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MG MGA - Product Review: MOSS brake calipers

I had reservations about these since it seemed no one else had bought these yet, but I found myself in need of a caliper fast. I didn't want to lose any driving time while finding a machine shop to repair mine or sourcing a core to rebuild. So, I took the plunge at $99.99 and here is what I found:

Upon first examination they are nearly identical to the lockheed casting. They are missing the "LOCKHEED" name and the casting is a bit rough but they're brakes, not body panels. The milled surfaces also look a bit different, this is most likely due to cost and milling techniques. The pistons are identical to the MGA pistons, which surprised me. I would have figured that they would have gone to the MGB style pistons and omitted the centering pin.

The brake pads fit right in and clipped into place, no issues there. The caliper bolted right into place and I had no issues whatsoever with fit. The bleed screws are an odd size. They're not a standard size- if I had to guess I'd say a 10.5mm wrench would work, if there is such a thing. I was able to use an 11mm, but prolonged use over the years will probably round the nuts. They also seemed to get loose in the threads right away when loosened but I didn't seem to gave any problem sucking air through the threads when bleeding. Bleeding was actually a snap.

The road test was key because I was only replacing one caliper. I was afraid it would adversely affect brake performance. It did not. I'm happy to say the brakes acted exactly the way they should with no pulling or dragging.

Keeping in mind that this is a reproduction part and not for a concourse restoration, I have to give this product an "A" for price and performance.
Mark J Michalak

Thanks for the report. Can you get a picture of the part, including the non-standard bleed nipple? I'm no concours enthusiast, so I don't care much about appearance. But I am a functionality geek. If it doesn't work or can cause problems it might as well be junk. I'd deduct a point or two from the grade if the bleed nipple is going to be a problem. Can you even buy a suitable bleed nipple to carry as a spare part? Do you have to junk the entire caliper if you break the bleed nipple?

Apparently you now need two different wrenches to bleed the brakes, and one of those wrenches may be entirely non-standard. If the bleed nipple ever gets stuck or rounded off you're screwed. It is very bad to have a metric size fitting on an otherwise all British standard car. It is even worse if it is not even a standard metric wrench size. Can you measure the exact width across flats? Also if possible, can you determine the thread size?

It has been a significant problem in recent years when parts are made in China, and the things come in with metric threads or metric hex sizes. Some years ago I bought from Moss some special and relatively expensive flywheel bolts that are supposed to have smooth shank for part of the bolt length. These were threaded all the way to the head with no pilot diameter, which was bad enough by itself for what should be a special purpose fastener. Additionally they had 12-mm hex heads on 5/16-24-UNF bolts, so they cannot be installed or removed unless you carry an extra metric wrench in the tool box. Apparently these bolts were made by cutting a 5/16 inch thread on an otherwise standard 8-mm bolt blank. In my book this crude practice is entirely unacceptable.

While we may not call this a "faulty" part, it is definitely non-standard in a way that does matter in the real world. If there is a source for a better part I would definitely like to tell the world what's wrong with this part and where to get the better part. On the flip side, if this would happen to be the only source for this part, then its hard to fault the supplier for trying to keep parts available (but we can still complain and try to get it fixed).
Barney Gaylord

!0.5 mm is not a standard metric size so it is not metric.

11mm is a 7/16th wrench isn't it? not sure without checking but is that not the normal size?

Robert (Bob) Midget Turbo

If it is between 10.5 and 11mm it's not a 7/16 AF either Bob, could it be an 0BA? Certainly seems an odball size.
Lindsay Sampford

11mm is 0.005" under 7/16". 7/16 wrench would be a little loose buy may work (prefer box end wrench or socket to preserve hex corners). Yes. 7/16" is standard size for MGA bleed nipples.

If it is in fact a standard bleed nipple, and everything else seems to work, then praises to the supplier. I personally would prefer the MGB piston, but kudos for originality here regardless. To little of that left these days. The picture looks better then the initial description.
Barney Gaylord

I have found that Chinese and Indian made parts of all kinds show widely variable quality across different parts of the manufacturing process. They are evidently made by farming out each operation separately, with holes and threads last on the list and worst in quality. Main castings and critical surfaces are frequently PERFECT, but then it goes to hell in a hurry. Holes not located correctly, not square to the reference surfaces, and threads moreso, And, they, esp. India, use surplus tooling, so that an Indian made milling machine vise has dead parallel and beautifully machined main surfaces because it was done on a state of the art surface grinder, but all the holes are wonky to an extreme and they are threaded badly with Whitworth threads. The worst parts of all are the bolts or other parts that go into the holes. The 1 1/4" long center pivot pin on said vise looked like it was made by rubbing on a rock; the two ends were not concentric by about 1/8", and were also visibly not round and were different end to end. All the bolts on this thing were different in all characteristics, including material qualities, some like mush, some very hard and brittle. I treated it as a semi finished casting kit and came out with a really nice vise for 1/10 of the American price (with all new fasteners!).

I suspect that your bleeders are of this ilk - figure out what threads they have (choice is very wide!)and replace the screws with real ones of whatever fits before you break them off or strip them or whatever.

FR Millmore

Hi Linsay I was not suggesting 10.5mm was a 7/16ths spanner what I did suggest was that an 11mm spanner was in fact almost identical to the original 7/16ths which Barney has kindly confirmed.

I am also the same as Barney and I use a single hex socket (7/16ths or 11mm which ever comes to hand first)to ensure as good a grip as possible, because I find the vast majority of bleed nipples tend to be a loose fit whether made in the UK, China or Timbuktoo!
Bob Turbo Midget England

Reactivating this link of July 2011 to see if anyone has recently purchased Moss reproduction MGA 1600 brake calipers (17H7734/5)and has positive or negative views. I would be grateful for comments.

Mike Card
M D Card


I replaced mine earlier this year with calipers from Moss USA and had absolutely no problem with them. The bleeders were a common wrench size (don't remember which) so there was no problem there.

They seem to work well.

Gene Gillam

Your advice helps me a lot, thanks. I need to replace my calipers and I was planning to buy the Moss units. I'll go ahead now.
Are you using DOT5 (silicone) fluid?
M D Card


Yes, DOT-5...entire system was rebuilt and is working great.

Gene Gillam

This thread was discussed between 12/07/2011 and 04/08/2013

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