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MG TD TF 1500 - Drive Shaft Allignment

I assembled the engine, trans and rear end about a year and a half ago. I remember having problems with the drive shaft clearing the rear frame member. I also remember thinking that I had finally got it right, although there was very little clearance.

The chassis, etc is now at the body shop to have the body mounted and we have noticed that the shaft is now rubbing the cross member. I doubt that the body is going to provide enough weight to bring the cross member down and the drive shaft up enough to be safe. Can the rear of the chassis be shimmed enough to raise the drive shaft? Is there a specific angle for the drive shaft to rear end? I don’t think the engine/trans are going anywhere so the adjustment is probably going to be at the back end. Help!

Bill
Bill Reid TD4618

Perhaps, is the rear axle rotated too far in one direction so as to cause the driveshaft to be at the wrong angle?
Lew Palmer

TF2071 has a similar problem due to the springs that came with it having the correct radius for a TD instead of a TF. This is causing the same problem as Bill has and the shackles are not sitting in a near vertical alignment as they should.
So far I have tried 10mm lowering blocks (the thickest I could fit without needing longer U bolts) slightly tapered towards the front which provides a little axle rotation as Lew has suggested. However, I am still leaning towards having the springs recambered to the correct shape.
Chris
C I Twidle

Main objective, aside from clearance, is to have the axis of the pinion shaft as parallel as possible with the axis of the engine & transmission.

U-joints are not constant velocity joints. When operating on an angle, they don't not transmit smooth motion, but more of a "herky-jerky" rotation that worsens the greater the angle.

However, the two U-joints on a driveshaft will effectively cancel each other for a smooth, constant velocity transmission of power, but only if the axes are parallel. This is why it is so critical that the yokes are welded onto the driveshaft in their precise relationship.

I cringe every time I see a raised pickup truck with the axle (or axles) tilted up towards the transmission. Shake, rattle & roll.
JIM N

Chris,
Seeing as the TD and TF share the same chassis the spring camber should make no difference.
This problem has come up a few times in the past. The chassis needs to be weighted at the rear and the rebound strap fitted. If you don't there is a chance that the shackles will over rotate and wreck the rear wings (it has happened). Fit the tub by all means but do not fit the wings until that strap is fitted.
As Jim says, the parallel alignment and coupling orientation are critical to stop cyclic variations in rotation.
Also Chris I have had TD springs on my TF for many years as it stops bottoming out when full of fuel and gear. No adverse effects and I think it reduces roll oversteer (no AR bar)
Ray TF 2884
Ray Lee

Does not look too bad with raised ride height.
Ray TF 2884

Ray Lee

Thanks for the reassurance Ray. I have fitted rebound straps but even when I bounce on the rear of the chassis my 80kg can’t move the axle off the straps! The shackles are less than 10 degrees off being in line with the spring instead of being nearly vertical as they would be if the springs were nearly an inch longer as I believe the TF’s were originally. I still need to try loosening off the shackle bolts to see if that allows them to move a little more freely. With nothing more than the mass of the tub the rear wing is sitting much higher than yours.
Chris
C I Twidle

This thread has been a great help so thanks to Bill for the original question and to Ray, Lew and Jim for their input. Today I slackened off the shackle nuts, applied a lever to the springs to bring them close to the vertical, then re tightened the nuts. The shackles stayed at a slightly better angle even without the bodywork, tank interior etc. in place there is already nearly 10mm of clearance between the prop shaft and the cross member and this can only get better when loaded.
I had already tried adding some slightly tapered lowering blocks under the axles and I think I will leave them in place to see if they help the alignment when fully loaded as suggested.
Chris
C I Twidle

Chris,
Do not tighten the shackle nuts until the car is fully assembled with the wheels on the deck (preferably with fuel in the tank). It will rip up the bushes as everything settles into place. If they are rubber bushes they tend not to last long anyway.
Ray TF 2884
Ray Lee

Good thinking Ray. The bushes (along with several other rubber items) are already looking tired after sitting for the three years of the rebuild so far. I wonder if the upgrade to poly bushes is worthwhile and if they are still available.
Chris
C I Twidle

Chris, If you wish to change from rubber bushes maybe you would like to investigate using urethane bushes. Thew ride is slightly harder but they will last a long time. Check with Pedders Brake and Clutch people in Queensland.
John
J Walton

This thread was discussed between 29/08/2019 and 08/09/2019

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