Brake issue

Some much needed advice would be grateful, when at a stand still in traffic or anything, and I hold the brake pedal down, it slowly loses breaking pressure and the brakes release, then if I pump the pedal a couple of times the brakes hold again, but then slowly release again, to the point where the pedal is nearly on the floor, this obviously shouldn't be happening, I've bleed the system, there appears to be no leeks as it's not losing fluid, could there still be an air block in the system somewhere creating this loss in pressure????? or a faulty brake servo???

yes to both as a possiblity I had a similar prob trying to clear a air lock from changing part of the system for the MOT, what order have you bled the system you should start the furthest away and work back so left rear, lspv left front and right front last also take the drums off and check for leaks at the rear cylinders as if in there it will bugger your rear shoes my air lock was in the pipe running accross the rear axle and had to put a pipe clamp on the flexy hose pump up the pressure then open the bleed nipple and let the clamp off. I will have to do a full bleed when it gets a little warmer as got a couple of bits to change and there was some loverly gunge that came out last time

the reason for doing the bleed was firstly the main line from the front to the rear was broken, then both cylinders on the rear were leaking so had to be replaced, but also I found the lspv valve to be seized, after working it out I figured that it was seized in the position as if it was under max payload, so decided to leave alone as it should always be giving max pressure to the brakes, or could it be that as this is seized it's leaking air into the valve. yeah, I bleed brakes from back to front.
Can the lspv valves be stripped down and cleaned or do they just get replaced??

the manual says not to strip it down, mine is also ceased in the max on position and I snapped the top off the bleed nipple as well but it shouldn't draw air in without showing a leak at the same time, as for a strip down I would have a go if I had a spare as the biggest problem would be the replacement seals they may not be a standard seal which means a huge some of money if you can find someone to sell them to you we use seals in our shocks and we have them made for us and don't sell them so others can't try to take them apart.

what would be the possibility of bypassing the lspv valve totally and removing it??

if your planning to remove it completely, id see if you can strip it down and clean. where seals maybe damaged, they may not be and can be reused.
i enquired about the load sensor last year as i had a weird experience with it on my way to the BMF with camping gear (everyones). the guy on the phone started sucking his teeth and said expensive! thats why they dont want you to strip them down....

If you remove the lspv you should end up with max power always but you also may end up changing the bias (front to back) if the master cylinder has even pressure out and is reduced at the valve, you would have to test at all points in stock set up to see what it does affect and then retest after doing the mod. Also You would need to tell the insurance coz if you crash and they spot its missing even if its not to blame it could invalidate the whole policy.

But if you replace the lspv valve with a mod with no valves in, basically straight through, fluid comes in fluid goes out, the whole system will be filled with fluid and there should be no lack of pressure either front or back, as soon as you press the brake pedal, fluid is then pushed anywhere and everywhere it can with the same amount of pessure. mmmm didnt think about that with the ins company though.

You are right about the fluid but the flow may have a restriction in it even when at full power on the lspv but I happily confess I don't know on our vans if thats the case generally rear drums require the same power/force as front discs but due to the difference in effiency the bias on the brakes is more to the front like on a bike you slow down with the back but the front does the stopping and on a car if you do a disc rear conversion you have to reduce the pressure to the rear to maintain a bias to the front basically to stop the back locking up before the front and causing a skid/slide.

Been reading the little label on the drivers door about break pressure, front pressure 100bar, rear 45 - 75 bar i think it was depending on weight

small insight in to the vans LSPV and what happens when over loaded..
Last May i loaded the van to the bottom of the windows with camping gear; sleeping bags, tents, personal effects (1 or 2 heavy bags of beer!) of my club members. set off and was doing 65mph on the duel carriage way, 20 mins in to the journey the van made a loud and weird noise and sensation! i slowed down and was getting prepared to pull over + the thoughts that i have everyone's camping gear in the van and am going to break down! decided if i was going to break down that i needed to do so as close as possible to our destination! and kept going.
it did it less than a minuet later again as i went over 65mph! this time it felt as if i was quickly pumping my foot on the brakes and letting go!
from then on we decided to not go over 65!, stuck to 60 instead. when we got to Peterbro BMF i read up the owners manual and found out the vans max load is 1/2 ton.. 500kgs! we could not have posible got near that with camping gear!

i have also heard that before a MOT its worth sitting a breeze block over the rear axle to set the LSPV off for the brake test.

leopard_pagan wrote:I have also heard that before a MOT its worth sitting a breeze block over the rear axle to set the LSPV off for the brake test.

When I took ours for test last year, the rear brakes weren't strong enough for the brake test.
So the tester got a large lady out of the office & 2 mechanics to sit in the back to trigger the LSPV.
It worked, they were strong enough to pass.

The payload on the label on my drivers door says 450kg - 750kg,

same here, must have been the 2-3 heavy bags full of beer!
it was kinda funny as end of the weekend it was raining so everyone put everything in my van while we dismantled the Marquee we'd camped under. my van was full to the roof! and no i didnt drive it like that.. even the driver seat had stuff on it! made sure only light stuff was in my van to the return journey.