 3 pipes for the front.

On the master cylinder the front fitting goes to the rear system and the rear fitting goes to the front.

You don't need to connect the wiring up unless you want a brake fail warning lamp on the dash.

[peterg1001]

Thanks Diana.

IOTW, the PDWA is a waste of time and money, and all the work that went into this Fixing the brakes (http://www.greenacre.biz/landrover/949_Brakes/949_Brakes.htm) was for the intellectual satisfaction only.

Andrew, if you're after T pieces rather than the PDWA, I can recommend this mob Car Builder Solutions - NF Auto. One-stop Shop for Parts, Tools and Accessories for the Car Builder. Neil and Matt Foreman. (http://www.nfauto.co.uk/), it's worth a look just to drool over the catalog for a while.

Peter

[isuzurover]

FWIW,

I had a rear line fail (rub through) on my 110 county. The shuttle valve activated the failure warning, however fluid spurted from the rear line every time I applied the brakes. This meant that the BF reservoir emptied completely, however the front circuit still worked - enough to get me a few hundred k's down the road to camp.

The next morning air must have leaked into the front circuit of the MC, as I had no brakes at all. (fixing the leak and topping up the reservoir fixed that).

As a temporary fix, I cut the line between the MC and shuttle valve, and crimped it at the MC end. No fluid leaked out the Shuttle valve for the next 4000 km (i.e. until I repaired it properly).

So, I therefore conclude:
The shuttle valve will not allow fluid to go between the front and rear circuits, however will not stop fluid gushing out a broken brake line.

[101RRS]

The 101 has a dual circuit system, including dual reservoirs. The master is a dual system, one feeding front brakes and the second feeding the rear brakes. Both lines go into each end of the PDWA, either side of the shuttle which is central and the switch is off.

If there is a brake with fluid loss in either circuit the pressure in the good circuit moving the shuttle to block the circuit loosing fluid and turn on the light.

Now I am not sure why the PDWA is actually in a fully dual circuit system as if there is a leak in one circuit in theory the other would still work - exactly what the PDWA does - this is where I believe that the story that the PDWA is just a switch comes from - in a fully dual circuit system this is essentially all it does.

In a single circuit master cylinder system - the PDWA provides a cheap (priced a PDWA lately) dual circuit system by keeping fluid going to the working circuit.

Garry

[Warb]

In a series and in most other systems AFAIK the shuttle is only a switch to operate the on dash warning. Yes I have held the beastie in my hand.

The way I read the thread, the people are talking of replacing the shuttle with "T" pieces for the front and an end to end connector for the rear only to remove shuttle from the system and not connect the two systems together.

From what I can see of the various cut-away diagrams that I can find, this is not always the case. Yes, people are using the T's to remove the PDWA and not connecting the circuits together, but that may still create a problem:

The PDWA was certainly designed to shut flow to one or other circuit, any pressure differential moves the piston to one side which cuts flow and activates the warning light.

The question is why is this required, and the answer seems to be that of the several types of dual circuit master cylinder, some are more "dual circuit" than others. If there is a physical connection between the pistons for each circuit, then even if one fails the other will still work (by virtue of the physical connection). However if the two pistons are in a single bore with no physical connection, the second piston is pushed only by the pressure in the first piston. In this situation, a lack of pressure in one circuit results in no pressure on the second piston.

In the case of the 109" dual circuit master cylinder, it appears that the two pistons are of unequal size, with the large one driving the dual front slave cylinders. The second piston is "pushed" by pressure from the first, but if the first circuit fails there is no physical contact with the second piston, so the second piston does not move. So a failure of one circuit in a "dual circuit" master cylinder results in total brake loss.

The 88" master cylinder appears to have identical cylinder bore and strokes, so if there is sufficient pedal movement either piston can depressurise and physically push the other one.

If this is the case, then removing the PDWA from a system with a 109" master cylinder (6467729?) results in a single circuit brake system, but removing it from the other type (can't remember the number but it doesn't have a bulge for the first half) might be OK. Note that the second circuit will work only after the first piston has completely emptied (so it can physically push the second piston), so much of the pedal movement has been used up - if the brakes on the working circuit are badly adjusted, is there enough pedal movement left to make them work?

Even in the case of the 88" master cylinder, every pedal depression/release refills both portions of the master cylinder which then empty on to the road at the next pedal depression depleting the supply of fluid and allowing half the pedal movement before any braking effect. With a working PDWA, after the PDWA has tripped no further fluid should be lost, and no extra brake pedal movement should be experienced (which is why there is a warning light, otherwise people would carry on not knowing a problem existed!).

If all this is true, overall I think that dual circuit brakes are not really worth having without a PDWA!

I would guess that the reason fluid still spurted from the failed circuit as mention earlier was that the PWDA was not working properly, or was releasing and reblocking with every pedal depression.

Edit:
It is also worth considering that as a PRESSURE differential unit, the PDWA must see enough pressure difference to activate. So in the case of a total failure of one circuit, a gentle depression of the brake pedal may allow all the fluid to leak from the failed circuit without creating enough pressure in the "good" side to trip the PDWA, simply because the two pistons in the master cylinder are linked hydraulically. In the 88" style master cylinder (if my thoughts above are correct) the "good" circuit would then create pressure and result in braking (in the 109", no so much!) and also trip the PDWA. On the other hand, a stamp on the brake pedal may shock the PDWA in to action, sealing off the failed circuit without much fluid loss or pedal travel. My (Haynes) cutaway of the PDWA shows no springs, which would suggest it does not self reset, so I'm guessing that the leaking fluid mentioned above was the result of the PDWA not working correctly.

[Landygirl]

Im currently setting up a brake upgrade in my 88 with ser 3 3in shoes on front and 2.5in on back with twin wheel cylinders on the front. i have finally decided now to go with a single system just to replace the circuit i took out but im wondering which master cylinder to use as the one i was going to use had the dual connector on it can i run a single circuit off this or is there another master i should use?

[Warb]

The earlier vehicles had a separate fluid tank (steel) that supplied both the brake and clutch master cylinders. These master cylinders obviously had two connectors, in and out! I seem to remember you have a IIA, which would mean that you probably have this system.

I believe you have an inline booster, so you do not need the booster style pedal box. In which case you need to know if you have a combined fluid tank, and whether you are going to keep it, or change to separate clutch and brake fluid tanks.

When all that is decided, then you buy a suitable 109" single circuit master cylinder (with or without a built in tank) and also a clutch master cylinder if you need one with a tank!

There are also remote mounted plastic tanks available (the ones on eBay from the UK are very expensive and can be bought cheaper!) should you wish to keep remote tanks but split clutch and brake.

[JDNSW]

As Warb says, but the important thing is if you are using the 11" brakes, you need to use the 109 master cylinder. As stated, these come either with integral reservoir or separate reservoir. The works are the same, but the ones with the integral reservoir perhaps a bit easier to find.

John

[NiteMare]

i have upgraded the brakes on my 88" bitsa twice in the couple of years i've owned it (along with a few other mods, 200tdi and 3.54 diffs)...

i started off with it having 10" brakes all round powered by a non assisted single circuit

i then decided i'd like bigger drums and shoes on the front axle so i stripped the brake parts off an old salisbury REAR axle, 11" drums, backplates etc', the rear brakes as standard utilise the same slave cylinders as used on the front 10" brakes, this meant my ratios (master to slave) were going to be correct

this improved my holding ability on steep slopes but being non servo meant i still had to apply a fair bit of leg pressure

eventually the master cylinder decided to give up the ghost and leak fluid into my footwellso i decided to go for my next upgrade

i had a Series3 (that had been on 10" brakes) dual line assisted pedal box complete sat on the shelf (it had been there for about 18 months) so swapped it in (not forgetting to connect the vacuum pump up)

i didn't bother with the shuttle valve unit, i just made up new pipes, the first (front one) went straight to the flexi pipe that drops to the rear axle, the second (rear of master cylinder) went straight to the Tee piece that feeds the front axle

i bled them off, adjusted the shoes (twin adjusters now on the front axle) and tested it

what a difference, i had good to excellent brakes before but now the only limit to the stopping power is the traction between the tyres and the tarmac (just be aware that excessive traction can make it really twitchy under heavy emergency braking, i've had mine trying to swap ends at speed even in a straight line due to the rear going "very" light) and all this is without giving my leg muscles a workout anymore

plus there's not the difficulty of bleeding two slaves per side on the front axle doing this modification

just thought i'd throw my twopennorth in