Chirping XX4

markwilliamson2001 · #1 11-06-2007

Hey guys,

took my car down for a shakedown test at the weekend. Ran the car with a brushless in it, but I could not make it stop making chirping noises under hard acceleration and generally while running.

I checked out both the rear diff and slipper clutch as per the manual, setting them correctly, so that the slipper clutch went before the diff, and that the diff was tight enough. This didnt seem to cure the problem, so I thought it must be the rear belt. I then proceded to change the rear belt tension from A forwards to B forwards, as I thought the rear belt might be slipping...

Come the final, the car sounded awful. When I got home I found that the front layshaft had a lot of slop front and back to the point where the motor mesh was none existent.

Could this be the problem and if so, it seems like I need a new chassis or car because I single part will not sort this, because the main chassis molding holds the bearing for the front layshaft.

Any other ideas?

Mark

Southwell · #2 11-06-2007

You sure the layshaft isn't bent?

markwilliamson2001 · #3 11-06-2007

No its not bent, there is a lot of slop on the slipper side where the bearing rests in the chassis. You can move it when the top cover is on for the side/rear belt and the front belt. It seemed loose when I was rebuilding the car after I bought it 2nd hand.

Thanks
Mark

Southwell · #4 11-06-2007

Did you take it apart and rebuild it when you got it? Might be something missing, i haven't heard of dodgy chassis on the part.

super__dan · #5 11-06-2007

I had this when I bought an old XX4 and ran it before converting to the X5. I bodged it by super gluing a peice of card onto the top deck(?) bearing face to remove some of the play. It really was a pain and I wasn't happy with the bodge but it was either the chassis or top deck, or both which is big £££. It did work though I only ever ran it for 3 meetings before converting so not sure how long it would last.

markwilliamson2001 · #6 11-06-2007

Yeah, big bucks for a new car/chassis, but I am tempted by a new car, then I would have a whole car for spare parts....

I did rebuild the entire transmission and everything seemed to run true and freely, apart from this slip around the front bearing on the front layshaft.

Thanks guys

Mark

Fiddybux · #7 11-06-2007

Forgive my ignorance...but might this be a cogging issue with the brushless? You're not running a sensored motor with a sensorless ESC (or vice versa) are you?

I might be wrong about any or all of this - just thought I'd try and help.

_sleigh_ · #8 11-06-2007

I suspect you've check this Mark, but it's not just a collapsed bearing??

If you're at the 2WD regional this weekend at Kiddy, I'll have a look if that helps.

Southwell · #9 11-06-2007

Alec Springer had a similar problem with his brushless yesterday, turned out to be a dodgy motor. Seemed like a bearing failure.

super__dan · #10 11-06-2007

I'd agree with motor except there is apparent play in the alipper shaft, so short of a collapsed bearing, it must be worn(?) or incorrectly fitting mouldings. To be honest, having the two sections of the bearing on 2 different parts is not a blinding idea, same on front diff bearing but they are bigger so the window of error (% wise) is smaller IMHO.

markwilliamson2001 · #11 12-06-2007

Yes the bearing has not collapsed, and their is severe wear around where the bearing seats on the right hand side of the car (Slipper shaft end) which is causing the slop. I think it is just worn and the torque from the motor is 'spinning' the spur gear away from it, and unmeshing the motor. I will try running the motor unmeshed to see if I can recreate the noise, although it sounds like a combination of belts & gears to me. I am also running a sensored novak motor with the gtb speedo which I bought as a pack. I hope that this is okay. The cells also had very little left in them [(3700's) 300mAh] after a 5 minute run. I also think that because the slipper shaft is loose it is causing the tension of the middle belt to loosen and tighten, which could be the belt noise I can hear...

Thanks guys,
Mark

markwilliamson2001 · #12 13-06-2007

Took the car apart yesterday to check out the problem...

Found that the slipper shaft was straight and true, so I don't think it is this. Checked for slop around the slipper shaft spur bearing with the gear top off and the movement around the bearing was quite bad. This affected the belt tension on the middle belt a lot, and their were black marks on the back of the belt (non-toothed side). Around the bearing holder, the plastic had 'splayed' out creating some 'flash'. This was obviously the slop.

The spur was also in bad shape and the teeth looked 'flattened' on the top. Inside the tunnel under the spur gear, extra plastic from the chassis had been worn away. Overall I think this is bad design on Losi's part. The front slipper shaft should have 3 bearings on it to support it properly There is . The bearings should also fit in housings which can wear, then be replaced as per the rear layshaft, rather than buying a new chassis as is my case!!!

Thanks guys
Mark