[SOLVED] TRF511 - Excessive Vibration from Rear Wheels
 

Hi again guys,

Looking to see if anybody has some insight on my problem.

My 511 has recently developed excessive vibration in the rear wheels under power. The best way to explain it is to say it's like the wheels are horribly unbalanced - or the outputs are running in elliptical rather than circular cycles.

The effect is significant, even under weighted load, to the point that it severely affects rear traction. 5 seconds a lap over a 35 second lap to not point too fine a point on it... and on a dead flat astro test surface the rear end hops like a bunny.

It's not that I'm inexperienced, this particular chassis has seen about 150 packs without a problem in the past...

So, first thing I did was check the wheels and swap them out even though they looked and felt fine (no cracked rims either).

Second was to disassemble, check, clean and reinstall the diff. There appeared to be no problems with it.

Finally I've swapped the outdrives (which were reasonably new) with brand new ones and made sure it was all seated properly.

None of this has fixed the problem. So I assumed the uni-shafts were bent (!) but have visually inspected these and also dipped them in gunk and ran them over a blotter sheet to check - they seem true.

Anything else obvious to check? The chassis squares up and the rear-end all seems tight and true... I'm at a bit of a loss here and this is killing me...

Separate question - do those of you using the Tamiya alu front steering assembly Hop-Up notice that the lay-back mounting posts can't be tightened to a "no-slop" config? At max tightness I still get ~0.5mm of play - is this typical?

Thanks!

Wheel/Diff bearings??

Although I haven't swapped this out I did do the 'finger-spin' test when I cleaned/swapped out the diff and wheels and they felt like new...

It's a perfectly valid suggestion though, thank you. I'll put them on a high-speed drill tonight to check.

I hope they're okay... they are good bearings and the thought of replacing them makes me cringe! :cry:

If "feels" like more of an inboard than outboard problem because it's affecting both sides.

Have you checked that the black plastic (K1) parts which hold the diff are the same orientation - both with 'circle' at the bottom???

Worth a look.

Yep, I did this before I removed the diff and then again when I installed it and also after the first new run. I also thought that was the obvious reason - i.e. that I'd put it back together wrong!

I would have been liked to be able to slap myself in the face and move on but it hasn't proved to be that easy! :confused:

I have a feeling this isn't such an obvious problem but I appreciate being able to collect opinions and cross off the likely causes! Thanks.

Have you tried it without tyres and foams fitted? Rotate on the bench etc. I.e. fit new wheels and see what wobble you get on the bench

No actually. I have my own pre-assembled wheel sets ready to swap on.

But that's not a bad idea... although I've now used two different rear-sets.

I can't detect any obvious vibration if I roll the car slowly over a flat surface, but under power on a test bench (no load) and on a test surface (loaded) they're crazy.

Might just rename her "Bunny" and move on lol... not really as I want to solve this.

So I'll test bearings and individual wheel components tonight. I have access to a high speed, high traction and glass-smooth test surface tomorrow and Sunday which is convenient.

balance your wheels

maybe your tires are not glued properly too

Okay, sorry it took so long to come back but I solved the problem.

Hairline fracture in the LR K1 part, never seen it before.

So basically, under stress this part was obviously stretching and flexing in the alu housing (vertically I assume). The fracture is impossible to see when K1 is installed and "just about" impossible to spot when it is removed. Even the bearing still "clips" into place... :eh?:

It was, unsurprisingly in retrospect, causing an imbalance across then entire rear diff.

Now that it's fixed my 511 is rear-end planted as we all want for that extra second.

Thanks for all the suggestions! :thumbsup: