|The MGA With An Attitude
LOOSE U-BOLTS Cause REAR AXLE SHIFT - RA-104
At 3:24 PM 6/21/04 Steve Demko wrote:
>".... handling problem. On the test run I noticed that the car has a slight but noticeable tendency to pull to the left upon acceleration and also a slight but noticeable tendency to pull to the right when I let up on the gas with no braking."
That's loose U-bolts holding the rear axle to the leaf springs. The axle mounting is packed with rubber pads above and below the leaf spring for shock isolation. When the rubber pads deteriorate, or just squash and settle a little thinner with time, the U-bolts can become a little loose. This allows the rear axle to shift fore or aft a little on the leaf spring with acceleration and deceleration. When one end of the rear axle moves more than the other end it changes angle a little, effectively steering the rear end of the car off line.
The cure for this is often as easy as simply tightening the U-bolts. The U-bolts should be double nutted, so the nuts can be quite tight, and you do not want to break the U-bolt while trying to loosen the nuts. Start with a generous soaking of penetrating oil. Then use two wrenches. Hold the upper nut to prevent rotation while you loosen the lower nut. Repeat for all eight u-bolt ends (2 u-bolts or 4 ends on each side of car). Tighten all of the upper nuts equally until they are all snug. Then run the lower nuts up tight against the upper nuts to lock them all in place. That makes the u-bolts tight so the rear axle can no longer shift around on the leaf springs.
If the rubber pads are badly deteriorated they should be replaced. If the U-bolts show significant signs of thinning from rust, those should also be replaced. There is some risk of breaking a U-bolt while attempting to loosen the nuts. So if this is your daily driver car, and you can't afford to have it out of service, you might consider buying new u-bolts before you start.
Addendum August 18, 2015:
This is what may happen if you continue to drive the car with the U-bolts loose.
On 8/18/2015, Halvor Arne Asland in Norway wrote:
I bought a spare MGA 1500 chassis with front and rear suspension. Upon removal of the rear axle, I was astonished to discover that the rear U-bolts had completely worked its way deep into the rear axle making the axle housing scrap. It looks like the leaf spring locating bolt is broken and together with perished rubber, has made the axle move extensively under braking and acceleration".
On 8/8/2015, Kevin Keats wrote:
"I did some work on housing, drilled a couple of holes and measured thickness with a little homemade jig. My best guess on housing thickness is 0.150-0.160" (possibly 8 ga.)".