Thread: diff upgrade options

Originally Posted by uninformed

socket or spanner haha. I cant see how you would get a socket with any driving device attached. I have some nice Snap-on Hi performance 12 point ring spanners. The 14-17mm version is their longest in 14mm so you can get some good torque on those double hex bolts.

but yes tool clearance was my reasoning for maybe a smaller dia bolt between the others? this may be of some help to the 7 bolt swivels. Or a person could cut off the axle flange machine a new one and weld up the holes in the swivels flange and add as many bolts as posible all the way around, allowing of coarse for tool size to tighten the bolts. I have seen high pressure flanges on pipe work that has bolts almost touching all the way around. I figure there must be some small similarity in these???

I realised after I posted that I should have said spanner, not socket.

Anyway I took some measurements as per my earlier post and pics and made the following comments.

The round bottom front diff housings, as found under early rangies, use imperial (not mm) dimensions and bolts for the bolted joint between the axle housing and swivels. They have 6 x 3/8" UNF bolts equally spaced (60* arc) on a 3.75" (95.25 mm) PCD (pitch circle dia).

These bolts sometimes suffered from loosening or breakage and when the later flat bottom housing was introduced an extra bolt was added (7 vs 6). Bolt size also changed to M10 fine (10 mm is 0.475 mm larger than 3/8" - from memory, comparing the root diameters, the M10 fine thread doesn't show as great an increase over 3/8" UNF). However the new 12 point bolt heads, given their larger intergral washer will improve the fatigue strength - see my earlier post about using a thick washer when the holes are slotted.

I have not measured the new PCD - I would be surprised if it was not changed slightly to a nice round number of mm's. From a quick look it appears that 5 of the bolts are still equally spaced on 60* arcs, but the lower bolt position was replaced with 2 new bolts on a spacing of 40* [40* = (2 x 60*) / 3].

For pricipally vertical (gravity) dynamic loads applied from the terrain at the tyres, the bolts located near the bottom of this joint carry most of the load - the other bolts see much less load. Note that the load tries to pull the joint apart at the bottom (increasing the pre-tension in the lower bolts) and push the joint together at the top (this compression reduces the pre-tension in the upper bolts).

In an earlier post I stated that for the early housing and swivels, an extra 2 bolts could be added, one either side of the bottom bolt, bringing the total number of bolts to 8. This would be somewhat stronger than the later 7 bolt version.

I have confirmed that the extra bolts can be the same size as the originals (3/8" UNF) - see comments and pics of an early housing below.

Check new bolt pitch if extra bolts are added mid-way between existing bolts, i.e. spaced on 30* arcs.

From simple trigonometry; chord = PCD x sin (arc / 2).

Then chordal bolt pitch will reduce from 1.875" (47.625 mm) to 0.971" (24.652 mm).

The new pitch is approx 2.6 x bolt dia (OK).

Check for spanner clearance between bolt heads.

Obtain the maximum allowable size across the outside of the spanner by subtracting the dimension of the bolt head across it's corners, from the 60* chordal pitch.

47.625 mm - 16.5 mm = 31.125 mm (OK for 9/16" ring spanner).

Originally Posted by c.h.i.e.f

... i am considering drilling a 10mm hole through swivel ball flange and then assembling it all back together to new adjustment point then marking diff side flange then remove swivel ball again drill and tap diff side flange and then i will have a lock bolt so to speak...

Originally Posted by rovercare

If you slot them in a mill over 5 degree's, they aill leave an edge that is good enough to stop any rotation, I ran these for years

...

Lots of people think (wrongly) that the bolt hole plays some part in preventing rotation of the swivel at the bolted joint.

The bolt holes only stop rotation while in the process of assembling the swivel to the axle housing. Once the bolts are properly pre-tensioned, the bolt shank bearing against the side of its hole does not prevent rotation.

The bolted joint relies on friction between the mating surfaces to prevent rotation. This is the way all bolted joints subjected to eccentric, dynamic loads should be designed - it is also the recommended method for any bolted joint where movement can't be tolerated. The only exception which comes readily to mind is where cone washers and their like are used, e.g. Toyota hub/axle flanges. Fitted bolts, fell out of fashion many years ago, because they expensive and not as reliable - bolts in clearance holes, even with less than 0.5 mm clearance are not suitable.

Once these bolts are tightened properly they are never subjected to any shear load whatsoever - this fact can be difficult to grasp.

BTW the only applied load that tries to rotate the swivel about the axle centreline (which is the rotation referred to here) is braking. With braking the horizontal (traction) force between tyre and road is transferred through the brake caliper mounts etc. to the swivel, then to the axle tube via the bolted joint in question. it is then transferred to the chassis via the radius arm.