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MG MGB Technical - Kangarooing

I have a problem with my MGB that when I change down into 2 gear to go over speed bumps and I applie the accelerator to pick up speed the car will start kangarooing for want of a better phrase, it will some times do this over rough ground when I'm in second gear, I find myself having to dip the clutch pedal and releasing it to gain control.
I've thought about it and sort of come to the conclusion it might be the pistons in the SU carbs moving up and down as if the damper oil was not thick enough, has anyone got some other ideas as to what might cause this.


Regards Patrick Tighe
P.T. Tighe

Patrick - Check the rear axle to springs U bolts. If they are loose it will allow the rear axle to do strange and unacceptable things. Cheers - Dave
David DuBois

Do you have big feet? No I'm serious! If the throttle return springs are weak it is easy to inadvertently release/press the throttle pedal! If it doesn't do it on smooth ground in 2nd.... The carb pistons don't move unless you open the butterfly by pushing on the accelerator. (Or soething else is shaken to push on the accelerator)

Long shot but maybe worth a thought!
Michael Beswick

definitely a problem with positive feedback from the car motion through your foot to the accelerator. You need to reduce the amplification here somehow. A sticky cable would make things worse, as would stiction anywhere. Maybe some lube on the linkage would help, maybe your shocks have had it.
Art Pearse

Bad rear dampers, loose rear axle locating bits, bad engine/gbx mounts, throttle cable sticky and/or caught on something.

FRM
FR Millmore

My feet may be a bit on the large size being a size 10'
Other than that the carb springs are good, back axle is secure but how dose one check the shock absorbers the suspension on my car appears to be very stiff

Regards Patrick
P.T. Tighe

Rear suspension can appear to be very stiff, but dampers still bad. Especially if it sat a lot and the springs are rusty and/or it has been driven gingerly. Spray the springs with oil and take it for a fast ride down a rough road. It will ride better but this will then make the rear dampers really necessary, showing deficiencies. Rear will bounce over bumps. The small amplitude high frequency damping required by washboard roads cannot be supplied by high friction in the springs, and frozen springs themselves may be causing the problem. Check damper oil, all around, and look for signs of leaks.

FRM
FR Millmore

We call this "bunny hopping" downunder :-)
John Minchin

This thread was discussed between 25/07/2012 and 27/07/2012

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