110 Rear drums locking before front disks

[western]

Interesting, I didn't realise that the PDWA could affect bias? Is there a valve in there as well as the switch then?

And point taken regards the bias valve, I'm going to remove the knurled knob once I'm completely satisfied with the bias.

I'm pretty sure the PDWA doesn't affect the front to rear bias, it's a shuttle valve inside which moves to close front or rear brake system off if there's a leak,

[tacr2man]

I'm pretty sure the PDWA doesn't affect the front to rear bias, it's a shuttle valve inside which moves to close front or rear brake system off if there's a leak,

Yes the pdwa is only a shuttle valve , it was introduced on lots of cars back in about 1975 as required to show split system fault , some vehicles even had a a test switch , later ones lit up and then went off on startup

[Orgasmic Farmer]

I,m in this club too. 110 van with TD5 type disc braked rear axle and the simple PDWA valve fitted on bulkhead. Will always lock rears first in an emergency braking situation. Been looking to fit a G valve or a bias valve for past few years, just never got around to it :-)

[pete3000]

for a 110 hardtop and drums at the back it should have a g-valve ideally from the factory, so the routes are several.

The g-valves new are expensive (second hand probably not a good idea), so you could fit a reducing valve as above which would make the rear less fierce, or upgrade the front discs/pads to balance it out. All depends on how good/bad the brakes are currently.

I'm still bedding my new setup in at the moment so will see if it needs the g-valve(or reducer valve) plumbed back in or change the pads either end for something more or less fierce.

[2dextas]

i take it a g valve /bias valve are essentially the same thing? being ignorant of such matters.

assuming i fit a bias valve like fitted to Dotty the 90 above - where do you fit it? can it be anywhere on the rear brake line or is there some advatage to having it in one position or another?

[Hazza]

My understanding is the g valve is very sensitive to its orientation. Needs to be mounted at a precise angle to function correctly I.e. Under braking.

The adjustable valve that i've fitted just needs to be in the rear brake line. Mine is in the engine bay.

[Ian Barrett]

Daft question maybe, but have you checked your FRONT brakes are OK?

If they are gunked up and not working very well the backs tend to lock up.

I had the same locking up problem which I put down to the lack of weight on the back wheels after I converted to a canvas top but it got so bad I pulled all the brakes apart and found the fronts were quite seized and corroded.

I fitted new seals, pistons and rotors at the front and new shoes and drums at the back and the whole braking system was transformed. I can stand the truck on its nose now without locking up a single wheel.

[pete3000]

bias valve is either fixed or adjustable, it allows a set percentage of the pressure to the outlet (brakes). So if you go the adjustable one linked, you can just back it off so that the locking only occurs a fraction before the front.

The caveat is though, especially with a 110 the less load (weight) you have in the back over the rear axle the easier the brakes will lock up. I suspect though for everyday use it wouldn't vary a great deal.

The fixed versions are fitted to defenders to split one feed from master cylinder and send 32/68 to the circuits as a percentage.

The G-valve is an attempt to automatically restrict the fluid based to the rear brakes. As far as I could make out braking hard and the inertia force wanting to act on the big ball bearing in the G-valve rolling uphill and restricting the fluid to the rear brakes. When the Gforce reduced the ball would roll away helped by a weak spring and the valve would open again.

Yet another variation is the brake proportioning valve found on commercial vehicles where a valve is adjusted based on the amount of weight in the load area, this is done with a lever and a spring which opens or closes the valve, based on the distance between the load bed and the axle.

[pete3000]

My understanding is the g valve is very sensitive to its orientation. Needs to be mounted at a precise angle to function correctly I.e. Under braking.

The adjustable valve that i've fitted just needs to be in the rear brake line. Mine is in the engine bay.

It is, mine is on a slight incline set by the mounting bracket, I have HD springs at the rear which add an inch of lift when loaded (2 when unladen), this is enough to reduce the effort on the rear brakes.

[Snagger]

PDWA valve should not affect bias ever - it is a "pressure differential warning actuator" valve which brings on a warning if there is a difference in hydraulic pressure between the circuits, so it's there to detect, not cause an imbalance. However, if the valve has shifted due to activation, it could be partially blocking one circuit (some owners are under the misconception that it seals off a leaking circuit - unfortunately this is not true).

I'm not familiar with the brake system on the 110, but the master cylinder more closely resembles the 109's than the late Defenders'. In that case, the rear brakes should connect to the end of the master cylinder furthest from the driver. Check this is still the case - on my 109, the brake lines crossed over to achieve this under the PDWA valve, not on exiting the master. Someone may have replaced the lines or "tidied them up" and removed the cross-over.

[Hazza]

Interesting, on mine the rear brakes come from the end nearest the driver (Original steel brake pipe). Goes to the right hand side (as you look at it) of the PDWA.

There's still no G valve though!

[GW8IZR]

I read this somewhere before and checked cos I wasnt sure.

for early 90/110 If you look in the manual it says the primary circuit goes to the rear and the secondary to the fronts, then the exploded diagram of the master cyl shows the primary and secondary the way you would expect them.

I concluded that the port nearest the pedal is for the rear circuit, that agrees with the drawings.

So I think yours (Hazza) is correct and thats how I piped mine.

Edited March 24, 2015 by GW8IZR

[Snagger]

That's why I said to check! It could be that you have them connected up reversed, all the same. I find it unlikely that the front brakes are operating normally though if you are locking rear drums. I suspect your calliper pistons are seized. Take the front wheels off and pry the pads back with a screw driver and have someoen pump the pedal to check each piston moves freely and isn't caked in rust and filth.

[Hazza]

Calipers work fine, the brakes are all brand new. I think it's simply a lack of g valve that caused all my issues.

[western]

just took this photo of the PDWA on my '89 110CSW.

the 2 upper pipes come from the master cylinder.

the lower left [as looking from front of vehicle at PDWA] goes to front brake calipers Tee piece on right front damper/spring mount.

the lower right goes to rear brakes.

if your isn't the same, it's been piped up incorrectly.

[GW8IZR]

That's why I said to check! It could be that you have them connected up reversed, all the same. th.

Thing is Snagger I'm not 100% sure it's correct - I'm only working on what seems correct from the info.

Going back to g-valves, every single one I have refurbished has had the same fault, rusty ball won't seal and rusty lump where spring used to be. It may as well not be there. In that state it's not a proportional valve its a connector.

Adding a bias valve or fixing the g valve may help in a lot of these rear axle lockup issues.

[pete3000]

Which ports go to the top of the PDWA also Ralph? i.e is the 13mm bigger port going to the LHS or RHS of th top of the PDWA. I know the ports on the master cylinder are different sizes to avoid mis-connection, then they go and give you two ways to reverse the circuits at the PDWA.

Just want to check for my piece of mind, i.e should the larger port on the master cyl go to the front or rear brakes.

TIA

Pete

[western]

Master cylinder front port to pdwa upper left nearest wheel arch

[Hazza]

Just a quick pointer, do not buy the bias valve I recommended. I picked up the Landy today ready to do a trip up to Scotland, jumped on the brakes to find the fronts locked and the brake warning light came on. Turns out the valve is leaking and letting air in along the shaft into the rear brake lines. The landy is now back to how it was before.

[jumping jack]

Going back to g-valves, every single one I have refurbished has had the same fault, rusty ball won't seal and rusty lump where spring used to be. It may as well not be there. In that state it's not a proportional valve its a connector.

How do you refurb them?

I don't want to pay the better part of £200 for a new one and have got an old one thats got a bit rusty.

[GW8IZR]

so its considered a none serviceable item and you cant get any of the internals as you might with a brake cylinder or caliper kit etc.. so I wouldn't recommend doing this.

What I did was disassemble, ultrasonic clean of the body, polish the bit where the ball sits with a fibreglass brush, replaced ball with an identical one sized at BSL trade counter, replaced neoprene O ring with one suitable from a caliper service kit ( some commercial van or other ) pressure test on hydraulic rig. flush and clean after test and stick a bit of paint on it.