Differential dead??!!

[Hrududu]

Hey guys, you may remember a while back i posted about some clunking that seemed to be coming from my rear end. I looked at it and it seemd to be coming from inside the diff. Well, for numerous reasons this problem went unattended until now. Yesterday while out for a short drive, i shifed into 4th gear and the most god-forsaken banging started coming from the rear end. It was so loud and seemed to send jolts thru the car. I got it home and parked it. Im assuming whatever was broken in the diff before finally bit the dust totally. Now i want to be absolutely sure its the diff and not something else before I go off and get another one. I will say that the transmission still shifts just fine and it all feels good, so i think the tranny is Ok. Under the car everything looks visibly good. Nothing looks broken or feels broken. Does this sound like a broken diff to you? I leave for college in 2 days and would like to get this car back on the road so I can take it with me insted of my Buick. Thanks. I can do my best to answer any questions you have.

[Pir0San]

Check your U-Joints. They can make some horrendous clunking, and are fairly easy to check. Crawl under the car, grab both sides of the driveshaft or halfshaft, whichever you want to check, and try to twist and move it around. There should be little to no play in the U-Joint, and if there is any, then the U-Joint should probably be replaced. I need to redo the U-Joints on my Z, they are clunking pretty good when I shift quick, and I've actually had them get so bad that they felt like they were going to vibrate the car apart.

Good luck!

[Hrududu]

Hmm, I'll double check those. When i was under there they all seemed pretty tight, but i may have missed something. Thanks.

[Hrududu]

Okay, i went out and checked the driveshaft and half shafts and it all felt solid. Also checked the mounting bolts for the diff and they were tight. I did open the drain plug a little on the diff to check the fluid and it was very dark, very smelly, and appeared to have little sparkly bits in it. The shop is telling me 600-900 so that is out of the question. I'm gonna try for a used one. Can someone tell me what year Z's i can get a diff out of with the same gear ratio? Z's are not easy to come across here in salvage yards, so i need as many options as possible with the 3.54 ratio that will bolt right up. Thanks again.

[Carl Beck]

Can someone tell me what year Z's i can get a diff out of with the same gear ratio? ...

See: <a href=http://zhome.com/ZCMnL/tech/GearRatios.html TARGET=NEW>the Z Car Home Page</a>

If you can't find a rear end locally call Idaho Z, they are not too far away, in Napa,Idaho..(208) 466-0004. Tell em Carl Beck said to say hello...

FWIW,

Carl B.

Carl Beck

Clearwater, FL USA

http://ZHome.com

[zeiss150]

the clunk from the diff could also be from the mounting plate "above" the differential. I use to have that clunking problem then I replaced that and no more clunking. Its a steel plate with rubber on it, over the years the rubber goes away and you are left with a "free floating" differential. If you want to check your diff, jack up the back end a little and spin the tires that will tell you if its your U joints or the differential mounting bracket or if it is the differential. Differential fluid always smells like hell BTW. I hope this helps.

If your gonna go through the trouble of putting in a new diff why not put in a 3.90? Just wondering.

if you are worried about the speedo being correct just have them send you the speedo cog from the Z they pull the diff from and you'll be set. or just buy a "white" 19 thooth cog from nissan and you will be set too.

[jmortensen]

I third the U-joint suggestion. If you're just driving along, it's very unlikely that the diff is going to break. What usually happens in a diff is that the spider gears go. This manifests itself when you turn, usually sounds like a crunching noise when turning. A less common problem would be shearing a tooth or teeth off of the ring and pinion. The pinion is a smaller diameter, so you can usually identify which one is busted by figuring out how long it takes for the noise to happen. If it's every 5 feet its the pinion, every 20 feet its the ring. For the whole thing to just grenade is pretty much unheard of. I've seen a few who have managed it over at hybridz.org, usually the crosspin shaft backs out of the carrier and it all goes to hell from there, but very rarely does this happen.

The halfshafts however go bad fairly frequently and it wouldn't be at all surprising if that happened to you. Best way to check is to pull them OUT. After 10+ years of Z ownership, I still can't test a halfshaft U-joint on the car. Pull it out, grab the middle of the halfshaft and the flange on the end and twist back and forth. If you feel play, it's needing replacement. The problem with testing on the car is that everything is at weird angles and it's a lot harder to twist since you're fighting the resistance in the diff and the brakes and wheels on the other end.

Here are some pages about diff noises that might help:

http://www.ringpinion.com/content/technicalhelp/default.asp?pid=109

http://www.ringpinion.com/content/technicalhelp/default.asp?pid=110

[Arne]

Best way to check is to pull them OUT. After 10+ years of Z ownership, I still can't test a halfshaft U-joint on the car. Pull it out, grab the middle of the halfshaft and the flange on the end and twist back and forth. If you feel play, it's needing replacement. The problem with testing on the car is that everything is at weird angles and it's a lot harder to twist since you're fighting the resistance in the diff and the brakes and wheels on the other end.

Yup, I thought the ones on my main car were OK, after checking them in place. But when I had them disconnected while changint the rear springs, I found that one of them had a fair amount of play in it. I replaced it with one out of my parts car, and found that one of the noises from the rear of my car is now gone.

[Hrududu]

5 feet sounds right. I bet its the pinion. See, this problem actually started back in October not 2 days after racing at the drag strip. It stated as a slight vibration sound and occasional knock. it got a little rougher over time and would make shifting a little rough if it was a quick shift. I've taken it pretty easy, but then yesterday I took a turn and shifted into gear and it was like someone was slamming a ball bat into the bottom of the car. Super loud like something was really busted. I got it home okay though. It seems to do it every 5 feet or so.

[jmortensen]

5 feet sounds right. I bet its the pinion. See, this problem actually started back in October not 2 days after racing at the drag strip. It stated as a slight vibration sound and occasional knock. it got a little rougher over time and would make shifting a little rough if it was a quick shift. I've taken it pretty easy, but then yesterday I took a turn and shifted into gear and it was like someone was slamming a ball bat into the bottom of the car. Super loud like something was really busted. I got it home okay though. It seems to do it every 5 feet or so.

That sounds just like a halfshaft U-joint.

[Hrududu]

That sounds just like a halfshaft U-joint.

Even if the sound would go away when the clutch is engaged? I don't know if i mentioned that before.

[jmortensen]

It might go away if it was the halfshaft, but it wouldn't if it was the diff IME.