Rear end woes

[dohc]

Hi Guys,

Finally got my Zed running well and been driving it pretty hard. I didn't realise how much I missed it until I started driving again.

Anyways, the problem I have is in the rear, but not the normal bumps, knocks and groans. Basically, when I down change (5 speed manual) abruptly the rear makes a horrible grinding noise that sounds like steel on steel! I almost sounds like something repeatedly hitting the floor pan?

For example, the car is doing say 4500rpm in 3rd and I drop it to second while braking. Normally I would expect it to try and pressure lock, lean forwards abit and be fine. Instead I can't do this because of teh horrid noise from the rear (it sounds like the car is being torn apart!

I can avoid this noise by "heel-toeing", so all i can think is the diff is moving in its mounting.... but i can't see any evidence of this and can't really get under the car when I'm doing 60kph :classic:

I've got up under there to check it out and needed to replace a broken suspension bracket (one of the four little ones holding the rear lower wishbone in place) and I've noticed a crack in the subframe that holds the diff in but nothing that would account for this noise!

Does anyone have any ideas at all?

Cheers,

Ross.

BTW How hot should a diff get in day to day driving? Mine seems to be getting pretty hot?

[2ManyZs]

Does it only make the noise while under braking? Could it be the rear shoes? I'm wondering if they are getting low enough, and with some heat checking on the drum that it could be shuddering, and causing the noise to be amplified a bit....

Or is it while shifting? Which would lead me to suspect the throwout bearing and/or pressure plate.

As far as the heat of the rear diff, they do get very hot if used hard. BTW, the more wear on the bearing and ring and pinion there is, the more heat that will build up. Have you tried a different gear lube? If you can, try some of the Redline synthetic lube in the rear and see if that helps. Hard to tell if there is a big difference without a temp sensor on the rear, but every little bit will help.

[dohc]

Hey 2Many,

It happens with or without braking, so i'm pretty sure it's not that and when a mate rode in the back he said it sounded very central but couldn't pin it.

As for heat, that makes me feel a bit better :classic:

I'll have to check out the other possibilities but it is definatly rearward and not trans associated.....

Cheers,

R.

[2ManyZs]

OK, that clear it up a little but you won't like my response.....:disappoin

It sounds like the rear may be the culprit. It may be the ring and pinion or the bearings. On decelleration you are hearing a grinding because the ring and pinion clearance is changing and possibly the pinion gear is gouging the ring gear. Either that or it is one of the side bearings that is shot or a spider gear. It could also be the front bearing also, and the pinion shaft is moving back and forth and causing the problems with the ring gear.

Either way, the best thing to do now would be to pull the diff cover and see if there are any deep gouges on the ring gear, or if the spider gears look to be damaged.

Any way you look at it, pulling the cover is going to tell the whole story. If you see any gauling on the gears, it still could be a something fairly simple like bearing, but it will depend on what you find on the gears.

But then again, it could still be something as simple as a u-joint or a loose flange. Check you u-joints and seals for leaks, a leak might pint you in the direction of your problem.

Pop the cover and check the u-joints and let's here the rest of the story....

[Ed]

You could start out by taking off the drain plug on the back cover of the diff. If you have grinding then you should definately have metal chunks in there. After you drain the fluid stick a magnet or your pinkie in the hole and feel around. Good luck.

[Ben]

If you want someone to have a look at your diff (if you have to take it out). Contact Dave Meaker @ Mitsi-Bits (Lonsdale). I've known him for many years via the Club-Car circuit & he's rebuilt both my R200 LSD's (and plenty of H190's, Supra diffs, Mazda diffs etc). Years ago he worked for Bill Hanson.

Tell him I sent you.

[mjyikes]

Ross,

If it's making a repeated banging sound when you down shift,

it could be a broken rear differential mount. You sometimes can't tell it's broken until you remove it. I had that happen on one of my previous cars.

[dohc]

Hi Guys,

Thanks for all the replies. I think you might be right 2Many, the more I listen to it and the way I get around it doesn't sound good. I'll pull the back cover and check what's in side, but I'm guessing it will be a mess

All I can say is it is a good thing I've got a spare R200 kicking around in the shed that was out of an auto so should be in better condition.

Thanks for the contact Ben, I was wondering where to take it if it came to needing a rebuild. Approximately how much would it cost?

Just two more questions: Is it worth getting the other diff rebuilt while it is out of the car and what can be added/strengthened? and will the current (stuffed) diff make it on a thousand km journey over about a week?

Thanks again,

Ross.

BTW the rear diff mount was replaced by the previous owner and looks to be in pretty good condition.

[Ben]

You won't know if the current diff is worth rebuilding util you remove the rear cover. If it's just bearings then it can be fixed, but if it's worn through the hardening on the gears then it's another story. If you can take photo's of it (assuming that your problem is the diff....) & post them a better assessment can be made.

Based on your description, I wouldn't trust the current diff down main Nth Rd in peak hour...

Let me tell a story.... :classic:

My '82 MR30 Skyline runs a L28ET engine, 6psi boost ~220HP.

The gearbox (at the time) was a beefed-up 3N71B (factory Auto - soon to be re-fitted, along with the engine, into my 240Z for a while...). Diff was the stock, open, 3.90:1 R180.

I'd run this combo for ~18 months, no issues at all. No burnouts, but wheelspin would occur on full-throttle shifts.

It's around 35 deg C, summer, mid afternoon....

I was gently accelerating from a standstill @ Days Road/South road (heading North). I'd barely got the engine to 1500rpm (car was just moving) and there was a little 'crack' & I lost all drive.

Inspection revealed that the tailshaft was spinning, but the diff wasn't functioning - at all....

After removing the diff, it was apparent that there was a tooth missing from one of the spider gears (must've broken off before I bought the car, as it wasn't in the bottom of the diff). I'd loaded the diff up at this point & then split both spiders into many pieces, taking chunks from the carrier & crownwheel. The diff was completely lunched. No burnout, no 'bang'.....

The moral to this story - if it's gonna let go, it'll do it a the time you least expect it, and in the most inconvenient place.

[dohc]

Just thought I'd put a follow up note in, for interests sake.

Unfortunatly I ran out of time to swap diffs etc before my two weeks holiday. As I was driving the Great Ocean Road in Victoria I wanted an interesting car to drive (my girlfriends '75 BMW just doesnt' cut it ).

Anyway, to cut a long story short I've just got back from doing a 2,800 km round trip (including detours) and it is still holding together. This included a couple of runs over 180kph and some of the windiest (read fun) roads in Australia.

Now I can give the car any gas in reverse or it screams, but all in all I think that these diffs are very sturdy little units!

Thanks again for all the input and I'll get to swapping it soon as I don't think I should try and take it on the track next season like this:classic:

Cheers,

R.