Changing Diff Housing - practical or best left alone

[Exminiman]

Can anyone offer any advice on how practical it is to change diff housings on gearbox...or is it best left alone

IE Magic Wand or AD016 to Mini remote

Does it have to be line bored ? if so, any recommendations or is it a general machine shop job ?

Thanks in advance

[GraemeC]

HRE did a youtube video on this I think - a machine shop job unless you happen to have a nice mill in your workshop.
There is also a train of thought that you can 'get away with it' and with enough diff covers to pick from you will no doubt find one that's close enough.

[bwaminispeed]

Probably done 10 in the last 50 years, never had to machine anything, nothing broke, nobody died, so, I guess it works.....

Taking the locating dowels out usually gives enough movement to allow everything to line up.....the bearings themselves take over the job of the dowels.....

If the diff is too narrow, or, too wide, I allign the left side flush, then use a gasket plus a half gasket (sometimes two half gaskets) to make up the difference on the none flush (right hand) side......

Simple, easy to do for the home garage guys.....I suspect I will get an earfull from the machinist types, but, as I say, it works......

[Peter Laidler]

No earfull from me BWA. Done much the same with Norton Commando and Triumph gearbox and engine casings a couple of times AND got them oil tight - and you can't do that too often with a Commando! Where the dowels are within a few 000s" of true I have also slightly oversized the holes and machined dowels to fit

[Exminiman]

HRE did a youtube video on this I think - a machine shop job unless you happen to have a nice mill in your workshop.
There is also a train of thought that you can 'get away with it' and with enough diff covers to pick from you will no doubt find one that's close enough.

Cheers, will have a watch, nice guy, but does like to chat….

[Exminiman]

Probably done 10 in the last 50 years, never had to machine anything, nothing broke, nobody died, so, I guess it works.....

Taking the locating dowels out usually gives enough movement to allow everything to line up.....the bearings themselves take over the job of the dowels.....

If the diff is too narrow, or, too wide, I allign the left side flush, then use a gasket plus a half gasket (sometimes two half gaskets) to make up the difference on the none flush (right hand) side......

Simple, easy to do for the home garage guys.....I suspect I will get an earfull from the machinist types, but, as I say, it works......

So am I right in thinking the bearings centre the casing rather than have them inlined bored ? In some ways it cant be wrong…do you not get an issue withe the diff pulling to one side?

[bwaminispeed]

Yeah, the bearings effectively become the dowls to centre the bore.....

Nope, never have....

Usually the bores are pretty close, worst I've measured was .012 vertical offset.......the width is much more often the problem than the bore, and, using half gaskets solves this quite easily......

[timmy201]

I was lucky with mine, I test fitted it with the dowels in place and it was a perfect fit in all dimensions

[Polarsilver]

Project gear box & on inspection the Diff Case aligned & all looked good .. However on removal of this diff case there were no dowels fitted .. so on my trial rebuild i fitted the two Dowels and the Diff case was now out of align .. so as BW has said i left out the Dowels and all seems to be ok with the diff case to main casting aligned on the mounting studs ok .. time will tell.
if you are in real trouble contact 251eng.

[spoon.450]

Sounds like some good practical advice here.

[Jason]

I have done a fair few magic wand diff cases onto 4synchro remotes over the years. Been fortunate to have enough cases to try to find one that was a good fit. Dowel removal gives you that bit extra ‘wiggle’ room for the ones that refuse to line up.

[850man]

It is rarely an issue. I have swapped hundreds of them, the bearing holes are always perfect, sometimes the flat side plate surface can be slightly offset, but its never enough to cause any problem either. The paper gasket takes up any hight difference.

[mk1]

As you have probably gathered. There are varying views on simply swapping the back of the diff housing from Box to box. It can be perfectly successful, but it can also be a route to knackered diff bearings, oil leaks & even bust diffs.

If you do decide to do a swap. CHECK the roundness of the diff bearing holes. And examine where the gearbox & dif housing meet, I have seen large steps here, up to maybe 2 or 3mm if this is the case DONT PROCEED!

In my experience there are more matches that have been too far out to risk, than ones that look OK. So Please beware!

If it was me, I'd rather use the correct1300 remote with a steel conversion plate, or even the standard rubber one than risk swapping diff housings, if I had the option.

Swapping diff housings is a BODGE! It's a bodge you may get away with, but if you don't get away with it then the stakes can be very high indeed!

[Jason]

Very true Mark, from my experiences converting 4synchro remotes to a pudding stirrer gear change it is vital to ensure the bearing aperture is round and true. I used a bearing outer race machined 4thou undersize to check the aperture and with feeler gauges to ensure even gap. Any 'step' observed where the diff housing meets the gearbox casing = stress on the bearing, which ultimately can lead to premature failure, or even worse bearing failure resulting in your diff exiting the casing!. Only ever done this to convert a 4synchro box while maintaining the correct 3synchro long gear lever at the customers request and the end faces were machined flat by Beagle Engineering.

[251 ENG]

Gearbox/diff housing boring

[spoon.450]

Worth bearing in mind how much the gaskets vary in thickness between manufacturers too….

[Jason]

That’s the tool Simon to get them online and parallel. Will it fit in a 1/2” drill chuck

[1071bob]

Have to agree with Mark, I had six diff caps to try on my '190 case and most were miles out of alignment. On the one that was closest I removed the two dowels and made some tooling to bore out the holes in both the cap and the casing. I then made a stepped dowel for the casing and sleeved the cap to suit, so I ended up with tight fitting cap to the main case and not relying on the diff cap studs to clamp it tight. I skimmed a few thou off the cap and set the boring bar zero to the main case and machined the cap to size. Took ages to set up and a couple of minutes to machine, had to turn the casing over to do the other side.

[Exminiman]

HRE did a youtube video on this I think - a machine shop job unless you happen to have a nice mill in your workshop.
There is also a train of thought that you can 'get away with it' and with enough diff covers to pick from you will no doubt find one that's close enough.

Worth a look at this vid as GraemeC says, just like inline boring end caps and quite simple solution to clocking it all in.

Shame about elongating the bolt holes in the covers, but wouldn’t stop them being used on another box…


https://youtu.be/EZI-k3hpH1o

[Exminiman]

Gearbox/diff housing boring

Interesting tool (ooh er misses ) is the the tool self centring or suppose more accurately does it self centre the work ?