Model: (Click to see more) 99993: Parts
Status: Extra info
Date: 29-Jan-2006
Comments: 0
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There is some good information about all the models of SRB differentials here ;-

http://www.tamiyaclub.com/showroom_model.asp?cid=43390&sid=5475


This is a MIP brand ball differential for the SRB series of R/C vehicles (RR, SS, XLT, SC). None of the SRB's come with a diff. as standard. I got this MIP diff. for 40 GBP from Nick Walker ('Motorsportnicko'). This MIP ball diff. is essentially the same design as the Thorp ball diff., but they used three slot screws instead of hex screws, the main gear is silver in color, is probably made from aluminium (?), and the gear is about 1/2 the width only, compared to the original SRB Final Gear, and is very light weight [when compared to the Thorp ball diff. with it's brass main gear].


This MIP ball diff. is currently in my Ford Ranger XLT. In my case, the diff. does make a *huge* difference because without it the turning circle on my XLT is rediculously large on carpet, and I run my cars indoors on carpet quite a lot.


I am currently trying to get hold of a scanned copy of the instructions for this MIP ball diff.


The machining is very nice on it! When I first got it, I spent the first 10 minutes trying in vein to adjust it with a small flat bladed screwdriver, until I then finally twigged that you need an Allen key of the correct size instead. Doah! Then I was able to adjust the diff. to my heart's content. It has a silky smooth action [MUCH MUCH smoother than my Thorp ball diff., when they are both set to the same tightness, and in turn, my Thorp diff. is 20 per cent or so smoother than my brand new Tamiya TA-01 ball diff. (stock kit diff.) from my NIB Toyota Celica GT-4 RC that I assembled recently. This MIP ball diff. can be set from very tight to very free. It's not a geared diff. that I really would have preferred, but I feel very pleased that I managed to get one of any diff. at all.


It's a perfect fit in the stock kit XLT SRB gearcase. I did have one major problem though at first - the flats on the 2 output shafts either side are very shallow on the MIP ball diff. (not 1/2 the shaft end, like the original Final Shaft is) and as a result the grub screws in the Universal Joints stick out more than they did before, and on one side the result was that the grub screw was thus rubbing on the bottom of the clear case (over the gearing), which was very annoying . I had to get busy with the small set of 3 Tamiya fine files and rectify this by filing away about a 1/8th inch squared area of the bottom of the clear case.


I carefully filed down the clear gearcase in one small spot and it **JUST** had enough clearance to clear the grub screw. Crikey it was by the skin of my teeth, the gearcase was very nearly penetrated, but fortunately not actuallly. There must have been like 0.1mm left ! It was a tricky job. Fortunately you can't see any evidence of this modification when it's complete and assembled etc..


Now the wheels go round perfectly without any binding due to the grub screw.


I found that I had the diff. way too slack. After some adjustment I now have it perfectly adjusted to my liking, it works very well. I am a very happy customer!.


My TC pal Mike said to me ;-'Why are you so bothered about the fact that it is a ball differential instead of a geared diff.?', and I replied 'In general I am not overly keen on ball diff's for a couple of reasons... a) I have to set the diff. to be slack enough so that when I am on any indoors surface such as my vinyl flooring in my kitchen, the diff. is slack enough to still allow the wheels to rotate at different speeds. If the diff. is too tight then one tyre is dragged around the corner (as it were) and there is no diff. action. However when I set it slack enough to achieve the above, then it acts like a poor torque converter (i.e. fluid clutch / hydraulic oil / impeller blades set up) on an automatic gearbox, in the sense that there is a lot of slip in the drive (kind of like a slipper clutch) and you can't climb steep gradients or get one wheel to drive over an obstacle since the drive to the back wheels slips... A proper geared diff. does NOT SLIP, EVER, and gives correct differential action, permamently.


...and b ) Real vehicles DO NOT USE ball diffs. Ever. This bothers me since I am always wanting maximum realism...! Some vehicles do have limited slip diffs, but they must use a different mechanism (clutch plates / spring), see ;-

http://auto.howstuffworks.com/differential8.htm


Here (not in the showroom entry pictures, they are below, and are of the diff. after I had stripped it and cleaned it) are some pictures of the ball diff. as it came. It shows the 2 other shafts and gears that the seller included that match this diff. ;-
http://www.geocities.com/prescotmes/IMG_1211_small.jpg

http://www.geocities.com/prescotmes/IMG_1212_small.jpg


I was concerned about taking it apart and cleaning it, but Theo said to me 'Don't be afraid, just open the [ball diff's] up, clean them and use some Tamiya ball diff. grease, if you plan to run them, it would be a shame if it starts slipping and thus wearing, due to non-servicing and old/bad greases'. 'terry.sc' added 'They aren't that complicated, just lay the parts out in the order you take them apart so you know which order to put them back together. For grease use any ball diff. grease. Most manufacturers make their own version of ball diff. grease. Ball diff. grease is designed to allow the the balls to press against the washers to give drive. Any other grease will not work. At the time the diff's were made specific ball diff. grease was not around, so using a modern grease designed for it will give better performance than it originally had'.


A while ago I figured out why the flats on both ends of the MIP diff. are so shallow and make the grub screws on the U.J.'s stick out so much (and why I had to modify my clear gear case to stop the grub screw rubbing against it thus stopping the wheels from going round!)... It's simply because one end of the ball diff. output shaft has to be hollow (tube like) so that you can get an Allen key into it (in the case of the MIP diff.) in order that you can adjust it properly!! Doah!


Some have said that the MIP ball diff. is much lighter than the Thorp ball diff. and indeed it is, but when you put the MIP-supplied brass Drive and Counter gears along with the MIP ball diff. into the SRB gearbox, the weight of all of them is about the same as the Thorp ball diff. with the brass main gear.


After I had stripped it and cleaned it and put Tamiya ball diff. grease in it, I tested it and found that it felt exactly the same as when I got it, so there must be almost no wear on the diff. balls, it is the smoothest ball diff. that I have ever owned :-)


For my Thorp SRB ball diff., see ;-

http://www.tamiyaclub.com/showroom_model.asp?cid=43755&sid=5475


I have learned that I need to use actual specific 'Ball Diff.' grease on these SRB ball diff's (when these SRB ball diff's first came out there was no grease used at all on them since ball diff. grease was not available back then).


I have also learned that if I have the tension set low on the ball diff. (for indoors driving) then if the drive slips a lot then it is WEARING AWAY the diff. balls since both side plates will be stationary and the ball ring holder will push round the balls (since it is connected to the motor via the main gear that it is part of, as it were) and the balls will NOT turn on their axis
and will simply develop flats and be worn away thus making the diff. action rough, so it is important to re-grease and maintain the diff. regularly if you think about it.


UPDATE : 8th February 2006 ;- Today was a revelation for me. I used an R/C car (my Ranger XLT) outside in the street for the first time in about 15 years LOL. It was very interesting. I had the MIP ball diff. in it and set very slack and to my suprise found that my hill that I live on was so steep
that the car could not get up the hill i.e. along my pavement outside my house since the diff. kept slipping!! So back inside I went and tightened the MIP diff. by 1/8th of a turn. Checked to see how tight the diff. was now by running the car over
a shoe and it now climbs over large obstacles easily, no diff. slip!


Then back outside and YEAH loads of torque from the motor and now the car got up the hill easily. Back inside to check the turning circle in the kitchen (lino flooring) and it's still about 90 per cent as good a turning circle as before but
just a touch less, and I can hear my rear tyres squishing / squeeling slightly when on full steering lock since one wheel is being dragged along just *slightly* since the diff. is now tighter, but still *just* about turning and providing satisfactory diff. action and good steering lock.


UPDATE : 15th February 2006 ;- In a conversation with my TC pal Mike T., he said '>A geared diff' would be awesome, with your diff' setup how it is, if you hold the car in the air and turn the right rear wheel forwards, does the left rear wheel turn forwards or backwards?', and I replied 'At my current diff. tightness setting, if I try this that you suggest, then sometimes the left rear wheel turns backwards, as expected, but also sometimes the left rear wheel turns forwards [because the ball diff. is set reasonably tight], and my motor is getting turned over (I can hear the gears whine and can feel the lumpyness from the armature and the poles of the magnets). This is because the 'side plates' of the ball diff. are holding the balls in the centre very tightly and not allowing them to rotate on their axis, so the balls get dragged along at the same speed that the 2 side plates are rotating at (the side plates in this case are at equal speed, and going in equal directions), which drags the cage that the balls are in, around in the same way, and the cage is part of the main gear, so the motor gets turned over at this speed.


If I hold onto the left wheel and stop it turning and then turn the right wheel forwards, the motor is getting turned over at 1/2 the speed. This is because the left side plate is then stationary, and the right sideplate is rotating at the same speed as in the above, and in the same direction as the above, therefore the balls rotate on their axis, at 1/2 the rate (think about it) so that the ball cage that the balls are in gets dragged along in the same direction but at this same 1/2 speed, so the motor gets turned over at this same 1/2 speed.


If I now rotate both wheels, in opposite directions, at the same rate as each other, then the balls rotate on their axis but stay STATIONARY. Therefore the cage doesn't move, so neither does the motor.'


UPDATE : 18th February 2006 ;- In another conversation with my TC pal Mike T., he said '>BUT, when i turn my wheel [on his SS with a Jakes diff., I later bought this diff. off Mike, see my showroom entry for it], the other turns in the opposite direction (as you can imagine), and there is NO slip in the diff. Wonder why?', and I replied '
Funny how you diff. doesn't slip even though it would appear to be loose enough to allow the other side plate to move in the opposite direction! I've no idea why! However mine still slips quite badly if I open the throttle too much, too quickly.
This will wear the balls quickly and they will develop flats since the motor is rotating the main gear and thus ball cage, but the side plates are not yet moving, so the balls get flats on them as they are dragged around with the cage whilst the
side plates are stationary. Ball diff's are a problem LOL. To be fair I am getting diff. action in my XLT with this MIP ball diff. on my linoleum kitchen floor and enough drive torque to accelerate away at far beyond scale acceleration when going e.g. uphill. I'd still love to get a geared diff. though.'

The main gear is 1/2 the original's width! Stripped down for cleaning. Now done. With the MIP supplied Drive and Counter gears

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