T25 brake regulator

[California Dreamin]

Just been asked a question about the T25's brake regulators and thought it would be a good topic for discussion.

Whilst I cannot see any explaination of their precise operation I have managed to find a couple of pictures buried in the Vanagon manual. Looking at the pictures I believe the front of the vehicle is to the left and looking at the 'testing' information it seems to imply that mounted in it's normal position (30 degrees nose up) the brake fluid pressure is set even between front and rear whilst the vehicle isn't moving or at a constant speed. However, under braking, pressure is reduced to the rear brakes dependant upon decelleration and or vehicle angle under braking (dive).
I'm not really interested in anything other that FACT..so has anyone got factory info on this?
Does the Bently or other information have a definitive description of this? I assume that the regulator has a ball bearing or plunger operated by inertia or angle? that controls the degree of brake pressure restriction to the rear brakes.









Martin

[billy739]

you are NOT supposed to strip them down and rebuild them , but i have done a few.

some were not able to be reused due to there inner state

quite a few are seized

quite a few hold a fair bit of grunge and dont work correctly!

i have run vans with them retilted or even without any insides to allow full rear brakes.

i have NEVER had the rear brakes lock up while driving , even with the larger LT cylinders and thats the very big LT cylinders

based on the fact they are designed for a ' normal van ' as soon as you add wider / bigger tyres, wheels then the braking is messed about so it will be interesting to see how the brakes react with a standard brake valve - hence why i have played with mine.

also worth noting is that early vans ( not sure on precise date) use the bay window regulator , later it was changed , looks visually different but presume works the same

[bigherb]

Know anyone with a Haynes manual for a bay window? Cutaway and good description in there.

[California Dreamin]

Any extra 'official' info would be great as there appears to be a little 'voodoo' surrounding these.

Again another observation based on the Vanagen 'testing' info.

Whilst mounted at 30 degrees nose up (normal chassis leg position, mounted on two studs) the static brake pressure balance appears to be 100% (both gauges front and rear reading the same..in this case 50bar)

But

Unmounted with the nose of the regulator pointing down by 30 degrees:

With the front gauge kept at 100bar (pressing the brake pedal) the rear should read between 55 - 65 bar...this implies a restriction to the rears of 35 - 45%.
Also...as this is just a simple 'static' test and all that has been done is to tilt the unit, the mechanism (ball/plunger or other) must simply move freely in the cylinder (no springs or leavers).

I think this much we can be certain of.

The statement simply says " if NO then change....I take it means non adjustable and not serviceable.

Martin

[billy739]

there are no adjustments and non servicable

for some reason officially you arent ment to strip the valves down , just the same as you arenot meant to split caliper casings

i will split one and get a picture to post up if you would like

[bigherb]

It's pretty simple all there is a ball which if the deceleration is sufficient rolls forward and blocks off the supply to the rear brakes the fluid then has to push two different diameter pistons. Using a simple hydraulic ratio of a larger piston pushing a smaller one the brake pressure is reduced to the rear brakes, it also houses the residual brake pressure valve for the rear brakes.

[Hacksawbob]

i will split one and get a picture to post up if you would like

Ooh yeah cutting up stuff just get a decent camera Julian, that one on your phone wants binning

[1664]

get a decent camera Julian, that one on your phone wants binning

you get a bit of an unforgiving audience on this forum at times

[California Dreamin]

i will split one and get a picture to post up if you would like

That would be good mate...I'll put it on Wiki as it'll be a rare event seeing inside one.


Martin

[billy739]

yes i know.
i have a camera , just not always with me , and now i have a different phone with a better camera, still to tight to get a new one!

[Hacksawbob]