Torsion bar adjustment

[Alan Hopla]

Hi,
I'm not sure if this is the right place for this but here goes.

I have an 82-83 ish GTV and it has either drooped or been lowered at the fornt considerably.
When I look in my trusty Haynes manual (page 203) it advises that the ride height is correct when,
The distance from the ground to the bottom of the lower wishbone inner pivot, less the distance from the ground to the bottom of the lower ball joint taper pin,
Is between 39 and 49 mm.
On my car this is about 0 mm.
The Haynes manual also states that the torsions bars have 35 front splines, and that each spline will adjust the ride heigt of the car by 1.5mm.
When I do the math this means that to adjust the ride height by 45mm I need to rotate the wishbone by some 30 splines or 7/8 of a turn!

This to me does not make logical sense.

If with the car sitting static, I scribe a horizontal line across the front face of the torsion bar.
Then after I adjust the ride height won't the scribed line on the torsion bar still be horizontal.
i.e. The torsion bar is in the same loaded location, only the lower wishbone has been rotated to adjust the ride height.

If so then with 35 splines the spacing between splines is 10.28 degrees
The lower wishbone is about 110mm long from pivot axis to ball joint.
So using high school trig, the ride height change that I get should be more like.
RH = 110 x sine(number of splines x 10.28)
Which for 1 spline is ~19.5mm and for 2 splines is ~39.5mm

As you can see a far cry from what Mr Haynes tells me.

Has anyone out there done this. If so how many splines did you move and what ride height change did you see?

Many thanks, Alan.

[Beatle]

Alan,

Best advice I can give is to follow the instructions religiously AFTER having read and re-read the text.  Don't read stuff that isn't there, and don't try to second-guess the logic. !!!

The secret is that the bars have one less spline on one end than the other (34 and 35 ?) so this gives a fine 'vernier' adjustment but only when you  rotate the bar the same number of splines BOTH ENDS at the same time. 

1.5mm height adjustment is achieved by turning both ends simultaneously by one spline.  If you turn the bar 35 splines, you may as well turn only one end (the 34 spline end) by one spline because the 35 spline end is back at the original position !  Now, to do the maths, if you turn the bar 35 splines both ends, this is 1.5mm X 35 = 52.5mm.  That's 2 inches.  The same is achieved by turning one end, one spline. 

52mm by turning one spline one end, Vs 1.5mm by turning the bar one spline, both ends !

My numbers might be out a bit, but you get the idea. 

MARK A MASTER SPLINE ON BOTH THE BAR AND ITS HOUSINGS - BOTH ENDS OF BOTH BARS !!!   I do this with a very sharp centre punch.  Keep a good written record of what changes you make. Use white-out or similar to draw rotation arrows before you start.  It will save confusion.

To move the bars you may need to disconnect the lower wishbone completely, but sometimes you can be lucky.  Bars are often stuck in the splines and there can be bumper discs inside the wishbone which can fall over and prevent the bars going all the way home on reassembly.

Now, given your car seems very low, you could probably begin by moving just one end of the bars one spline.  Then if this is close, you can fine tune by using the 'correct' method of turning both ends simultaneously.

I'll bet some previous owner simply dropped the car by turning one spline, one end.  People usually do this by rotating only the rear of the bar in the 'bridge' across the floor because it's easier than dismantling the front suspension.  This is lazy at best, and can be dangerous and expensive..   Note that late model cars have shorter bars and the rear splines are part of the floorpan.

It sounds tedious but is actually quite satisfying if you get it right.

Paul 'Beatle' Bayly

[Alan Hopla]

Paul,

Thanks for the input.
I had come to a similar conclusion over night that the difference in the number of splines in the front and rear of the bar would allow very fine adjustment of the ride height.
Very cunning of some engineer.

Much easier to visualise what is happening when you really understand what you are doing, and your description is most clear.

I suspect that either the rear or front of the bar has been adjusted by one spline.
My plan of attack now is to move the lower wishbone on the front of the bar by one spline, which as you say could raise the car by up to 52mm.

I'll then reassess the ride height and if required make fine adjustments by rotating the whole torsion bar.
After all, If a jobs worth doing it's worth doing twice!

Looks like I now have a project for saturday.

Many thanks,
Alan.

[Beatle]

OK Alan,

Now, it's been years (decades ??) since I've done this but from a rusty memory I suggest trying the following before you dismantle the front suspension, particularly the balljoints: 

MARK THE SPLINE RELATIONSHIPS FIRST !!!!.

1.   Remove the front wheels.  Disconnect the front shocks at the bottom and compress them outa the way.

2.   I think the splines on one end of theTbar are longer than the other.  If they are longer on the front(wishbone) end, then it may be possible to extract the torsion bar rearward, free of the 'bridge', while leaving the splines engaged in the wishbone.  Then, just turn the bar one spline and re-engage in the rear spline.

2a.   If this doesn't look feasible, you can remove the bolts holding the bridge to the floor and move the bridge rearward to clear the splines (I think ?).  This might take some juggling as you will probably need to do both Tbars simultaneously.

3.   If you can't budge the bars in their splines, loosen the lower wishbone retaining bolts, even pull them completely. Keep the camber spacers and shims in small bags and mark them accordingly.   

You need to get all the rotational tension off the splines, and ensure the splines are parallel, or the Tbar won't want to slide out.  Just the weight of the wishbone twisting the bar can be enough to make Tbar extraction difficult, so have someone jiggle it while you work on the rear end.    Get it right and the Tbar will hopefully move very easily (though I've seen 'em rusted in place).   

If all this still fails to budge the bars, then you may as well pull the lot apart.  I've never had much luck in pulling and reassembling balljoints so you may want to add the cost of new balljoints.

Of course, you will require a full wheel alignment regardless.  Make sure the alignment shop checks and adjusts all three parameters (toe, camber and caster).  A lot don't.

If you have standard Tbars this should all be pretty easy.  Thicker Tbars and wild camber adjustment add complications to the process.

Hope this helps and sorry if I'm telling you how to suck eggs !

Beatle
Katherine NT

[Alan Hopla]

Paul,

Thanks for your help, the job is now done.

I ended up dropping the front wishbone at the ball joint to get enough droop to relieve all the tension off the torsion bar.
Dropped the rear bridge mount and rotated the bars 1 spline.

Put it all back together and have raised the bottom of the lower wishbone inner pivot by ~60mm.
My ride height measurement using the Haynes manual method is now 50mm, which is 1mm above spec.

I'll let the car settle for a week then recheck and have the wheel alignment carried out.
I'm not too worried about wrecking the tryres in a week as they are alrerady pretty scrubbed out on the inside, probably from excessive negative camber.

Once again many thanks.

Alan.

[Beatle]

Excellent, I love it when a plan comes together 

If your tyres were already scrubbing on the inside, I'll bet the alignment is now spot on. (ie:  the person who lowered the car by one full spline also failed to adjust the alignment !!).