.........or should that be 'Another bleeding brake question' ?

Will be replacing the brake fluid on my 88 V12 as soon as the weather warms up. Pretty much the first job I will have done on the car since picking the car up last Oct.

I think I have it sussed. Use the Teves procedure not the one prescribed by Jaguar. To keep it a one man operation was planning to get some one-way speed bleeders for front and back.

My understanding is that the pressure for the rears comes from the pump/accumulator, not from the master cylinder via depressing the pedal. Depressing the pedal does however actuate the valves which release brake fluid to the rears. With this in mind, is it possible to use a suction-type device attached to the rear bleed screws (I have a vacuum gun type device, and also a mityvac) - am I correct in thinking no benefit for the rears, as you still need to have the ignition on and pedal depressed? However could be used on fronts.
Any other tips?

 

You must bleed the entire system, rears included, as prescribed, not using suction on the rears. Without the valves opening by using the pedal there will be no supply of fluid to the rears to extract.
Read PTJS1's and Orangeblossom's posts on this matter, they are the Gurus of the Teves system.

 

Mozambique,

You're partially correct in your understanding of the system. Firstly, any fluid going to any of the wheel circuits comes through the ABS valve block. The valve block is attached to the Actuation Unit. All fluid going to the ABS valve block comes from one of the areas of the Actuation Unit. The fluid feeding the front brakes normally comes from the "Master Cylinder chamber" - that's just a small chamber at the front of the Actuation Unit. Pressure applied from the pedal drives the movement of fluid from this chamber to the ABS valve block and hence to the front wheels. However, under ABS conditions, the master cylinder pressure is replaced by Boost pressure via the Main Valve. (When talking about the Teves II ABS system, it's best not to refer to the "Master Cylinder" if you mean the Actuation Unit.)

The rear brakes are always driven by Boost pressure (limited by the in-line pressure reducing valve) This fluid is still coming from the Actuation Unit to the ABS Valve block and thence to the rear wheels. It enters into the Actuation Unit from the Accumulator. The movement of the pedal opens a Control Valve which allows the boosted fluid to enter the Actuation Unit to power the rear brakes, and also allow some boost pressure assistance to the front brakes.

So, you can't get fluid sent to the rear brakes from the Actuation Unit unless you depress the pedal which opens the Check Valve and allows fluid ingress from the Accumulator. However the chamber at the front of the Actuation Unit (the "master cylinder chamber") has a direct feed from the reservoir (opened and closed via a typical sleeve valve). So failure of the boost circuit means you have no rear brakes, but will still leave you with front unassisted brakes, hence a heavy pedal.

As you're changing the fluid, not trying to release trapped air, you won't have to bleed the low pressure circuit (the feed of fluid from the reservoir to the pump).

I change my fluid this way:

Syphon as much old fluid as possible from the reservoir chambers. Fill with clean fluid. Wait 30 mins to aloow it to mix with any residual fluid. Syphon out again and fill with clean fluid.

Now bleed the rear brake circuits using the Teves procedure. Self-bleeders are fine, but I'd try and get an assistant to help so you can see the colour of the fluid.

Then do the rear brakes again! Remember you're trying to move as much fluid as possible through the Pump and accumulator, through the Actuation Unit, through the ABS Valve Block and down the length of the car. So you have to do this using pedal movement to open the Check Valve to allow fluid to make the full journey from Reservoir to Pump to Actuation Unit to ABS Block to wheels. If you use a suction method, the Check Valve will not be open.

Now do the front brakes. When you're sure you're just seeing clean fluid, the job is done!

Hope that helps.

Good luck,

Paul

 

Peter (and Orangeblossom)
Thank you for posting such a clear explanation. I feel that a diagram plus photgraphs of the units concerned would be a great addition to the clearer understanding of the system by those new to it. Also, if anything needs a stickhy, this is it. Maybe you could consider writing one and asking Graham (GGG) if he would sticky it?

 

Hi Mozambique

Paul (ptjs) is the Brains of the Outfit, as he was the one who showed me what to do, so if there is going to be a 'Sticky' as I hope there is, then I would rather it were Pauls (ptjs) as he has forgotten more than I will ever know about the 'Teves System'

Having said that I accidentally came up with a way of Bleeding the Teves Brakes, using 'Gravity Bleeding' that doesn't require the use of any Assistant, or even falling out with same, when you suddenly realize they haven't got a Clue what they are doing

Where because of this they suddenly find themselves off the 'Christmas Card List' and wonder why those Party Invitations have dried up, blissfully unaware of the fact that because they were unable to follow simple instructions, they are now considered 'Person non Gratia'

Even though I still don't know what that means and so might have to ask 'Greg'

Gravity Bleeding is so easy, that all you require is a Spanner and a piece of Clear Plastic Tubing (without the non-return 'Thingy' on the end!) Plus a Deck Chair and a Cup of Coffee, or Cup of Tea if you are based in the UK

Other Stuff Contained in this 'Thread' How to Rebuild the Calipers, a little bit quicker than I did the first time round (4 Hours just to do one)

But I've got the hang of it now!

Also how I Polished my Diamond Cut Alloy Wheels

How I found an easy way to Bleed the Teves Brakes

 

Gents,
Thank you for the explanations and info. Much appreciated!
Quentin