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grimlynsan

Horrible sound when engine braking at high speed

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Hi lads,

 

Not sure if this is the right section as I'm not sure what is the cause of the problem but here we go...

 

I took the 260z for a strap around Mt Glorious and Mt Nebo on the weekend (went out on a cruise with a new 86, and Evo 8 and the new OPC Astra (I wooped all of them by the way!).

 

I have an angry L28 with a 280zx SII Gearbox and standard everything else diff-wise.

 

Basically, as I was howling around the mountains, I'd approach a corner and drop it into second gear and release the clutch (let's just say with a 'racing' as opposed to 'cruising' level gentleness).

 

Doing so resulted in a horrible noise from somewhere in rear of the car. The noise sounded like a battery drill once it has reached the torque setting - not a grinding noise but a very loud and unhappy sounding high-speed clicking that vibrated and shuddered through the car.

 

This also used to happen a bit during regular driving when I first had the engine put in, but seemed to disappear (or I altered my use of the clutch - not sure now!).

 

Anyone have any ideas as to why it's making that noise?

 

I am taking it in for first service (5000km) later this week so will have the mechanic see to it if anyone knows what it is (i told him when I got the car originally and he couldn't reproduce the noise...).

 

Lee

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I'd get your mechanic to drop the diff oil and take a look for bits as a start

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Car rolling,, clutch in, is it there?

Car rolling clutch out, is it there?

Try both in gear, and in nuetral.

 

Does speed/frequency of nose go up and down with speed?

 

Suspect tailshaft unis, or half shaft unis??

Suspect diff pinion flange nut loose?

Suspect nuts/bolts taillshaft to diff flange, also suspect half shaft nuts/bolts.

 

 

Also could be a bit of fencing wire or crap flicked up and wrapped around tailshaft!

 

I heard you lot, as well as the bikes, then about hour later the emergency services go up Mt Nebo rd. i look over it from my place!

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Its probably not the diff if its doing it only when you shift gears. If you think about it, the speed of the diff shouldn't be changing that much when you shift. So either you are not hearing which part of the drive train has the noise or you aren't giving us the full story.

 

 

It could be anything from a broken diff mount to dodgy unis. You will have to give us better information and maybe look under the car to see if you can see anything.

 

 

You're not granny shifting and double clutchin' like you should right?

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The sound only occurs when the engine revs are low and I release the clutch (too) quickly in order to slow down without braking.

 

That is, if I blip the accelerator on the downshift - to match the engine revs with the speed I am going for that gear -  there is no sound.

 

The sound only occurs when there is a big difference between the engine speed and the car speed (for the new gear).

 

For example, I am in third, doing 100km/h, I see a corner I wish to take in 2nd (at say 80km/h), so on approach I shift to second, without matching the revs, using the engine to slow the car prior to the corner. If I let the clutch out to quickly, I get the noise.

 

If this is a diff issue, there is the added bonus of me 'needing' to replace it with an LSD :-) damn! :-)

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What are you doing downshifting with a big RPM miss-match and not blipping the throttle?

 

 

It could be just locking the rear wheels? How new is the clutch and does it slip?

 

 

If driving your car correctly stops the noise i would just stick to driving it properly...

 

 

 

 

 

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I agree with d3c0y, if the noise is only occurring through poor gear changing technique suspect clutch slip/chatter or a bit of compression lock up. Learn to heel  and toe properly. Might save your car and life one day if you hit a bit of a damp patch under compression lock up.

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I'd check all the mounts too, engine, gearbox, diff, exhaust hangers. If one of these is gone you may get enough movement with sudden load changes or rough driving.

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I agree with d3c0y, if the noise is only occurring through poor gear changing technique suspect clutch slip/chatter or a bit of compression lock up. Learn to heel  and toe properly. Might save your car and life one day if you hit a bit of a damp patch under compression lock up.

 

I remember when I had my Datsun 1600 I got real good at very smooth changes both up and down with a lot of double declutching even though the gearbox was in new condition. I could heal toe when the brake pedal was down if the drums needed adjustment. The Art of driving these cars, I think, is to do things as smooth as possible so that a passenger thinks the car is an automatic even in performance driving and you won't wear things out.

 

Richard

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Thanks for all the advice guys,

 

Its a brand new clutch with the engine, a pink exedy one.

 

It definitely wasn't the rear wheels locking up, as there was no change in speed or of the angle of the car. Plus it wasn't that kind of noise.

 

I admit that we wouldn't be having this conversation if I had good driving technique. In daily driving, I always use the engine to slow the car down albeit more smoothly. I only blip the throttle when downshifting if i dont want a reduction in speed. I use the same technique on the mountain as I am not good enough to heal and toe. But I still think, despite the abuse, the sound was not normal (the car should be able to handle it).

 

I'll get the mechanic to check all those bits you listed. Thanks guys,

 

Lee

 

 

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Definitely learn to shift properly, especially if it's stopping the screaming banshee noises.

 

It's not too hard to learn, watch a few youtube vids, hop into the car (turned off) & get a feel for the motion you need to do. Then just try & practice during your daily driving at a normal driving pace. Pretty soon it'll become second nature and you'll be heel-toeing like a pro all the way to the supermarket. You'll wonder why you didn't try to learn earlier since it's so easy. Easier to learn than riding a bicycle. But it's a weird feeling to be twisting your foot like that if you've never done before. practice practice.

 

 

It's a hell of a lot more satisfying to downshift properly, everything feels smoother, faster, more in-control & sounds waaayyy better than the jerky awful engine braking. Puts less wear and tear on the expensive bits of your car too, which is always a plus.

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Come for a drive out to The Gap, on Thursday arvo, there will be a few Z guys at my place that can have a look/listen etc.

PM me if you can make it, and for address/times etc

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Thanks for the offer Jason.

 

I finish work at 5, I work at Gaythorne so could be there for 5:20ish...

 

Is that too late?

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UPDATE:

New standard diff mount and a new diff strap from the States, coupled with a NISMO LSD R200 and the noise is gone - I can shift as poorly as I want and no noise. I suspect it was the diff mount although the mechanic showed it to me and it looked fine.

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