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trailing arms
AndyGT - 21/6/10 at 12:12 AM

looking at fitting a ford english axle into my chevette project but want to retain the rear seat IF POSS.

Anyway, I think it is possible but only if I used different length trailing arms on the 4-link (upper ones shorter than bottom ones). Would this cause a problem for the propshaft?

Thanks
Andy

A1 - 21/6/10 at 12:20 AM

like the cortina ones? i recon your best getting them made up to your design. only problem with the prop would be length.

MikeR - 21/6/10 at 07:33 AM

if you use different length trailing arms (with the top being shorter) as you go over a bump the nose of the diff will rotate and start to point to the floor. The amount it moves depends on the difference in the length. If its a few mm then i'd imagine it would be ok.

Get some paper and draw up a scale drawing and see what happens.

A1 - 21/6/10 at 08:39 AM

you can fit a fifth link going into the top of the diff to stop that, also to stop wind up during acceleration, doesnt eliminate it though.

MikeRJ - 21/6/10 at 09:36 AM

quote:
Originally posted by A1
you can fit a fifth link going into the top of the diff to stop that, also to stop wind up during acceleration, doesnt eliminate it though.


You couldn't just add a fifth link to prevent movement induced by unequal length trailing arms, this would simply cause the suspension to bind solid and probably something would break. The only way this could be done is if the outer axle brackets were free to rotate on the axle, and a fifth link was provided which deals only with the torque reaction forces. I think the US calls these floating brackets "birdcages"? There is a roller bearing between the axle and the bracket)

Unequal length trailing arms - not really a good idea IMO. This will cause the axle rotation that Mike mentioned under 2 wheel bump, which will cause vibration as the UJ angle changes, but it may also increase roll steer and it will likely introduce some level binding itself (a bit like the Sylva rear axle system). This may be surmountable with enough compliance in the mounting bushes (rose joints could not be used). I would certainly model any designs to check this before diving in.

MikeR - 21/6/10 at 10:44 AM

oooh, just thought, one wheel bump could be really interesting ....

one side of the axle will try and twist whilst the other side will try to remain still. This happens to a small degree on a normal live axle, but you're going to be magnifying this.

A1 - 21/6/10 at 11:47 AM

Im just going on the cortina setup, they have a fifth link to reduce axle wind up. Personally I dont much care for the system, I think an independant system is far superior.

MikeRJ - 21/6/10 at 02:09 PM

The Cortina is a rather different system though (Satchel link), it only has one trailing arm at each end of the axle. The other "trailing" arms are attached closer to the axle center line, so there is less motion in roll.

They still managed to chew up void bushes regularly though, so the design was not without it's flaws.