401 mysterious brake problem

[RALPH M]

I have rebuilt many hydraulic brake systems over the years but have encountered an odd problem. Refurbed drums, slave cylinders and new linings, bleed system, adjust for good clearance on master cylinder pushrod BUT the rear brakes do not release and if either rear bleed nipple is opened a squirt of fluid shoots out. So there is residual pressure. Disconnected the handbrake pins just in case. The front brakes work fine, going on and immediately releasing.

How can this be happening? It is as though there is a one way valve just in the rear pipe. Any ideas?

Mike Ralph, Devon, UK.

[Geoff Kingston]

Did you renew the rear flexible brake pipe? if not that may be the problem.

[mikeh_408]

Exactly the same thing happened to my 408 which turned out to be the flexible hose to the back axle . It had perished / collapsed internally and acted as you describe.

Mike Haig

[MICHAEL JEPSON]

This is often caused by the flexible brake hose delaminating internally which allows fluid to pass under pressure to the cylinders but will preventing the return of fluid not under pressure - exactly like a one way valve as you rightly say.

Good luck,
Mike

[RALPH M]

Well thank you all! This is a new one on me and as I already had a new pipe in the garage I fitted it and what a result. Having replaced the wheel cylinders and blamed the handbrake linkage it was as simple as a faulty flexible pipe. I would not have believed they could do that. So, never too old to learn.

Once again thank you all.


Mike

[STELLWAG P]

Well, dear kolleges, I can add a new experience to this theme.
When my 400 gets hot, and also the brake fluid gets hot, I loose all my freeplay in the brake pedal to that point, that all four drums start to get hot and hotter, and finally start to fix and smell. When I now open the connecting nut of the brake line from the master cylinder fluid comes out und a lot of preassure.
So, unfortunately, I have to remove the master and dismantle, cleane and fit a rep kit inside.
And thats my question now, " Where to buy that brake master cylinder kit in best possibly quality?"
I think that some if you may had a similar problem, and may therefore know to whom I have to go for a good rep kit, possibly with that little check valve.
I thank you very much for your help and efforts.

With very best regards to all

Peter

[RALPH M]

Hi Peter. Before you rebuild the master cylinder have you tried setting greater clearance on the brake pedal pushrod. It may be that simple. Good luck. Mike

[STELLWAG P]

Good morning Ralph.
You are the secound one who tells me that, so there must be something with it.
At first, I wonder, wy it has to be readjusted, as it worked for 18 years, and
Secoundly, at the moment I see no possibility how to do that , because I dont see where to adjust or how to com to. Any idea?
By the way, do you know a good adress, where to buy rep kits, ore possibly let the master cylinder overhaul?
I thank you very much Ralph.
Very best regards

Peter