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TR2/3/3A TR3 Rear Suspension Geometry

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Moseso

Moseso

Jedi Knight
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The full explanation of what I am up to will be forthcoming, but I am jammed-up real good at work today, so -- later for that...

I seek, from anyone who may be able to provide this information:

1) If someone has an uninstalled rear spring laying about, what is the measurement, if you take a straight-edge and place it across the top of the spring, from the front eye to the rear eye and measure down to the top leaf at the point where the bolt goes through the spring? Disregard any pads or spacers -- the top of the main leaf.

2) This is easier. What is the distance between bottom of the rear axle tube (disregard the rubber stop) and the top of the frame, when a TR3 is sitting on the ground, unladen?

"Close" is good enough for both of these measurements -- This is rear suspension -- thousandths don't count.

3) If memory serves, there is little, if any, spring pre-load when the vehicle is on stands and the axle is resting on the frame -- which is to say, if you remove the nuts from the u-bolts, the spring does not drop more than "just a little bit" away from the axle mount point. Am I correct in this memory?

As always, a huge thank you for your help!
 
Moseso said:
1) If someone has an uninstalled rear spring laying about, what is the measurement, if you take a straight-edge and place it across the top of the spring, from the front eye to the rear eye and measure down to the top leaf at the point where the bolt goes through the spring? Disregard any pads or spacers -- the top of the main leaf.
Click to expand...

I get 40 1/2 inches from the centerline of the front eye to the centerline of the rear eye.

And 4 1/8 inches from the top of the spring to the top leaf.
 
Thank you, Twosheds.

OK -- As promised, the story thus far. All drivers of pre-IRS TRs are familiar with the TR "sidestep," where, when enough body roll is induced in a turn, the frame hits the rear axle and lifts the inside wheel off the ground, causing a momentary reduction in rear end traction. I know that I am certainly familiar with the phenomenon. It is my plan to build a better handler in my current project.

I may be using too big a hammer, but this is what I have on the schedule:
1) Stiffer springs, front & rear
2) 3/4" front sway bar,
3) Lower the frame at the rear (increase the distance that the frame must rise to contact the rear axle).

I have seen TR "competition" rear springs. They differ from stock in having an extra full length leaf under the main leaf. I took my springs to the local spring guy and asked him to straighten the springs "a bit" (1/2" out of the unladen camber was the figure we came up with) and add the extra leaf. Being a dope, I didn't measure the existing camber in the "before" state.

I have begun the attempt to reassemble my rear end -- and have encountered difficulties. My recollection of disassembling the rear end is that I simply undid the nuts from the u-bolts holding the springs to the axle, and things just came apart. There was no appreciable preload when the axle was sitting on the frame and things did not "spring" apart when the nuts came undone. It's worth noting that the rubber bumpers on my axle were pretty badly decayed and didn't lift the axle off the frame as much as the new ones do. Even so, I have about a 2" gap now, between the axle and the top of the spring and the u-bolts don't even come close to being long enough to reach through the bottom plate so I can clamp things together.

Given Twosheds' measurement, it looks as though my spring guy DID decamber the springs about as much as we had talked about, so I am a bit mystified by the apparent <span style="font-style: italic">increase</span> in the gap between the axle and the springs.

Right now I am trying to figure out, what next? I can have the spring guy straighten 'em out a little more -- or -- (cheaper, I am sure) get him to make me some longer u-bolts and insert some spacers between the spring and axle. I don't want to make it so low that I drag-ass every time I enter a driveway, but I am afraid that if I just clamp the springs on as is, I will not have enough clearance between axle and frame.

I can see that this is going to be a "cut-and-try" adventure -- and I won't have wheels on the ground for another 6 - 8 weeks if I am lucky.

Anyone wishing to share prior experience with this sort of thing will be gladly read.
 
Not that it helps at this point, but I was able to eliminate the "side-step" with the stock rear springs and moderately sticky tires, just by adding sway bars front and rear. Now that I've gone to wider wheels and 205/55 Potenzas, I need a little more bar in the front. But IMO adding spring rate in the rear is the wrong way to go; instead you need more roll stiffness at both ends.

Even the stock springs seem to "relax" off the car ... I had to use a block of wood and a jack under the plate to get the nuts started when I installed original springs (from another TR3 since mine were broken).

From where you are, I'd suggest longer bolts and a spacer. If you get the bolts extra-long, you can play with spacers to set the ride height, using spacers under the nuts if necessary for the extra bolt length. Then when you're happy with the result, measure and replace the bolts with ones that fit.

Or even take the spacer thickness to your spring guy and have them de-arched some more. But since the spring camber appears to be a Good Thing, perhaps it would be better to stick with the spacers. Even Triumph went to a highly arched spring and a tall spacer, right at the end of TR4 production (and for the solid-axle 4As).
 
Moseso said:
Anyone wishing to share prior experience with this sort of thing will be gladly read.
Click to expand...

I didn't like having the inside wheel lift because the tire would spin when you tried to accelerate out of a hard corner, causing the driver to delay mashing the loud pedal until the tire regained traction. This slows lap times!

On the TR3 racecar, the front had a 7/8 ADDCO swaybar and MGB/GT springs. I put the competition rear springs Moss sells on the rear. I think I remember a space between the spring and axle because I made a 1 inch lowering block from 2024-T3 aluminum bar. I had 1 inch longer U-bolts made at a spring shop. I also put Ken Gillanders' rear spring locating kit on.

But I still had inside wheel lift on hard corners. It was a lot better than my stock TR3, but still there. Maybe a 1 inch sway bar would be better.
 
FWIW, Richard at Goodparts told me he could bend up a bar for a TR3 in any thickness you want. His bars are also a more complex shape so they can attach farther out on the A-arm (giving more of an increase in roll rate for the same diameter bar) than the ADDCO bars. (Plus hopefully not rub the wide tires in hard turns.)

Unfortunately the car got wrecked before I got a chance to try one of his bars.

I feel that stiffening the frame would also help; mine flexed noticeably in turns and going into driveways. Probably better yet to just start with one of Ratco's frames for a purpose-built racecar.
 
Twosheds said:
On the TR3 racecar, the front had a 7/8 ADDCO swaybar and MGB/GT springs. I put the competition rear springs Moss sells on the rear. I think I remember a space between the spring and axle because I made a 1 inch lowering block from 2024-T3 aluminum bar. I had 1 inch longer U-bolts made at a spring shop. I also put Ken Gillanders' rear spring locating kit on.
Click to expand...

I probably have very similar dimensions on my rear end to yours, now. The overlooked problem is now the shock link. The shock link connects to the bottom of the spring which is now a good deal farther away from the axle than it used to be. The left shock installed OK, albeit <span style="font-style: italic">almost</span> bottomed. The right shock was bottomed just slightly higher than the axle's rest position on the frame. That can't be good.

Looks like I have to reduce the spacers, or lengthen the shock links. Anyone else encountered this? This post by PeterK is about rear spring spacers. PeterK? Twosheds? Did either of you over-reach your shocks with the installation of these spacers? If so. what was your chosen solution? Anyone else?
 
No, my shock links reached their attachment points with the 1-inch spacers installed.

What you are describing can't be good at all as the shock travel should not function as the droop stop! I wonder if something is bent on your car, especially since only one side is affected. Was your car ever wrecked? Do the rear spring shackles look bent?
 
No apparent accident damage. It all looks fine and straight.

Perhaps the shocks were rebuilt weirdly at some point. The arm goes up past vertical on the up stroke -- which is useless range -- but stops at about 4:00 or 4:30 on the down stroke. BTW they feel fine, firm and smooth.

The actuator shaft is a spline fit of some sort in the rocker arm inside the shock. Has any one here disassembled a shock to that point? Does it require an act of Congress to rotate the actuator arm in the rocker arm?
 
FWIW there are longer shock links available. ISTR the late TR4 links were a little longer, while some MGs use a link that is much longer (but has the same fittings on it).

However, what you describe does sound like an incorrectly assembled shock. Sorry I've never had the arm off, but I believe it takes a press to get that joint apart and likely some special tools to support the shaft when you put it back together.
 
I agree; sounds like a mis-indexed lever arm.

Can't help you though. Never had the arm off.
 
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