TheSamba.com :: View topic

Fri Feb 06, 2009 9:41 pm

I’ve finally fixed my car’s rear end!

It started when I noticed that the rear torsion bars on my 1610 lb. oval were the same ones used on a 2000 lb. 356B. With the aid of the spring rate chart on the SAW site, I compiled some data comparing the spring rate/weight of various vehicles.

Oval 151/1610 = .094
356B 151/2000 = .076
356C 147/2100 = .07

“Hmmmm, I wonder if the reason my rear axles dance around every time they hit a bump is because they’re too stiff for a car as light as mine?” Since the 356C is reputed to be the best handling of the early Porsches, I decided to grind down my torsion bars so that spring rate/weight ~= .07. I reduced the diameter from 24mm to 22.5mm, and installed the bars last night. The ride is nice and smooth, but still flat because I have a front sway bar. Most importantly, the rear doesn’t feel like it has an agenda of its own.

As always, there’s a downside. Machining the bars cost me $80, removing, installing, re-installing, etc. the torsion bars is always a pain, and I’m sure my rear end will de-camber more than it did before with a car full of passengers. But I don’t care, because my car is finally fun to drive!

If you have one of the lighter VW’s (split, oval, kit car, etc.), grind down those torsion bars. You’ll be glad you did.

Paul

Sat Feb 07, 2009 11:58 am

Interesting! :idea: I've never given that any thought.

Sun Feb 08, 2009 1:37 am

gimmesomeshelter wrote:
I reduced the diameter from 24mm to 22.5mm,

This is what VW did in 1967. Torsion bars went down to 22mm.

Sun Feb 08, 2009 5:11 pm

paul
your a nut bag!
but thats fine
it's entertaning :lol:

Sun Feb 08, 2009 6:29 pm

Is it possible to just buy some sway a ways that are that diameter with the correct splines for an early car?

Sun Feb 08, 2009 6:36 pm

Get the spring plates from a 60-68 Beetle, torsion bar covers and grommets too. Then the later torsion bars fit.

Sun Feb 08, 2009 6:38 pm

Hello-

Not that I know of. I purchased a set of stock sized torsion bars from SAW last year, but I found them to be too stiff. I contacted them to see if I could order a smaller than stock set, and they suggested that I have them ground down.

Paul

Mon Mar 02, 2009 5:09 am

Bruce wrote: gimmesomeshelter wrote:
I reduced the diameter from 24mm to 22.5mm,

This is what VW did in 1967. Torsion bars went down to 22mm.
60-66 torsion bars are 22mm. 67 torsion bars are 21mm unless car was ordered with M86, no Z-bar, in which case they used 22mm bars.

Mon Mar 02, 2009 8:30 am

Hello-

Keep in mind that the stiffness of the bar is a function of both the thickness and the length. If you go to http://www.swayaway.com/TechRoom_VWguides.php, you'll see a chart listing the dimensions of the different bars used by VW (and Porsche) as well as the amount of pressure it takes to twist the bar 1 degree.

Paul

Mon Mar 02, 2009 7:26 pm

Very interesting, I had never considered this before.

Mon Mar 02, 2009 7:47 pm

Are you running a stock engine and trans?

How much engine can a 21mm torsion take?

should i not compare suspension "smoothness" to wheel hop under load?

what about running a camber compensator or sway bar, does the softer torsion work with or against??

Tue Mar 03, 2009 8:34 am

Hello-

Quote: Are you running a stock engine and trans?

I'm currently using a tunnel trans with a DP 1600. I would like to run a vintage speed type motor with 65-70 HP.

Quote: How much engine can a 21mm torsion take?

Keep in mind that I reduced the stiffeness of the rear torsion bars to 1) make the rear end more comfortable, and 2) mimic what Porsche did. If you have a much larger motor than mine, I would imagine that the rear end would 'squat' more than a normal car during hard accelerating.

I've always had small engines, so I don't know anything about wheel hop.

Quote: what about running a camber compensator or sway bar, does the softer torsion work with or against??

A camber compensator will still work normally (keep the wheels from tucking under.) As for the sway bar, if you have one in front, softening the rear will give the sway bar more influence over the car (more understeer).

All in all I wish I hard better data/correct formulas to work with. I've definately made progress with my suspension, but a lot of it has been (expensive) trial and error.

Paul

Tue Mar 03, 2009 7:18 pm

What sort of finish did they do when grinding to address fatigue issues?

Tue Mar 03, 2009 11:47 pm

Hello-

My machinest turned them down on a lathe and then bead blasted them. I covered the bars, as well as the inside of the tube, with several layers of cosmoline prior to installation. Asuming I keep these bars, I'll have them powder coated when I paint/powder coat the pan. He indicated that 1) I needed to careful not to ding them during install, and 2) cover them so they don't rust again.

Paul

Tue Sep 19, 2017 12:35 am

Ok, so I know I'm digging up a rotting corpse...

This is craziness.

60-66 torsion bars are torsions are not that much softer by virtue of being shorter. So 2mm less diameter doesn't make as much difference as you think. And the the long 24mm bars are more progressive by being longer.

In effect what you're doing is swapping oversteer on the limit for understeer at much lower speeds. Ie. a sturdy pair of pants for a skirt. I think you'll find porsche was trying to counter all the rumors about the 356 being a tail happy widow maker... Which is only true if you can't drive.

I like the stiffer bars in my oval. It makes it easier to throw the rear of the car around in khanas.

Sun Oct 14, 2018 4:14 pm

interesting topic... as I would like to get new torsion bars in my 57 oval. If I understood right, a 1957 has originally 24mm 627mm long torsion bars, am I right?

And slowlearner, have you fitted thicker diameter torsion bars in your car? Or have you just renewed it?

I have some doubts if the 60+ year old torsion bars have the same spring rate as they were new, therefore I thought about renewing them for new SAW torsion bars.

please advise