jbenajes Posted January 21, 2015 Report Share Posted January 21, 2015 I am installing new Girling 9-inch brake drums to the rear of my TR3A. As it is well known, the drum holes for the wheel studs need to be enlarged for the stud shank. In order to reduce any eventual excessive clearance between studs and drum orifices, I am proceeding stepwise, drilling from a small diameter on. So far, I have drilled three times up to 15 mm, and the seating of the drum against the axle face is still not perfect, apparently due to some interface with the stud shank. The recommended diameter for these holes was given in the old Moss-Europe web page (I cannot find it now in the new site– well, right now, I cannot see anything related to rear brakes, even using different browsers). What is the correct drill diameter for these orifices? Thanks for the comments. Jesús Quote Link to post Share on other sites
Fireman049 Posted January 21, 2015 Report Share Posted January 21, 2015 Hi Jesus ~ I recently fitted new 'Alfin' rear brake drums to my wire wheeled TR3A and they fitted without having to drill the holes so I don't understand why you have to enlarge the holes? Forgive me if I'm missing out on something here. Best regards ~ Tom. Quote Link to post Share on other sites
AlanT Posted January 21, 2015 Report Share Posted January 21, 2015 You dont tell us HOW you are drilling these. If you are using a hand-drill you can easily drill holes that are not ROUND. Examine them with a magnifier to see if this has happened. Also if you use a drill-press and don't clamp down properly you can get the same thing happen. If it has then you can recover by using a REAMER, there are other ways. Quote Link to post Share on other sites
RogerH Posted January 21, 2015 Report Share Posted January 21, 2015 Hi Jesus, the Moss cat (paper version) states to use 9/16" (0.5625"). If you pass the drill as far through the hole as possible, this allow the drill shank (last remnants of flute) to cut the hole rounder than the tip of the drill alone. Roger Quote Link to post Share on other sites
steve clark Posted January 22, 2015 Report Share Posted January 22, 2015 A machine reamer is the ideal tool for the job mounted in a drill press and run at the lowest speed Quote Link to post Share on other sites
RogerH Posted January 22, 2015 Report Share Posted January 22, 2015 Hi Jesus, I've had a thought. If you are opening the holes out on a pillar drill or milling machine then it is relatively easy to ensure that the drill and holes are in very good alignment. If you are drilling by hand (and it can easily be done) get a 9/16" drill (or a fraction smaller if following up with a reamer) and machine a pilot on the end so that it starts concentric. It is easy for a drill to be off centre even with a decent sized hole to start from. Roger Quote Link to post Share on other sites
mleadbeater Posted January 22, 2015 Report Share Posted January 22, 2015 Hi, here's another idea to help you, if you can clamp the old drum back-to-back on top of the new one, preferably using a piece of round bar or pipe of a good-fitting diameter in the central hole of the drum, then the old drum will act as a drill guide for the new holes. Drill on a drill press at a low speed with the size to clear the stud diameter. hope this helps Mike Quote Link to post Share on other sites
tomfpurves Posted January 22, 2015 Report Share Posted January 22, 2015 Picking up on this thread I see Tom the Fireman fitted Alfin drums and was considering the same for my 3A. I would like to know if there was any noticeable difference to the braking performance? Tom Quote Link to post Share on other sites
2long Posted January 22, 2015 Report Share Posted January 22, 2015 I run factory 9 inch Alfins with circumferential fins on the rear of my TR2 and they work great with good performance and no fading as far as I can tell. But then again, I never drove hard enough to generate fade on the original drums either. I think they look great though. I had mine polished for a little bling peeking out from behind the wire wheels. Dan Quote Link to post Share on other sites
jbenajes Posted January 23, 2015 Author Report Share Posted January 23, 2015 Thanks for all the comments and suggestions. I drilled the drums with a robust stand drill press, so the off-round holes should not be the problem. The figure of 0.56252 is what I missed, but going step wise, I had to drill larger holes for the shanks (0.5905”). Initially, with too small holes, the drum cocked on the stud shanks, but even with large enough holes (0.5984”) the drum sits not perfectly on the hub flange, and this is what upset me . I have found that the cause is a slightly warped hub face, and the drum can tilt slightly when offered over the studs before bolting the small retaining screws. I hope that the two small retaining screws will bring the drum in its correct position, and that it will remain so if the wire wheel adapter is bolted down carefully. Jesus Quote Link to post Share on other sites
Dave Larnder Posted January 23, 2015 Report Share Posted January 23, 2015 Jesus Run a DTI on the splined hubs when you fit them to ensure concentricity. Dave Quote Link to post Share on other sites
RogerH Posted January 23, 2015 Report Share Posted January 23, 2015 Hi Tom, I fitted Alfin to my 4A ages ago. I was suffering from squeaky rear brakes and nothing would sort them. So I decided to get new drums. When in the shop I spotted these Alfins so bought a pair (nice and shiny - yummee). At the time they were not too expensive - today they are ridiculous . Anyway for normal driving/touring they are neither better or worse than the originals (no squeak though). Going down big hills there may be some benefit but most of the braking is done at the front end. Roger Quote Link to post Share on other sites
ianc Posted January 23, 2015 Report Share Posted January 23, 2015 The standard brake drum is a casting and castings tend to be somewhat granular and therefore difficult to drill, as, unless clamped tight on the platform of a pillar drill, the tip of the drill will tend to wander. As stated, it's advisable to use a reamer to finish the job. Ian Cornish Quote Link to post Share on other sites
RogerH Posted January 23, 2015 Report Share Posted January 23, 2015 Hi Ian, for flat plate you would be about right but the drums have holes to start with. A decent drill with a pilot would do the job easily. Indeed a reamer would put the icing on the cake but more expense. Roger Quote Link to post Share on other sites
jbenajes Posted January 24, 2015 Author Report Share Posted January 24, 2015 I have drilled the other drum more carefully (again with an industrial stand drill press) and had to drill up to 15 mm (0.590”, definitely more than the recommended 9/16”) to get the drum sitting on the hub. Dave, thanks for the suggestion. I did the test with the DTI and found that the maximum deviations on the drum surfaces and rims is of about 0.3mm (0.012”), which I accept as correct. Now, I have finished the installation and will do a test drive today. Jesús Quote Link to post Share on other sites
Dave Larnder Posted January 24, 2015 Report Share Posted January 24, 2015 Jesus Run iot round thesplined hubs as well to make sure they run true or you could have a bumpy ride if out a lot.. Dave Quote Link to post Share on other sites
jbenajes Posted January 24, 2015 Author Report Share Posted January 24, 2015 Dave, I found the same maximum deviation on the hub. The only reason for changing the drums was an intermittent braking at low speed. Otherwise, the ride has been always very smooth. Jesús Quote Link to post Share on other sites
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