13 replies to this topic

[rally1380]

Hi guys.

 

Had a little breakdown today when my bottom arm pin nut popped off - ripping the driveshaft out and causing a real mess of my inner cv.

 

Soooo.....i'm wondering if my adjustable tie bars are adjusted wrongly (too short) thus putting strain on the bottom arm bushes, pin and obviously the nut that has been lost somewhere!

 

How do you all set your tie bars to the right length? If anyone says just set them to standard length - then what is the point of having them?

 

How can you measure castor? (i'm assuming tie bar length and castor angle are relative to each other)

 

 

Suspension specs - Minisport Group A tiebars, -3 degree bottom arms (I think) that are getting replaced for -1.5 in due course as -3 is too much, uprated bottom arm offset bushes, Hi-lo's, Red dot cones.

 

Car is used for rallying, so want it to work, not look pretty.

 

Cheers in advance folks.

[blacktulip]

Any adjustable suspension parts need to be set up using the correct measuring tools. I don't believe an eye can do this.

Your pin nut should have been fitted so the nut was on the bottom side of the assembly so if it were to come off the pin remains in the arm to hold it all together still.

[blacktulip]

Any adjustable suspension parts need to be set up using the correct measuring tools. I don't believe an eye can do this.

Your pin nut should have been fitted so the nut was on the bottom side of the assembly so if it were to come off the pin remains in the arm to hold it all together still.

[Spider]

Sorry, I'm not 100% sure which "bottom arm pin nut" you are referring to, got a pic?

 

If you do dial in too much neg camber, the inboard CV can disengage. You need to set it where you'd like it, then jack it up, letting the wheel dangle (that put the drive shaft in the worst situation) and pry back the inboard CV boot to see where the centre line of balls are, they need to be at least 2 mm from the outer edge on the bell on the Inboard CV.

 

But first, let's see what 'nut popped off'.

[rally1380]

Sorry, I'm not 100% sure which "bottom arm pin nut" you are referring to, got a pic?

 

If you do dial in too much neg camber, the inboard CV can disengage. You need to set it where you'd like it, then jack it up, letting the wheel dangle (that put the drive shaft in the worst situation) and pry back the inboard CV boot to see where the centre line of balls are, they need to be at least 2 mm from the outer edge on the bell on the Inboard CV.

 

But first, let's see what 'nut popped off'.

 

 

The large curved bottom arm pin that holds the bottom arm to the sub frame - it was this that the nut came off - pulled the pin out when I went over a speed bump

 

http://www.minispare.../classic/bottom arm pin.aspx|Back to search

 

 

I'm not sure if you are getting confused about my question - i'm wanting a rough ball park figure for TIE BAR length, i'm going to replace my non adjustable bottom arms for less camber ones, and i'd like t know how to measure castor?

[rally1380]

Any adjustable suspension parts need to be set up using the correct measuring tools. I don't believe an eye can do this.

Your pin nut should have been fitted so the nut was on the bottom side of the assembly so if it were to come off the pin remains in the arm to hold it all together still.

 

Wrong pin mate.

 

It's the pin that holds the bottom arm to the sub frame that lost its nut.

 

 

Just looking for a rough ball park for tie bar length - will get it set up properly as and when I can. I'm just wanting a starting figure to work out if mine is miles out and thus causing strain on other components within the front suspension causing failures.

[stoneface]

Approx 362mm from center of hole to front of round flange.

Flange thickness approx 4mm

 tie bar.jpg   54.32K   41 downloads

 

[Cooperman]

Dave, you need to set the caster to 3.5 degrees for what you do at standard ride height.

By the way, I always fit the bolt which holds tie bar to the lower arm upwards on my cars and use a Nyloc nut, which I change for a new one each time it is removed. This is to enable the tie bar to be removed during a rally should it get bent, which can happen, without having to split the lower ball joint. I got this from the 'works' rally cars which did this and for competition it makes sense. Also, I use a castellated nut & split pin on the front end as that nut has been known to work loose in rallying. I spilt pin that end because the tie-bar is in tension and the end loads are what can loosen a nut. The other end is in pure shear so there is no direct load on the nut other than the clamping load for which a Nyloc is acceptable.

 

Hope all is well with you.

Edited by Cooperman, 17 August 2015 - 11:21 AM.

[The Matt]

I believe the nut on the bottom arm wobbly pin is a nylon - insert locknut. If this has been reused several times then there's a chance it's just vibrated loose, rather than it being a problem with geometry?

[Cooperman]

In aviation engineering a Nyloc nut should never be used more than once, even if it is only taking clamping loads.

[The Matt]

Yep. Indeed. The nylon - insert is possibly doing nothing now in terms of being a locking device.

[Cooperman]

If ever a Nyloc nut is removed a d a new one is not available, there is a way of, hopefully, making it still 'lock'. You put the nut onto the back of the vice and hit the top with a small hammer to slightly deform it. Not ideal, but safer than just re-fitting a previously used Nyloc.

[rally1380]

New bottom pin and several nylocs ordered to ensure this does not happen again.!!!!

 

Measuring castor DIY stylee???  Anyone brave enough to explain??

[Swift_General]

Measuring castor is fairly straightforward and not a black art as some would have you believe.

The greater the caster angle then the more the camber angle will change with steering input. You therefore need to be accurately able measure to things.

1. Camber angle (or change of - i.e. relative values are important not absolute)

2. Steering turn angle

Now the values are linked with the following formula:

Change of camber angle = castor angle x sine (change of steering angle)

So set you car up with wheels straight ahead (not strictly necessary but does mean you'll have a decent range of movement) then turn 20° to the left (20° for the wheel you're measuring that is as each wheel will turn different amounts). Measure the camber angle. Then turn the wheel 40° to the right. Measure the camber.

Re arrange the above formula gives:

Castor angle = Change of camber angle/sine (change of steering angle)

So say that your camber is 1° one way and -3° the other then the change is 4°.

Sine 40° = 0.643. 4° divided by this figure gives 6.2°. This is your castor angle in the above example.

As long as the camber on the wheel when it is turned so it is on the outside of the turn has less positive (or more negative) camber then when the same wheel is turned so it is on the inside of the turn then you have positive camber.

With this method you can turn your steering through any measured angle, not just 40° as I have used in the worked example. The more the better however as it reduces measuring error.

EDIT

Note that 1/sine 40° = 1.55 so if 40° is your turn angle (20 either side of straight ahead) you can simply multiply your change in camber by 1.55 to give your castor angle.

For 30° (15 + 15) the relevant figure is 2

For 20° (10 + 10) the relvant figure is 2.92.

Edited by Swift_General, 18 August 2015 - 01:38 PM.