3rd member: how much play to expect?

Dangerous Doug · #1 (**permalink**) 09-16-2009, 08:54 PM

Out this evening for a short drive. I could hear a light ticking noise with the clutch in during a coast to a stop sign under light braking. So being the retentive type, when I got it home I jacked it up and checked the brake calipers front and rear. The ticking noise appears to be coming from the 3rd member. I rotate the tire slightly back and forth, and I hear the ticking noise. I did this while watching the drive shaft bolts and I can move the wheel back and forth (1 or 2 degrees) without moving the drive shaft. There is play in the 3rd member.

How much play should I expect? A couple of degrees of play and issue?

I'm not a burn-out guy, though I do drive fast (on closed courses, of course).

Anyone care to provide some expertice?

DD

undy · #2 (**permalink**) 09-17-2009, 03:05 AM

What rear end do you have?? 9", 8.8", Jag, Dana??? Tell us everything you know about it. If you had a 8.8" or a 9" and had a Detroit Locker ... while ... making a slight radius turn when you hear it then I'd say it is normal.

Yes, you will have some play in the differential. A couple degrees would be normal. Again, thats dependent on mfr, design etc. Some diffs make a noise when you rapidly load/unload them too. Typically more free-play = more noise.

I'd strap it down on a chassis dyno (50 to 75 bucks or so) and you'll be able to truly duplicate conditions to find out for sure where it's coming from..

Dave

blykins · #3 (**permalink**) 09-17-2009, 03:43 AM

Play in the rearend is normal, it's just gear backlash. It's difficult for us to give a unit of degrees as a standard, as backlash is measured in thousandths of an inch with a dial indicator on the ring gear.

However, if you were coasting to a stop, rearend play would not be the culprit here.

A chassis dyno would be a good way to check everything out, but I would look for something contacting/rubbing something else, or maybe something in the brake system.

Argess · #4 (**permalink**) 09-17-2009, 05:14 AM

Maybe have a close look at the u-joints for play, particularly the rear one.

I find there's a bit of play in most differentials, but havn't ever heard a click from one.

ERA Chas · #5 (**permalink**) 09-17-2009, 05:33 AM

Doug,
Do you have a Jag or ERA rear? U-joints -including the drive shaft-is a good and easy place to start looking. Hold one flange and try to twist the other.
Also, I would call Bob or Doug and they'd help.

Dangerous Doug · #6 (**permalink**) 09-17-2009, 07:37 AM

I have the ERA rear.

I didn't see any play between the wheel and the 3rd member stub axle. I could, however, see play between the stub axle and the bolts on the driveshaft. This tells me the play is in the 3rd member.

In retrospect, I'm not sure this is the source of the sound. Might have been that beer I was drinking while I was working on it last night.

Chassis dyno. Good idea.

I'll take it out for a diagnosis ride tonight. I had checked each of the calipers last night (that's where I started), and they were tight and the pads had minimal movement/sound.

Need to find a quiet slope to coast and listen to the sound again.

DD

Dangerous Doug · #7 (**permalink**) 09-18-2009, 08:29 PM

I took my Cobra out for a drive this evening, and in a quiet neighborhood shut off the engine and coasted.

The sound is coming from my driver's side rear wheel/brake/hub when I turn to the right. I'll have to pop the wheel off and look for any signs of rubbing. When I lifted the rear the other night, the wheel seemed tight, so I don't suspect a bearing. It may be something as simple as a wheel weight rubbing the brake caliper. I'll figure it out.

DD

Dangerous Doug · #8 (**permalink**) 09-19-2009, 08:11 PM

Weird.

I pop off the driver's side wheel and poke around. Caliper is tight. No rotation slap on the pads. No movement in the hub back and forth, side to side. U-joints are all solid. No rubbing on the wheel, wheel weights or calipers. The only thing amiss was the o-ring on the dust cap got squished and wasn't set right.

I put it all back together, and with a shrug and high hopes I take it out for a drive and coast it snake-wise through the quiet neighborhood down the hill.

The noise is gone!

I shred around town for a few minutes, then come back and test it again down the hill.

No noise!

Now, what the hell? I'll have to keep an ear out for it. I didn't see anything that would be causing the clicking noise.

Oh, well...

DD