Disassembling BN6 Front Brakes

[BN6_2197]

Hi all,

I am loosing break fluid in my front brake. I removed the brake drum and saw that the sealing of one of the cylinders is defect. I now want to remove the cylinder and repair it. Any hints on the removal procedure? It it my first time I am doing this and I did not find the right information in the workshop manual.

Cheers,

Volker

 

[steveg]

I have pictures of the brakes here: https://www.pbase.com/stevegerow/bn6brakes2013

It is pretty easy to remove the shoes. Once that's done, you could pull the pistons, etc out of the cylinders and examine the bores for pits. If clean, install a new rebuild kit; if pitted, install a new
cylinder. Suggest marking the shoes so you can reinstall them with the correct orientation.

The cylinders are attached to the backing plates with nuts (see pictures at link).

 

[steveg]

Just realized the springs are installed backwards - they're pulling on the "swivel" end of the shoes, rather than the "piston" end:

Brakes always worked fine, when I had them installed.

 

[Bob_Spidell]

Take pictures so you know how everything goes together (you'll be glad you did). Gently clamp the flex line to the wheel so you don't lose all your brake fluid before breaking the fitting loose, else you'll have a nice mess. Use a flare nut wrench to break the fitting loose if you have one or can buy/borrow:

https://www.summitracing.com/parts/sxt-980906?seid=srese1&gclid=CPaJgru9jsICFU1gfgodnU4AQQ

I believe you'll need a 7/16" (working from memory--someone please correct me if I'm wrong).

If the shoe(s) have brake fluid on them they should be replaced (probably best to do both sides). I've tried to clean fluid-soaked shoes, and no matter how much sanding and cleaning with brake cleaner I did they kept oozing fluid. If by chance the shoes are original--not likely, but possible--they might be lined with asbestos, so wear suitable breathing protection. Not just the paper filter type, but rated mask and cartridges (I think they're a pink color).

Bleed the system if it's been a few years, and might as well replace all the brake lines, overhaul the engine, install that 3.54 rearend, replace the wiring harness, etc. while you're at it.

 

[steveg]

FWIW - Harbor freight has inexpensive flare nut wrench sets.

Update: Oops - overlooked Cologne!

 

[Bob_Spidell]

That's where I got mine, but don't know if HF is in Germany.

 

[BN6_2197]

Gents, thank you very much for the hints. But I am still at the first step: how to remove the return springs. The workshop manual says "It will be found quite simple..." To be honest, I have no idea how to do it in the right fashion. Any help on that is appreciated.

Volker

 

[BN6_2197]

I also want to remove the flex line to the wheel before removing the wheel cylinders. I am asking me if this is required. It seems not to be an easy job since it is hard to get there due to the connecting pipes of the wheel.

 

[Bob_Spidell]

Gents, thank you very much for the hints. But I am still at the first step: how to remove the return springs. The workshop manual says "It will be found quite simple..." To be honest, I have no idea how to do it in the right fashion. Any help on that is appreciated.

Volker

There are tools and kits for doing this job--disk brakes are MUCH easier--and, yep, I think Harbor Freight has them:

https://preview.tinyurl.com/nbhroma

[Volker: If you're not familiar with Harbor Freight, it's a big chain store in the US that sells cheap tools and other stuff--usually imported from China--of dubious quality but often good enough for occasional use: https://www.harborfreight.com/# ]

Anyway, you can just grab one end of the spring with pliers and muscle it off. Wear eye protection in case the spring gets away from you.

 

[Bob_Spidell]

I also want to remove the flex line to the wheel before removing the wheel cylinders. I am asking me if this is required. It seems not to be an easy job since it is hard to get there due to the connecting pipes of the wheel.

I've done brakes on a BN2, which is similar. IIRC, the flex line is from the chassis to a point on the suspension and thence it's a rigid line to the wheel backplate, with a short length of pipe connecting the two cylinders (one cylinder has an 'out' fitting to the other cylinder). The flex line does not need to be touched--just break the rigid line at the cylinder. However, if the flex lines are very old you might want to replace them while you're at it, as they can collapse internally and cause brake lockup (this time I'm not kidding).

 

[steveg]

Volker,
I used right-angle needle-nose pliers to pull the one end out of the hole in the shoe. The springs are not that stiff.

 

[BN6_2197]

The flex line does not need to be touched--just break the rigid line at the cylinder. However, if the flex lines are very old you might want to replace them while you're at it, as they can collapse internally and cause brake lockup (this time I'm not kidding).

The flex lines are still pretty good. So there is no need to change them. Unfrotunately I did not get your idea not to touch the flex lines. I want to remove it either from the back plate of the brake or from the connecting point at the chassis to be able to place the brake on my work bench for repair of the wheel cylinder.

 

[steveg]

The flex lines are still pretty good. So there is no need to change them. Unfrotunately I did not get your idea not to touch the flex lines. I want to remove it either from the back plate of the brake or from the connecting point at the chassis to be able to place the brake on my work bench for repair of the wheel cylinder.

In order to get the cylinder out on the bench, after removing the brake shoes and springs, you'll need to:
1) disconnect the hose connector to the hard line at the chassis, so you can rotate the hose.
2) disconnect the hose from the cylinder, saving the copper washer
3) disconnect the balance pipe
4) remove the two nuts holding the cylinder to the backing plate

Suggest taking photos of everything before beginning work.

Suggest examining other cylinders carefully as they're probably the same age.

 

[BN6_2197]

Steve, how can I prevent the brake fluid to leave the system? My idea was to clamp the hose conntecting the hard line at the chassis and the back plate of the brake. And then remove the flex line from the back plate.

 

[steveg]

Steve, how can I prevent the brake fluid to leave the system? My idea was to clamp the hose conntecting the hard line at the chassis and the back plate of the brake. And then remove the flex line from the back plate.

Hi Volker,
You said you wanted to remove the cylinder to the bench. In order to do that, you'll need to use some kind of syringe to remove the fluid from the reservoir.
You won't be able to remove the hose from the wheel cylinder without undoing the connection to the pipe. Otherwise you cannot rotate the hose enough to unscrew it from the cylinder.

Personally, I'd attempt to rebuild the cylinder on the car without removing it from the backing plate, before going to the above process as a last resort.