Rear End / Drive Train noises

[BB767]

OK, I might be overly sensitive, but thought I would "ask the experts" here on the forum.

First Item;

First go kart last week, 2 miles, no problem. Second go kart this week, after about 3 miles the rear end started making an intermittent whining sound, sometime so strong it would set up a vibration in the aluminum panels. I still have the tunnel top and the upper trunk uncovered so I can hear things there really well. Noise is mostly during acceleration but some under deceleration (coasting in gear) at any speed. Put the car back up on stands and checked everything thoroughly, no indication of what it might be. Another drive, the noise doesn't start again until after about 3 miles or so. This time I keep going waiting for it to either get worse or better. After another 5 miles the sound starts getting a little weaker and a little more intermittent. That is where I ended the day. Any thoughts? Is this normal break in noise? If not, what to look for?

I was doing starts and stops as in normal city driving as recommended in the break in literature for the rear end, transmission, and brakes. Never exceeded 40 MPH or third gear. Noise was there in any gear. Rear end is 8.8 Moser, 3.55 LS as supplied by FFR. Have 80W90 gear oil as recommended as well as the required amount of limited slip additive. Total mileage on the car now is 14.

One other oddity when I got the car back up on the stands. After the rear end was first installed, if I would rotate one rear wheel, by hand, the other rear wheel would rotate in the same direction, as LS should do. Now when I rotate the right wheel this still happens but when I rotate the left rear wheel the right one does nothing. Is this normal?

Second Item;

There is a noticeable single "clunk" somewhere in the drive train whenever transitioning from coasting in gear to acceleration and again when the throttle is released. This only happens under moderate or greater throttle application. Slow smooth throttle pressure and everything is quiet. It sounds like it would if the rear axle were rotating (as in a loose control arm with to much play) back and forth. A through check and everything any where near the rear end is tight (control bars, shocks, wheels, frame bolts, transmission bolts, etc.) so the sound must be internal. Is this normal? If not, what should I look for?

TKO600 with correct amount of fluid, FFR driveshaft, above described Moser rear end. Only a small (normal) amount of play in the drive train from the output shaft to the wheels is present (can rotate the wheels freely about 1 inch).

Thanks in advance for sharing your experience.

[edwardb]

Sounds like something is broken or not right in your diff. LS should work the same on both sides. Move the tire/wheel on one side, the other moves the same way. The 1-inch of free play you're describing is pretty normal. Noises will always be amplified with the body off. Probably you don't have carpet, etc. It will sound different once it's done, body on, everything installed, etc. But what's happening to you doesn't sound normal at all. I'd pop the back cover off the diff and see what's happening in there. Even though I would hope it's under warranty, I'd still want to take a peek before taking off the car and shipping.

[GFX2043mtu]

Clunk or vibration can be a drive shaft issue. Check that out and make sure it is tight as from the tail shaft of the transmission, both u-joints and the bolted rear flange. Also when turning the right wheel does the drive shaft turn and not the left wheel? If so put the car in gear and try it again. My first thought is your left brake is sticking (possibly a mis adjusted parking brake) a little bit. Causing your intermittent driving noise. Gear sets usually wine or they don’t as the gear meshing is fixed when they are set up.

[BB767]

Thanks Edward. When double checking to answer the second reply I turned the left rear back and forth a few times and the right one started to follow it, in the correct direction, but not at the same RPM, it was turning slower than the left when rotated forward. The car has cooled down since I last messed with it. Does the fact that is responds differently when cool as compared to warm change anything?

GFX, as I wrote before, I checked every thing from the transmission tail shaft aft, all tight. Also as indicated above, when turning the right rear wheel by hand with the car on jack stands the left rear wheel turns the same direction, at the same RPM, as the right one is turned. The driveshaft turns when either wheel is turned. I am not strong enough to turn either wheel with the car in gear. You may be on to something though. Perhaps the RIGHT rear wheel brake is dragging a little? Only thing is, I cannot feel any difference in effort necessary to turn either wheel so unless an imperceptible difference in drag on it could cause the problem I don't think that is it either.

[edwardb]

Thanks Edward. When double checking to answer the second reply I turned the left rear back and forth a few times and the right one started to follow it, in the correct direction, but not at the same RPM, it was turning slower than the left when rotated forward. The car has cooled down since I last messed with it. Does the fact that is responds differently when cool as compared to warm change anything?

Thought about this some more since my first response. Trying to think what might break inside the diff that would cause it to act like you're describing, and not coming up with anything. If something were catastrophically broken, I think it would act differently. Sounds like what you're describing, and this comment about it acting differently whether cool or warm, suggests (to me anyway) your clutch packs aren't working properly. Either assembled improperly (e.g. not stacked properly, not shimmed properly, etc.) or maybe they're worn? It hasn't happened to me personally, but apparently they can make a lot of noise when not working right. You did say you have the friction modifier? Was this a rebuilt diff? Maybe a call to Factory Five and/or Moser is the way to go as a first step.

No, I doubt you would be able to turn the back wheels with it in gear. Unless you have the clutch down. When testing the diff with the rear wheels elevated it should be in neutral. In all cases, the driveshaft should move along with the rear wheels.

[CraigS]

Can you get someone to ride w/ you w/ a 3 foot piece of heater hose. Hold one end against the ear and move the other end near the trans, the diff, and each rear brake. This may help narrow the source of the sound. I am leaning toward a brake noise. The clutches in the diff only come into use when the car is turning and I 'think' you are hearing the noise in a straight line right?

[edwardb]

The clutches in the diff only come into use when the car is turning and I 'think' you are hearing the noise in a straight line right?

Agreed, assuming they are working and locking up properly. The odd behavior when testing (other wheel not moving, or at a different speed) said diff clutches to me. But agree a dragging rear brake could be a culprit as well. That aligns better with the different behavior whether warm or cool.

[jlfernan]

I'm assuming he has a 3 link. Pinion angle? After my first few miles go-karting my suspension settled almost an inch. Pinion angle was way off and the "banana arm" was hitting the panhard bar frame, causing a clunking sound.

[phileas_fogg]

An IR Thermometer (https://smile.amazon.com/Infrared-Thermometer-Pancellent-Non-contact-Temperature/dp/B072BN7995/ref=gbps_tit_m-7_e196_dea691e4?smid=A3BQ31VG0PY7J4&pf_rd_p=883cd3ec-1a7e-4e37-b01d-279d873ae196&pf_rd_s=merchandised-search-7&pf_rd_t=101&pf_rd_i=5550343011&pf_rd_m=ATVPDKIKX0DER&pf_rd_r=Y8EGZ3HPGKPBXY3MBAT6) can help you determine if a brake is dragging.


John

[NAZ]

Always hard to diagnose problems through a forum but here's my first thoughts:

A wining noise that changes when under load and sometimes when coasting is typically gear mesh. If you can change the intensity with the throttle (louder under acceleration or engine braking) that's typical. As stated above, these noises will be more audible when in an open vehicle with no body or other noise damping materials to muffle the sound. Whether it's a problem is probably best assessed by an experienced ear as there will typically be some noise from gears meshing. The noise may lessen over time as the gear faces wear in and then again at some point in its life it will start to come back as the gears wear beyond their serviceable limit.

The clunking sound when transitioning from acceleration to coasting is usually caused by gear backlash. There will typically be some clunking on a properly set-up rear end so again, determining if this is 'bad" or not is best assessed by an experienced mechanic. If the backlash is not set-up properly you will have some loud clunking. This will never get better with time as it is a result of the space between the teeth of the meshing pinion and ring gears. This clunking will get worse as the teeth wear.

As for the vibration, if it happens mostly under load (accelerating and or engine breaking) my fist suspect is an out of phase vibration of the u-joints due to incorrect pinion angle. This is the easiest to check for and fix. For the wining and clunking you have to pull the rear cover and check the gear set-up and while not rocket science is usually beyond the skill of most folks. If you check YouTube there are probably videos of how to set-up a rear end that will show you how to paint the teeth and look for a proper engagement pattern and how to use a dial indicator to check backlash. If you find the set-up is out of spec you are probably better off taking it to a shop who is experienced with this type of repair.

[Gromit]

google how to test limited slip differential break away

using a torque wrench you should be able to get an idea if the clutch pack is working correctly. Since you are not looking for the exact break away torque you can just go off a lug nut.

It's a pretty simple test. Trans in neutral, parking brake off, Chock the front tires, jack up 1 wheel. and see how much torque it takes to spin the wheel in the air. I would be suspicious if it turned with less than 40 ft lbs

Chris

[BB767]

Thanks for all the great input! Just got off the phone with Moser. First, the wheel spin thing is not abnormal, he says a lot are like this. Second, that whine noise may be normal break in wear. His recommendation is to get 500 miles on it and then see where we are. (I know the LS is working, I found out accidentally:)) One caveat, he was concerned about my pinion angle as am I. See the new thread I will start.

As for the clunk, no clear answer on that yet. Thanks again for all the good recommendations and hypothesis!

[BB767]

Another new clue, excessive brake dust inside the right rear wheel, not present on other wheels. The right rear brake is becoming more suspect, I think I'll pick up on of those IR thermometers someone suggested, I always wanted one anyway!

[edwardb]

Thanks for all the great input! Just got off the phone with Moser. First, the wheel spin thing is not abnormal, he says a lot are like this. Second, that whine noise may be normal break in wear. His recommendation is to get 500 miles on it and then see where we are. (I know the LS is working, I found out accidentally:)) One caveat, he was concerned about my pinion angle as am I. See the new thread I will start.

As for the clunk, no clear answer on that yet. Thanks again for all the good recommendations and hypothesis!

Good stuff. First I've heard of that behavior but I trust Moser way more than me (today's understatement...) and they have a good reputation. You'll find, especially early on, you hear every squeak and rattle and wonder if something is wrong.

[BB767]

Good stuff. First I've heard of that behavior but I trust Moser way more than me (today's understatement...) and they have a good reputation. You'll find, especially early on, you hear every squeak and rattle and wonder if something is wrong.

Isn't that true of all new parents? ;)

[42Bfast]

Another new clue, excessive brake dust inside the right rear wheel, not present on other wheels. The right rear brake is becoming more suspect, I think I'll pick up on of those IR thermometers someone suggested, I always wanted one anyway!

X2 on the IR thermometers. They are a great early warning tool for any new project for problem investigations or even as part of a preventive maintenance routine. I regularly use mine when trailering. At each fuel stop I take quick measurements of each tire and hub/wheel bearing to tell me if I have a problem developing. Hundreds of uses to let you know if something is out of norm.