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MG TD TF 1500 - TF - loose rear? (strange movement)

I'm a new owner of a 55 TF-1500. The car is all original and has less than 20K miles on it.

The car runs and drives great, but behaves strangly under acceleration and lift-throttle. Under acceleration, the rear of the car seems to shift to one side, then when you lift, it seems to shift to the other. It's quite noticable, and almost feels like a loose spring U-bolt or something that could be causing the rear to shift around within the spring mounts under torque.

I've looked (quickly) at the rear suspension, and don't see anything out of order. Any ideas what could be causing this or where I should look?

Thanks!

Dave
DEL Leonard

Two thoughts:

Tire pressure and rear spring pads.

Tire pressure is lower on these cars than most people think. Try playing with diifferent presures front and rear to check for stability. You could start with 25 front, 25 rear, and then reduce the rear to 22, and if you don't like that, reduce to the fronts to 18. It will give you an idea of which way to bias your pressures.

There are rubber mounting pads under the rear springs and under the rear axle (where it sits on the springs). They can get old or hard, and then the location of the U-bolt becomes suspect.

There are also rubber mounts (and sometimes urethane) at the end of each leaf spring. Those might be needing to be freshened.

Moss motors has an adapter plate that can be placed over the top of the axle to make up for wear in the axle (I believe the plates were standard equipment on the MGA) and can also supply a new set of rubber mounting pads.

At least, that's my take!

dave
D. A. Braun

I think you diagnosed the problem. TD/TFs are notorious for this. The rubber pads crush and rot (a pad above and below each spring) and the axle twists all over the place. There should be double nuts-penatrating oil first, then loosen the outer one, and tighten the inner, retighten the outer to lock, do all 8. See if that helps. Also, the u-bolts often wear a notch into the axle case. There is a "buffer" sold (basically a curved piece of steel) that fits under the u-bolts to stop further chafing. Lastly, the pads may be so deteriorated the upper nut may bottom out (run out of threads) without really tighening, a stack of washers will temporarily cure this. Two other things to check- eyeball and tighten everything on the suspension- make sure the front lever shocks aren't loose from the frame, etc. Recently my TD with freshly rebuilt rear suspension still had a bit of wander off/on throttle that I could not eliminate. Eventually I found one front shock had mostly failed with little damping, while the other was fine. Rebuilt shocks totally cured that. George
George Butz

Have someone stand and watch the rear end while you take off... look at both sides. Certainly more then a "torque" shift?
gordon lawson - TD 27667

PS- Dave is right on about the spring end rubbers as well. Gotta disagree about tire pressure though- read the archives. My TD plows like a sloppy pig with anything lower than 28PSI front and rear- I usually run 30ish cold. More fun to slide on our sandy corners in central Fla!. George
George Butz

Good point on the tires, George. I was thinking bias-plies which an original car may still have (mine did until I took it apart in April!)

The buffer plates you describe are the same ones I was talking about, you just did a better job!

warmly,
dave
D. A. Braun

Thanks folks - good thoughts! I suspect the rubber pads may well be it, so I'll get it in the air and take a good look at them. It certainly feels to me like the axle is moving around in it's mounts.

It's not excessive torque reaction :-) A humerous thought however...

The car has bias-ply tires currently by the way, so I'll also look at the pressures as noted.

Dave

DEL Leonard

Del, Dave is correct for bias ply tire pressure- I have run Michelin XZX radials forever, so my pressure rec. was for those radials only. George
George Butz

No one has mentioned one other obvious possible cause: The TD/TF rear shock absorbers are notorious for having the linkage arms slip out from the axle mount, especially if the link bushings are old and hard. However, you say a visual inspection revealed nothing so I would also have a look at the level of fluid in all the shocks. If the car sat for a number of years, there is likely no fluid left.

Cheers,
Lew Palmer
Lew Palmer

Dave L. - If you are going to replace the pads (and even if you aren't, get a set of protective shells to go over the axle housing to keep them from groving as a result of the axle working back and forth in hte U bolts. These shells are actually for the MGA, but I think that Moss now offers them in the T series catalog. Good luck - Dave
David DuBois

I think that it may be a sheared off spring centre bolt. This allows the diff to move along the spring on acceleration and deceleration. Should leave some scrape marks however.

Cheers,

Paul.
Paul van Gool

I recently found that the rear axle on my 69 MGB-GT is offset from the c/l of the car by about 3/4" to the left. I find out that this offset is common on all MGB's and is built in to counteract when torque is applied to the rear axle. the axle shifts over to the c/l. The only way to control this is with a Panhard rod and that causes other issues. It is unclear why MG did this.
In the TF the axle is not offset. When torque is applied/released to the rear axle it moves in a lateral direction and because of the design of the suspension, and the axle/wheel changes direction slightly, thus giving that "sway" feel or a steering effect.
This is similar to the rolling effect that moves the axle out of line when cornering.
ref: Colin Campbell, The Sports Car, Its design and performance. Pub 1954

DEL....send me your email, I would like to talk to you about your orig. TF.
Colin Stafford

Something else I should have thought of...

The rubber mounting pads sit in metal plates, with center holes for the heads of the centering bolt, and four holes for the u-bolts to pass through. If the holes for the u-bolts are elongated, you can get some major shifting under load. There are four plates, two on each spring. Usually at least one plate is worn on each spring. You have to weld and re-drill, or purchase some new ones.

dave
Dave Braun

I had this problem on my MGB. The main leaf of a rear spring was broken near the center of the spring and it was sliding back and forth in the spring clamps. This allowed the rear axle to move about 2 inches back and forth on one side. The break was under the rubber pad and not visible.
Don Harmer

This thread was discussed between 03/08/2005 and 10/08/2005

MG TD TF 1500 index

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