Subject: Re: [trikes] Touchy Drum Brakes
Date: Fri, 28 Jul 2000
List-Id: Recumbent Human-Powered Trikes <trikes.ihpva.org>
Todd Heagy wrote: I have a pair of Sachs drum brakes (model HT5020) on the trike I just finished building. The right brakes is very touchy and wants to lock up almost as soon as I apply it
Drum brakes are self-enengizing, so any difference in coefficient of friction gets multiplied. Considerable differences can come about from seemingly insignificant surface contamination, by, for instance, finger oil. You might try taking both brakes to pieces, cleaning all friction surfaces with solvent and then lightly sanding them with fine paper. If this does not even them up, there may be differences in linkage or hand strength.
From: Giles Puckett
Subject: [trikes] Re: Touchy Drum Brakes
List-Id: Recumbent Human-Powered Trikes <trikes.ihpva.org>
Sachs Vt brakes are one-leading, one-trailing shoe brakes. They are not self-energising - that layout uses a floating pivot. The leading shoe looks a bit different to the trailing shoe. I've used them either way round and it doesn't seem to make any difference, but that's probably because having independent cables to either hand, one compensates unconsciously by pulling on each side until the braking force is equal.
Date: Sat, 29 Jul 2000
Subject: [trikes] Re: Tounchy brakes
List-Id: Recumbent Human-Powered Trikes <trikes.ihpva.org>
Todd noticed that one of the two shoes on his Sachs VT hub brake has a shorter but thicker lining than the other shoe. This thicker lining shoe is referred to as the 'leading shoe'. Most drum brakes for bicycles use a single leading shoe design. This arrangement is also commonly referred to as a self energizing brake. I have published a couple of paragraphs explaining this brake system on my trike plans located on the IHPVA server. Therefore, I'm going to save my fingers and time by not going into elaborate details on this technology. The actual brake that Todd is describing appears to be an older Sachs design, as the hubs I used back five years ago didn't have a prominant appearing leading shoe. Perhaps they have reverted back to this configuration? I really don't know. I can only tell you that this leading shoe should face against the rotation of the wheel in relationship to the Cam actuator. Again, refer to my web page for details. If one hub appears to grab during braking, a misalignment is suspected. When welding the brake back plates to the axles it is best to actuate the brake while the hub is installed. This causes the back plate to center itself in relationship to the hub and axle. Once this is achieved, the back plate is tack welded in place (to the axle or knuckle weldment), the hube is removed, and the assembly is than completely welded. Presto! the brakes should now be aligned.
From: "Ian Sims" ian@greenspeed.com.auDate: Sun, 16 Sep 2001
Subject:Disk Brakes ? & Hydraulic vs. Mechanical
I've used both drum brakes and disc brakes on my personal trikes, and on our demo trikes over an extended period.
I used drum brakes on my old GTS for many years, and found them quite adiquate for my use. And although I have carried heavy loads and descended mountains, and have never done both together, not do I have any wish to do so. Never the less some of our customers have done, and found the drum brakes prone to fade in this situation.
OTOH we started fitted the disc brakes to our tandem trikes as soon as they were available from Sachs, back in 1994. This was a revolution in braking. Sachs claimed they exceeded the German standard for bicycle braking by two and 1/2 times. For the first time one could lock up a wheel at will on the tandem, and this was such a novelty, that many test riders did so on the demo trike, leaving long black lines of rubber on the road :-(
A couple of years ago, my family thought I should have a new trike, as my old GTS was looking slightly tatty, and boys thought I should have the disc brakes on my new GTS. At that time the Sachs had been discontinued and the best disc brake that we could get hold of was the Hayes. I was not particularly impressed. Although they stopped very well, they had a sort of grinding noise when you stopped and were rather vicious compared with the drums, thus the modulation was not that good, plus they were prone to squeal once they got wet, and continued to squeal for a long time afterwards. The other thing that I was not happy about was the fact we had to mount one up and one down, because they were only made for left hand mounting, unlike the Sachs. Besides looking rather odd, this meant one was pushing against the disc or mounting, and one was pulling away from the mounting. The final annoyance was the fact that there was no positive retraction system - they just relied on the relaxation of the seals to retract the piston, as is done on cars, where a bit of drag is not noticed. Thus in a couple of cases, after prolonged use, they tended to drag.
So after getting no response from the manufacturers or their agents here about the problem, I visited Hope in the U.K., and managed to secure a supply of their brakes. At least these brakes had a universal fitting, so they could be mounted the in the same way on each side of the trike, PLUS they had a positive retraction system like the Sachs. So our factory changed the brakes on my trike to the Hope units :-)
I found them much quieter, without the grinding noise, AND the modulation was much better. I could still lock the wheels, but it took quite a bit more pressure to do so, so there was more control over the braking. With the positive retraction, there was more clearance between the pad and the disc, so there was no contact between the pads and the discs on hard cornering like there was with the Hayes, due to slight movement of the hub on its bearings, or axle flex.
Having used them for some time, I now find I prefer them over the drums for three reasons:-
1. Maintenance. I found with the cable operated drums I had to replace the cables on both of the previous trikes I used for my personal transport, yet on both the two demo tandems we have had, and the GTS, the hydraulic systems have been untouched, and the present demo tandem still has the original Sachs discs.
2. Stopping power. I find it really nice to know that I have enough braking to be able to lock both front wheels at will. Thus the braking power is awesome, and perfect for an emergency stop. It is certainly every bit as good, if not better than a car.
3. Modulation. The lack of friction compared to a cable set up is quite noticeable. There is definitely a much better feel to the to the brakes IMO. The operation of the lever has a really silky feel to it, compared to the cable set up.
Thus I normally make sure that people coming for a test ride, ride both a trike with the cable drums and a trike the disc brakes. For some the drums are completely adequate, for others there is no question - they want the discs!
We have bought a number cable operated disc systems and tested them out on our trikes. Like testing different trikes or different cars, some are better than others, but IMO none match the Hope brakes for all round performance.
The only thing I find as a disadvantage about the discs is the fact that it is easier to remove the wheels with the drums, if you need to remove them for packing the trike down in any way. With the Hope discs, you need to loosen the two caliper screws and withdraw one, to allow the caliper to pivot the clear the disc, before the wheel can be slid off the axle. This procedure is shown on our web site at :-
http://www.greenspeed.com.au\GTO_Packing.htm
Thus from the point of view that no cable disc brakes are made so that they are handed left and right, and that I've found cables less reliable than hydraulics, I am not interested in using cable disc brakes. After all, cars stopped using them many many years ago, and I want a product which is superior to cars, if I am to have any chance of making a real difference to the pollution on this small planet.