MikeR
|
| posted on 11/5/06 at 11:46 AM |
|
|
A Frame and de-dion vs watts or panhard?
Just looking over a mates caterham and i suddenly remembered (ok, i'd forgotten and noticed it again) that it uses an A Frame.
Any reason why i shouldn't do the same?
Seams easier to fabricate than a watts link and better than a panhard rod.
Whats the down side?
|
|
|
|
|
NS Dev
|
| posted on 11/5/06 at 11:59 AM |
|
|
If you can fit it in then it also means you only need 2 trailing arms, which then means I don't have to make one up to replace the cut one and
you have one spare!!!
Good idea, go for it!
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
|
|
|
Surrey Dave
|
| posted on 11/5/06 at 12:01 PM |
|
|
Didnt they used to break quite often?
Either the A frame or where they were fixed to the diff case, could you turn the A frame round and have one fixing on the chassis?
|
|
|
britishtrident
|
| posted on 11/5/06 at 12:08 PM |
|
|
Long history of axle breakages with the A frame both on the Seven and Mk1 Cortina Lotus, A frame seems OK with the de -dion but not on an english axle
as the apex bush tears the bottom out the axle banjo. Not really surprising the english axle is paper thin.
As weights and tyre grip level increased Caterham resorted to all sorts of external bracing none of which worked well, later they switched to using a
Marina 1.8 axle which didn't fail as quite often.
edit Just to add Lotus dropped it on the Seven S4 and also the Cortina Lotus Mk2 reverted to leaf springs and most Mk1 were also retro-fitted with
leaf springs.
[Edited on 11/5/06 by britishtrident]
|
|
|
3GEComponents
|
| posted on 11/5/06 at 12:47 PM |
|
|
The down side wil be pivot location, OK if you're building from scratch, not so good if you're using a kit, tailing arms will need to be
the same length, so will an A frame and the 2 trailing arms. Where the A-frame mounts on Caterham's de-dion is in line with the trailing arm
mounts, this is a straight tube, most other de-dion tubes have a bend or a series of bends to clear the diff, this puts the mounting points out.
|
|
|
MikeR
|
| posted on 11/5/06 at 03:23 PM |
|
|
Thanks John.
grrrrr.
At least you can understand why the idea apealled. From my quick glance i didn't notice the caterham beam being bent, but that also implies the
'ears' from the beam to the drive shafts must be quite large. Looks like i'll just have to crawl under the caterham again on my way
out of work  something nice to look forward too
|
|
|
britishtrident
|
| posted on 11/5/06 at 03:24 PM |
|
|
A frame dosen't have to be exactly the same length, no conflict of arcs
|
|
|
NS Dev
|
| posted on 11/5/06 at 03:25 PM |
|
|
Mike is building a De-Dion, so the downsides above are not too serious......
yes I can make one Mike, with the usual time proviso!! 
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
|
|
|
MikeRJ
|
| posted on 11/5/06 at 05:13 PM |
|
|
The A frame exerts a torque on the axle under braking (and to a much lesser extent acceleration) that a four link system does not. Is the de-dion
strong enough to take that torque without bending anything ?
|
|
|
MikeR
|
| posted on 11/5/06 at 10:49 PM |
|
|
late night post pub thinking (along with any time) isn't my strong point.
But why would a a frame be any different from any other mounting?
the twist is still the same where ever it mounts surely? Arguably the bend in the tube (if used) would reduce the twist factor by giving leverage.
|
|
|
MikeRJ
|
| posted on 11/5/06 at 11:08 PM |
|
|
Imagine what happens when you apply the brakes. With a conventional 4 linked axle, the torque is resisted by the two trailing arms which are mounted
close to the brake caliper.
With just one trailing arm next to the caliper, and the A frame in the middle of the axle, the torque from the caliper will try to twist the axle
around the trailing arm pivot, which is only resisted by the A frame in the center of the axle, so the entire length between the two axle locations
experiences a torque.
|
|
|
NS Dev
|
| posted on 11/5/06 at 11:39 PM |
|
|
Yep, but I don't think it would be a major issue on a car of this weight.
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
|
|
|
britishtrident
|
| posted on 12/5/06 at 02:28 PM |
|
|
A lot of the problem is the english axle is paper thin.
The A frame is a carry over from the Eleven de Dion -- unlike Caterham the Eleven had a pure de Dion in that it used inboard brakes so no torque
reactions were transmitted through the de dion tube. Caterhams version transmits braking torque but not acceleration torque.
Essentially the MK3-5 Cortina rear is just an inverted version off the Lotus/Caterham live axle suspension --- anybody who worked the Cortina will
remember how they tore up rear axle bushes..
The live axle Eleven used either a BMC or Stadard-Triumph axle as did the early Sevens -- this axle was not quite as pronre to the problem as the
Ford unit -- but the engines were less powerful then.
Chapman used 2 different axle location methods on the Eleven the other was basically 4 link with one of the links in the form of an A frame.
[Edited on 12/5/06 by britishtrident]
[Edited on 12/5/06 by britishtrident]
|
|
|
