Club 80-90 Forums

PostPosted: Sun Dec 02, 2018 5:17 am Post subject: Girling VW Vanagon T25 Rear Brake Regulator 1985 Reply with quote


Had some problems with the rear brake regulator - dismantled this and found a very simple mechanism - 3 moving parts.
Floating piston, ball and pin.
On hard braking with no load- the ball moves forward - pushes into the piston seal and reduces the back break pressure and lock up.
On steep hills - the ball will move forward with gravity and when you brake the ball pushes the piston foreward 5mm - but the clever bit is the pin pushes back against the ball releasing pressure difference and allows rear braking.
Automatic resetting of the floating piston happens next time the brakes are used on the flat - apply brakes and the pressure is greater on the larger surface area of the piston and pushes it back into place.

Small hole venting to the support lug is a weak point - as this vents to outside and hence any O ring failure will mean loss of brake fluid and failure of brakes.

The main weakness - is when you drive down a steep hill the ball has rolled forward - you then brake to slow and the ball/piston moves forward - then the pin releases the pressure - allows rear brakes to work - but if you then drive on the flat after a steep slope the piston is still forward - so if you then have a emergency brake situation without resetting the brake regulator - you will get full pressure breaking to the rear and a skid etc.
So solution is light braking after a hill - before an emergency - low probability - but that's my crude interpretation.

Girling UK created a very simple device that VW used.

Clean the chamber , put on new O rings(suitable for brake fluid) - buy a new one if the piston chamber is pitted with rust.

You can test it all with a air footpump or a large syringe and some tubing.
The ball and the piston must move !!!!! so just the ball rattling inside is not enough to ensure it works.

Test the brakes on the flat and down a hill and when wet and see what happens - do they lock up the rears
I have 15% difference on rears ( within UK MOT test) and the back end slides to the right in the wet -
So after renewing rear brake cylinders and shoes - needs new drums as one is just on tolerance for internal diameter.

Thanks.

Indeed, many thanks! Isn’t this forum fab?

Should there not be light spring inside the inertia valve?

Sent from my S60 using Tapatalk

If any one has a image of the spring set and / or ideally a spare I can buy please PM

I assume a light spring would go between the piston and ball ?

I could not find on any forum a internal image of the ball / piston set up only on different versions

thanks

http://what-when-how.com/automobile/hyd ... utomobile/" onclick="window.open(this.href);return false;

Many thanks Simon (Brickwerks) for the images and excellent document -

In the two Girling Brake Pressure regulators I have opened - my DG Transporter 1.9 1985 and from a spare I found in the scrapyard - they only had the pin through the intertia piston - with no spring

The spring version may be a earlier / later modification doing away with the pin ?

When you push the intertia piston in place with O rings - it takes good thumb pressure to do so.

Where as if you try the set up with a large 60ml syringe or footpump it easily pops back into place emulating hydraulic action

This topic link shows the same set as mine
https://www.thesamba.com/vw/forum/viewt ... p?t=685421" onclick="window.open(this.href);return false;

Do be careful when you clean it all out - use brake fluid only - flush thro with a syringe otherwise the seals will expand if you use any thing else.

This regulator is still available ( see Brickwerks) but can easily be missed in your DIY brake service - at cost when your back brakes lock up/skid/loose the back end in an emergency. The MOT rolling roller test does not test the action of this device.

Very robust part that needs little to no servicing, we've only ever changed them due to excessive external corrosion around where the pipes enter and exit.

Interesting! ...hmmm, I wonder if that part is to blame for my bus' apparent lack of rear braking. Works OK on a double pump, but never really bites on the first

Also, not really an issue for me, but a nose-down stance would probably affect brake functionality as effectively the bus will almost always be 'traveling downhill'

chris7ian wrote:Interesting! ...hmmm, I wonder if that part is to blame for my bus' apparent lack of rear braking. Works OK on a double pump, but never really bites on the first

If you need to double pump then the rear brakes need adjusting.

bigherb wrote:

chris7ian wrote:Interesting! ...hmmm, I wonder if that part is to blame for my bus' apparent lack of rear braking. Works OK on a double pump, but never really bites on the first

If you need to double pump then the rear brakes need adjusting.

I should've said - I've had them adjusted so many times with no improvement!