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trekker · Posted: Sat Feb 14, 2015 8:57 Post subject: Peugeot 306 rear wheel cylinders

My daily runabout Pug 306 has drum rear brakes with Bosch fittings.

Six months ago I had brake fluid running from a rear brake drum. On stripping I found the whole brake system was soaked in fluid, hence a new cylinder kit was fitted to both sides and the shoes relined.

Last week brake fluid again ran from one of these drums, and when stripped I found the same condition, soaking in fluid. The opposite side was not much better.

Some firm talking with the reputable brake and clutch shop led to one of the managers examining the longer of the two pistons, and showing me a pin hole drilled radially from the dust boot groove into an internal axial drilling where a valve ? is fitted. Fluid had passed this internal valve ? and literally run out of the cylinder and into the brake chamber.

I've replaced the two cylinders with pirate parts which look good and are made for this model, had the brakes again relined and all is now well.

I'm keen to understand what role this radial drilling plays in what should be a simple and pretty safe brake cylinder.

I cant find any specific mention of this design feature on the net, other than these Peugeot cylinders having a short life.

Any one have the reasoning behind this drilling ?

dave

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peteinchad · Posted: Sat Feb 14, 2015 9:03 Post subject:

Some sort of pressure relief valve maybe ???

trekker · Posted: Sat Feb 14, 2015 10:04 Post subject:

Hi Pete. The only pressure in that piston is from the brake fluid forced by the master cylinder, and if pressure is relieved through this drilling, then the fluid squirts into the brake drum.

I can't believe this could be a Bosch design, to relieve fluid onto the brake shoes and drum.

Thanks for giving this some thought.

dave

peteinchad · Posted: Sat Feb 14, 2015 11:33 Post subject:

I've never come across it before Dave - it does seem a bit odd - and French!!! Very Happy

trekker · Posted: Sat Feb 14, 2015 12:08 Post subject:

Yes, if I could find an exploded diagram of this Bosch cylinder, the piston drillings will be clear, and so will the failure route.

This wheel cylinder is identical to that of the 206, the box in which my Chinese replacements came are marked as such.

peteinchad · Posted: Sat Feb 14, 2015 13:13 Post subject:

A lot of the French cars use identical parts - my son has a Citroen Saxo and most things - including the seats are the same as a Peugeot 106.

trekker · Posted: Sat Feb 14, 2015 17:24 Post subject:

Pete, I've mailed a close up of the piston to venn, he'll post it on here for me. He's a great help.

You'll see the small dia hole in the very left groove, that's where the dust boot sits and the brake fluid leaks out !

peteinchad · Posted: Sat Feb 14, 2015 17:39 Post subject:

OK Dave - I'll keep an eye out for it.

venn105 · Posted: Sat Feb 14, 2015 18:40 Post subject:

Here you go Smile

peteinchad · Posted: Sat Feb 14, 2015 20:14 Post subject:

I assume the left hole is connected to the centre holes - I can't think of any reason for it except to relieve pressure - but then again I can't think why you would want to relieve any pressure in a wheel cylinder.

trekker · Posted: Fri Feb 20, 2015 19:32 Post subject:

And release brake fluid into the brake drum, seems pretty daft of Bosch, not fail safe at all.

So I've now cut the piston in half, along the centre line, and yes there is a valve with seals in the core of the longer piston. Failure of this valve will result in brake fluid in the drum, wrecking the brake linings in the process.

peteinchad · Posted: Fri Feb 20, 2015 20:08 Post subject:

Yet another "improvement" - what was wrong with solid metal pistons?

trekker · Posted: Sat Feb 21, 2015 11:57 Post subject:

What's wrong with a solid metal piston ?

Well they last too long.

They're not techy enough, so old fashioned and simple.

Anyone can make a solid piston, only clever manufacturers can make some thing so unnecessarily complex. I read these rear brake linings can last a long time, but the cylinders need more frequent replacement as they can leak.

Incredible. Mad

peteinchad · Posted: Sat Feb 21, 2015 12:06 Post subject:

That's progress !

Apparently, according to the News, we will be able to buy cars that drive themselves within 15 years!

I like simple, mechanical cars with minimal electronics.