ok now I'm really confused-torsion bars

sleepy911 · 01-04-2009, 03:47 PM

Just took apart my donor track car I bought for drivetrain and suspension. The car was built by Otto's and Jerry Woods so I assume everything was done correctly. So here's where I get confused, when I removed the pass side torsion bars both front and back were stamped with a L. When I took apart the drivers side they both were stamped R. Am I missing something? I thought it was the other way around. Is there some kind a racers trick in running the bars on the wrong side?
I'm up to the point of putting this stuff in the other car but want to make sure I do it right.

euro911sc · euro911sc's Garage

Got me on that one... maybe ask in the track forum?

-michael

unclebilly · unclebilly's Garage

All I know is that you don't want to turn around a used torsion bar. Keep running them on the side they were on.

janz · 01-04-2009, 05:25 PM

Everyone I talked to, everything I've read and everything I've seen says "R" goes on right (passenger) and "L" goes on left (drivers) side. They are manufactured to be installed this way or you take the chance of really premature failure (break). Either someone was looking at the front of the car and said this is the right side and thats the left or they figured they could get more mileage out of them by reversing them. Even the stock car guys wouldn't try swapping them no matter how much they were sagging. Sounds like someone didn't know correct sides of car or they were pulling a fast one.

Elombard · 01-04-2009, 05:29 PM

I think its not that big a deal when they are new, who knows maybe the driver started doing his own wrenching at some point and did not realize??? Better be safe and sell them to me and start over :-)

RWebb · RWebb's Garage

how paranoid are you? enuff to buy new bars?

maybe they just had 2 new ones lying around marked L and stuck them in

how many miles have been put on the car since the bar work was done?

sleepy911 · 01-04-2009, 09:23 PM

Quote:

Originally Posted by RWebb

how paranoid are you? enuff to buy new bars?

maybe they just had 2 new ones lying around marked L and stuck them in

how many miles have been put on the car since the bar work was done?

all four were on the wrong side!!!

SteveinTO · 01-04-2009, 09:36 PM

"all four were on the wrong side!!!"

A foolish consistency is the hobgoblin of little minds...

Clearly Ogden Nash never race prepped a 911. Everything I've read indicates torsion bars should not be switched side to side, once they've been used.

chris_seven · 01-04-2009, 11:05 PM

I think that the marking of the bars is quite important and the reason for this marking needs to be considered.

The vast majority of springs are 'scragged' as the final stage of manufacture. With a coils spring this ususally involves loading to the point of coil binding and with a leaf spring it is taken to a fixed displacement which is slightly further than would be seen in service.

This procedure not only sets the spring to ensure that the correct load at fitted length is obtained but also slightly yields the spring cisung a small increase in strength.

As both coil and leaf springs can be fitted either side of a vehicle there is never any marking.

Torsion bars are slightly different in that they are obvioulsy handed in service and the sense of torque applied is different in both the left and right hand location. If you consider the torque direction as a screw thread one will be a left hand helix and the other right hand.

I would assume, but am not 100% sure, that being good, thorough Germans that Porsche 'scragged' all torsion bars before they were installed in the vehicle.

There is a metallurgical phenomenon known as the Bauschinger Effect which means that if a material is yielded in one direction and then reverse loaded its yield strength in the opposite direction will be slightly reduced.

This could mean that even new bars could yield slightly if installed in the incorrect side or fatigue life could be affected.

In practice I would imagine all torsion bars have sufficient margin of saftey to work in either side without too many problems but they were marked for a reason.

The age of the bar really doesn't matter because apart from Baushinger Effects the material doesn't have any memory of the sense of torque or rotation.

RWebb · RWebb's Garage

I disagree that age or usage is unimportant. Empirically, we see these bars fail after some time in use - perhaps due to rust, but who knows.

My query re paranoia level vs. wallet size is still open...

as is the issue of how the car felt while driven w/ these bars -- and for how long.

Also, what did JW say when contacted??

Elph. has some nice hollow & plugged ones...

chris_seven · 01-05-2009, 10:17 AM

I think you have misunderstood my comments.

In general terms torsion bars are probably designed to operate well within the fatigue endurance limit of the material they are made from and as such should have an infinite life.

I don't know what fatigue design tools Porsche would have used back in the Sixties but something such as a Goodman Diagram is most likely backed up by some S/N data. I can't imagine that they were not designed for infinite life.

Any surface corrosion and pitting will of course create a stress concentration and cause a fatigue crack to initiate and after a certain number of stress cycles then the bar will inevitably fail.

These issues are not related to the sense of torque being applied to individual bars.

Any torsion bar that has been 'scragged' in a specific direction new or old will have a problem if it is reverse loaded and this was the main fact I was trying to explain.

A bar that has not been scragged can be used in either sense of rotation and either sense of torque without problem as long as the stresses applied are below the yield stress of the bar.