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Thoughts on the Madcap?

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On 10/4/2016 at 10:03 AM, sqfab said:

Pascal

Madcap_21.jpg

Madcap_23.jpg

Awesome design.  May look at your car for inspiration 

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1 hour ago, Saito2 said:

Traditional ball diffs use an adjusting screw that goes through the center of the diff, adjusting clamp load on the inner balls and thus the "tightness" of differential action. After a few previous attempts at center ball diffs in the Celica, Avante and Vanquish, Tamiya tried their hand at making a new-design ball diff in their new batch of cars, the Astute, Madcap and King Cab. Tamiya, being Tamiya, chose to use varying amounts of shims installed on either side if the diff housing halves to provide adjustment vs the traditional adjusting screw. The benefit would be that the diff would never "loosen up" as there was no adjusting screw to back out/off. The downside was their was a limited range of adjustment.

Unfortunately, Tamiya was very vague about what adjustment did or meant for novices in their instructions. The Madcap calls out no shims for the "standard setting" (whatever that meant) and to add a a pair is necessary. That means nothing to a novice. The Astute, using much the same style diff (different thrust bearing) just says it can be adjusted with more of less spacers. Without proper shims, the diff could slip. The diff's small size and limited balls meant it was not overly tolerant to the heat from slippage. I've seen King Cab diffs (same design) with the centers completely melted out of them due to the added stress of the larger tires. 

So the simple fix would be to add shims, right? No quite. The pot metal alloy diff halves would often bend and distort when tightened down if too many shims were added. Only the Egress (again using a similar shim design), which had superior alloy diff halves proved successful with his design.

If the diff is carefully and properly built with components in decent shape with the proper grease and a reasonable motor, it can be made to work. If the housings are warped, it may be tough to get it to adjust properly.

Intense write up and much appreciated.  I need to find a copy of the instructions (I don’t have at moment) and read up on the assembly. Sounds like I need Egress diff parts to make the diff bulletproof.   Not looking at racing but would like to flog this car around. 

@Kol__ I am not sure if you knew there was a dedicated chat group on the Madcap

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27 minutes ago, Frankster said:

Sounds like I need Egress diff parts to make the diff bulletproof.

Sorry, I should have been more specific. While the original Egress used the same internal shimmed design, the outer diff halves/housings are different than the Astute/Madcap/King Cab ones.

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20220710_110055

It might be tough to see, but here's a pic of an overtightened/warped diff housing I pulled from a Madcap that had too many shims installed. In the background is a diff gear with the center melted out from overheating. There should be about 9 little holes for diff balls in there. not one big one I can poke my finger through, lol.

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1 hour ago, Frankster said:


@Kol__ I am not sure if you knew there was a dedicated chat group on the Madcap

NiceB)

I have spare metal motor mount from the Astute (used) and spare new original sticker set if you're interested mate.

The manual is available on here, depends how you like working from a pdf or print out?

https://www.tamiyaclub.com/manuals.asp?cm=396

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16 minutes ago, Saito2 said:

20220710_110055

It might be tough to see, but here's a pic of an overtightened/warped diff housing I pulled from a Madcap that had too many shims installed. In the background is a diff gear with the center melted out from overheating. There should be about 9 little holes for diff balls in there. not one big one I can poke my finger through, lol.

Thanks. All new to me.    I am sure my brother build this stock and to spec back in the day.  Will need to find time to take it apart later on when I get a chance.  
 

Thanks for all the advice!   May need to follow up with this group for support later 😊

 

I check the Tamiya website and there are no PDF instructions for the Madcap.  Anyone have a link handy they can share from a reliable resource?

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16 minutes ago, Kol__ said:

NiceB)

I have spare metal motor mount from the Astute (used) and spare new original sticker set if you're interested mate.

The manual is available on here, depends how you like working from a pdf or print out?

https://www.tamiyaclub.com/manuals.asp?cm=396

Thanks.  Reading these messages backwards and see you attached link to manual. 🙏

I would be glad to purchase the metal motor mount if you are selling 🤗

For the look, I was considering what @Madcap74 did and order custom MCI decals for a black and silver look.   Stuck between stock decals or MCI options  

https://www.tamiyaclub.com/showroom_model.asp?cid=127186&id=39595

image.thumb.jpeg.6dfaff627ecb16af449ceaf510543a8f.jpegimage.thumb.jpeg.cdfbda4b9bd7f746b2ef73dbc1edc628.jpeg
 

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Yeah the silver/grey and black thing can be a good look. I picked up a gun metal grey shell and did similar, but then went grey and yellow instead:)

She still ain't finished yet and quite a few changes since my last post on there, need to do an update.

PM me re the motor mount

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54 minutes ago, Frankster said:

I check the Tamiya website and there are no PDF instructions for the Madcap.  Anyone have a link handy they can share from a reliable resource?

Check this site: Tamiya Manuals

You can search with the Kit-No or with the name, but with the name it‘s a little bit tricky.

Regarding ball diff. A guy replaced his King Cab diff against the diff from a Super Astute (Re-Re). The main gear has one tooth less than the King Cab/Astute/Mad Cab gear, but this was negligible.

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44 minutes ago, Sgt.Speirs said:

Check this site: Tamiya Manuals

You can search with the Kit-No or with the name, but with the name it‘s a little bit tricky.

Regarding ball diff. A guy replaced his King Cab diff against the diff from a Super Astute (Re-Re). The main gear has one tooth less than the King Cab/Astute/Mad Cab gear, but this was negligible.

Nice. I have been looking at the Tamiya US website for manuals.  

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6 hours ago, Kol__ said:

She still ain't finished yet and quite a few changes since my last post on there, need to do an update.

PM me re the motor mount

On the flip-side, my Madcap is finished. But it's also now more Super Astute than a Madcap - suspension arms, uprights, bumpers and shell might be all that's left...

y4m5MHunbxd8VTmECMKE0rv_NFjsyxBnJ_XzBGfM

 

 But seeing as I need the front shocks for an Avante build, it's got one additional upgrade to go: long front shocks from a discount Top-Force purchase. Eventually I'll have to do a pitch change on the pinion and spur, because 0.5 mod parts are simply unavailable, but it's not run that often and the motor's not that hot for me to worry about it just yet.

Just to warn you - my build started from my OG complete Madcap, except for a missing counter gear and a worn ball diff.

Looks like I ought to do the Showroom thing before I break it.

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On 7/10/2022 at 2:37 PM, Saito2 said:

Unfortunately, Tamiya was very vague about what adjustment did or meant for novices in their instructions. The Madcap calls out no shims for the "standard setting" (whatever that meant) and to add a a pair is necessary. That means nothing to a novice. The Astute, using much the same style diff (different thrust bearing) just says it can be adjusted with more of less spacers. Without proper shims, the diff could slip. The diff's small size and limited balls meant it was not overly tolerant to the heat from slippage. I've seen King Cab diffs (same design) with the centers completely melted out of them due to the added stress of the larger tires.

Some excellent information in this thread. Thanks guys!

One question remains...

@Saito2, and all others ofcourse, I am a novice with NOS Madcap diff parts, metal motor mount and bearings and I would like to try building a diff and running it in a Madcap powered by a silver can.

Is it possible to say with how many shims I should start? Or does it depend?

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40 minutes ago, bavee said:

Some excellent information in this thread. Thanks guys!

One question remains...

@Saito2, and all others ofcourse, I am a novice with NOS Madcap diff parts, metal motor mount and bearings and I would like to try building a diff and running it in a Madcap powered by a silver can.

Is it possible to say with how many shims I should start? Or does it depend?

Others may advise differently, but I'd say build it box stock without shims, nip up the 3x diff case screws to the point that they stop turning with a medium pressure on the turn of the wrist (using the long end of the allen/hex key in the screw, not the short end). Then running it gently with a silver can, you should be ok mate. And by gently I don't mean don't run it fast or crash it etc., what I mean is don't do a million donuts or any burnouts or get it stuck in a pile of leaves or something and let it sit there spinning a wheel at full throttle trying to get it's self free😉

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3 hours ago, bavee said:

Is it possible to say with how many shims I should start? Or does it depend?

It could depend on how worn your parts are. Also, if the diff housing has started to warp and bend, it won't be of much use anyway. I would go with Kol's suggestion of building it box-stock first, drawing the 3 diff case screws up tight (they are not there for adjustment). Before putting the assembled diff into the gearbox, put it on the bench with the diff outdrives/cups installed. Place something in the slots of each outdrive like an allen/hex key. These will be braced against the bench to keep the outdrives from turning. Grab the diff gear between your fingers and try to spin it with finger pressure. This will simulate slippage. If you can turn the gear by hand without tremendous force, add some shims. 

When testing the buggy. give it a launch on a reasonably high traction surface. If the hear the motor rev up with comparatively less movement than would be expected from the buggy, the diff is probably slipping and needs more shims. Again, don't go crazy on the amount of shims because at some point the diff housing will just start to deform and the diff won't get tight no matter how many shims are installed.

Egress Diff Assembly - General discussions - Tamiyaclub.com

Here's a picture of what I was describing about placing things (hex keys) in the outdrive slots from the re-re Egress manual. Disregard the part about how the diff pictured is adjusted as the new Egress uses a more standard diff screw adjustment method. Just try shimming it until the "differential spur gear no longer moves freely" as the literature suggest.

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12 minutes ago, Saito2 said:

Before putting the assembled diff into the gearbox, put it on the bench with the diff outdrives/cups installed. Place something in the slots of each outdrive like an allen/hex key. These will be braced against the bench to keep the outdrives from turning. Grab the diff gear between your fingers and try to spin it with finger pressure. This will simulate slippage. If you can turn the gear by hand without tremendous force, add some shims. 

Having just put my Top Force EVO ball diffs together a few days ago, I followed the very same instructions as in the Top Force manual. I'm not sure they describe it that clearly. I kept slowly tightening the diff until I physically could not longer move it with my finger and thumb, whilst holding the outdrives still in my hands. You reckon that's correct?

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Thanks @Kol__ and @Saito2! So with box-stock you both mean, in case of the Madcap, no shims and proceed from there? Even as the Astute manual says to use two shims?

Parts are brand new.

Just trying to make sure I do understand the both of you ;).

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34 minutes ago, Kol__ said:

Having just put my Top Force EVO ball diffs together a few days ago, I followed the very same instructions as in the Top Force manual. I'm not sure they describe it that clearly. I kept slowly tightening the diff until I physically could not longer move it with my finger and thumb, whilst holding the outdrives still in my hands. You reckon that's correct?

The Top Force and Top Force Evo diffs are each adjusted differently. The standard TF uses the old Manta Ray hop-up ball diff IIRC. At any rate, the TF diff isn't really adjustable going by the manual. Tamiya just tells you to screw the adjusting screw all the way down  or as the manual states "fully screw in using box wrench". The Evo manual says to screw the adjusting screw in until the diff gear no longer moves freely and not to over tighten it and "hinder movement". The Evo diff is actually considered adjustable. 

 

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20 minutes ago, bavee said:

hanks @Kol__ and @Saito2! So with box-stock you both mean, in case of the Madcap, no shims and proceed from there? Even as the Astute manual says to use two shims?

Parts are brand new.

Just trying to make sure I do understand the both of you ;)

Seeing as the only difference between the two diffs is the Astute has the upgraded one-piece thrust bearing, I would figure it would be safe to try either no shims, for the Madcap's standard setting, (although the Madcap's manual shows the shim pictured in the assembly diagram, just with a star note about not being used in the standard setting) or the Astute's pair of shims. Both buggies were 540 silvercan powered out of the box. I can only guess Tamiya expected more powerful motors might be sooner installed in the more-competitive oriented Astute and opted to start with two shims vs the entry-level Madcap. As long as you don't get slippage with the bench test. Sorry if this sounds vague but ball diff adjustment can be very much a "feel" type of thing.

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37 minutes ago, Saito2 said:

The Evo manual says to screw the adjusting screw in until the diff gear no longer moves freely and not to over tighten it and "hinder movement". The Evo diff is actually considered adjustable. 

Cheers mate👍 I suppose my concern is the word 'freely', and what exactly does that mean? That the diff gear mustn't be able to move at all by hand whilst the drive cups are held still? I assume that is what it means.

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1 hour ago, Kol__ said:

Cheers mate👍 I suppose my concern is the word 'freely', and what exactly does that mean? That the diff gear mustn't be able to move at all by hand whilst the drive cups are held still? I assume that is what it means.

I think the directions are a bit ambiguous but I kinda agree with how you read it. 

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Thank you both! I will start with no shims and will do the bench test to get some feeling for it. Never done a ball diff before...

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On 1/4/2023 at 12:08 AM, Kol__ said:

Cheers mate👍 I suppose my concern is the word 'freely', and what exactly does that mean? That the diff gear mustn't be able to move at all by hand whilst the drive cups are held still? I assume that is what it means.

Off topic for the Madcap, but I tried building my TFE so it didn't move "freely", whatever that means. I allowed it to still turn by hand. That was nowhere near tight enough and it definitely slipped on the first or second run. Then I tightened it just enough so I couldn't turn it by hand and now is great.

If it helps, I'm thoroughly disappointed by the performance of the stock motor inthe TFE. Much happier having gone 13.5T brushless.

Back to talk about the Madcap - box stock and nicely tightened up is the answer, per Kol's suggestion. But then I never ran anything stronger than a 27T motor in it and still melted the diff...

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2 hours ago, naturbo2000 said:

I tried building my TFE so it didn't move "freely", whatever that means. I allowed it to still turn by hand. That was nowhere near tight enough and it definitely slipped on the first or second run. Then I tightened it just enough so I couldn't turn it by hand and now is great.

Ah nice one, thanks mate, that's good to know. And yeah I think I'll go brushless too on my converted runner TF👍

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I rebuilt a Madcap nearly 10 years ago now, I managed to find a brand new rebuild kit for the diff, it was rebuilt and with a 27 turn stock race motor it runs great, 

My opinion is that a Madcap drives very similar to an Astute, I am lucky enough to own both,

‘Decals are available from MCI in Canada, 

I would finish the build , they are a lovely car

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Some random shots of my first Madcap in action, about 22 years ago. We were both younger then...

MC1 MC2 MC3

 

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