Semi Girling Drums

[Erich]

Hi All,

My rear brakes were seriously out of round so I had them turned. On remounting them I found that on one of the drums, the backing plate is not even, having a large gap at the bottom and nearly touching at the top. I can't see that there is any adjustment of the back plate. I will note that the axle and I presume the back plates as well, were modified. It is a short chassis with a long chassis rear axle which has been modified to take the springs off the short chassis. It appears that the back plate on one side was mounted(welded) not perfectly plumb with the axle, or am I missing something?

Erich in Mukilteo

[Ian Williams]

You have have a hub not sitting straight on a half shaft taper. And if the axle tube has been welded badly out of line with it's correct location you may well break half shafts on a reasonably regular basis.

[Erich]

Thank you Ian. It turns out that both sides are out, though the right hand one is not out as much. I wonder if this was some strange way to introduce some negative camber. The odd part is that the spring hangers have been welded in the correct position(LWB axle to SWB chassis with 1931 CWP housing pre D type) in a very professional looking way. Outriggers were once cutoff at the chassis rails and then replaced at some point. Maybe a monoposto at some point?
All pretty mysterious mods to a neophyte, including the chassis being semi boxed at the rear of the CC.

Erich in Mukilteo

[Bob Culver]

To cut and reweld axle tube ends exactly parallel as made is no mean feat. For diff alignments much can be deduced with levels, with the axle as normal horizontal and stood vertical The bearing mounting  surfaces should be level. For 3/4 floating hubs ball races with max tolerance shake should be used to help absorb cornering deflections and slight errors.
it would be a lot of work but I dunno if there is any scope to sleeve the axle tube ends, turn as an assembly,  and sleeve/pack the hubs and use different bearings. Modern bearings are much higher rated.
I take it the backplates attch with bolts and are not welded. Are they flat ? Is the machined shoulder on the axle tube end exactly square with the bearings set, or has it or backplate been bent in a prang or when wheel lost?

[Stuart Giles]

I see the thread is titled semi Girling drums; do you have hydraulic brakes on your car? the hydraulic backplates, being as they were/are modified Morris Minor items are  often not square to the brake drum -this doesn't seem to affect their effectiveness as the brake shoes self-align.

If the axle ends do happen to be out of line to the half shaft axis, the wheel bearing life will be very short (hundreds rather than thousands of miles) and the oil seals won't stop diff lubricant reaching your brake shoes. Welding the axle casing to attach spring hangars etc. on any live axle usually pulls the casing out of line. Even after machining axles cases and ends to shorten them it's not unusual to need to tweak the casing after welding as  a result of weld distorting even when the parts have been jigged. I have straightened a lot of casings, A7 and others, the method is quite low tech....

[Renaud]

Hi Stuart,
Very interesting but how do you decide that it is now in line?

[Stuart Giles]

Hi Stuart,
Very interesting but how do you decide that it is now in line?

In the second photo, there's a red dot visible on a "target" in the centre of the differential bearing. There's a laser pointer just visible at the hub end in that photo.

The widget bolted across the differential casing of the F750 rear axle in the first photo is there for the same purpose.

A7 axles can be a bit trickier, because the hole at the hub end isn't always absolutely concentric to the hub bearing seating which is the true axis.

[Renaud]

Thanks Stuart, excellent. Got it.
Not so low tech then!

[Erich]

Hi All,

Thank you for the sage advice and comments. At this point, I've decided to risk not attending to this. My reasoning is that the car was rebodied with a second replica body by the fellow I bought the car from. He put the CC body on circa 1994. Prior to that, the car had another Replica body and was raced and the chassis had been modified with the wider track rear axle and semi-gilding brakes. So the car has been running with the same rear axle set up for at least around thirty years. So I have to assume that since it worked well enough for that period with no breakages, then I won't look for trouble. If it does break an axle, then I will tackle it at that point.

Erich in Mukilteo