Thread: County rear disk brake conversion, pics & p/n's

I will take three sets.
PM sent.
Keith

Originally Posted by rijidij

It looks like this kit might work with other combinations of stubs, hubs etc.
SteveG tried fitting a Defender stub axle and a D1 hub. It worked out that the 16mm main bracket and a 1.6mm shim gave the correct offset to centre the caliper to the disk.
So, having the brackets adjustable might allow for various combinations, depending what parts you have laying around, but remember the two caliper mounting holes at the top of the 16mm main bracket are drilled and tapped to suit the later type calipers with the M12 x 1.25 bolts @ 82.5mm centres.

Cheers, Murray

Some more info on that..
I used the FTC1740 Defender stubs, and D1/Defender hubs with D1 rear discs. Used BX110071M (M10x35 grade10.9) bolts through the stub into the caliper bracket. Sorry, but I don't recall if I also used them with nuts for the 2 holes that only go through the stub and housing or if I re-used some original stub bolts.

The reason I went this way rather than sticking to County stubs and front hubs was that I also needed axles as one of mine had a twisted spline. I managed to pick up some slightly used Defender Maxidrive axles and I already had the D1 hubs so it worked out cheaper for me to convert than buy new upgraded county axles.

Steve

Thanks for making the adapters available Murray, they arrived this morning
Now to accumulate the rest of the bits and talk to an engineer...

Originally Posted by Lotz-A-Landies

Just some questions,

About your comment that the closer bearing spacing puts more load on the bearings. I'm a bit confused, if the mass of the vehicle is unchanged where does the additional load come from?
And.
Could it be an artifact of the change in offset of the wheels, the wheels became more positive (inwards) in offset and therefore the bearings needed to be closer to the centre of the load?

The disk brake Defender has a different part number for the halfshafts, I understood there was a difference in length. Did you have to change your halfshafts (even the Maxi ones).

Is the track unchanged front to rear?

With regard to the question about whether the bearing load is higher with narrower bearing spacing, it is something that often comes up particularly in discussions of rear disk conversions:

If each bearing is equi-spaced either side of the wheel centre, then the component of the radial bearing load due to vehicle weight will be equally shared by both bearings and won't change if the spacing is wide or narrow.

If the bearings aren't equi-spaced with respect to the wheel centre, then the loading due to weight will be proportioned to the offset of each from the wheel centre - the closest bearing having the greater proportion of load. It is not the spacing between bearings, but the ratio of the offsets that makes any difference.

What does make a big difference to the bearing load between wide and narrow spaced bearings is the horizontal side load on the tyre. Usually this is the centripital force when negotiating a curve in the road, but there are other situations such as side slopes.

For sake of example, to get some idea how the spacing affects bearing load, assume the mass on one wheel is 600 kg and the horizontal side loading to be half the weight.

Assume the inner bearing is 50 mm inside the wheel centre. Note this is an approximate guess, not from measurement.

Assume the outer bearing is 50 mm outside the wheel centre for the narrow hub and 60 mm outside for the wide hub. Again approximate guesses not measurements.

Further assume the height from the road to the stub axles is 400 mm.

The total radial load on each bearing is made up of three components, one from the vertical gravitational load (weight), another from the side load acting on the tyre at road level. The third, which I'm going to ignore here, because I expect it to make little difference between narrow and wide hubs for the sake of this discussion, is from the tractive force at the tyre.

Take the outer bearing to be on our left, and the side load to be acting toward the right. e.g. looking at left rear wheel from behind.

For our mass of 600 kg, the weight is 600 kg x 9.81 m/s^2 = 5.886 kN
where 9.81 m/s^ is acceleration due to gravity

And the side load we are going to use is 0.5 x 5.886 kN = 2.943 kN

Start with the narrow hub:

Find the radial load due to weight on the inner bearing:
Wi = 5.886 kN x 50 mm / 100 mm = 2.943 kN vert down
where 50 mm is horizontal distance from outer bearing to centre of wheel
and 100 mm is spacing between bearings

Find the radial load due to weight on the outer bearing:
Wo = 5.886 kN - 2.943 kN = 2.943 kN vert down

Find the radial bearing load due to tyre side load on the inner bearing:
Vi = 2.943 kN x 400 mm / 100 mm = 11.772 kN vert up

Find the radial bearing load due to tyre side load on the outer bearing:
Vo = - Vi i.e. = 11.772 kN vert down

Then the resultant vertical radial load on the inner bearing is:
Ri = 11.772 kN up - 2.943 kN down = 8.829 kN vert up

And the total vertical radial load on the outer bearing is:
Ro = 11.772 kN down + 2.943 kN down = 14.715 kN vert down

Note if the side load direction was reversed, i.e. right to left the results for the inner and outer bearing load would be swapped.

Now for the wide hub:

Find the radial load due to weight on the inner bearing:
Wi = 5.886 kN x 60 mm / 110 mm = 3.5316 kN vert down
where 60 mm is horizontal distance from outer bearing to centre of wheel
and 110 mm is spacing between bearings

Find the radial load due to weight on the outer bearing:
Wo = 5.886 kN - 3.5316 kN = 2.3544 kN vert down

Find the radial bearing load due to tyre side load on the inner bearing:
Vi = 2.943 kN x 400 mm / 110 mm = 10.7018 kN vert up

Find the radial bearing load due to tyre side load on the outer bearing:
Vo = - Vi i.e. = 10.7018 kN vert down

Then the resultant vertical radial load on the inner bearing is:
Ri = 10.7018 kN up - 3.5316 kN down = 7.1702 kN vert up

And the total vertical radial load on the outer bearing is:
Ro = 10.7018 kN down + 2.3544 kN down = 13.0562 kN vert down

Note if the side load direction was reversed
Ri = 10.7018 kN down + 3.5316 kN down = 14.2334 kN vert down

Ro = 10.7018 kN up - 2.3544 kN down = 8.3474 kN vert up

However we need to include the axial load on the bearing due to the side load on the tyre.

For the case when the side load is to the right, this is imposed upon the inner bearing:

For the narrow hub the load combination is 8.829 kN radial with 2.943 kN axial at inner bearing, and 14.715 kN radial at outer bearing

For the wide hub the load combination is 7.1702 kN radial with 2.943 kN axial at inner bearing, and 13.0562 kN radial at outer bearing

If the side load is reversed the axial load is carried by the outer bearing:

For the narrow hub the load combination is 8.829 kN radial with 2.943 kN axial at outer bearing, and 14.715 kN radial at inner bearing

For the wide hub the load combination is 8.3474 kN radial with 2.943 kN axial at outer bearing, and 14.2334 kN radial at inner bearing

Originally Posted by isuzutoo-eh

Thanks for making the adapters available Murray, they arrived this morning
Now to accumulate the rest of the bits and talk to an engineer...

what are you chasing, may have some bits and happy to send your way

Got my adapters today,great kit,thanks Murray

Jim.

Many thanks for organising this Murray. Just sent through a PM requesting a set. Ignore the first PM. The computer decided to send it while I was still typing.

Regards,

Michael

Well, the adapter kits have proved quite popular. I had 10 sets laser cut and I have one set left at the time of this post.

I can have more cut, but the laser cutters have a minimum charge, so to keep the cost to a minimum I need to order 10 sets at a time.

Please let me know if you want a set and I'll order them when we get sufficient numbers.

Cheers, Murray