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Thread Pitch?


tuko
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Another of many projects I have on the go with the hybrid is replacing the rear drum brake axle with a disc brake axle. The collection of parts that I have assembled include an early RR rear axle and a complete set of rear hubs including the rear brakes from a 2002 110 SW. My plan is to replace everything from the hub flange outwards with the 110 stuff.

Careful measuring and matching up of the parts show that this combination will work for me, with only one area that will need to be altered, which is the bolt holes on the axle that the brake caliper bolt up to. The early RR's used an 11mm bolt

picture a:

50117.jpg

But later on, Land Rover upgraded to a larger 12 mm bolt

picture b:

31603.jpg

The problem that I've ran into is the pitch of the thread on the bolts. I can't find anything that matches over here and to be honest, I have no idea what the pitch is..... 1.25 ???

What I'm looking to find out is what's the pitch of the threads on the 12mm bolt? What size tap should I buy over in England and have sent over next week with a good friend who's coming to visit? I really don't want to use a more course thread that is readily avail here, as I don't think that they would provide the best security for the calipers.

Once I have this sorted out, I will be looking for advice with properly boring/taping the holes. I've only done this once before and it went OK, but I did find that the tap was very stiff and needed lots of lubricating oil when taping. I would like advice on what is the proper hole size to have before attempting to tape. ie: if I buy a 12mm tap, then what is the correct hole to bore before tapping?

Thanks in advance.

Todd.

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Normally the hole you need to drill is the bolt diameter minus the thread pitch as the thread is normally square. So for a 12x1.25 you'd be looking at using a 10.75 mm drill although a 10.5 should be fine as I suspect the thread depth will be 1.5 rather than 1.25. Given that the current bolt is 11mm outer you'll only have a 1mm thread depth in some places.

When tapping the thread use plenty of lubrication and keep backing the tap out quarter of a turn as this helps clear the swarf. Normally you turn the tap clockwise until you feel it tighten up, back it off anticlockwise, rinse and repeat. The key to a good clean thread is plenty of lubrication, keep it clear of swarf and take it a little at a time.

You are always better off buying a 3 stage tap set for the thread rather than trying to do it in a single pass, any decent engineering supplies place will be able to supply you with a 3 piece tap set.

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Thanks for the information guys and confirming that the thread pitch is actually 1.25. Now the problem is as I suspected is that I can't find 1.25 locally. I've found M12 x 1.50 & 1.75. Therefore any suggestions where I can order one over there? .....I'll look on eblag for the time being.

Dave, thanks for the instructions/tips as I said, I've only done this once before. ;)

Cheers,

Todd.

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Todd

Those calliper bolts are dealer only. They at not available anywhere else.

mike

Yes, Mike and they cost dearly for the 4 early Range Rover originals. :o

The 110 ones are the original ones and look to be still in good shape, I will though use locktite when I install the calipers.

Thanks Dave, I'll hit the "buy now" button shortly. ;)

Todd.

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Todd

I carry four as spares in my Defender. I take my callipers off every 6,000 miles to do the hubs. I run a die down each bolt and a tap down each hole. I threadlock the threads. Any bolt that the head looks dodgy on I replace straight away. Making my life easy for the next service

mike

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