TA-02S Lancia 037 Rear Differential Problem

[lefmir 3]

Hello Tamiya Club!

I am new member of this forum and I need your help. I've built a TA-02S Lancia 037 about 2 months ago and I have problems with the rear ball differential.

As far as the manual goes, the differential is built correctly and it does its job well, It does not slip. The problem is the right pressure plate, the grooved part that connects the diff to the right cup keeps shearing off. I've sheared 2 so far and the dealer that I got the model from suggested I convert to a gear differential on the rear also and kindly provided me with a discount to do so. I'm awaiting the package.

I use a Torque tuned motor in it, nothing extreme, and a 2s LiIon battery.

What I did do with this model is i've run it on mix grip terrain, on patchy short grass and I sometimes like to punch the throttle mid conver to get the back to kick out.

As far as engineering goes the fault here seems to be that the rear dogbones are at an angle(being the short wheelbase version) and they do not press enough on the inside cup to keep it seated in correctly the diff, it slides a bit out of the diff, it's seated halfway let's say and it keeps rounding off over and over until there is nothing left there. There is no retainer system on the cup(like the XV-01) and this action of sliding out it seems to be it's undoing. And yes, I've included initially 1 o-ring in the drive cup and the last time i've put 2: one on the wheel side, one on the diff side, it still did not matter...  

I do not know if I drive it wrong, if I've built it wrong or if it's an engineering problem. I've contacted Tamiya directly and they said that this is not a known issue.

Does anybody have this issue and even if not, can you tell me if I did anything wrong with the build or driving style maybe?

 

Thank you!

Mircea

[Superluminal 3528]

This isnt you doing anything wrong, Im pretty sure this is a result of the dies/moulds used in casting of the aluminium pressure plates being nearly 30 years old and just not holding the tolerances needed. Theres a couple of ways that it can be slightly improved - you can add a blob of the Tamiya red thread lock to the splines on both sides when you assemble it which will help hold the outdrives into the pressure plates and reduce any movement but isnt permanent enough to not be able to pull them out later. Also instead of the o-ring i find the Tamiya 53577 urethane foam spacer in the cups better as it can be built to a tighter fit with the dog bones but then can compress enough when the suspension raises without binding. You can make your own with some foam sheet and a hole punch.

You could also replace the diff joints with the later Top Force Evo style ones with the machined collar on it which is a better fit into the gear box - part number 19805419 (The TA02 Racing Special had a separate brass collar that fitted over the old style diff joint to do the same thing so Tamiya must have identified there were shortcomings in the original design)

Or If you want to replace it completely you can look out for the TA03 lightweight ball diff assembly 53267 or the 19805420 Top Force Evo diff plates which are CNC machined aluminium and of a much better quality and fit than the original castings.

Fantastic job on the Lancia body, it looks great.

 

 

[WillyChang 1808]

2 hours ago, lefmir said:

this is not a known issue

rubbish, that same diff fits TA01/TA03/M03/FF/FF02/TL01 so we’ve known about the wobbly outdrive splines for about ~30yrs 

Our solution = GLUE IN the outdrives 

Use a rubbery mastic like shoegoo or Tamiya oldskool blue Threadlock in a tube.  Try apply only on the splines. You want it to stay slightly flexible, not set hard/brittle/permanent. (Don’t forget the 1150 bearings )

TA01/2/3 I think you can extract whole diff by opening a hatch so it’s no huge deal opening chassis later. 

Others like the M03 u need to get the outdrives off (well, at least 1) before u can split the chassis spline. That can take a bit more effort but nothing that stronger cuss words can’t fix. 

That diff is not adjustable by its screw anyway, so always snug down the main screw until it bottoms out & locktite it.

[lefmir 3]

Thank you both for the insight, it seems rather poor customer service(and overall product quality) to not admit that some parts are defective or that they have too much tolerance to function as intended. 

I'm going to run the geared diff, because the dealer paid for it and we will see in the future if I may hop-up to another ball diff or pressure plates, but as of now I'm fed up with investing in this chassis.

Here is another photo with the lights, It was an hour job with Tamiya clear yellow and orange lacquer to try to get the correct "incandescent-halogen" tint for the lights. 

I really enjoyed building this model, it's a shame that it was tainted in my mind by this problem. 

 

[WillyChang 1808]

4 hours ago, lefmir said:

It was an hour job with Tamiya clear yellow and orange lacquer to try to get the correct "incandescent-halogen" tint for the lights. 

Could’ve bought “warm white” type LEDs 

[lefmir 3]

1 hour ago, WillyChang said:

Could’ve bought “warm white” type LEDs 

They actually are warm white, but the little gremlins inside my head did not like the colour temperature. 

[lefmir 3]

Just wanted to report back after changing the rear diff to gears.

So all in all it's a bit unbalanced especially if there is little grip on the road(i.e. dried dust) and the rear just shoots out. It does not bother me that much, it feels more like a RWD car but with a bit more control. I want to believe that it's similar to the real car.

At the end of the run, after I got the hang of it it was quite enjoyable and it slided very "scale-ish" in the corners.

On fresh tarmac it's fine, a bit tail happy and it turns sharper. What seems to be the common denominator is that if you shift the weight of the car from one side to the other rapidly you will 100% lose the rear and spin and it did not do that before.

I need a few more runs to have a definite picture. 

[Pylon80 1374]

1 hour ago, lefmir said:

Just wanted to report back after changing the rear diff to gears.

So all in all it's a bit unbalanced especially if there is little grip on the road(i.e. dried dust) and the rear just shoots out. It does not bother me that much, it feels more like a RWD car but with a bit more control. I want to believe that it's similar to the real car.

At the end of the run, after I got the hang of it it was quite enjoyable and it slided very "scale-ish" in the corners.

On fresh tarmac it's fine, a bit tail happy and it turns sharper. What seems to be the common denominator is that if you shift the weight of the car from one side to the other rapidly you will 100% lose the rear and spin and it did not do that before.

I need a few more runs to have a definite picture. 

You can try slowing the diff down a bit with AW grease if you haven't already. It will not last very long, i.e. less and less stiff as you run the car but better then nothing 👍