Reasons for this arrrangement are -
When he took the original spring seats off they were not welded “square” to the tube. The threaded seat would be.
No welding of the sleeve to tube necessary.
Spring seat can turn as it is compressed.
I cannot think of an immediate objection, other than the spring load would be directly into the hub.
Would that matter? Any comments??
After that he can work on producing some proper adjustable rear wishbones!
when looking into the actual dimensions and clearances you may want to check your target springs ID (need a bit of clearance for the spires to move up and down without rubbing the alloy sleeve thread), esp. if you want the narrow springs (I imagine you meant “spring seat can*'t* turn as it is compressed” … which becomes obvious as one tries to adjust his setup)
then since the hub is cast it is likely that the sleeve will not seat on a perfectly square face.
My main concern is with the spring pushing up through the damper and hence damper tube, and the bottom end pushing down on the alloy hub, is there a possibility of the tube being pulled out of the hub?
if the spring is quite short (so stiff) and catches on the bottom plateform, when you get airborne there may be a way for the spring to pull the tube up a bit - that would not be my main concern as minor and transient for most drivers (more the point effort on the cast hub, that should rather be spread at least on the total circumference - on the Chapman setup the load is spread between top and bottom press fit areas, which is a lot larger).
Sorry, I’m missing why this is any better than the presently available adjustable spring platforms? (Ok you need to remove the old tube)
Proper adjustable rear A frames…now you are talking. Preferably not rose jointed and will accept bushes and also be adjustable in situ without having to remove the supporting bolts each time.
I would expect the hub to be deformed by the tube over time as it not a very hard metal.
If I under stand the main advantage it that the tube can be spun to adjust the height with out teh spring having to rotate, so easier adjustment.
Personally I’d look at adding a small lip to top and bottom of strut tube to hold the sleeve in place. Possibly a simple circular clamps. Or machine the top of the hub and add a hard metal “washer” between tube and hub.
I think Spyder sell adjustable rear A frames (wishbones). I made my own adjustable turnbuckles, and found they had seized after brazing, and had to do the job again, using a mixture of metals (brass and stainless). Would probably have been more sensible to have purchased.
this I don’t get : either there is tension in the spring, and that will cause friction on what holds it, so adjustment will be difficult, or there is no tension in the spring, and adjustment will be relatively easy, tube or no tube… or did I miss something?
Spot on. I had raised my concerns with the man and he has suggested a 5mm steel collar welded to the bottom of the damper tube to take the sleeve. Solves both problems.
His next job is to mod a spare pair of arms I have along the lines of the attached. It still would need the bolts taken out to change camber! I cannot see a realistic way around it so I may give the back one a miss and just have the front toe in adjusted done.
I have that type of adjustable rear control arm on two Elans.
True, you have to remove the inner pivot bolts to adjust, but how often do you adjust camber or toe? Going to the heims on the inner end pretty much eliminates any toe change from bushing deflection or “set” over time.
Btw-I’ve run the heim inner and outer bearings for years on the street with no issues.
A nice inversion of the normal design and avoids the issue of how to attached then new threaded tube to the shaft. Sure some detail design issues to deal with but nothing that is not solvable.
I love creative design thinking and this sort of thought processes is what drove development of Lotus back in the 60’s
Rohan
Any design issues I haven’t considered other than the additional of a 5mm steel ring to rest sleeve on?
We wanted a (nearly) full length sleeve from the start. The idea was that -
As the spring can be wound fully down it will be virtually uncompressed.
So, even with the strut assembled, it should allow the strut to be raised up to a point where the wishbone is horizontal. (Jack under the 'bone with a spreader - light as no spring compression.)
This would allow the camber and toe in to be set at the, theoretically, ideal ride height with the wheel off and everything easy to get at.
Bonus - The spring could (MAYBE) be fitted without separate compressors.
Making the sleeve out of aircraft spec alloy saves unsprung weight and prevents corrosion. Indeed it would protect the damper tube. It may even act as cooling fins
Having the adjustment “holes” at the bottom of the sleeve, rather than the conventional nut, is easier to get at. 6 round hole (drilled around the sleeve bottom) would give a more secure hold for the C spanner. Although it will need a special C spanner with a round end.
Strange the engineer was concerned with unsprung weight as he makes half scale traction engines!
Any comment or criticisms welcome, preferably before we start .
Some great observations and recommendations.
Another concern I have is having an alloy tube (the threaded sleeve) over the steel strut tube. Add moisture between the two metals and galvanic corrosion will occur.
Any thought to replacing the original strut tube entirely with a threaded anodized alloy one?
The seating of the floating sleeve on the top of the alloy housing
The fit of the loose threaded sleeve on the strut tube so it does not rattle around and does not corrode and lock up.
Issues such as how straight and round the strut tube and flatness of the top of the alloy hub casting becomes important
With any new installation you need to ensure the spring remains seated and loaded at full droop and with a floating support sleeve this becomes even more important.
I have an adjustable C spanner with a round pin end that fits multiple diameters as my front and rear adjustable seats are different that I use and this would be ideal for your sleeve with drilled holes. They are commercially available and you should be able to find at a tool shop or EBay.
Further to my comment on roundness and size of the original damper tube, there will be a high friction area between the two tubes unless a good working clearance is designed in.
Possible idea may be arrange the bottom support ring be made as a two face collar so as to make a small area bush between the inner and outer tubes, do the same at the top with another collar so the outer tube is rotated on these top and bottom bushes.
This will help on friction and alignment if the original damper tube is not straight.
ps or lots of grease.