Bleeding 11" Front Brakes

[jac04]

The 11" front brakes on my SIII are just like to front brakes on the 109. They have 2 wheel cylinders at each wheel - one top and one bottom. The flex line comes into the top cylinder. A hard line then connects the top cylinder to the bottom cylinder. The bottom cylinder has a bleed screw.

Now, if I'm looking at this system correctly, how am I ever going to get the air out of the system? The inlet & outlet on the top cylinder are located at the high point of the cylinder, which is good. This means that fluid coming into the top cylinder will push out air and the fluid will eventually fill the cylinder, come out of the cylinder, and head into the bottom cylinder through the connector pipe.

However, the inlet & outlet on the bottom cylinder are at the bottom of the cylinder, meaning that air will get trapped in the bottom cylinder. Even if I try to reverse bleed (force fluid in through the bleed screw), there will always be an air pocket.

Is there a trick to bleeding these brakes? The Green Bible specifies a normal bleeding procedure.

[greenmeanie]

Jac,
THe well known and accepted trick with 101 owners (They have the dame brakes) is to modify the brakes slightly. The trick is to move the bleed crew to the top cylinder and add a second line.

You end up with the flex hose from ther chassis line down to its little bracket. The new hard line then goes from the end of the flex line to the BOTTOM wheel cylinder. You keep the original hard line which now takes fluid from bottom to top and finally you bleed from the top cylinder.

Bleeding is then a simple 5 minute affair and the line roiuting has no other effect on brake performance. I just did this mod on the 109 IIA I am building.

[jac04]

^^ I understand what you're saying, and I had actually seen that somewhere before. It will certainly give better access to the bleed screw. However, the fittings on the bottom wheel cylinder will still be at the bottom of the cylinder - allowing an air pocket to remain.

I'm leaning toward 'bench' bleeding the wheel cylinders with them mounted to the backing plate and all the lines attached up to the flex line (per the original arrangement). That way I can turn the assembly while bleeding to get rid of all the air. After mounting on the vehicle, I would reverse bleed to push all the air in the lines up to the master cylinder.

[greenmeanie]

Now don't ask me to explain how the air bubbles react but the mod as suggested gives a rock hard pedal with very little effort. No stripping, no disassembly, just easy.

[jac04]

^^ Can't argue with results.
Did you make the new hard lines (if so, what did you use for fittings & the flare tool to get the correct bubble flares?) or can they be purchased somewhere? Thanks.

[greenmeanie]

Yes I made a new hard line. I got some of that dark green tube that you can buy at most automotive shops. I robbed the fittings from the existing short hard lines that go from the flex hose to the top cylinder. I had new lines to install mind you. They can be obtained from Fedhillusa.com. I may have to check that address if it doesn't work.

For the flare/bubble tool I used something that I brought with mer when I came over here. Worst comes to worst any british car garage will make the ends for you.

I tried taking a photo of whay I've done but black on black at short range that is at the limits of my camera doesn't allow for anything meaningful to be posted.

[bobzinak]

you must back off the brakes to minimize the air space in the slve cyl. if you don't you will have a hard time bleeding the brakes.... I had a friend take his and place it at every angle possible. didn't work till the shoes were backed off...also he was a distributor of LR parts and even called england to try to figure out the problem...it was from my original white (now green) book... try it and let us know how it worked...BOBZINAK

[jac04]

you must back off the brakes to minimize the air space in the slve cyl. if you don't you will have a hard time bleeding the brakes....
You know, once the brakes are backed off all the way I bet there isn't much room left at all in the wheel cylinders. So the amount of air left in the cylinder may be so small that it doesn't really matter. Thanks.