NA6 Diff going ??

[Robbo107672]

Hi,
I have a 1990 NA and it has slowly developed vibrations intermittantly when gently accelerating and it can be reliably produced over 100kph. When travelling over 100kph, the car gets a vibration that you can feel through the bodywork, the rear view mirror shakes to the point that vision in it is blurred.

Have had the front end completely checked by my mechanic. I put the car on stands tonight and checked the drive shaft, uni's, diff pinion and rear wheel bearings. The only thing I can find that is slightly suss is where the half shafts exit the diff housing has slight lateral movement in both sides as if the bearings may be in early stages of collapse. I'm not sure what is normal here so thoght I'd post and see what experiences others have had ??

Can anyone help ?

Thanx, Rob.

[StanTheMan]

cheap things first

wheel allingment
wheel ballance
check to make sure the actual wheels are straight.


the early NA6's have a famous 100km/ph shimmy staight from the factory as standard accecory.

you may also require a little exctra bracing.

the cheap one is the rear lower brace...... about $50 or so.
if you want to get real serious.... a roll bar. $650-$850 for a Brown Davies. but the lower brace together with a wheel ballance would most likely fix the problem.

[Robbo107672]

Thanks for the ideas, I am due for a wheel alignment and will check the balance but this seems a lot more like a drive train problem..

I had the alignment done about 20k ago when I had Koni's & Kings inserted but have spun out and hit a gutter in the wet since then.. (hence the front end check)

I've had the car for over 30,000 k's and this has only just started in the last few weeks and is slowly getting worse, so I don't think it's a factory thing..

More info:
The shudder/shake is only present with positive acceleration either slight or significant. as soon as you coast or declerate, the problem stops, even at the higher speeds...

hmmmm.......

[STV]

i am an absolute novice, so i may well be TOTALLY wrong...

Engine mounts?

Only reason i say this is that i saw an NA that i was going to buy
The engine twisted ridiculously on its mounts when under accel, in neutral.

As i say, i may be WAY off the money, but its just a thought.

STV

[nath]

OK. This is going to sound absolutely crazy, but hear me out on this one...

I got a strange vibration on thursday night... felt like the wheels were out of balance or something had seriously gone wrong. Felt most noticable when accelerating, regardless of speed, was still there when coasting, but not as severe....

Took the wheels off to check if one of the balance wieghts had come off and was causing the problem. All were there, and it didn't look like one was missing.

Problem still there.

Tried my second set of rims. Only new tyres fitting 1000km ago. So I knew these would be balanced. Vibration still there. It was starting to get really bad, like Robbo was describing - the whole car shaking. Starting to get VERY worried.... Thought that I would leave it till the morning to think about it some more....

When tidying up and putting the jack away, I realised that the spare tyre was loose. The 'key' was still in it's thread but had unwound just enough for the tyre to dislodge and sit at an awkward angle.... and shake around like crazy. And aparantly enough to produce the vibrations.

Tightened it up.

Problem solved!



So, how tight is your spare? Could be worth checking.

[NMX516]

I had noticeable vibrations after a track day spin in my NA6.... Turned out to be a slight flat spot on one of the rear tyres. NA6's without the chassis bracing are very sensitive to anything like this.

[NMX516]

More info:
The shudder/shake is only present with positive acceleration either slight or significant. as soon as you coast or declerate, the problem stops, even at the higher speeds...

hmmmm.......

hmm ok, maybe rear subframe mounts?? What condition are the suspension bushes in??

[Robbo107672]

Hi, thanks for all the ideas... I got right under the car today and have found that the front Uni joint is stuffed.. That'll be it I guess.

Now have to find a solution, Mazda will only sell me a complete prop shaft @ $430.00 inc GST... Wreckers $250.00 for second hand...

Has anyone used a Timken or similar replacement Uni joint ?

I have heard that Mazda press the caps in and you can't use the old CirClip type Uni's, such as my first car, HK Monaro with poverty pack, had on it.

Any ideas will be gratefully received !