Anyone install coil overs instead of using torsion bars?

Yes, based on descriptions here of typical use and service history, I believe a car modified in accordance with the blue lines in the picture below will be adequately strengthened against loads due to currently available dampers and/or coil springs.

(My personal opinion based on professional experience of similar situations, offered here in the context of helpful advice. Risks assumed by the user).

Just say what our late, departed friend, Jerry Mouton, used to say…YMMV.


If I were to have a go at this, given that I’ve just spent a few grand on new frames from Uruk, I would want to bolt the thing(s) in place. One to avoid messing up new frames and a hood paint job, and two, to be able to put the car back to original config should the need arise.

Given the problem of bonnet gap changes per Terry, could the L plates be bolted on top of the bonnet carrier and suitably bent/formed around the flange to meet up with the shock location.
In doing it this way I realize that the forming around the flange would have to be tight.

Would that approach degrade the performance of the mod? I’d also want to put plates on the front and back.

Lastly would be to find a suitable shock and adjustable spring combination…….thoughts anyone?

I always thought a piece of angle iron 90 degree bend up, welded to the top of the picture frame and extending back past the inside of the vertical pieces would do the job - not esthetically perhaps, but practically.

I’m sure you’re right, anything that adds depth will help.
I think extending further inboard - or full width - would take some stress off the corner next to the upper control arm mount.

Do you mean mounting the stiffener ahead of the existing mount plate, as in green below?

I think that should be OK, maybe you could add spacer plates behind, to take up the gap? (like the red lines)

Maybe even roll the edges to make a stiffening flange, if there’s enough space?

Another issue may be finding a skinny enough coil spring to use in this application. This photo comes from that scary E-Type restomod from BaT we discussed a couple of months ago:

You can see that the spring was too fat, so they hacked at the “ear” of the picture frame and extended it forwards to get clearance from the control arm. Yikes…

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Did you happen to notice if this car had any reinforcement on the upper shock mount area (as has been discussed on @CliveR’s Advanced-Physics-in Automotive-Suspension thread??)

That photo is the best there is of that area, and as you can see it is not very clear. It appears that the rear and top faces of the picture frame ear have been cut and a pie-slice inserted in the top and a section inserted in the rear face. The net effect is that the ear now points forward at 20-30 degrees or so. No obvious sign of any additional strengthening being added. Judging by the rest of the work on this car, not a lot of engineering to give structural integrity was done.

There is a shock and spring setup sold that fits the stock configuration, and has a narrow spring. It’s described as a helper to the T.B.s but you could probably buy a stronger spring for it. It’s a tight fit - the spring would probably need to be 500 inch pounds or so (What each side of the rear suspension has - 250 inch pds per spring, if I recall correctly.)? Issue is wire size, number of coils and length to dance between coil bind on full jounce and to number of coils to avoid excess twisting of the wire leading to breakage. Need an engineer who knows springs.

I calculate a front coil spring would need to be 204* lbf/in to match (replace) the standard torsion bar (0.80in diameter?). I can develop that to a spring spec if someone can give me the details of the matching damper - overall length, travel and distance between spring platforms, spring (inside) diameter

*I calculated the torsion bar as 108 lbf/in at the wheel, which matches quite well to the figure of 100 quoted in some of the old books. I didn’t attempt to adjust the result for the bending of the bar that occurs as the suspension moves, that’s way beyond my ability and might account for the difference.

(Update) I recall a long-running discussion about some apparent anomaly in rear spring rates - old spec sheets vs actual hardware. I don’t think it was ever clearly resolved.

I respectfully suggest it lacks ultimate finesse in the area of engineering integrity

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I respectfully suggest that it lacks any finesse in the area of engineering integrity: that said, there’s only one kind of really ugly weld, and that’s one that breaks!

If that held up without significant deformation under dynamic loads, it was good enough!

…and then there are the ones I perpetrate on bits of steel angle in order to test suspension bushings. They are a whole new level of ugly.

Perhaps I missed it, but what about the increased loads on the lower shock bolt and the lateral link(s)… (shear, bending,twisting}…

That’s a reasonable question, I didn’t cover it in detail here because the bolts (top and bottom) have so much headroom for likely loads that I focussed on the weakest link - in my judgment, the frame at the top damper attachment.

The longer answer is that I compiled this chart of loads for various dampers, the jounce bumper and the added coil spring. Using a severe compression load of coil spring + jounce bumper for a combined shear load of 4000N gives a factor of safety on the bolts of more than 12. Other combinations of load, such as extreme damper settings, would not be significantly different so I left it there. (I don’t use a combination of all maximum loads applied simultaneously because they would be mutually self-limiting, to an extent that is difficult to predict).

Is your reference to twisting for the load being offset outside the control arm structure, so there is twisting of the control arm in vehicle side view? I didn’t consider that a significant loading mode relative to the wide spacing of the chassis mounts, and again the increase due to a coil spring is small.

I’ve done some rough numbers around a typical after-market coil-over damper, I think a spring with appropriate rate and travel is feasible if - as someone previously noted - there is enough space to accommodate the outside diameter. Would anyone care to estimate what OD would fit in that space?

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Not enough?

My car has a 2 inch diameter shock absorber. It has a 3/4 inch clearance to the upper control arm. So a 3 inch OD will have a quarter inch of clearance.

What if the upper spring seat had a hat shape to space the coil spring down below the upper control arm? It would need to space the top of the spring down about three and a half inches. Does that make the coil too short?

At curb, my shock is a little less than thirteen inches, eye to eye.

Maybe a custom upper control arm could be used to make more room.

I made a first look with a Quantum damper which has a collet for spring ID 2-1/4 in. That plus 12mm spring wire gives (small) clearance to the control arm. Sounds like a reasonable basis for a more detailed study.

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