First go-cart irs clanking

Hello everyone,
Hope you all had a great Holiday and New Year and are well and not freezing!
FINALLY got to drive my chassis around the community. Everything works, tracks straight, goes, stops. However, when on/off gas or just idling along in 3rd the somewhere in the rear there is clanking. I then put it up on jackstands and wiggled the rear wheels back and forth and can hear looseness in the diff (or somewhere). It is all new stuff; everything is torqued; so what could be the cause?
I was read to put the body on for fitting, but now I will have to solve this issue first.
I would appreciate any help you can give me.
Thank you,
Jeff

I hope you have lube in the rear end. Check the driveshaft. Look for marks on the driveshaft and half shafts.
A second set of hands and ears will help, big time.

Check the length of the bolts connecting the driveshaft to the adapter. I remember someone have reporter that they can be a bit to long.

I checked the free play in the diff by putting a magnetic digital angle gauge on the prop shaft, then rotating the prop shaft just so that wheels don't move. I have 6 degrees of prop shaft free play. I think this is causing the noise. These are new Ford parts. It seems to me that is too much free play (in the pinion to ring gear). Anybody know the spec?

You set your pinion angle correctly?

6 degrees isn’t nessassatly bad, as back lash on the ring gear is what should be measured as a good or bad indicator. All gears needs slop so they can develop a film of oil to prevent wear. Diffs use heavy Oils and require more clearance then gears that use thinner oils, which shows up as slop in the outputs. It does sound high but not crazy. Did you fill the diff with the correct fluid prior to driving? Did you break in the gears on stands prior to driving? What is the driveline angle? Is the drive shaft to diff solid or can you wiggle it any no matter how small? Are the U-joints good or is there slop? Did the caps and pins ever fall apart on a ujoint? Could a ujoint pin be missing? Are the half shafts fully seated in the diff? Can you wiggle them up and down at either end? Are the half shaft nuts torqued correctly? Are the wheel bearings torqued and locktighted? Are the lugnuts tight? Start here and if everything is yes check the breaks and if yes again I would pull the rear diff and then check the pinion back lash. New OEM parts have a lot of QC done and are usually a safe bet. Yes stuff happens but OEM stuff is about as dependable as it gets compared to the aftermarket. My bet is you’ll find the answer outside of the diff. FYI if the back lash is out it will require the pinion to be shimmed more towards the ring gear and the carrier will more then likely need to be shimmed more to the left to compensate for the longer pinion protrusion to maintain the proper gear mesh.

What type of differential are you using?

Jeff,

Have your parts been sitting idle for a while? It could be that it's just a case of the bearings needing to get themselves properly lubed via use. The only reason I mention this is that it happened to me. My IRS (old style) sat for a couple of years as I plodded along, then "clicked" audibly when I started go-karting. After some miles, it stopped. Just my 2 cents.

Quote:

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Originally Posted by Sigurd

Check the length of the bolts connecting the driveshaft to the adapter. I remember someone have reporter that they can be a bit to long.

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2 x this... the bolts will torque down but not really be pulling the driveshaft adapter tight to the rear end. grab your drive shaft and try (Hard) to wiggle it back and forth or twist it. If you are confident this is not the problem, I can tell you that I've personally checked two other IRS builds and yes, there is some play, about what you discribed, in the rear gears and you will only see/feel it when you are actually lugging the engine at a bit lower RPM than you will most likely ever drive once you are driving it for "real"

My bet is on the driveshaft adapter bolts being too long. Check out my first go-cart drive, (especially at 2:34 into the video) you can hear the effect of this problem. Fixed with just a couple minutes on a grinder for me.

Hope it is as simple as this for you...

Carl

Hello all,
Thank you all for your suggestions. I will re-check everything: the driveshaft adapter, the halfshafts, all the bolts. I slpent a day setting the pinion angle; it is straight on.
The Ford 3.55 center section came with fluid and friction modifier as per the attached tag and I checked it out--OK. The car had been sitting for a year while assembling.
I did run the car on jackstands prior to go-carting; however just a few minutes. The noise happened when I WAS LUGGING IT in third at 15 MPH (shame on me).
So...I think I will just put some miles on it and make sure everything is run-in before even thinking about pulling the center section (oof, that's a lot of work...the whole rear suspension has to come apart).
Thanks again for the help.
Jeff

Jeff,

All great info above. The one simple check I would do is make sure the half shafts “snapped” into the diff. Sounds like a no brainer but I did have that happen to me. As you know, there is a snap ring on the inside that holds the shafts into the diff. I had this on my first t-bird IRS car.

Henry

ALL IRS cars have 'slop' in the rear end, it's just how it is. Remember every thing has to have some movement. The half shafts have some clearance in the side gears, as does the axle joints, it all adds up and seems a lot. If you where turning the driveshaft and looking at the wheels, then all that play is there. In an IRS car the driveshaft angle isn't an issue, also in go-cart with no body on, you're going to hear things that normally you wouldn't.