Rear Torsion Bar Fit

Tspringer · 04-04-2004, 06:15 PM

I have replaced the rear torsion bars in my '69 911S with solid 28mm units I bought from Smart Racing Products. I have also upgraded to Sway-A-Way adjustable spring plates and Elephant Racing poly-bronze spring plate bushings.

I got all the new parts installed and the correct spring plate angle set. Everything looks good, except I am worried about the torsion bars themselves.

They dont seem to fit properly relative to length. The torsion bars are clearly bottoming out against each other at the center of the torsion tube. They are also not filling out the spring plate cap. When one torsion bar is all the way against the outer stop in the spring plate cap, the other torsion bar has almost a full inch of bare teeth showing in the torsion bar cap. I can use a steel rod to gently tap on the bar that fills the spring plate cap and slide both bars across until they swap relative positions.

When I installed each torsion bar to begin with, I slid them into position until they bottomed out. They did bottom... it was not possible to slide one through the inner tube teeth all the way. Still, when both bars are installed they are meeting in the middle because pushing one one bar does move both.

I am very concerned about leaving it this way. When one bar is all the way at the end filling the spring plate cap, the other bar has only perhaps 1/8 inch of grip on the teeth in the opposite sides spring plate cap. I can picture it being a pretty bad thing for these teeth to lose grip in turn 12 at Road Atlanta and collapse the suspension.

Any ideas? It would seem the torsion bars are both going in too far. I had a terrible time getting the original bars out, see the story here:

stuck rear torsion bars

I really spent a lot of time cleaning out the tube, treating it for rust and rust prevention and making sure the inner teeth were clean. With lots of anti-sieze on the torsion bars they slide on the teeth quite easily. The spring plates are gripping the bars well it seems and I see nothing wrong at all except as mentioned.

It actually seems the dang torsion bars are about 1/3 inch too short each!

Anyone ever run into this before?

Terry

Jeff Alton · 04-04-2004, 07:39 PM

Can you compare the lenghts to the ones you pulled out of the car?

Jeff

Randy Webb · 04-04-2004, 08:44 PM

You may need to call SRP and ask them.

Based on this and the other posts recently, it seems like you should avoid working on the rear suspension of that car!

Good Luck!

Tspringer · 04-05-2004, 06:00 AM

You said a mouthful Randy! The entire front end rebuild was pretty straightforward. I ended up having to do lots of rust repair... but the mechanical assembly was normal. The rear end on this thing has fought me every step of the way. At times I have felt like rolling it into the driveway, dousing with gasoline, lighting it on fire and dancing around it in glee whooping for joy as it burns to a crisp. My neighbors might not invite us for dinner again if I did it, so at least so far the car is safe. So far.

Terry

ttweed · ttweed's Garage

Quote:

Originally posted by Tspringer
I can use a steel rod to gently tap on the bar that fills the spring plate cap and slide both bars across until they swap relative positions.

Terry-
My understanding is that there is supposed to be a "stop" for each torsion bar in the center of the torsion tube which should prevent your being able to do this. I would guess that yours are rusted out or something. Could you use a solid spacer between the inboard ends to keep the bars in the right place? Or install a couple new stops in the torsion tube by drilling and tapping a couple of bolts into the bottom at the appropriate locations?

TT

Randy Webb · 04-05-2004, 05:03 PM

Of course, if you BBQ'd the car, you would not need BBQ invites from anyone.

It is posts like yours that give me the heart to work on (beat on and curse) my own car -- no matter how screwed up, I am secure in the knowledge that somebody has a worse problem.....

Ya gotta call SRP -- they can advise you. Craig is an engineer - nobody there is dumb... As to the stop, who knows - maybe PAG added it a year after they built your car...

ChrisBennet · ChrisBennet's Garage

The torsion bars on my '86 touch in the middle. You can move one out by pushing the other one in. I never pushed them far enough to see if they bottomed out but I don't see why they would - the splined area is the thickest part of the bar.
-Chris

Tspringer · 04-07-2004, 01:00 PM

I spoke at length with Rich at SRP. The bars on his car also touch in the middle and he can move one out by pushing the other in. The extra space in his spring plates is not as much. WE did lots of measuring and comparing... but came up with no real good reason why there should be about 1 inch of total extra space there.

I have inspected the inside of the torsion tube with my bore scope pretty close. There appear to be no issues in there, the splines on both sides are very clean and shiny (I cleaned them with a wire brush attached to the end of a long steel rod). Everything upon inspection appears as it should.

Rich and I at this point have determined to ignore it. I am going to carefully install the bars such that they are centered on the internal splines and are not touching in the middle. Then I will make sure each bar maintains that position when the spring plates are installed. This will ensure I only have .25" or so of spline showing in each end cap. I will thus have good solid engagement of both bars on both ends. Once the car is back on the ground and 700+ pounds of twist is being applied to each bar... they wont be able to move laterally and thus should stay in position on the splines.

When I drive the car for the first few times I will of coarse check the torsion bar position to ensure that in fact they cannot move around when under weight.

Terry

Jdub · 04-07-2004, 01:40 PM

You will not be able to be sure that the bars remain centered as you push the spring plates on - trust me.

Your option is to drill a small hole in the center of the spring plate cap - this will not compromise the spring plate. Doing this lets you 1) get penetrant in there at a future date, God forbid, and 2) measure exactly the amount of room from cap to 'bar end, thus knowing you have the exact amount you expect and thus the exact amount at the center.

John

EDIT: The hole you drill can easily be "capped" using a small (1/8") rubber bung you can find at Home Depot. It actually looks pretty cool -- I did this to my car to get the penetrant in there and to force a pin tool in to push the tbar out. Worked the charm.

ChrisBennet · ChrisBennet's Garage

I just pop the endcaps out and then put them back on after the bars are in place.
-Chris

Jeroen · 04-07-2004, 04:05 PM

Maybe a stoopid idea, but is it possible that you got G50 t-bars (87-89) instead of 915 t-bars?
The G50 bars are shorter, I just don't know by how much...

cheers,

Jeroen

ttweed · ttweed's Garage

No. The spline counts on the ends of the later bars from the Carreras w/ G-50 are different. They would not even mesh with the early torque tube splines.

TT

Tspringer · 04-07-2004, 06:52 PM

They are not G50 bars. I compared them to the stock bars and they match in length perfectly.

The spring plates are sway-a-way adjustable units. They do not have caps on the ends, you can clearly see the bars during and after installation. With these spring plates you have a plastic slip on cap that covers the end of the unit and protects the bar from dirt. This mean I can very quickly just glance in and tell at any time if the bars have moved.

Terry

Zeke · 04-07-2004, 07:54 PM

When i cut the Targa down the middle. I didn't see anything that would stop the bars from going right on through the center spline tube.

I think the spacer is a good idea, but for some reason it is apparently not needed. I bet if you center the 2 bars, they will stay right where you left them.