Hi All. Fantastic forum! I purchasd my 300zxTT a month. Lovely car, what I always wanted. However, I have noticed, that the car seems to have a mind of its own somtimes. When driving at normal/legal speeds, the car seems to be unstable in that it is sometimes difficult to drive in a straight line. It's a little worrying a its seems a little unsafe at times. Also, the car tends to swerve a little under braking. Is there something I can do about this ? Pls help!

Have a few things checked out:

 

-alignment of the car.

-play on wheel-bearings,steering and/or hicas

-tire-pressure

 

Is your car a 2+2 or a 2-seater ?

I've noticed my 2-seater sometimes gets very unstable at highway-speeds if there are tracks/grooves in the road

 

-Eric

 

[This message has been edited by lymon (edited 30-08-2001).]

Yeh a good idea to check all the mechanical gear,the rear steering track rod end etc,however tyres play a real important role in stability of a car like the zed,is it a Jap import with Jap spec tyres on? after changing the tyre on my Jap import to Uk tyres (Directional Dunlops) the ride improvement and stability were immediately obvious,added to the fact wet weather was no longer a 10 mph crawl around islands..check your tyres.

Jeff TT

Hi,

i found on my car that tyre pressures were very important, to prevent wandering and crabbing across the road...Plus, get some Bridgestone, or other top make of tyre...the difference is amazing.(+try to avoid white lines in the road )

JEZ

Could be all of the above or your HICAS could be malfunctioning. Intoroducing rear wheel steer when your going in a straight line could cause the syptoms you describe.

 

You can do a diagnostic on the HICAS. Go to twinturbo.net and look in the technical section for a diagnostic routine.

 

The other option is to disconnect the HICAS and see if it improves things.

 

Simon

I'd jack each rear wheel up in turn and check for play. Put one hand at the front of the wheel and one at the back and try and wobble it. Sounds like the Hicas control rods.....

 

CheerZ,

 

Andy

After you have had all that checked out (dought it's the Hicas), check the free play on the front tension rods, maybe the bushes are gone.

 

Where are you RockTT?

Bushes are a good check. Luke Borg at the Zed centre in Nottinghma does a complete polyeurethane bush kit to replace all your aging bushes. Has anyone done this and is it a tough job?

 

I am considering this job as i think the Zed will be buried with me so I'm planning to kit it out!

 

Simon

What is the optimal tyre pressure for a nod mods 300zxTT?....

Thanks for the Advise.

 

Things I have checked so far are:

 

*Tyre Pressure. The table at BP petrol station recommends 36(Rear) and 33(front)

*The Tyres are in reasonable condition.

 

Having read the comments posted, I feel that there is a little rear wheel steer, which may be causing the problems. How do I go about disconnecting the HICAS?

 

My car is a UK spec 93 model.

 

I have a feeling its something to do with the HICAS system, as someone else also mentioned it. I will perform the HICAS test tonight.

 

Is the HICAS system very expensive to put right?

 

Thankyou all for ur comments

Agree with the pressures, but get yourself a decent pressure gauge. I have one of the little digital jobs from Halfords - they are close enough and only cost about £8. Garage ones are notoriously inaccurate and sometimes 20%+ out !!!!

 

What type of tyres though ? This can make a HUGE difference to the Z as it is particularly sensitive to the profile. When I first got mine it had Marshalls (v. cheap) that were bad to start with and got worse as they wore. I changed to Bridgestones and the difference is amazing.

 

Tracking is also important. Unless the toe-in is set appropriately then stability goes out the window.

 

The HICAS definitely needs checking. It can be expensive to fix, but it is easy to disable.

How would i go about disabling the HICAS. Also, what is the toe-in?

If you measure the distance between the rear tyres at the back and at the front (I know what I mean ) the difference should be between 0 and 4mm. Not sure about front tracking though.... To disable the hicas, I think there is a fuse you can pull. It is either just behind the drivers side front suspension turret, or on the passenger side at the front.

 

Good luck,

 

Andy

Toe-in is the angle relative to straight-ahead that the wheels point inwards. o deg will generally lead a car to be unstable. The specs are in the manual, but I can't recite them (we have Tim for that sort of thing)

 

The HICAS can be disabled electrically, i.e. it will stop trying to move the wheels by pulling the fuse (I think), but it sounds like you need to check the integrity of the links, bushes, bearings etc etc. If you want the wheels locked in the correct position, thereby erradicating some of the steering arms etc. then you can buy a locking plate type affair that does this. Not sure how much this costs, but in terms of some Zed repairs I think it's quite reasonable.

Have a look at the following link....

http://www.300zx.co.uk/forums/ubbforum/Forum1/HTML/001761.html

 

It shows the fuses in the drivers footwell. I think there is another fuse in the engine bay as I mentioned above. If you remove the hicas/power steering fuse you will have very heavy steering I'll keep searching for a better solution for you though.....

 

CheerZ,

 

Andy

I had this problem when my speed sensor had gone faulty.

The steering went heavy/light at the wrong speeds and the car seemed to be all over the place - HICAS trying to do it's thing but far too much because it didn't have a clue what the road speed was...

 

 

Also check for sticking brake calipers!

Cheers guys. I think I will be having a busy weekend troubleshoot my Z. Will be checking everthung from tracking, rear track rod ends to speed sensors !!!!

 

Hours of fun.

I would advice an alignment of the car, whether it's the problem or not, after checking the T-rod bushes/free-play of course...!

 

The spped sensor, if it is going can be noticed if;

1)Your power steering fails suddenly

2)Your Speedo drops to nothing all of a sudden.

3)Your 'Power' light flashes a number of times as you put the ignition on.

 

The Hicas was mechanical on early versions and electrical on the later ones. If it is electrical then it can be disabled (look on TT.net for details).

 

I think a failed speed sensor would effect both types but definately effected the mechanical one as that happended to mine.

 

Speed sensor is a

 

Simon

Any other suggestions to run by the mechanic over the w/e ? Thanks again.