Why doesn't my Thorp Ball Diff fit in my BF gear case?

[Leethal Driver 86]

Am I being dim ?

I've managed to get all the parts for a complete diff Thorp diff for my BF. As is common they are usually missing the spring and thrust bearing washers and 1/16 bearings so I set about tracking some down over the last year or so with the help of TC member NJHopper.

Now, having put this little lot together I noted that the hex bushing doesn't sit flush with the LH pressure disc because of the insertion of the spring & thrust bearing washers and 1/16 bearings. These cause it to sit well above the top of the LH pressure disc thrust bearing housing and when the LH universal is inserted it's really loose, and clearly not meant to be. I did think this a little odd at the time but realised something was deffo wrong when I couldn't get the side plate of the gearbox flush with the housing when trying to assemble it all together, caused by the the LH universal not sitting flush with the top of the LH pressure disc thrust bearing housing.

Here's a diagram. I've followed this to the letter. It doesn't appear to show that the hex bushing will fit over the top of the spring/thrust bearings:

http://www.rcchopshop.com/thorp/thorp4500.html

Probably a small audience but has anyone else had the same problem or am I fitting it incorrectly (don't think so...)? Happy to provide some pics if it helps (I realise I should have done that now but it's getting dark, I've shut the garage and washed my hands ).

Cheers all

Lee

[HunterZero 76]

Have to ask - You don't have the Fox version, do you? They share a lot of common parts, but the pressure discs are different.

- J

[Leethal Driver 86]

Nope looks like the BF disc in the drawing, although I've yet to see a pic of a Fox equivalent (or any instructions for the Fox diff).

I tried the set up without the thrust bearing washers and the 1/16 steel balls and the hex bushing fits nice and snug. With them, it sits about halfway out and wobbles about. Took a couple of not great pics:

With thrust bearing washers etc - note the hex bushing is protruding about halfway out of the LH pressure disc housing

Without thrust bearing washers - nice and snug

Scratching my head a bit here. Half tempted to leave out the thrust bearings but that kind of makes the point about searching them out a bit wasted, and obviously the diff won't work as intended.

Hopefully someone will have a view.

[matman 1499]

Nope looks like the BF disc in the drawing, although I've yet to see a pic of a Fox equivalent (or any instructions for the Fox diff).

I tried the set up without the thrust bearing washers and the 1/16 steel balls and the hex bushing fits nice and snug. With them, it sits about halfway out and wobbles about. Took a couple of not great pics:

With thrust bearing washers etc - note the hex bushing is protruding about halfway out of the LH pressure disc housing

Without thrust bearing washers - nice and snug

Scratching my head a bit here. Half tempted to leave out the thrust bearings but that kind of makes the point about searching them out a bit wasted, and obviously the diff won't work as intended.

Hopefully someone will have a view.

That still LOOKS too high to put the side cover on ?. Or is it just the angle ?.

How many spring washers are you putting on / in .

Are the bearing right size ? Was there an error when they printed this info out ?. So the sizes could be wrong .

Are the parts right ?. As in the pic or diagram in the above shots i see two outer hubs , But not in the link pic .

Maybe take a pic of all the bits so we can see them & have a clear picture of what you have .

Hope some one can help you , As you must be pulling your hair out . working this out .

[Shodog 1835]

Got a pic of the other side of the diff? The thrust plate on the side not pictured is very thin. You may have the wrong part

[Leethal Driver 86]

Right then, spent half an hour pottering about whilst listening to this evening's free practice (I live roughly 3 mins from one of the fastest parts of the TT course, the run from the Grandstand down Bray Hill to Quarterbridge) and took a few pics.

Shodog

Posted Today, 04:53 AM

Got a pic of the other side of the diff? The thrust plate on the side not pictured is very thin. You may have the wrong part

Yep, fitted in the gearbox nice n tight:

And out of the gearbox:

Here are the Thrust Bearing Washers w/bearings:

On the screw - note how tall the two washers inc bearings are:

One thing I did note is that the Spring Washers also don't fit within the Hex Bushing, so I went from 4 in the pic to 1 and that helped a little (see pic 2 above).

I then fitted it together into the gearbox alongside a stock gearbox from the donor chassis just to compare. The width of the Thorp set up, from end to end on the drive cups is c. 5.7cm whereas the stock gearbox is pretty much bang on 5cm (using a ruler and a decent reckoning with my eyes). I suppose some of that is the fact that the Thorp universal cups are prob longer than the std hex cups anyway but in the Thorp set up on the left, the screw head and Thrust Bearings are on the left hand side of the gearbox, hence the drive cup sticking out miles:

Notwithstanding the fact that when it turns the counter gear is catching on the LH pressure disc thrust bearing housing, it'll be getting stripped and regreased anyway.

As in the pic or diagram in the above shots i see two outer hubs

Yeah Thorp did a std hex drive cup and the dogbone version.

I'll take a pic of everything laid out tomorrow as I need to get on with some physio this eve but maybe something for people to go on. The only diff between this and my last ball diff is the addition of the thrust bearings as far as I can tell.

Anyway, cheers for the help so far guys.

[NJhopper 0]

Hey LD! I got your pm. For clarification, what P/N LH pressure disc do you have? To me this really seems as a parts mismatch somewhere rather then an installation issue. Also, are those thorp joints? They look almost chrome.

[HunterZero 76]

Here's the Fox diff sheet, found on TamiyaClub thanks to member Jimbo:

http://tamiyaclub.com/showroom_model.asp?cid=3234

[Leethal Driver 86]

OK then.

I've been through the Fox and BF instructions/diagrams and the only diff between the two are the LH and RH Pressure Discs, with the key LH side and Thrust Bearing Housing being part no 4503 for the BF and 4583 for the Fox. Everything else is the same.

So I pulled mine apart this eve (although I left the Thrust Bearings inside the LH Pressure Disc because I cba getting it out) thusly:

What I did note is that inside the LH Pressure Disc, the Thrust Bearings/Washers actually sit within a recess. Now, when the Thrust Bearings etc aren't present this means that the screw head would sit within the recess, rather than above it when they're in situ. I thought this might be an issue but the Hex Bushing is wide enough to fit over the screw head. However, the LH drive cup won't fit all the way into the Hex Bushing because of the screw head sitting above the Thrust Bearing recess instead of within it when they're not present.

Can't imagine that the Fox LH Pressure Disc is that diff to the BF one. Can't tell from the diagrams.

I also considered the drive cup itself but the diagram for the diff clearly shows the LH drive cup having a longer shaft than the RH.

Here's a pic of the LH drive cup with the Hex Bushing fitted. Note it's flush so the drive cup is clearly meant for the Hex Bushing I think:

Hey LD! I got your pm. For clarification, what P/N LH pressure disc do you have? To me this really seems as a parts mismatch somewhere rather then an installation issue. Also, are those thorp joints? They look almost chrome.

Yeah, I'm positive I started a thread a couple of years ago where I compared these against a set of Thorp. The Thorps are much greyer, and they didn't have the pinhole on the axle as they used the CRP hubs with the hex screw fitment (why oh why did I sell them ). I've had a look but can't find it, maybe it was a post in an existing thread already, just can't remember. I have a vague idea that we deduced these were CRP items? Either way I know they fit as I had them in my MB before I gave this to my Dad for his birthday one year (he gave me it back last yr as he didn't have time for his BF project).

I noted that Beefmuffin recently bagged himself a full set up so I'm going to drop him a note and see how he's got on.

I have also contemplated using a longer countersunk screw through the actual drive cup itself, along the lines of OldFrogShot's diff mod but I don't think that would work as you wouldn't be able to apply any pressure to the LH side of the diff itself, again denying the point of the diff, so that's out of the window.

As an aside I thought I'd drop in a couple of pics of a gearbox mod that should (theoretically) stop the gearbox plates from moving apart. When I picked up the gearbox this eve to pull it apart it felt really smooth and firm with the counter gear having settled in nicely which was quite pleasing but anyway, the spindle on which the counter gear spins is replaced with an equiv length of ali tube and then the two cups at either end that sit in the gearbox plate are drilled out to 3mm. Then a plastic washer is placed on the gearbox plate fitting just round the raised edge around the outside of the hole where the spindle cups sit. Thread a 3mm hex head screw through with washers either end, secured by a lock nut. Doesn't look too shabby If anyone's interested I can take a pic of the parts and scan the instructions as well:

I think I'll take another pop at fitting it all together tomorrow eve jic.

[blackfoot dave 13]

I've run Thorps for years, looking at your pics it appears those spring washers you are using are way too thick. When adjusted all 4 washers together should have between 1 and 1.5 mm thickness.....they are paper thin washers. Also the adjusting screw should be 17mm length from top to bottom. I have an entire Thorp catalog if you need part #'s.

David

[NJhopper 0]

The LH pressure plate housing is P/N 4583 for Thorp ball diffs P/N 4580 and 4581. Both Fox diffs(different axles) the LH Pressure plate housing for BF thorp ball diffs is 4503. This P/N difference may only be for ordering and such, but without the parts next to each other or measurements from each I don't know. The depth of the pressure plate may differ between the two diffs. Also I am questioning the clearances with those CRP? Outdrives. Without any knowledge on where they came from or measurements to compare to Thorp outdrives I would think about that as well.

[beefmuffin 1156]

yeah i'm 99% sure that's the wrong pressure disc/bearing housing. too long. will post pics of s couple i have and you can see the diff (pun intended!).

[beefmuffin 1156]

here's a pic of a bunch of thorpe parts. notice the length of the bearing housings. the shorter ones are correct for the blackfoot, etc. i'm not sure if the longer ones are for the fox or not but i have both and yours is the wrong one!

notice the super grungy one... oh yeahhh

[Leethal Driver 86]

OK onwards and, er, onwards

I've run Thorps for years, looking at your pics it appears those spring washers you are using are way too thick. When adjusted all 4 washers together should have between 1 and 1.5 mm thickness.....they are paper thin washers. Also the adjusting screw should be 17mm length from top to bottom. I have an entire Thorp catalog if you need part #'s.

David

They're genuine parts and the four come in total around 1mm with a bird's eye view on my trusty ruler, so maybe it's the pic that doesn't make them look so great thanks for the look though. Forgot to measure the screw but I would say 17mm is right (will do it next time I take it to bits just to be on the safe side). I've got both the Fox and BF Thorp manuals, inc the part no's for the BF uni's and dogbones if I need to order anything but will give you a shout if I'm missing a part no, cheers.

yeah i'm 99% sure that's the wrong pressure disc/bearing housing. too long. will post pics of s couple i have and you can see the diff (pun intended!).

Right then, this is where it starts to get confusing.

Here's a pic of my LH Pressure Disc. The well into which the Hex Bushing fits is c.7mm from the rim of the pressure disc itself to the top as it's shown in the pic. Can't really work it out from the manual Ben so if you have a short long knocking about could you measure up?

Now, I thought this was the easiest way to explain my problem (sorry for the pink mark, had to rub out a duff pencil line and the only rubber I could find was a crummy little one in my golf bag) with a cut away side view:

The issue I have is that with the Thrust Bearing in place, the head of the screw at line B prevents the drive cup from slotting fully into the hex bushing so that the bottom of the drive cup sits level with line A. Here's a pic of the diff with the Thrust Bearings and screw in place, you can see how the head of the screw sits prominent in the space where the drive cup sits:

Hopefully that explains it

Here's a pic of my gearbox sans Thrust Bearings, so that the screw head sits in the recess where the Thrust Bearings are positioned, and is therefore level with line A in my diagram:

I'm not sure what difference a shallower LH Pressure Disc would have. Presumably it's still got to be deep enough to fit the Thrust Bearings, Screw and Hex Bushing which would still give me the same problem?

Not sure if that gearbox is the right way round either, I think the LH disc is on the right :lol:

[beefmuffin 1156]

alright let's get to the bottom of it! i'm going to experiment and be back with some results...

[beefmuffin 1156]

ok - well it looks like you actually DO have the correct bearing holder, as i measured one of mine and compared it with a stock diff straight out of a gearbox - to check they were the same overall length (ie, width when installed).

a couple things to note: the head of the adjustment screw should be recessed from the surrounding edges of the housing. you should be able to install the hex bushing without it hitting the screwhead at all.

not another thing, which might be the root of your problem, is that your adjusting screw looked a little long to me. i have thorp adjustment screws with two lengths: 17.5mm (right) and 20mm (too long). i assume the longer screws go with the longer pressure disc - but i guess you have the shorter disc, as you should have. but can you measure your screw?

[matman 1499]

I love trying to find out problems like this .

But with looking at it & playing it is hard to sort out .

So most of us can only sugest things .

But by the looks of it "THE Beefness " can help & doing a great job .

So i hope you can sort it out & would love too know what it was , that has

screwed up this diff .

& WOW!! Beef , you must have some rear parts there .

[blackfoot dave 13]

OK onwards and, er, onwards

They're genuine parts and the four come in total around 1mm with a bird's eye view on my trusty ruler, so maybe it's the pic that doesn't make them look so great thanks for the look though. Forgot to measure the screw but I would say 17mm is right (will do it next time I take it to bits just to be on the safe side). I've got both the Fox and BF Thorp manuals, inc the part no's for the BF uni's and dogbones if I need to order anything but will give you a shout if I'm missing a part no, cheers.

Right then, this is where it starts to get confusing.

Here's a pic of my LH Pressure Disc. The well into which the Hex Bushing fits is c.7mm from the rim of the pressure disc itself to the top as it's shown in the pic. Can't really work it out from the manual Ben so if you have a short long knocking about could you measure up?

Now, I thought this was the easiest way to explain my problem (sorry for the pink mark, had to rub out a duff pencil line and the only rubber I could find was a crummy little one in my golf bag) with a cut away side view:

The issue I have is that with the Thrust Bearing in place, the head of the screw at line B prevents the drive cup from slotting fully into the hex bushing so that the bottom of the drive cup sits level with line A. Here's a pic of the diff with the Thrust Bearings and screw in place, you can see how the head of the screw sits prominent in the space where the drive cup sits:

Hopefully that explains it

Here's a pic of my gearbox sans Thrust Bearings, so that the screw head sits in the recess where the Thrust Bearings are positioned, and is therefore level with line A in my diagram:

I'm not sure what difference a shallower LH Pressure Disc would have. Presumably it's still got to be deep enough to fit the Thrust Bearings, Screw and Hex Bushing which would still give me the same problem?

Not sure if that gearbox is the right way round either, I think the LH disc is on the right :lol:

The Big Beefy guy from NJ is 100% correct, your adjusting screw should fit BELOW the recess that the hex bushing sits on. I don't have a dial-caliper ( I use a metric ruler) but what the Beef posted of 17.5 mm is the right size screw. The only other thing I can think of is to make sure that the RH universal is fully seated in the pressure disc...hex male into the hex female

[beefmuffin 1156]

if it turns out your screw is the too long kind - every man's dream, but sometimes it just won't fit - here's one of the proper ones for sale pretty cheap:

http://www.ebay.com/itm/Thorp-4579-Adjusting-Screw-Kit-4582-Tamiya-Blackfoot-Hot-Shot-Kyosho-Ultima-/251271828898

[Leethal Driver 86]

Keep on truckin!

Screw is the right size, so that's another piece of the equation ruled out:

Here's my LH pressure disc without anything in it, so you can see the recess:

Now, can we look at my diagram - that recess is for the Thurst Bearings/Washers and here's a pic of mine (not got the full 8 balls in, I've...erm..."mislaid" a couple what with all this piddling about but have spares):

Back to my diagram, once these are fitted into the LH Pressure Disc it means that line A is the lowest point at which the bottom of the screw head can sit, so here's a pic of the LH Pressure Disc with the Thrust Bearings/Washers in situ:

Now, having looked at Beefy's pics above I have a couple of questions:

1. Have you got Thrust Bearings in there? Doesn't look like it otherwise hos can the top of the screw be below the top of the recess?

2. If you have then that would suggest that the LH disc you are using is deeper than mine otherwise how the badword does yours fit together?

Here's a couple of final pics without Thrust Bearings and then with Thrust Bearings:

1. Without - universal sits on line A in my diagram:

2. With - universal sits on line B in my diagram:

Still none the wiser although I've just had a horrid thought that mine might already have Thurst Bearings in it and I'm trying to put another set on top . If Beef comes back and says, yes he has Thrust Bearings in his his and the screw is still below top of the recess it's the only thing I can think of. I'll nip out and check now whilst the wife is out shopping.

[Leethal Driver 86]

So, yes, it turns out I've been trying to stick a second set of Thrust Bearings on top of the original set which were caked in grease and just looked like part of the LH Pressure Disc. When I wedged them out the bearings had dried up in a thick residue so they'll be getting replaced whilst the Pressure Disc gets a danm good clean. And at least I now know that every part of my diff is the right one for my BF.

Thanks BF Dave, Beefmuffin and NJ Hopper for comments, much appreciated.

BTW, anyone need a set of Thrust Bearings and Washers? :lol:

[Leethal Driver 86]

And yes, I do feel a bit of a tool for not spotting it earlier

[matman 1499]

HAHA , Well atleast you have worked it out .

That is great news & who would have known

buy the pic's . It looks like it should be & would not

of guest you still had the thrust washers in there .

Good point to look at for some one else , Next time .

So have fun & get it in there & run it .

[beefmuffin 1156]

that is both great and hilarious! glad it's sorted. and i'm sure all the pics in this thread will help others sort out their thorp diff issues as well !

[NJhopper 0]

WHATTTT! No way! I bet you feel a lot happier now? haha. I guess you didn't need the Thrust Bearings you got from me now huh? Are they usable? Spare parts score!!