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Mugen bulldog's differentials are not known to be smooth. There was a design flaw. There was no pressure washer or any spring in the design, the only 'give' in the system was the long 3mm screw, which hardly give at all, which makes proper adjustment of the differential almost impossible, it is either too loose or too tight. (in a moment of weakest, I almost decide to run the rear as straight axle and oneway in the front, I must be sitting in a bathroom .)

I read about this super rare MIP ball differential hop-up about 10 years ago, never seen one in real life and never even heard of it before. I am sure it was due to the relatively low circulation of Bulldogs and therefore low circulation of this MIP hop-up.

My luck, found one NIB for from and rear differentials on the Xbay and got it for less than USD$5 in October, 2008, almost quarter century after this car was born!!

I had a SRB MIP differential before and I know they are good with their machine work. Here you see the beautifully machined parts, very nice tolerance and precise fit. Keep up with the old tradition of MIP good work. The parts are mostly stainless steel, I think. Super hard, do not even need differential rings. The end result is different looking differential, silk smooth!!!!

Top photo was the finished diff. The front one is the MIP hop-up and the back is the Mugen version. MIP was very very solid. As you can see, the Mugen differential has the small differential balls all exposed!!, which is something I can't agree with especially in an offroad car. No wonder they almost never work well.

The bottom photo was my work bench, I used Associated ball differential grease and black grease. I can't think of better grease for ball differentials than these AE products.

My apology for out of focus photos.

Will post more when I get more work done on my version of hop-up bulldog.

thanks for sharing these pics: I love seeing what's going on in those obscure cars.
too often one can only find pics of NIB ones or the build result

That is amazing. My first RC car was the Mugen Bulldog, and I remember how difficult those diffs were. I messed them up pretty bad because at the time, I didn't know how to adjust them. But eventually, I made the holes larger where the balls sat and had to constantly adjust the tension. Out of many runs, I may have had one or two really memorable ones.