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MG MGA - Rear springs

I enter motorkhana (autocross) and speed events. From a standing start I find the rear springs "wind up" which results in a violent shudder through the car and can cause it to jump out of gear and once cracked the windscreen. Is there any solution rather than a gentle take off such as tramp rods or an extra leaf in the springs?
I Hazeldine

Short answer first. I suggest you check condition of the leaf springs and all of the rubber interface parts, and tightness of bolts.

The longer answer is, I have been seriously autocrossing my MGA with various SCCA organizations (and other local clubs) for years, definitely more than 200 events resulting in a house full of trophies (long since lost count of both). I have been in competition using skinny street tires, wide street tires, and sticky treaded road racing tires. I nearly always do a jack rabbit start involving some tire spin so the engine does not bog down before it gets moving. I have never once encountered any hint of axle hop on start up.

Bottom line is, I have no experience with this problem, which gets back to the short answer.
Barney Gaylord

Hi Barney,
I broke a leaf spring about 5 years ago so both sets of springs and the bushes were replaced at the same time. Then fitted a Quaife L.S.D.and checked all the mountings etc. again. The car is fitted with a "fast road" 5 bearing MGB engine and a Datsun 5 speed gearbox which required a heavy duty clutch plate as part of the modification so maybe uprating the rest of the drive train highlights the weakest link.
Thanks for a quick response, Ian.
I Hazeldine

Ah, posi-traction. That may have a lot to do with it. I always run an open differential, so the car will commonly spin the RR whee, while keeping the LR wheel firmly planted. With the two wheels out of sync one can serve to dampen the other.

With posi-traction you can get two wheels doing the same thing at the same time, so when one wants to hop they may both hop in harmony, following the beat of the same drummer, so to speak. My answer is still the same, no experience with the situation. Traction bars might be worth a try, but read the rule book first.
Barney Gaylord

I fabricated a pair of tractions bars for my first MGA many years ago. The traction bars effectively create a more modern multi-link supension, prevent the leaf springs from winding up and help keep the tires in contact with pavement during hard acceleration. I just had a 1600 and no posi, so I don't know how the bars would work for you. And as Barney notes, check your rule book.

Ken
k v morton

Bit puzzling as I run a Quaife as well and have never experienced bad wind up like that even when running with no traction arms.

I suggest that you may want to install an upper locating arm - it requires welding a couple of hefty tabs on the top of the diff and on the round cross tube right behind the vertical plywood panel behind the seats. This will absolutely limit the ability of the axle to rotate on its axis as you've experienced.

You can do it with traditional lower traction bars too, as long as you use the kind that has a snubber that contacts the spring rather than a fixed attachment point at the front of the spring. If you do that, you'd need to allow the springs to float between the spring plates - too much fuss for a street car.
Bill Spohn

Ian,
If you're experiencing a sudden thrust that breaks the windshield, I think you have a different problem. You may wish to check your driveshaft joints and possibly the amount of backlash in the diff. Look to a possibly broken transmission mount. What you're looking for is something that allows the drivetrain to move (when it shouldn't) before the wheels do.
mike parker

Hi Mike,
When the 5 speed box was installed an extra cross member was added to support the transmission mount so in that section it is stronger than original also engine doesn't move forward under heavy braking and on track days the mounting points get checked by scrutineers.The drive shaft is the Datsun unit which is heavier duty than an MGA's. It was shortened and balanced and has heavier duty greased for life universal joints that were replaced when it was modified. The diff was rebuilt when the L.S.D. was insatalled so backlash is minimal. If the drive shaft was out of balance I think the vibration would be continual and vary with transmission revs rather than just on a fast take off.The car is very smooth to drive daily in traffic and doesn't have any unusual rattles or vibration, It only has this problem if the clutch is released quickly at high revs so a gentler take off may be the best solution (and hope I'm not rear ended) or finding some kind of traction bar as mentioned earlier.
Thanks for your input, Ian.
I Hazeldine

Ian, if I read correctly, your rear spring bushes were replaced five years ago.

Soft or slightly worn rubber would give the symptoms you describe.

Did you use nylon or poly bushes? I would look again at the bushes and pads and if not already done upgrade to performance poly. Also reproduction rear springs have been of varying quality over the years so worth another check there too.

Probably already done, but a recheck of rear shock absorbers and link arms wouldn't hurt either. (not strictly a likely cause but a possible contributor)
Neil McGurk

Hi Neil,
The bushes were replaced about 5 years ago with what I think is called nylathane (red colour) bushes. At the time a few club members said they would be too hard and did not have enough "give" which is perhaps what I need but they are still installed so I will recheck them. How do I check the quality of the springs? The ride height appears O.K., no thumps or bottoming out during normal driving and no broken leaves, Anything else I should consider?

Thanks Ian.
I Hazeldine

OK Ian, how much horsepower and torque are you putting out? If you're putting enough out to twist the frame, that could do it. Also, you ought to check your body to frame mounts. They might feel good but be loose enough to cause some consternation under torque.
mike parker

Hi Mark,
I don't know what the output of the engine is, as I said before it's a road car not a race car and the frame of the MGA was over engineered so I doubt very much that a mildly tuned 1800 engine would twist the frame. The problem is that the rear springs twist into an S shape under heavy acceleration fron a standing start( a rolling start doesn't have the problem) when they snap back to the usual U shape a shudder is sent through the body and frame so some kind of secondary mounting to locate and support the rear axle or uprated rear springs (may be poor quality but how do I find out?) to prevent them twisting is what I think is required. All I need to know is if anyone has had the same problem and did they uprate the springs or know of bar to support the springs to stop them distorting. People race and have put V8's in A's so I've assumed they would experience the same problem.
Thanks for the response,
Regards Ian.
I Hazeldine

Please forgive my lack of technical knowledge, but is this like "tramping", a problem that some MGBs have, and they fit "anti-tramp" bars? If it is then B bars won't fit, but surely something similar could be devised for the mighty MGA?

Kind regards,

Grant :-)
G Hudson

Hi Grant,
Yes that is the problem. I was hoping that someone may know of suitable bars either available commercially or drawings to make them. The other option was to insert an extra main spring to stiffen the springs.
Thanks Ian.
I Hazeldine

Ian,

The bars I built for my MGA 40 years ago as a high school student used a bracket made of heavy angle on each end of a junk-yard tie rod. The rear brackets bolted to the axle u-bolts and the front brackets were welded to the frame. The tie rod ends were bolted into holes that were drilled and files to a taper in the vertical plane of the angle iron. The design came from a mid-60s Hot Rod magazine, and worked quite well until my amateur welds failed. But I would check some of the other recommendations, too. Your tramping sounds way more serious than anything I've noticed in my current 1800-powered MGA.

Ken
k v morton

This thread was discussed between 19/02/2009 and 24/02/2009

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