Hello. I’m just rebuilding my standard Chapman rear struts on my S4 Elan.
I’m looking at replacing the old Armstrong inserts with SPAX adjustable types which raises a couple of questions.
Do I need to fill the cavity between the strut tube and the insert with grease or oil to protect against water ingress?
The original Aeon bump stops and dust covers are to suit a piston rod of 22mm whereas I believe the SPAX have a 20mm piston rod. This means the Aeon bump stop will no longer grip the piston rod and will just fall and rest on the insert clamping nut. What is your advice here?
Thanks Bill
Just fitted Spax inserts as part of my resto - not because I favour them but because a forum member had a spare pair going cheap! (otherwise I would have bought Konis)
I bought new Aeons and found no problem on the Spax strut tubes - they were a tight slide on fit and the hold in place at the top nicely.
I filled up with engine oil as per std spec - I’ve heard it said that this is to promote heat dissipation but to be honest I’ve never really understood why but corrosion protection is a good idea.
Hi Jono,
The piston in the shock absorber is pushing fluid through a restriction and therefore absorbing energy. This is similar to an oscillating pump and heat will be produced. The oil is there to conduct the heat to the outside casing and keep the temperature rise within tolerances. It surprised me at first but then I am not a suspension designer.
Hope this helps.
Eric in Burnley
1967 S3SE DHC
When, many years ago, I put some Konis into my rear struts I put oil around them.
I used some motorcycle fork oil as I figured that if any were to find its way into the struts it’d be a safer oil for all the oil seals etc.
I guess engine oil is safe anyway, bearing in mind the number of seals in an engine, but I had the fork oil going spare and it has anti foaming properties, is designed for suspensions etc etc.
Hello
I have just done this job and fitted tt adjustable inserts and springs with just engine oil for cooling between strut and shocker
I have a pair of almost new 1 inch shorter springs with two almost new spax shockers
2inch shorter anti droop for fitting with solid driveshafts which will fit the original struts if interested
Regards
G
I fitted Spax replacement rear dampers about 5/6 years ago, but I didn’t know about filling the space with oil. I’m not in a hurry to tear these apart again, I suppose accelerated wear from excessive heat is the most likely problem with time. Or should I be doing this on safety grounds?
Malcolm
Hi Malcolm
Nah dont bother. You will know soon enough if they are weakening when the back end goes a bit bouncy. You can easily test them just by pushing the back corner down and watching the overshoot. I dont think most of us give them a hard time the way these cars are used nowadays.
Eric in Burnley
1967 S3SE DHC
Bill
I am restoring an S4 and have replaced the narrow springs fitted by the PO with standard 4” springs and Spax adjustable dampers. I am now on to engine rebuilding, but have nagging doubts about what I have done.
The top spring platforms are unavailable new and I obtained a pair of good s/h ones from a Lotus specialist. I believe they were from the Ford Popular originally. I am now
worried about the damper rod punching through the thin top seat. It is only being retained by the difference in area between the circular section and the flat on the damper rod which to my mine is insufficient for the stress.
Unless someone can tell me that I am worrying unnecessarily, I am thinking of stripping down again and machining some brass? Spacers to slide onto the damper rod and take up the clearance to the seat, in order to spread the load across a greater proportion of the seat.
On the other hand they were made like this originally so am I worrying about nothing?
Hi Peter
I’ve had similar thoughts after reading Brian Buckland’s excellent manual.
My original (late 1970’s) damper inserts were made by Armstrongs of Beverley. The rod diameter was 22mm reducing to 19mm for top platform to butt up against. My replacement dampers (SPAX) were 20mm but had a groove and circlip which effectively increased the abutment diameter.
Providing your top platforms are in good condition and you have either 22mm rods or 20mm rods with circlip then I wouldn’t worry.
Bill
I have done what you suggested, made brass spacers to fill the void. My car is not back on the road so I cannot comment about how this works, except that the D shaped holes in the top plates were originally so badly worn that the the damper shaft passed through them.
Richard
That is very interesting. I think the latest type of lotocone must be different shape to the original so it makes sense to ‘fill the gap’
Do you have a sketch you could post, or better still, sell me a pair of your brass spacers?
I just rebuilt my rear struts, right now they’re on a rolling chassis while I’m working on the body. New Koni’s, lotocones, and bump stops.
This thread makes me think that I’m not thinking about the struts correctly. I was already wondering, because I’ve read Buckland too, and his worry about the upper spring platform and the strut ‘step’ passing through it, and didn’t get it at all. So hopefully one of you posting about that concern can set me straight.
Here’s my problem. The bottom spring platform is welded to the strut, so it isn’t going anywhere (or shouldn’t). The upper is being forced by significant spring forces into the lotocone. In addition, the bump stop is sitting in between the strut shaft ‘step’ and the spring mount. When you hit a bump, there’s even more force pushing the platform up as the spring compresses. On the rebound, less force, but still considerable, I would think. Meanwhile, the strut shaft doesn’t actually move, anyway, relative to the upper platform, anyway - it’s the strut housing that moves - up when you hit a bump, down on the rebound.
So, how would it be possible for the strut shaft ‘step’ to pass through a worn hole in the upper platform? Neither should be moving relative to each other. And the bump stop is sitting between them, even if there was relative movement. Yet, Buckland, and several of you, are quite concerned about it. Which makes me think I’m missing something.
So, what is it I’m missing?
Thanks,
Steve
P.S., my new lotocones, from DBE, seem to have the same shape as the originals, per Buckland’s photos. I did have to reshape the top of the bump stops a bit to have them nest more closely to the upper platforms, so that I could get the top strut nut on completely. I’ve got pictures of this reshaping in my ongoing post about my project.
Sorry I don’t have a sketch. The conical shape of the Lotacone and the top spring platform are not the same, so there is a void between the two, I don’t know if the two components were the same shape when new, but my replacement Lotacone did not fit my original top plates or my replacement second hand top plates. I made my brass spacers to fit the gap between the two.
Steve,
I am sure you are correct that the spring force is exerted onto the top plate and into the Lotacone directly. The damper force will be exerted through the damper shaft into the centre of the top plate. I have no idea what these forces are, but a slow movement will exert little force whilst a rapid movement will be much more. I think part of the problem is that the top nut is difficult to tighten to the workshop manual figure of 45 to 50 lbfft. Well before this torque is achieved it becomes almost impossible to restrain the damper shaft against the turning force applied by a spanner. The workshop manual does not mention this difficulty, I think a special tool is required. The damper shaft has a slot in the top, I had a local machine shop produce a concentric screwdriver bit and socket so that I could tighten this assembly. I suspect that the rear suspension was based on a Ford design from the early 1960’s. I remember helping my dad change a damper on the front of his Ford and the bits on a Lotus look similar to my memory of this old Ford. Perhaps someone in the old Ford world knows more about how to tighten this top nut. My car is a coupe S4, the hole in the body does not line up with the top nut I can only tighten this nut with the body off.
I still don’t get it. I don’t see how the damper applies any force at all to the top platform - the damper shaft is bolted to the lotocone - the only force on the top platform is from the spring, unless the suspension bottoms out, in which case the bump stop is also putting a vertical load on the platform. But it has nowhere to go, since it’s nesting in the lotocone.
I hear you on the challenge of torquing up the top strut nut. I asked Ken Gray at DBE about that, his response was basically - do the best you can, he’s never heard of a case of the nut backing off. Really, the purpose of the nut is to keep the damper shaft from falling out of the lotocone. As long as there’s enough torque on the nut to do that, we should be good. It is kind of interesting that the Koni’s had no cotter pin hole in the strut shaft. Maybe Koni knows something we don’t.
People posting on this thread should include pictures about the parts they are enquiring about to help explain their situation. I sometimes have difficulty understanding what part folk are asking about and the problem they are encountering.
You do not have to worry about what torque to do the top nut up to if you are using a castellated nut. You just do it up until you can get a split pin through the nut, but I am aware that some later supplied damper inserts come with nylock nuts, so they could be problematic when trying to tighten them.
My Koni’s didn’t come with nyhlock or split pins/castellalted nuts. The struts are adjustable, and the adjustment mechanism is accessed through the top of the damper shaft, so no room for a split pin. And the nuts are ‘stepped’ - the step fitting down into the lotocone, so it would be a pretty fancy nylock, if that type even exists. (If they do, point me to them, and I’ll let DBE know as well - it’s not too late for me to change the nuts out).
On my car the damper shaft does not bear directly on the Lotacone. The damper shaft shoulder bears on the spring top plate before passing through the Lotacone to the top nut. With my top plate and Lotacone there is a void between the two. I hope this explains what I have done and why.