Moss Motors, Ltd

I put new rear shocks and springs from Moss in my 73B roadster yesterday. As soon as I was done I road tested the car and found that the rear end is swaying back and forth when I step and and release the gas pedal.  Stepping up acceleration makes it surge to the right, while releasing the pedal causes it to drop back to the left.  

After reading the instructions in the factory service manual again I realized I had not had any weight on the rear axle when I tightened up all the spring bolts.  I had just tightened up everything as I went along on each side.

So I loosened up everything and retightened.  This made it a little better, but it still isn't right.  When I did this I also loosened the U-bolt (axle to spring) nuts....which I now realize was probably the wrong thing to do.

I'm thinking the primary factor is this whole equation is the position of the U-bolts holding the spring to the axle. If the U-bolt is leaning too much in one direction or the other then the axle will be out of position either too far forward or too far backward on that side of the car. Is that correct?

So, assuming I do not have the U-bolts positioned properly here is what I'm going to do:

1. Put the car up on jack stands front and rear so it will be level.  It will be supported from the undercarriage with the rear axle left to hang.  Leave the rear wheels in place so they can give extra weight to the axle to help it "self center".

2. Loosen all bolts once again.....spring front eye bolts, rear shackle bolt nuts, shock link arm lower connecting nut and 4 U-bolt nuts on both sides.  Also remove the rebound strap.

3. With the wheels still on for extra weight, retighten the 4 U-bolt nuts on both sides.  The front and rear spring mounting nuts/bolts will still be loose.

4. Replace the rear jack stands with ramps so the car weight will be on the springs.

5. Now retighten the spring front eye bolt, the rear shackle nuts and the shock link arm lower nut.  Reconnect the rebound strap.


I'm thinking that by first letting the axle hang down under it's own weight with the wheels, the U-bolts should self center. Is this correct?

If this doesn't do it I'll have to find someone close to eastern CT who can straighten this out for me.


Thanks,
BH

If I understand your description right, here's what I suggest. Hoping the axle will self-center is probably asking too much. It does need to be square to the centerline of the car but you need to actually measure it. Go from the same fixed point on the chassis to the axle on both sides and ensure that the measurements are the same. Just in case of manufacturing or other defect, do the same from another pair of fixed points.

For the U-bolts, again, don't depend on weight. If they are not perfectly square to the spring then they are not at the shortest distance. The result will be slack and allow the axle to move forward and back. After the axle is squared then be certain that the U-bolts are square to the springs and tighten them to the proper torque. All should be fine then.

 

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Bayless
Never express yourself more clearly than you can think
'48 Prefect
'67 Sprite (project)

I think you'll find that tightening the U bolts will cure your problem. Had the same problem on my Midget and tightening the U bolts did the trick. They need to be "tight". If they allow any movement in the rear axle against the rubber spring mounts then the axle can shift a tiny bit when torque is applied and removed. It doesn't take much movement at that point to really affect the direction of the car. As far as the U bolts self centering, I don't know about that, the axle is pretty well centered on the springs by the spring center bolts and mounting pads. The U bolts should pull perpendicular to the spring mounts as they are torqued. If they're not aligned a couple of taps with a hammer won't hurt anything to move them over as tight as needed against the bump stops.

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'73 Midget (V6)
'59 MGA (I6) under construction
'73 Lotus Europa

"There is a fine line between a hobby and mental illness"