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Hudson

King cab differential help needed

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Hi everyone, having viewed some previous threads it seems that I have a familiar problem: mashed up differential, the parts that I need to replace are 'diff housing A and B' and Differential spur gear. I've already tracked down both diff housings but the only spur gear I can find is for the Astute, the advert states that it's compatible for the King Cab but there are clearly 12 holes for the steel balls instead of 9 for the King Cab. Does this matter and do I simply buy some extra steel balls to make up the 12?? If anyone can help on this I would really appreciate it, the part in question is also rather expensive so if anyone has alternative workable options then I'm definitely listening. Also, in view of avoiding the problem reoccurring any advice on re-assembly is most welcome, I'll be running the King Cab 100% stock as it's for my little boy. Thanks very much for anyone that can help..............

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The diff gear with 12 holes is the Thorp version which is designed only to work with Thorp parts. Unless you have a Thorp diff, it cannot be used. Thorp "Dirt Burners" was a popular aftermarket company based in the US in the 1980's and early 90's and then they went out of business.

There are sellers on eBay with complete sets of replacement aftermarket Thorp gear sets but the prices are absolutely highway robbery. I would not bother unless you are at your wits end.

A couple years ago there was a guy selling Thorp parts for cheap (relatively) because he was the guy that bought the trailer truck of parts from Thorp when they went out of business.

Then that guy sold all of his parts to a few eBay resellers who are now selling parts individually and in sets (cty300, fireboy125, etc.).

If I had known he was going to stop selling individual parts I would have bought more from him because I will not pay those stupid prices now.

Anyway, you are looking for Tamiya 50377 Astute gear set which includes the diff gear with 9 holes that you need (and others you don't).

If you've fried the other internal parts like spring washers, balls, ball races, shims, etc. then you will want to look for Tamiya 53043 Ball Diff Internal Parts.

Be prepared, however, the parts are expensive. Not as much as Thorp, but not cheap either.

As for rebuilding the diff, make sure you are using BALL DIFF GREASE only. Do not use regular grease. Ball diff grease is specially designed to prevent the balls from slipping whereas normal grease is the opposite.

Though you should be able to get away without them when using the stock 540 motor, I would recommend using the two 5mm x 10mm x 0.05mm extremely thin shims if you have them from your diff.

The shims were optional so not everyone built the diff with them and then probably lost the shims in the meantime. The shims are only available in 53043. I've tried sourcing them from other parts places but they wanted about $5 per shim which is crazy.

The bottom line is that the diff destructs because it gets too hot (melting) due to slippage. If the motor spins and the gears move but the tires don't spin, then the diff is slipping and will overheat and die quickly.

The problem with the King Cab is the large wheels and tires compared to the Astute and Madcap, which all share the same gearbox. It is much easier to mess up the diff in the King Cab because the larger tire diameter means less torque hits the ground which means more power is required to overcome friction and spin the tires and the diff is just a bit weak in this chassis. It is a long-understood weakness.

Tell your son to feather the throttle if he will listen and has the dexterity and understanding to do so.

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I locked mine (glued) on my runner as finding the parts was too expensive and my runner Kingcab is not in the best of shape so I figured it wasnt worth it (cracked chassis, homemade bodymounts etc.). Too bad there isnt a gear diff out there that will fit in the Kingcab

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I had similar concerns with my Madcap. I read somewhere (on this site - probably this sub forum) that you could use the Avante Unitized Differential gear set (#50349) instead of the ball diff set-up. These use a planetary gear diff arrangement, rather than balls.

I have got this set, but I also managed to secure the hop-up ball diff (#53043) so have never tried the Avante set.

Perhaps someone else with experience could jump in as to whether this is a suitable alternative or not?

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Thanks for the replies guys, especially Champ 85 for the super informative reply, all the internals are A ok and the shims are present, in fact I seem to have a surplus of these, I think there were 6 of these when I took apart the differential. The diff housings had been bent out of shape from over tightening of the cap screws and the spur gear all fried. So it seems that my best solution is to just keep my eyes peeled for the 50377 Astute gear set.........

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No, you will destroy the gears in minutes. for sure. They fit but better don't do it.

Max

I had similar concerns with my Madcap. I read somewhere (on this site - probably this sub forum) that you could use the Avante Unitized Differential gear set (#50349) instead of the ball diff set-up. These use a planetary gear diff arrangement, rather than balls.

I have got this set, but I also managed to secure the hop-up ball diff (#53043) so have never tried the Avante set.

Perhaps someone else with experience could jump in as to whether this is a suitable alternative or not?

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This is the problem. The diff housing material is too soft and you can add all shims you want but the diff housing will bend everytime you will tight the screws.

The only solution is to make new diff housing with a better material like aluminum alloy. I did it and solved the problem, just a lathe and an alloy bar.

Max

Thanks for the replies guys, especially Champ 85 for the super informative reply, all the internals are A ok and the shims are present, in fact I seem to have a surplus of these, I think there were 6 of these when I took apart the differential. The diff housings had been bent out of shape from over tightening of the cap screws and the spur gear all fried. So it seems that my best solution is to just keep my eyes peeled for the 50377 Astute gear set.........

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Ok so if I re-assemble the diff with new original parts, use plenty of ball diff grease and run it completely stock am I still gonna have problems??

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If you use 2 shims (one on either side to keep the pressure the same on both sides), ball grease and stock motor you should be OK.

But since the diff is a weak item (by design) you could still have problems either immediately or after a few runs.

There is no way to guarantee there will be no problems.

I've got a couple Madcaps with pretty powerful brushed motors (Tamiya BZ 23T and some unknown Fantom motor (maybe a 13T?)) and I built the diffs with 1 shim in either side and I haven't had them die on me yet, even after romping on the trigger and doing some 360 burnouts on pavement. But my cars don't have 2.2 tires so it isn't the same. And most of the time I feather the throttle because I don't want to hurt the diffs. Vintage runners.. ya know... :)

If you have problems again, I'd switch to a different truck that can take more of a beating. The money spent just isn't worth it over and over again.

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For sure yes. You have 75% of possibilities to have problems again.

Hotter the motor, bigger the problems.

Bigger the tires, bigger the problems.

Max

Ok so if I re-assemble the diff with new original parts, use plenty of ball diff grease and run it completely stock am I still gonna have problems??

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By material.


The diff housing are made of pot metal.
Vintage Egress has the same differentials with the same design. You can say that they are not smooth or that they are old design but they work and never slip even with big tires or hot motors because the housing are full aluminum alloy instead of pot metal.
I really don't understand Tamiya some times...
The problem is not vintage or not, the King Cab ball diff never worked, it didn't matter how the model was new or no.

There are several way to solve the problem:

- Modify Egress diff housing (vintage ones obviously)*

- Built by yourself the new reinforced diff housing.

- Swap the entire transmission with a modern one.


*Note: I'm not sure but probably you can modify also the modern Egress ball diff. It should, once modified, fit inside the King Cab transmission.


Max

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I really like my King Cab, I've enjoyed stripping and rebuilding it, I think it looks great and by all accounts they are great fun to drive, so, I am fully committed to continuing with the project and getting the King Cab on the road. I've already accepted that this project is gonna cost me some money (you win some and lose some). I'm now a little put off by the idea of simply replacing the spur gear using the Astute gear set, this involves waiting for one to become available, spending 30 odd quid and then just waiting for the problem to come back, I'm also absolutely not capable of making my own parts. So, based on all the responses I've had I'm left with; replacing the whole differential with a Thorp one if I can find it or afford it, or modifying an Egress differential. I don't want to say that money is no issue but I'd rather fix the problem properly and then have trouble free driving.

So, based on all that I've just said can anyone suggest the correct solution for me. Can anyone elaborate on the 'modifying an Egress diff housing' option?

Thank you to anyone that may reply to this.........

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Hi Hudson,

I own two King Cabs, a King Cab and a Hi-Lux Monster Racer to be precise, and I can advice you about the model.

I agree with you, I believe the King Cab is one of the best and funny truck ever built but it has some structural problems and the worse one is the gearbox that is weak.

You can do many things to solve the problem but probably you will enter into a tunnel of pain and frustration because all parts are weaks.

Please let me explain. The bigger problem is the differential as you can see.

Now you know the solutions to solve the problem that are:

- replace the whole differential with the super rare and expensive Thorpe one

- change the housings with original super rare spares (not solving the problem)

- building the parts, as I wrote, by yourself (you can ask to a machinery workshop, they are easy to do)

- modify the Egress parts (but you will need the machinery workshop)

One of these solutions in some way will solve the problem of the differential (I suggest to building the parts) but the problem will be discharged over another part of the transmission.

With easy you will break the plastic iddle gear support and if you will not be quick to understand that the part is broken you will break the gears. Another time there are some solutions:

- replace the plastic part with the aluminum machined super rare and expensive Thorpe part

- building the part by yourself (machinery workshop).

Once solved also this problem you will have another one that you cannot solve so easly. With a mild motor (I'm speaking about a brushed 23 turns motor) the torque and the power is enough, united with the dust (the gearbox is not perfectly sealed), to wear out the gears and the diff cups very fastly. And if you are unlucky, with a firm differential and a firm iddle gear brace, you will break the gear teeth, for example after a jump, easly the iddle gear of differential gear teeth and there's no solution for this.

Or better, there's a solution:

- replace all transmission gears and cups with the super rare and expensive plastic/metal Thorpe ones.

Substantially with all Thorpe transmission the King Cab should have enough strenght.

This is very hard to do and very expensive, I have a complete Thorpe transmission but I needed years and years to collect all the parts.

I repeat, the best solution is to replace the entire transmission so here you have two solutions:

- A&L Lethal Weapon 2 belt transmission with Slippery Clutch

- Another modern transmission with slippery clutch, better if metric like Traxxas.

I also own the A&L. The part is rough but strong and does the job but I don't suggest it due some minor multiple problems.

- I don't like the belt system but this is s a question of tastes.

- The part is given with lower FRP lower plate but you must do some works like to drill the correct holes in the lower plate (they are wrongs), cut the top of the king Cab chassis and at the end reducing the rear dampers travel because the diff cups are too long and they touch in the shafts. I cutted the diff cups making their width like the Tamiya ones because I didn't want to reduce the damper lenght that is one of the good points of the King Cab.

- You must reverse the motor direction.

- If you need a very high gear ratio you have a problem because the A&L is missing one internal gear due the belt (this is also the reason for the inverted motor rotation) and it misses some reduction on the gear ratio. With the bigger spur gear and the smaller pinion gear you will have the same gear ratio of the original 77T spur gear and a 14T or 15T pinion gears. Not too much considering that the King Cab can mount also 13T and 12T pinion gears.

The A&L is sold like a direct fit but this is not real, you must do many works to adapt it and have some limitations.

For this reason I suggest another modern transmission. The only things you need to know is the diff cups width and their inner diameter. Then you must cut and build a your own lower plate using as template the original one, mount the trasmission and make a brace between the top of the transmission case and the King Cab chassis.

If you solve the problem the King Cab is an extremly strong model, I abused it like crazy and the suspensions, the steering links, the dampers, the chassis are very very strong and don't gives problems.

My two cents.

Max

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Agreed with kontemax on this one - the King Cab was one of those models that was quite poor in its box-stock form, due to that incredibly-undersized differential. The Astute, sharing the same gearbox and even with smaller tires, had problems with it too. If you upgrade to an A&L gearbox, you should have far fewer problems - especially with it being a runner and all.

A slight deviation (which is quite expensive but also all-Tamiya) is to look for the Super Astute TTC Gear Train set. These are rare and pricey, but are more durable as the differential is a gear type. You would be building and swapping an entire gearbox - the gears in that set are 0.5 module where those in the stock gearbox are 0.6 module. It was a unit that was standard on Tamiya's Super Astute (hence the name), and listed as an upgrade for the Astute, King Cab, Hilux Monster Racer, and the Madcap. It is possible to build one from parts, and the frustrating search got a little less aggravating with the elusive gear cover now being produced by aftermarket manufacturers.

It could represent a nice vintage investment for the future even in a runner as you can swap in a more powerful motor - those gearboxes were designed for modified motors and Tamiya's high-performance brushed types. But again, it is expensive and at this point in time less reliable than the A&L, which features new materials and parts.

However, I interpret your original post's "100% stock" stipulation as that only the original factory parts for the King Cab will do. In that case I can offer no solutions, unfortunately.

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I didn't mention the TTC from the Super Astute because I consider it absolutely not adapt for the King Cab.

In fact the TTC, with the clear polycarbonate spur gear cover, is prone to wear out quickly the gears. The gear teeth are smaller, 0.5 module instead of 0.6 of the Astute/King Cab. This make the geartrain more efficient but more weak and this is no good for a heavier car with bigger wheels. The dust that ineluctably enter inside the gearbox from the clear gear cover make the rest.

The TTC has a slippery clutch almost impossible to perfectly set because it has not the clutch spring. Instead of it, infact, there are two cone washers, that are thick no more than 1,5 millimeters. This is the range you have to set up the slippage. You can understand that 1/8 of lock nut rotation is a very little movement to have a simple set up.

At the end TTC has few pinion gears due the strange module. Fortunately the arrival of the Dark Impact allowed more pinion gears to choose but anyway it is always a nice part to have but difficult to use.

TTC does its dirty job and if you clean everything everytime you use the model it can live last long but I strongly believe that Tamiya solved all the problems with the Multi Disc Clutch from Dyna Storm and Dyna Blaster. This geartrain and this clutch are almost bombproof and efficient but collecting al the part is a PITA imho.

I continue to suggest another geartrain.

Max

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I hate to sound so pathetic but I just don't think my skill set, dedication, or bank account is sufficient to put into action the solutions that are being suggested. I guess I was really hoping to hear about a less drastic solution. I actually own 3 King Cabs, one NIB, one mint condition with aftermarket body and decals

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I hate to sound so pathetic but I just don't think my skill set, dedication, or bank account is sufficient to put into action the solutions that are being suggested. I guess I was really hoping to hear about a less drastic solution. I actually own 3 King Cabs, one NIB, one mint condition with aftermarket body and decals

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I hate to sound so pathetic but I just don't think my skill set, dedication, or bank account is sufficient to put into action the solutions that are being suggested. I guess I was really hoping to hear about a less drastic solution. I actually own 3 King Cabs, one NIB, one mint condition with aftermarket body and decals and one would be runner. Perhaps I should keep the first two for their collectibility and sell the third and find a less troublesome truck for my boy to play with........

I know I'm probably starting to sound a little tedious now but is it really not conceivable to run the King Cab in 'out of the box' form without having problems??

Sorry about the two previous incomplete posts, not sure what happened there!!

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In a word: yes. A lot of time has told us that the King Cab, completely stock, is a very poor runner. It is possible to run it 'out of the box,' but not particularly well or reliably. Even the Astute required lots of shims, careful adjustment, and careful driving to keep the same differential intact.

At this point, it would be better to go for a better truck. If you are still wanting a Nissan on a classic buggy chassis: I hear that somebody is making Nissan truck bodies for the Team Associated RC-10 re-release ;)

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I hate to sound so pathetic but I just don't think my skill set, dedication, or bank account is sufficient to put into action the solutions that are being suggested. I guess I was really hoping to hear about a less drastic solution. I actually own 3 King Cabs, one NIB, one mint condition with aftermarket body and decals and one would be runner. Perhaps I should keep the first two for their collectibility and sell the third and find a less troublesome truck for my boy to play with........

I know I'm probably starting to sound a little tedious now but is it really not conceivable to run the King Cab in 'out of the box' form without having problems??

Sorry about the two previous incomplete posts, not sure what happened there!!

Why not have some faith, re-build the diff with standard parts using 2 x shims in each half (if you have them) and see how it goes. Just make sure not to over-tighten the screws that secure the diff halves and use some thread lock so they don't loosen. If you are running a silver can 540 and you drive within the limits of the car, you will surely get some use and enjoyment out of it.

If you've given it your best shot, without being too hard on the car and your re-built diff does fail........then consider retiring it, or selling it and buying a modern runner. That's my two cents. Fix the immediate problem with the standard parts and see how it goes.

Best of luck

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I've tracked down the Thorp ball diff kit in the US or Canada, seems there are 2 options - 32 pitch part no 4960 or 48 pitch part no 4985, both about £100!! Am I mad to entertain the idea of buying either of these?? 32 pitch or 48 pitch the best option? I have a friend in Canada who happens to be coming over soon so I could at least save on delivery and duty.........

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Personally if you can't find a solution with the parts that you already have to hand, then keep it for future spares (in the event you utilise one of your other 2 kits) or sell it.

Spending $100 + shipping on parts for a model thats worth $150 tops is a bit silly

would you spend 2000 euros to fix a 3000 euro 1:1 car ?

The question then is what do you replace it with as a reliable runner ? - buying a used model like a RC10T, and fixing a few issues, could also cost you as much as fixing the KC :rolleyes:

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I agree Percymon but from what I can understand the only way to have trouble free ish running of the King Cab is to do something fairly drastic, either that or ditch the project, it's kind of a lesser of 2 evils situation......

I picked up my NIB King Cab about 2 years ago purely because it was offered to me for a good price, since then I've kept my eyes on most things King Cab related on our favorite auction website, and there's no doubt that the King Cab is a desirable truck, in terms of price. Why do prices remain buoyant for an RC car that is so fundamentally flawed? It's hardly an iconic tamiya, but it looks good I suppose, it hasn't been re-re'd, how many people buying King cabs and King Cab parts are actually running them, is this more of a model to make in to a shelf queen and then watch the price rise, but then there'e plenty of chat on this very forum about what a great runner the King Cab is, but then if it's almost guaranteed to break without very expensive mods..............I'm not sure I understand!!!!!

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Look again - how many of those runners are completely stock, or did not require fine-tuning? If they are driven and last, they were probably driven carefully. Once the gearbox issues are sorted, these trucks actually do perform quite well.

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I always drove my King Cab like an animal. I drove it through 3 meters high jumps (10 feet for imperial measures), I crashed it like crazy, I used it in the skate park with a very big half pipe. Everything done with a modified Dtna Run Stock Motor and 8.4Volts battery that pushed it a lot.

The car survived to everything, the chassis, the arms, the dampers, the wheels, the steering linkages did their dirty job very very well so we can't say that the King Cab is a delicate model.

I finally destroyed the chassis after several and several 5 meter jumps but repaired it.

The King Cab is a pure fun basher and my friends had it also and they used it with the Dyna Run Modiefied motor that is a 13 turns, more and more faster than my Stock one.

I had problems with the transmission, yes, this is the problem but if you solve the problem you will have one of the best and funny model Tamiya ever produced.

http://www.tamiyaclub.com/showroom_model.asp?cid=7881&sid=24

http://www.tamiyaclub.com/showroom_model.asp?cid=16210&sid=24

http://www.tamiyaclub.com/showroom_model.asp?cid=16211&sid=24

Max

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