Thread: 11in front brakes on late 2A swb - upgrade option when new?

Story so far....

I have used the original 10 in drum set-up for the rear. New drums and all components.
i have used 11 in drums from a 109 S3 on the front, all new components and also fitted the matching master cylinder. No servo assist.

I have retained the single line setup, without proportioning valve.

When I jump on the anchors, the rear locks up. When tested it was way below the criteria to pass for a safety certificate.

I am am guessing the line pressure is less than required at the front drums.

Do do I need to convert the single line using a proportioning valve? Will this resolve my braking issues? If so, which proportioning valve?

I think the problem you have may be that the rear brakes are suited to the original master cylinder and the front brakes to the lwb master cylinder. It may be able to be corrected by using a smaller wheel cylinder at the back.

However, this is not to discount the possibility that there may be more mechanical type issues, such as the shoes not fitting the drums closely enough, or poor (too hard) lining material. Or possibly incorrect assembly of the wheel brakes. My 109 with 11" brakes all round has no issues meeting the requirements.

The rear brakes locking before the fronts were working adequately would result in insufficient deceleration.

Thanks John.
The 5 way brake line junction that distributes the fluid to the brakes has 1 receiving join, 3 feeding fluid to the brakes, and one join for the brake light. I have possibly connected the lines into the junction block out of original position. I was wondering if the hole leading to the break light switch may be a different diameter and therefore restricting flow to the front brakes.

Strike that last post.
brake light switch is in correct position. However, I do have input for master in incorrect position and one of the others in the wrong spot. I can't see how this could be a contributing factor.

I've read elsewhere that some with TLS 11inch front brakes (as I have) are best matched with 10 inch rear brakes with a 1 inch brake cylinder instead of a 1 1/4 inch cylinder. How is the smaller cylinder helping???

Does it make any difference which way the brake cylinder pistons are facing with the TLS setup?

The smaller cylinder reduces the brake effort for the same pedal pressure, stopping the rear wheels from locking before the front brakes are working properly.

I am not clear what you mean by which way the brake pistons are facing. I don't think you can assemble the pistons in the cylinders the wrong way, but if you mean "does it matter which way the entire wheel cylinder is facing, it most certainly does. The cylinder must be pushing at the end of the brake shoe which is leading with the wheel turning forward, so that the braking force is transferred to the fixed end of the shoe, and the drag on the shoe pulls the shoe into more forceful contact with the drum. If they are the wrong way round, achievable by swapping left and right, you have practically no front wheel braking going forward.

It seems as though I may have put the brake set, i.e., backing plate and all attachments on the wrong wheel.

Every pic that I have googled shows the top piston pushing in a clockwise direction, whereas mine are pushing the other way. It looks as though everything is put together correctly, that is springs, shoes etc., but I just have L and R incorrect.

Looks like a morning on the spanners tomorrow....