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Restore a Ball Differential

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Hi all, I have an old stock-built Madcap I'd like to restore. I have stripped it all down to the base components and given it all a good clean and check - except for the differential. 

I was wondering if anyone can provide some tips and advice on how to clean and restore the ball differential. It's a relatively complicated part obviously, and replacement parts are hard to come by as far as I can tell. Any advice on clean-up and restoration techniques for such a component would be very much appreciated - I'd like to restore the diff but I'd like to do it correctly, and have zero experience in the restoration of such a component.  
 

It’s a specialist question I know. But thought worth asking here, as where better to find such a knowledgable bunch!

 

Cheers guys :)

 

 

 

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One i would soak and clean all the parts to remove any grease. I would replace all the diff balls, the diff plates if they have grooves in them you can sand to flatten back out or possibly just flip them. Depends on the use the diff had. 
i had an astute back in the day and remember that diff had washers or something as spacers. Many had problems with these ball diffs, i ran a twister hurricane motor in mine and never had any issues.

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I have an Astute from my childhood and love it, uses the same trans as your madcap. For years I kept it going with spare parts I had collected. This past year I gave it a fresh rebuild and I couldn't source the differential parts, so I installed the Rere Super Astute Transmission. It has a gear diff that I put putty in for some resistance and a slipper clutch that you can use TRF201 48P Spur gears or even easier to find Associated spur gears. I recommend this route for your Madcap.

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I restored some ball diffs for my older cars recently. In general, the diff balls often are not the problem, and can be reused when cleaned thoroughly. The diff plates are the key. But these can be sanded on a flat surface on some higher quality wet sand paper. Doesn´t have to be too fine, I used 240 - 400 grit (hope this is the correct phrase). Then I would look up the manual and rebuild the diff completely with Tamiya anti wear grease instead of the old ball diff grease. This gives a more sticky effect and protects the parts from overloads (at least in comparison with the gel-like ball diff grease). The screw I would secure with a tiny amount of Tamiya thread lock to prevent it from loosening during driving. This would be my first try. If it´s still not working properly, you still can use some new balls from Tamiya. The diameters never changed, it doesn´t have to be NOS Madcap parts.

I think, that would be the cheapest route to go first, and something you can consider.

Unfortunately, my own Madcap is gone after all the years, just some Tiny bits left from it.:wacko:

 

Br,

Matthias

 

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240-400 is pretty coarse... I use 600-800grit on a tile or pane of glass.

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1 hour ago, ruebiracer said:

The diff plates are the key.

Never had a Madcap, but are the plates spinable? I've done that before, just turn them over to a fresh side, when they've worn a groove.

There was a vid on YouTube recently, by Schumacher's Tech guy, building a Laydown diff, but some good ball diff building tips none the less.

 

 

 

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Don't forget to break it in correctly after the rebuild too.

 

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Also check the alloy diff housings, if the 3 screws joining the halves are over tightened they can deform. Place the flats across a piece of glass or similar to check. These are known to be quite soft! If deformed once rebuilt the diff will still slip badly, adding more washers and further tightening will only worsen the issue.

Madcap metal parts bags have been on a well known auction site recently (includes diff housings). I had this issue on a used king cab I purchased, in addition to pitted washers due to over tightening.

All the best

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Thanks all, some really useful advice here, appreciated as always. 

4 hours ago, DGunn1 said:

Madcap metal parts bags have been on a well known auction site recently (includes diff housings). I had this issue on a used king cab I purchased, in addition to pitted washers due to over tightening.

I was thinking about doing this. Part of me just wants to use the old diff and components, however to get a new diff and parts via the well known auction site is sort of tempting, if potentially expensive.

Was looking at super astute bits also.... I presume these will fit but I need to do some research to ensure they’ll be compatible. (which inadvertently is triggering the hop up cascade of ‘well if I get the super astute diff and case then maybe I’ll get the super astute  chassis and then maybe I’ll need to get the super astute dampers....’ - but I’ll probably avoid this path, would might as well purchase a super astute 🙄 !) But, am definitely tempted by this option, I presume this is possible.

I think first step is to pull it apart and give it a visual assessment. Also will give it a good clean  and a good soaking, perhaps also a whirl in the ultrasonic. 
 

will let you know how I get on :) 

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I went down the restore route for one vehicle and the super astute rere TCC for the other. The difficult parts to obtain for the restore option are the thrust washers with the hexagonal centres, and if badly pitted I don't think the sanding option will work. Mine would have been half thickness!! Got all the parts in the end but it took a while and cost almost as much as an SA upgrade.

Almost nothing from the original gearbox is reusable if upgrading to the rere SA TCC, including the A parts gearbox case.

 

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