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Long brake pedal travel

Posted: 18 Oct 2007, 19:26
by John Simister
When I press the brake pedal on my S2, it goes down quite along way before reaching a firm bite but has the feeling of moving something rather than just being free play. This doesn't change if I pump the pedal several times. If I do this with the engine off to use up the vacuum in the servo, there's again no change in the movement, just more effort needed once the excess travel is used up. I can hear the sound of a small amount of air being displaced before the pedal reaches firmness, even when the servo vacuum has gone, which I think might just be air being sucked into the rubber boot over the rod between pedal and servo - although it could well be something else.

I've bled the brakes with a pressure bleeder (Gunson's Eezibleed) and it makes no difference. All caliper pistons are free, all pads are new as are front discs. I suspect the problem may be either in the master cylinder or the servo. Any ideas before I take it all to bits? Have I just not bled it properly?

Many thanks

John

Re: Long brake pedal travel

Posted: 18 Oct 2007, 19:48
by P. de R. Leclercq
I would be inclined to suspect the master cylinder. Careful inspection is required, both for worn rubbers and damage in the bore of the aluminium cylinder which is very common. If the latter be the case, better to throw it away and source a modern replacement. The Peugeot 206 one might work although you may need an adapter. Another from memory is MkII Golf.

Although this is unlikely to be relevant, I recall a case from years ago where we (Evolution Engineering) had done some work on the brake hydraulics on a 1600 and the owner came back complaing of long brake pedal. The cause, which we quickly found, was a loosened hub nut, allowing movement in the bearing and thus pad "knock-back" giving of course a long pedal. The client was lucky: there was no damage to the bearing.

Paul

Re: Long brake pedal travel

Posted: 18 Oct 2007, 23:31
by John Simister
Thank you, Paul. The fact that when I bought the car its brake fluid was dark might also point to trouble with the rubbers, so I'll investigate the master cylinder's health. Hub nuts are tight, but thanks for the tip and the tale. I enjoy your blog page, by the way.

John

Re: Long brake pedal travel

Posted: 19 Oct 2007, 01:28
by P. de R. Leclercq
John,

You are welcome, and thanks for the comment about the blog

Paul

Re: Long brake pedal travel

Posted: 19 Oct 2007, 08:32
by tim
John

Maybe you are entering the interesting arena of Fulvia mastercyclinders and all that they behold!

To dismantle you will have to carefully remove the plastic reservoir which from experience is not easy as the the little cap bolts have generally corroded (steel meets alloy scenario + 35 years).

After that generally it goes plain sailing. I assume you have the repair manual showing the cross section to rebuild?

You may have seen other threads about subsequent bleeding thorugh which is always a tricky area. I would recommend silicone fluid. Do you have copper lines fitted, and are the wheel cyclinders in good shape other wise overhaul the lot while you are about it.

The travel is interesting as on my 3 fulvias - all with fully overhauled brakes (2 with new discs all round) 2 have travel down c50% but my 20k mile (original discs etc) 1300 has it near the top. Providing the brakes dont vary in feel and performance you might be being a bit pickky esp if you are always swopping from modern to your fulvia.

Best

Tim

Re: Long brake pedal travel

Posted: 19 Oct 2007, 12:10
by John Simister
Tim

Fingers crossed I don't break those little cap bolts. I have the manual, plus all the past threads on brake bleeding, so should be OK there. Most of the pipes are old steel ones, some original, so I'll replace those with copper and do the flexi hoses (probably Aeroquip) and fuel lines as well. The calipers show no sign of leakage and the pistons retract easily, so I'll probably leave those alone - except that the bleed nipple has broken off the LH rear one so that caliper might need to be replaced if I can't safely extract the remains of the nipple. In which case I'd better replace both sides.

I'm determined to get the brakes to bite at the top of the pedal travel, because I know it's possible. I've driven two other HFs and both had brilliant brakes. In principle there's no reason why it shouldn't be possible, but reality may well turn out to be different, as you have found. Fingers crossed (again)... and thanks for your thoughts.

John

Re: Long brake pedal travel

Posted: 19 Oct 2007, 13:48
by Neil Cundy
I have just (yesterday !) finished replacing the brake pipes in my car. What I found concerning was that the long run under the car (from the union under the front bulkhead to the rear flexible) was full of water !. Now my car had been sitting for a long long time, and I think that that, and the fact it is an open system meant water from condensation had hydroscopic'd (sp!) to the lowest point on the system. Of course once there it is almost impossible to get out by bleeding or flushing, the only way is to undo the union and drain. I am sure this was the reason for my soft peddle, after a few pumps it would come back.
From your description of your problem (continually long peddle) Pauls diagnosis is the first port of call, not what I describe - but worth putting up all the same.

Point of special care !
When replacing the brake and fuel lines, the critical area is where they pass under the front bulkhead. The clearence to the subframe rear member is very small, any slight incorrect pipe run can result in the pipes being trapped and crimped as the subframe rocks backwards and fowards under acceleration and breaking.

Re: Long brake pedal travel

Posted: 19 Oct 2007, 19:27
by tim
And silicon fluid will prevent repeat of hydroscopic activity - it is more fussy to bleed however, but once mastered poses no prolem - you need to avoid it "frothing".

John - I have just sat in my HF and pressed on the brakes and they only go about 1 inch before firm yet my 1600 zagato from memory was a bit lower. Both however have excellent response and feel and stopping power.

to get the cap screws out on one reservoir I had to use a bit of heat from a cooks gas torch (v fine flame!) - trouble is it damaged the plastic so spent time scouring for a spare! - good luck. Also used a can of wurth penetrating oil that freezes ("rostoff ice"?) but it was the heat that shifted them.

Tim