Knocking noise

[JimiD]

Hi Guys,
in the go-kart stage and I'm getting this knocking noise when I turn or just when i go from reverse to forward. It doesn't happen all the time and I can't repeat it on purpose. It's not a drive train issue as far as i can tell. I did put in the solid rear mounts for my IRS and that's when I started hearing the noise; I think the rubber mounts were just hiding the noise. When the car is moving there is no noise it almost sounds like the suspension but visually it looks ok. The noise resonates through the frame. I jumped up and down on the rear and the suspension made no noise.

any ideas?

thanks
jim

[Hankl]

Jim,

Is it a single knock when you start moving, or is it a continuos knocking?


Hank :cool:

[JimiD]

good point. it's a single knock like something is shifting then settles in.

[skullandbones]

Hi Jim,
I know this sounds simplistic. You may have already checked all of these out but it sounds like one of your universal joints is damaged. It may be that the solid mounts accentuated the problem where the soft mounts took up the play without any noise. That's my thought. WEK.

[JimiD]

Everthing is new, lemon joint from the factory?

[michael everson]

Loose brake pads?

[JimiD]

to solid sounding of a knock

[skullandbones]

Jim,
If this was easy it wouldn't be so much fun, huh! Just kidding. I would jack up the back and move everything peice by peice to see if I could reproduce the sound (turn the wheels, shafts, etc). If you can't reproduce the sound in the diff area do the drive shaft and so on. Sounds like that really are hard because of the resonance as you indicated in the beginning (reference to frame). Be careful. Every time I get under the car, I think of some body part being smashed to a 4 inch thickness. On second thought it might be better to do this on a lift where you could get to the components easier and shake like H*** without danger of shifting the weight of the car. IMO WEK.

[JimiD]

gotcha. ten beer project..

[Avalanche325]

I would also back the car up, to load it for the knock. Then with the wheels on the ground and engine off give it a push forward. It may be something that only happens when the suspension is loaded. It could be anything from a bad u-joint, gear lash, a caliper shifting, the diff housing moving, an axle, etc.

See if you can isolate to left, right, or center and front, middle or back.

Could it be the posi-trac? Detroit Lockers were always known for a loud crack as they freed up. Thinking about the turn part here.

Good luck, sounds are often hard to isolate. I can imagine the tube frame makes it tougher. Mine rings like a bell if I whack it.

[CHOTIS BILL]

If you rock the car while it is in gear it might simulate the problem.

Bill Lomenick

[Mike N]

After you have checked all the lug nuts, suspension, driveshaft, trans mount bolts etc grab the driveshaft with your hand and rotate it back and forth. It will have some backlash between the trans and the rear end gears that can sometimes be noisy. Second it could be the brake pads moving in the calipers. If it only occurs when you change direction from forward to reverse and vice versa it could be the pads moving in the calipers. Without the engine running roll the car backwards and hit the brakes then roll it forwards and hit the brakes if it makes the noise it is more than likely the pads settling in the calipers.

[Someday I Suppose]

I am guessing too loud of a knock to be the friction disks in the diff? Do you know what lube you put in the the rear and did you put in a friction modifier?

The other one that I've seen posted before is lose bolts on the drive shaft.

Let us know what you find... funny on the 10 beer project...

[JimiD]

I did put the friction modifier in(not sure brand now I think from Summit). I will try to mess around this weekend i'm starting to think it's the posi cause when i turn around at the end of my street and make a tight turn i hear it so maybe it just needs to break in? (hope)

[Mesa Mike]

I replaced gears and bearings in my IRS because of the issue you described. All new stuff and still "clunk" when put in gear. That just must be the drive train when you start out. I raised the rear end and turned the wheels to listen to the clunk. Just enough slack (vary slight) in drive train caused this clunk. Have 23,000 trouble free miles on the "clunk".

[skipbaker]

I too am experiencing a strong clunk. I had the transmission out over winter and notices when I rotate the fidd input shaft CW then change to CCW I get the clunk in the diff. Next week I'm replacing the used 1990 CV joints with new ones but don't think they are the actual problem. Seems to be in the diff. I had it rebuilt and had new clutchs installed. Used friction modifier he provided. Do you think it may be something in the diff? I did find a loose bolt on the right caliper but noise is still there after fixing that. Everything else it tight and no visible issues. This knock happend every time I reverse the loads on the diff from reverse to forward including from slowing to speeding up.

[willy]

? did you rebuild the diff? if not I had the same with my solid axel diff and the posi clutches were wore out and that put sloop in the diff which will give you clunk sound when you take off put a new set of disks in it sould fix it.

[skipbaker]

Thanks. I had the diff professionally rebuilt from a local "Expert". He put in new clutches and I've drivin over 7,000 miles with no problem. He asked me to bring it back to him to check out. I was thinking about building a new diff using 3:55 gears insted of the 3:27 ones from the T-Bird. I am thinking about buying a new Ford Racing M-4010-G3 aluminum housing and building a new diff. Not sure if it will fit. Does anyone know if it will bolt in?