Weakest parts on the Yokomo 834

[Nemotron]

As I'm waiting for my 834 to arrive I started to think about the durability of this car. It looks pretty tough but there is always something that can break on a runner. So my question is this, what is the biggest issue/problem with these cars? What breaks ..


Øyvind Johansen
Norway

[coralguy1]

Where I used to run, the 834b's went through a lot of rear trailing arms. Some of the guys would reinforce them with a graphite, fiberglass, or aluminum plate mounted on the outside. I'm not sure if there was a second plate on the inside.

[Nemotron]

Thanks for your feedback, I thought gears and drivetrain were the weak spots. I saw someone in here(or TC) had a car with had custom alu rear arms. I really thought the plastic parts on the 834 were made from bulletproof Nylon or delrin, but maybe its just cheap plastic

[carloco8]

The gears and drivetrain are actually very strong (32pitch gears are bulletproof), except a lot of drag. Honestly, the entire car, in stock trim, is quite fragile in general. If going to be run, I suggest sticking with a 19t or stock motor.

The Alu. rear arms are Dr. Robotnik's. Not custom, but made by Delta. I believe he is working on a full 834b delta project too.

[coralguy1]

I'm afraid you're going to find that the plastic used on these is not as strong as you had hoped. I found a picture of the rear arm reinforcements I was talking about. I did a google search for Hot Trick Yokomo and saw several of the hop ups that used to be available. Hopefully it will give you an idea about how you can make your own. You'll probably need something a bit thinner than your 3 mm graphite blank. Another problem was in the early slipper clutch. I know the later ones had an improved clutch (like on the RPS SE) but people replaced the early ones with a Delta slipper clutch. You will also find that the shocks are great! (For the Arabs!) You are going to go through some oil. Should be easy enough to find replacement shocks but I don't know where you are going to find a slipper. Maybe someone here can help with that.
Best of luck!

[Mr. ED]

Aku told me the main problem is the stiffness of the rear arms. As I understood they don't break but tend to open up casuing the drive shafts to fall out of the cups. The side plates on the arms help ofcourse, but he also had tiny cables from the arm end to the rear of the chassis. I 've seen these on dr. robotniks pictures also.

I have no experience with the car inquestion , nor do I own one, but going from general experience I would say front arms and front arm mounting points are the parts which suffer a lot on any car.
We all drive forward most of the time and when a car hits something it's usually turning in too tight. When you hit one of the front wheels that's a big lever to and a lot of momentum on those hinge points.
The second largest treat comes from bottoming out on the nose after a jump.

[Nemotron]

Thanks for all you feedback! Too bad that it is such a weak design , I actually thought this was a tough car Haven't received it yet but I think it will be here tomorrow, looking forward to having a closer look at it

[Dr. Robotnik]

Hi mate,

As has been said before the car is really good fun to run(it did win a world championship after all) but they take a little looking after as with all vintage cars. If you follow some precautions and don't drive like a loon you should be fine. Here are some of my tips.

-Make sure to keep the gearbox tightly fastened (possibly silicone seal it) as gear damage normally occurs from gear slippage and ingress of dirt/stones. Also shim the gearbox to reduce gear wobble.

-For the rear arms, as with ALL trailing arm systems they can flex outward if not secured causing the loss of dog-bones and also excessive drive-train wear. This was part of the design and you are meant to zip-tie the arms to the rear bulkhead. This still flexes though so Hot Trick designed a stiffer system using wires. However the best system I have seen is the tie-rod system, this is the stiffest most adjustable system.

I don't have time to find pictures but if you search my name on Tamiyaclub and RC10talk you will find my YZ834B projects.

-The plastic on the early Yokes is quite soft originally but can become brittle over time after cleaning the parts try boiling them to reduce their residual stress.

-Finally keep it clean, grinding dirt on parts wears them out, not a problem with spares available, but they aren't for this car.

Good luck.

Cheers

Ed

P.S. The alloy arm cars are mine, any questions just ask

[Mr. ED]

Hey Ed, sorry but I need to correct:complete your answer a bit

A lot of trailing arm systems were made of casted parts and did not flex outwards at all

Warning: boiling parts to relieve stress is good for new injection molded parts but can also cause the parts to get a different shape then intended. The stress is from the rapid cool down after injection in the mold and yes, stress does make parts more prone to breakage. But when you boil the part it is no longer contained by the mold and takes the shape with least stress = the basic principle used for shrink-tube.
(So the stress does not come by age; actually for some plastics it will diminish by age as the plastic creeps to a stress-free condition).

Still: boiling is a good idea for parts made out of nylon: nylon contains whater and this helps the flexibilty. Nylon parts which are kept in a dry and warm environent for long time dry up. Once the nylon looses the waher it becomes brittle. Boiling for some time will restore the parts flexibility.

[Eccentric]

When I raced my RPS SE car back in 1986-88 I went through more chains and drive sprockets than anything else. Broke a couple of front arms. The rear arm flexing problem wasn't too bad as long as I had the tie straps adjusted correctly. Only lost a dogbone once or twice.