XRAY - Model racing cars

Take a close look at your front drive shaft while turning the wheels by hand. bet you the shaft in not eccentric and you will probably see a shiny spot at the outer most deflection of the shaft where its hitting the brace causing damage to the front bearing. dremel the brace a little and this will also aid in preserving the bearings. And stop bashing your buggy, that's what monster trucks are for! Or Losi's

Would dremeling the front brace weaken the brace at the relief point and allow even more chassis flex? Or would you just barley touch it? I'll probably try that mod with a new brace.

Here are my opinions on this subject.

I don't exactly know how the Front bearings would wear or break first, especially the outer bearing. The front end has the servo saver assembly which is pretty rigid, and the chassis brace has a 3mm gap in between in and the center diff, which leaves little to no room for the amount of longitudinal flex that would put access stress on the input shaft bearings. I also think the angle's effect on the the bearing wear is negligible as it is a bearing and it is constantly rotating as and the only thing that would get a /constant/ force is the outer race that sits in the bulkhead. The best thing to do here is get a high quality, high temp grease to lube this bearing. On the chassis flex issue, I don't know where casing a jump would hurt a car too much, as this will only cause the car/drivetrain to 'spread out'. (Casing is a motocross term where they land in shut a way where the engine 'CASE' will hit first on the peak of the landing jump.) The only thing I could see is lawn darting, but I don't think the chassis is flexing enough to do this. The last club race I ran, there is a MASSIVE double in the back that you have to hit full punch, I couldn't seem to clear it 9 times out of 10, so I lawn darted pretty much eevveerryy lap [tex1 knows which jump I'm talking about], and had zero issues, so I'm not sure what I'm doing right or wrong to get life out of these on my production and prototype cars.

As far as the inner bearing goes, 1/2 of a turn will not make this bearing more prone to wearing the diff case out. 1/2 a turn nets 0.2mm of additional clearance. The amount of play that's molded into the bulkhead is ~0.3mm, with the additional 0.2mm (1/2 a turn out on each screw) is ~0.5mm of play. With 4mm wide bearings this leaves 95% of the outer race of the bearing still in contact with the diff case. Furthermore, due to the angle at which the gears are cut, they will naturally force themselves apart on part power, which may explain the stress on the outer bearing.

I have several races/gallons on my car, and this is how things are wearing:
First two pics are of the front drive shaft and where it sits in the diff cup neither of which have one spot of wear.
The last two pics are of the rear in the same area as the front with just a very small amount of visible wear.

I only have one question.

Underground, please explain the process by which you clean your car.

I'm not trying to tell you, you're wrong, I'm just trying to work through it logically, and use my thousands of dollars of engineering classes, haha!

Tex - We make a turnbuckle type brace for the front end (352090) but that is something I've always wanted to rig up and test for the rear.

- Yes, during cleaning the possibility of getting dirt in the outer bearing is much greater, and that may be part of the issue. However, I have cleaned may buggy's the same way for years without issue, so it cant be the only reason this is happening to me and others.
- By casing a jump I mean nosing or darting, yes casing half way over would cause the pull apart effect. I too darted and cased jumps without issue, until about 3 gallons of fuel passed through my 808. Then issues began to arise. Like I said before, its happening more often as I put more fuel on the chassis. I believe you don't have these issue's, but many others are and thats why I'm working to get Xray to just take a look at the possibility of this being the problem. I am not bagging.

On your pics... I believe you have proven that the shaft ball end and pin has touched the back of the cup. While the wear is very minimal in your pics, it only takes a touch to use up the .5mm play set by the bearing retainer screws.
New shaft end (technically this ball end should never touch the base of the cup and remain as seen below when new):


Your shaft end:


Your drive cup showing that the pin has hit bottom also:


My quick not-to-scale drawing of what I think is happening (sorry no time to Autocad this):


While its crude, this may show what I'm talking about better. If you have time, take your gear and shaft with bearings installed and hold the bearings while putting pressure on the end of the shaft mimicking the shaft angle. You will notice the outer bearing receives more pressure due to its angle. I don't believe because the bearing is rotating that it makes the pressure at that point "negligible".

Although you could be onto something about the gears being cut/angled and forcing apart. Hmmm...

Simply put the shaft is plenty long enough to shorten by 2mm or so without worrying that it will pop out. I still believe this re-sizing the shaft will truly help resolve some of the issue. I'm also keeping a close eye on my chassis brace for wear, as that could also be an issue.

How do you clean your car? Please let me know what you use and how you do it. This may be an issue, because it's something I noticed. The dust guard on the bulkhead that covers the outer bearing will retain any oil/water/dust that my get in there and this will cause the premature wear on the bearings and the diff case to get worn out, especially if they cease or impede the rotation of the shaft. It is for this reason I have always said to only clean your car without any kind of fluids, as this will force debris that normally wouldn't be in small areas, in small areas (like behind the diff case that holds the 13x19 bearings). Any fluid, even water and especially WD-40, will force debris in these bearings along with degreasing the bearings, which will accelerate part failures.

If you go back and read my post, you can see that it is the rear that has touched, the fronts look brand new still, and I did take note of this, not trying 'skate' around anything.

I also understand what you are saying about the angle of the dangle in the shaft not being in proportion with the heat of the beat, but this is a constant drive joint, just like on your independent suspension car, and should perfectly translate rotation within a certain range of angles without binding which would. But as you could see there is not a spot of wear on my front drive shafts, and trust me, I fool around on the track, wreck, lawn dart, etc, as much as everybody!

Like I said before I am just trying to understand the part failure, as I do not enjoy my customers not finishing races! But I don't know if shortening the drive shafts is the problem solver. I think it may be a mix of things, because I don't necessarily trust the dust shields and diff case design, but I guess, I will have to spend a weekend running gallons and gallons of fuel to see if I get any failures in stock form, but so far so good.

For those you that like to skim through the posts PLEASE READ THE FOLLOWING!!!

BE SURE TO CLEAN YOUR CARS USING DRY METHODS AS ANY LIQUID CAN WASH OUT THE GREASE AND/OR GET MORE DEBRIS IN YOUR BEARINGS THAN WHEN YOU STARTED!!!

Ohh... you are going to kill me....

For the first 15 times I ran this buggy I was so proud of my new kit, that I soaked the heck out of it every time I ran it with WD-40. Absolutely dripping wet with WD-40 I also had not one failure during my way too clean phase with the new 808.

After I let it go a few times with no cleaning at all, is when the first bearings disintegrated. After the first time that happened I quit using WD-40 at all, with the same results as explained above. In fact I have not cleaned my car at all in the past 1/2 gallon of run time. I will not clean it until it fails again.. (if it fails again), to see if your on to something here. I do agree with what you are saying about liquids taking debris into the bearings and such. I'll let you know. So right now I'm testing my mod, and the non-liquid cleaning method. Fingers crossed...X

P.S. The rear shaft shouldn't be hitting the bottom of the cup either. We have already heard of a failure in the rear also.

WD-40 is the WORST thing to use near bearings, haha!!!

Rocco, you stated you are going to test the the car in stock form, what are you usually using in relation to bearings and dust shields? have you taken the shields off and running the bigger bearings.

Stock form meaning, without dremeling the driveshaft ends and diff cups etc. But I'll always run the dust shields. I have been thinking about taking them off of the center diff because those bearings see the most abuse and highest RPM's.