F78 Sheared rear swinging arm

Submitted by basilb on

Forum: 

One of the rear swinging arms on my F78 has sheared off where the box section is welded to the bush tube at the chassis end (front of the arm).

Has this happened to anybody else?

I'm trying to work out why, no signs of excessive rust. Vehicle is used regularly on a bumpy track, but at low speed.

Bushes were replaced earlier this year.

Is it possible to over-tighten the bush bolts and restrict the arm movement too much?

I only have an F76 manual so don't know torque settings?

Any pointers will be much appreciated.

i have never had one go but

Submitted by parrotveasey81 (not verified) on

i have never had one go but have read of lots that have snaped,there is alot of stress on that bit as they carry the rear springs.
the bushes should have enough movement in them even if over tighten'd and poly bushes have even more movement in them.

best thing i can say is get a bit of steel welded along the bottom and up around the front of the arms

Thanks for that, good to know

Submitted by basilb on

Thanks for that, good to know I'm not the only one!

I'm in Romania at the mo, so hard to get a replacement part, so have welded a repair with extra reinforcement, similar to what you suggest.

I think I will get the other side done as well, seems to me that part is a bit under-engineered.

The bushes are poly, so must just have been bumping up and down our track, that and the Romanian pot-holes

F78 Sheared rear swinging arm

Submitted by jw on

This happened to me and I'm pretty sure polyurethane bushes were the cause. The unequal length of the top and bottom trailing arms on F78 causes roll-binding of the rear suspension if poly bushes are fitted. If you look carefully at standard bushes you will note that they are not solid rubber over the whole circumference and are designed to allow movement to prevent binding as the body rolls in corners. Ideally four link rear should have equal length arms that are always parallel to allow unrestricted long travel. I guess the F78 design was intended to keep costs as low as possible by adapting the existing leaf-sprung chassis rather than designing afresh. However it seems to works acceptably so long as polyurethane is not used, at least not in both top and bottom arms.

Unfortunately Daihatsu do not appear to supply replacement bushes on their own which further increases the temptation to fit polyurethane..