The Imp Site

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Brakes

From: Michael Handy
Date: Mon, 1 Mar 1999 23:40:20 -0000
Subject: [imps] Brakes......Help !!!!

In September last year, I drove my Stiletto out of work and down to a roundabout and applied the brakes but... Nothing... My foot went to the floor and as I frantically pulled on the handbrake I noticed that as I kept pumping the foot brake, the pressure built up and eventually stopped the car.
Upon taking out the Fuel tank, I changed the Master Cylinder over to one which I had spare from a donor Imp Super.
When bleeding the fluid through, I noticed the front right Wheel Cylinder was leaking as well.
So I ordered a new one.
When I attached this one, I bled the brakes through again only to find that the left hand Cylinder started leaking.
I have ordered another Wheel Cylinder for this side.
I know that the master cylinder from the Imp Super is smaller, but would this have any effect on the other wheel cylinders. i.e... Am I going to end up replacing the whole lot before I can finally get the brakes to work properly.

Date: Tue, 02 Mar 1999 09:09:24 +0000
From: Andrew W. MacFadyen
Subject: [imps] Re: Brakes... Help !!!!

Firstly the master cylinder bore on single carb models is only smaller because of the lack of servo, the purpose of the bigger cylinder on the Sport models is to give more pedal feel and slightly reduce pedal travel. It will have no effect on the wheel cylinders. :-)
Incidentally with master cylinders fiting a repair kit is successfull 100% of the time unless the bore is very badly rusted or the internal spring is broken. If I was doing the job I would probably strip all the wheel cylinders and fit new seals as a precationary measure as cleaning out the wheel cylinders and fitting new seals before the old ones fail effectively doubles the life of the cylinders but if you leave it till they start leak it is often a waste of time

From: Impmann@aol.com
Date: Tue, 2 Mar 1999 05:17:23 EST
Subject: [imps] Re: Brakes... Help !!!!

Just a thought, but could the smaller cylinder be giving a greater fluid pressure than the original .70 inch unit, exassipated by the servo, causing weaker cylinders to leak?

Also, I personally would say that there is a 50/50 chance of a repaired master cylinder being perfect, as if you think about the pedal force action it is in one plane and the wear regions will be identical each time. I.E, the cylinder becomes oval and doesn't seal - I've had that one on many occasions...

I agree that when one cylinder starts to leak, it is false economy not to relace all the seals, as sod's law dictates that one will leak when you bleed up the system. It's worth the aggro (and the few quid) and will spare you the expense of replacing fluid soaked brake shoes...

With servo equipped Imps, it is worth checking the servo over. These have an alarming habit of leaking and dumping their fluid into the engine, where it is burnt. This can cause a total brake failure without any visible signs of leaking. The only give away is white/grey smoke out of the exhaust. A lot of people have bypassed their servos for this reason (and that it costs over £100 for a recon unit). Some servos have an intermittent leak, that can be lived with as long as the fluid reservoir is kept full and can really fool the unwary.

So the point is Mick, are you absolutely sure that it was the master cylinder in the first place? If there was no real huge signs of leakage (and there would be if the whole system went down that quickly), it points to the servo... that is if it is still fitted:-)

From: Mark Norman
Date: Tue, 2 Mar 1999 10:27:23 -0000
Subject: [imps] Re: Brakes... Help !!!!

Sorry, but that can't be right - if the arrangement is giving higher pressure to the slave cyliners then the only effect will be that the brakes will come on more heavily. If this happens then the driver (possibly unconciously) won't press the pedal as hard. The end result is that the slave cylinders will end up under the same pressure as they were always used at. (Unless you stand on the brake pedal with the car stationary, but why would you do that?)

Date: Tue, 02 Mar 1999 17:29:00 +0000
From: "Andrew W. MacFadyen"
Subject: [imps] Re: Brakes... Help !!!!

The feel from the brake pedal is quite a hard thing to quantify, the non servo version of the Imp had brakes that were very light by the standards of it time (try driving an Super Minx without servo - even Tarzan would find that a strain) but the small master cylinder bore on the standard car could give quite long pedal travel and slightly springy feel to the brakes. It really all depends on what you are used to driving.