Geoff Lowe
<geoff.lowe@survey-inspection.com>

SB1946
UK

If you would like to ask any questions or require any help to do these jobs on you own car please drop me an e-mail at: Geoff.Lowe@survey-inspection.com

Standard 10-rear Axle Diff Flange Reinforcement

If the bolts that hold the diff to the axle are giving you trouble read on. I have a 1500 Cosworth S2 Seven SB 1946. When I obtained the car it had been stored for about 30 years in a garage. I soon had the car on the road in a safe but a bit tatty condition. I eventuallly noticed oil leaking from the diff, so being an optimist I tried to nip the bolts up and to my horror I found the bottom one snapped and the top one stripped with bits of gasket hanging out of the jointing faces.

Nothing else for it the axle had to come out
On stripping it down I found some one had been in there before me and had put bolts from the inside coming out. This made me start to think about the forces and how they worked on the axle. On acceleration the bottom bolt is under stress and deceleration it is the top bolt under stress, and with it having a thick gasket between the diff and the axle this only emphasised the problem of the diff rocking from top to bottom. This works because as the gasket compresses under load the bolts become slack and the problem gets worse resulting in snapped and stripped bolts. What could be done? As the faceplate on the diff is only .25 of an inch thick (that may have been ok for the Standard 10 with its 20 or so HP but we are talking over a 100 hp now) I looked at it, lit my pipe up, and had a think, opened a can of beer, re filled the pipe and smoked it again, then the plan started to come together. If I was to get a ring of steel burnt out about 8mm thick the same size as the axle face plate I could cut it in half and feed it inside the axle casing in two pieces then weld it in and drill and tap it to take 3/8 bolts instead of the 5/16... so this was the plan.

You always need a plan
How the plan worked: I measured the axle face plate at 6.25 inches (159mm) ID x 7.75 inches (197mm) OD and went along to a local fabrication firm that had a profile burning machine and got them to burn a ring out of 8mm steel BS40B -- still a weldable steel but a higher grade than mild steel. I then obtained a set of 3/8 BSF taps and socket headed allen bolts as these are of a very high-grade steel (ever tried to cut one with a hacksaw?) Armed with all this, work had to start, bearing in mind all the equipment I had to perform this feat of engineering was a 4 inch grinder a hand held drill and a welding set.

The profiled ring

I cut the ring in half and ground a chamfer in the areas where I would be welding; this is for when you fit the diff you don't grind all the weld off. I fed the two halves of the ring in to the axle.

Now at the top of the axle there is an oil baffle so with a new grinding disc I cut this away where the new ring was to go, leaving the rest still in place. Once I had the ring in I clamped it to the axle flange and tack welded it in, so what we have now is a flange of about 14mm thick.

The ring cut in half

This is where it can all go wrong with only having a hand drill, so a friend of mine (Woolly to his mates--he has a thing about sheep!!!) came round to help me square the drill while I am drilling. We clamped a square to the face of the axle and Woolly eyed the drill with the square. As the tapping drill for 3/8 is slightly bigger than 5/16 we drilled it 5/16 first to give the tapping drill just a shaving to remove. Once all the boltholes had been drilled they were tapped out 3.8 BSF. I chose BSF because it is a bit coarser than UNF but still fine enough to give good locking potential.

Welding the ring in place

Tapping the holes

Fitting the Diff
Obviously the bolt holes have to be drilled out the take the 3/8 bolts, but before you do that the diff has to fit back in the axle, and where you have tack welded the ring in will need grinding to allow the diff to fit. Once this has been achieved look down the holes to confirm that you made a good job of drilling the axle. If one has wandered a bit you can make the adjustment when drilling it to 3/8 inch. The holes in the diff want to have minimum clearance between the bolts as this will help with rigidity when driving.

Over 9/16 inch thick flange.

With all the grinding and welding going on in there you need to take great pains in cleaning it out because bearings do not like carborundum dust. When I did this job I stuffed rags down the half shaft holes and taped them off with thick tape and this helped with the clean up operation. When fitting the diff you may find that the faceplate of the axle is distorted around the holes. I got round this by filing across the faceplate and moving round to keep it flat.

DO NOT USE A GASKET
On the final assembly use a suitable silicon gel as this will not compress under load and will fill in any dips in the face plate. With the new thick high tensile bolts and the thicker flange I flogged the bolts up with a hammer until they give a pinging sound. I also used stud lock just to make sure. I did this work back in March 07 and have given it some stick since with not a hint of trouble -- all bolts are still tight and no oil leakage.

One other tip:
if you are putting half shaft bearings in use sealed bearings and remove one side of the seal, and if you remove the inner oil seal just behind the bearing then the bearings are lubricated by diff oil and not by grease. I hope this is of help to some one out there, and if you are going to tackle this job please contact me if you need any advice. Once I had the ring, bolts and taps, Woolly and I started one Saturday morning about 9-30 and I was down the pub in the car at 1700h so even though it sounds complicated it's not, all it is, is a progression.

Good luck! Geoff SB1946 back to Geoff Lowe's page