For the 10 years that I have had my H4, the brakes have been to say the least underwhelming, in fact almost "underlorrying" on some occasions - a lot of free pedal movement and far too much effort for the level of retention achieved.
Over the last year I have experimented with shimming out the fulcrum end of the shoes and the results are quite dramatic as far as braking is concerned - first there is less free movement and now I get really good progressive braking but even now it cannot be described as earth shattering compared say to the astoundingly good braking on Trish's Micra - smaller brakes, smaller servo. I have replaced the front discs, all pads and shoes and have noted a degree of ovality in the rear drums. What does all this mean? In brief it is a matter of the geometry of the system such that the radius of curvature of the shoes does not match that of the drums and by shimming out the fulcrum the shoes now first contact nearer to the fulcrum giving a potential of more contact between shoe and drum as the braking pressure is increased. The first efforts at this were encouraging to the extent that I turned up a mandrel on which to mount the drums and then skimmed them to remove the considerable ovality, ~ 0.3 mm on diameter for each drum. This then required further shimming of the fulcrum to get back to my previous "Good" state with the knowledge that I had actually worsened the situation with regard to mismatch of radii. As the shoes now bed in to the drums the brakes are getting better! If anyone is contemplating following this approach should do so with extreme caution as the shoes get very near the edge of the retainer bar at the fulcrum at the stage where most effect is achieved. Check that the spring retainers for the shoes are working effectively and have not rusted away. N.B. The brakes come with hardened steel shims of ~ 0.5 mm thickness, around 2 or 3 on each side of the fulcrum block. I have now replaced these with custom-made shims of ~3.5 mm thickness each side for best effect but each situation will differ. My yardstick for effective shimming was to very lightly abrade each shoe with emery at right angles to the shoe then drive round and note how much of the shoe was now bedding - i.e. a very traditional and long-winded "suck it and see" method. I have gone from ~ 5% contact at the furthest point away from the fulcrum to nearer 75% from the fulcrum end with potential for further gains as the brakes bed in. One characteristic that I have never been able to eliminate is the sponginess of the brakes. I have bled them by conventional means, with pressure bleeders and even tried the old trick of wedging the brake pedal down overnight before bleeding them again next day, both facing up and down our 30° drive and including car ramps to increase the angle up to 45°, all to no avail - has anyone else managed to overcome this problem? Hamish ----- Original Message ----- From: skip_rat To: Quantum Owners Group Sent: Tuesday, February 09, 2010 9:00 AM Subject: [Quantum Owners] Re: RS2000 front brakes on a H4 & Rear suspension. The main issue I have with the brakes are that it seems to require a huge ammount of effort to slow/stop the car. They seem much worse than the 2+2 we used to have. There isn't a huge ammount of pedal travel but you seem to have to press really hard to get much response. I had a basic brake test done and they seem to be working well enough and would lock up on the rollers. I think the pads I used were AP/ lockheed(?), the disks are standard and fairly new with no scores/wear lip. I was also considering a servo upgrade, are there any options for this? -- You received this message because you are subscribed to the Google Groups "Quantum Owners Group" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/quantumowners?hl=en IMPORTANT NOTE: All information presented herewith is provided on an "As Is" basis, without warranty or the implication thereof. Neither the Quantum Owners Club nor the individuals associated with the Quantum Owners Club or in the preparation of the above information shall have any liability to any person or entity with respect to liability, loss, or damage caused or alleged to be caused directly or indirectly by the instructions contained within this or related message(s).
