Just put some new [aftermarket] calipers on the rear of my Mk1. After 20 years with this car, I think I know the answer to this question…but:
On the driver’s side, the handbrake lever is having almost no effect at the caliper - there’s no problem with the cables or mechanism (the lever on the caliper itself is moving fine) but it’s just not moving the piston on that side. The adjuster is working and is set within a gnats of dragging on the disc, so that’s adjusted OK, but it seems to take 98% of the travel of the caliper’s handbrake lever before the piston starts to move.
95% sure it’s a duff caliper, but if any of the geniuses on the list have any better ideas?
Are you sure the adjuster is ok? as i have had a few that have failed on refurb’s, did you adjust up until it was solid(disc will not move) and then backed off, plus when you had done both sides ,did you re-adjust the slack back of on the handbrake lever?
Basically it’s a ratchet on the screwthread. The piston can go down towards the disc but the screw stops the piston coming back so the handbrake adjustment isn’t lost. I think that the adjuster is used to set initial handbrake adjustment and wind the piston back but that the caliper would set and maintain working adjustment anyway by itself with use of the footbrake and handbrake.
Have you compared old and new calipers to ensure the levers and cable stop etc are the same? Could the cable itself need adjustment?
I would return the piston back with the allen screw and check that the lever on the caliper is able to be moved to the start of its travel. At that point the cable, with handbrake off, should not be under tension but about to start doing some work. If there is a lot of free play in the cable then that may be where it is being lost. Then set the piston on the footbrake. Then re-adjust the handbrake clearance with the screw and get someone to work the handbrake to see if there is now movement at the caliper lever. Then road test and give it a few careful miles around the lanes using foot and hand brakes to see if adjustment is back.
Thanks chaps - replacement caliper fixed the problem.
On removing the spring from the handset lever on the faulty “new” caliper, it was clear that it wasnt engaging at all with the piston mechanism.
Removing the handset lever from the caliper body (it just pulls out once spring is removed) made it clear why - the “hot dog” shaped pin (which links the eccentric hole machined in the shaft of the handbrake lever to the piston) was missing.
Good pics from Lance on Miata.net garage forum if you want to see what it looks like - click on the pics to enlarge.
Hmm, wish I had seen this thread I went against my own advice, and fitted a pair of “Willow” branded calipers to the rear, but jut can’t get the handbrake to set up that statisfactory. How easy is it to see this hotdog pin without stripping the caliper. The problematic caliper seems to be the drivers side; the adjuster feels stiffer than I expected. What has thrown me a little is that the instructions stat if you need to back off the adjuster, it must be backed off by half a turn, on order to get the self-adjuster to reset. I can’t recall this being the case with the original calipers. At the moment, the only way I can get the handbrake to hold decently is to really tighten the handbrake cable
Anyone know what Midland Sports & Classics are like for returns? They weren’t exactly hassle free for ordering…
Ok, some of the detail on that caliper seems a little different. As I said, the ones delivered to me were branded “Willow”, and came with MX5-specific fitting instructions. Before I fitted them, I had them photographed on the bench, side by side with the originals, showing the differences, where they existed, which I will post later on. Yes, the arm for the cable is a little different, though to be fair, the way it hooks on the cable seemed if anything, a slight improvement on the Lockheed brakes. Under the spring, there was a large star washer; can’t see it in those photos. The castings “looked” to be decent quality, nothing looked thinner than standard. The boots were identical to the pattern rear seal kit delivered to me from Autolinkuk; the boots feel a bit more plastic than the original rubber.
Thing is, the Yanks have been using the same sort of calipers from Autozone and O-Reillys for years, without apparent issue. I have seen reference to the adjuster being different, so can anyone shed light on this. Otherwise, I might just try the supplier.
Minor update: Robert Westward from Midland Sports and Classics has very promptly made contact with me, offering to provide phone instructions on these calipers, and has provided a pdf showing Engineered sections of the calipers (he’s taken a MX5 caliper and basically cut it in half, to illustrate the assembly of the handbrake mechanism, in order to aid the ongoing discussions).
There are more differences between them if you look close enough, send them back and get a refurb and have done with it , which ever way you look at them they are cheap copies, and only fit for the bin.
