Tore off a shock.

[aeronca65t]

After the tragic occurrence at Lime Rock, I didn't feel much like looking at my car for a while...
But this week I finally jacked it up and inspected the front suspension.
I knew there was a problem, because the front suspension was bouncing around like crazy on all the left-handers. Towards the end of the day it got so bad that I had to throw the car into the turns and steer with the throttle (to lighten the load on the front end).

Anyway, I broke an upper shock mount...tore it away from the chassis in fact.
Keep in mind I'm running tube shocks and the original lever shocks are "gutted" and just act as an upper supension arm.

This is not surprising. Besides everything else, the surface at Lime Rock is in dreadful shape with raised concrete pads at many key areas. I'd rather race in the streets of Manhatten (I can't figure out how the ALMS cars race there at all!).
I also had the Spax shocks set "full stiff" which didn't help things any.
At any rate, it's all repaired and ready for Watkins Glen in two weeks.
If you're looking at the picture, the green arrow shows where the shock mount tore off.
You may also note the upper trailing arm (red tube on right) I've added to the upper lever to triangulate it and make the upper suspension more like an "A" arm. Helps stabilty a lot during late braking into a turn.
A page on my front tube shock conversion is HERE . I don't have any build-info on the upper trailing arms posted yet.

 

[Dave Russell]

[ QUOTE ]

Anyway, I broke an upper shock mount...tore it away from the chassis in fact.
Keep in mind I'm running tube shocks and the original lever shocks are "gutted" and just act as an upper supension arm.

This is not surprising.
At any rate, it's all repaired and ready for Watkins Glen in two weeks.
If you're looking at the picture, the green arrow shows where the shock mount tore off.


[/ QUOTE ]
Hi Nial,
Really not surprising at all considering that at a compression or rebound rate of four inches per second or two inches per half second etc, a typical shock could easily transmit 200 pounds of force to it's mounts. I think this would come out to a bit over one horsepower.

While your lower shock mounts appear to be adequate, the relatively thin sheetmetal that the top mounts are attached to would appear to be totally inadequate for repeated forces of this nature. Remember that this is a cyclic force & working in both directions. There doesn't appear to be anything really solid within several inches of the upper mounts. I think metal fatigue finally got you.

The upper mounts could be tied into the main suspension structure or at least reinforced with a 1/8" plate that extends to & is tied to the surrounding structural members.

Just an opinion,
D

 

[aeronca65t]

I think metal fatigue finally got you.

I'm sure you're right, Dave.

But I unfortunaltely "helped" it along by cranking up the dampening (the Spax have an adjustment screw for jounce/rebound).
Lime Rock is our only muffled track (93 db max) so I run an add-on muffler....the increased dampening was intended to keep the muffler from bottoming out. (I know....a "jury rig" solution! What can I tell you.....I'm an amatuer!)

For the balance of our season (2 more events), I've riveted (and epoxied) an 1/8" backup plate that catches a larger area of the unibody. This Winter, with the engine out, I'll weld-stitch a permanent plate that joins to the heavier subframe steel. My car is definitely an example of "on-the-fly" engieering analysis! /ubbthreads/images/graemlins/laugh.gif

 

[Tim Hollister]

Woah! I think you just added another check to the checklist for the #2 "Sleep Cheap" Red Roof Inns Midget that my son drives! (the car behind me in the picture at left...)

For sure, I'll get a close look at the upper mounting area this winter and reinforce if I feel it necessary.

Thanks for sharing, Nial. May have saved an accident on the track!

Tim

PS: I'm curious about your reinforcement (A frame) to the lever on the shock. Any way you can send or post a picture or two of the entire thing? (at your leisure of course) thollist@comcast.net

 

[GreenHornet]

As long as you have the old Armstrongs on, I am thinking that it might not be a bad idea to put the inards back. With no dampining I do not think they are doing any good. You would probably relieve a lot of stress on both pieces, and have a dual front shock setup that is adjustable. On a rougher track it might help keeping good traction for steering, and body roll. Otherwise the gussett should be enough to get you by.

 

[Bugeye58]

Unfortunately, there is a rule in the book regarding tube shock conversions that says if the original lever shock is replaced by a tube type, the original shock shall serve no other function than acting as an upper control arm. Or, words to that effect. I know, "picky, picky, picky."
Incidentally, my upper shock mount is a piece of 1/4" plate that is bolted on top of the lever shock mount, and is bent to conform to the shape of the original sheet metal of the wheel housing. Then, there is a 1/2" through bolt attaching it to the shock Heim joint. This way, all the load is transmitted to the original shock mount at the reinforced
point of the chassis.
Jeff

 

[Morris]

Why is it a rule that the valve must be removed from the armstrong shock on a tube conversion? I have often thought that Green Hornet's idea would be the way to go.

Please bear in mind, I am nobody's suspension engineer....

morris

 

[Bugeye58]

Morris, I guess it is that with the valving in place in the original shock, it would give you multiple shocks at each wheel, which is another no-no.
Jeff

 

[Matthew E. Herd]

Well ... I can't think of any particular reason why it'd be unsafe, but it may be that it'd be excessively stiff without a custom (soft) valve. There may even be some advantages, if you could find a custom valve ... who knows?

 

[aeronca65t]

Honestly, with a decent adjustable tube shock, you simply don't need or want an additional dampener.
As I alluded to above, the Spax tube shocks were set up *too* stiff. It's not like I feel the need for *more* spring control.
Besides, the stock lever shocks tend to fade with very hard use (they can get too hot to touch), so you would lose some of the consistent response that more modern shocks provide.

And please understand: I'm not advocating for anyone to change to tube shocks on their street Spridget. My brother asked about doing this with his Midget and I told him to simply flush and re-fill the stock lever shocks....they're fine for street use.
Jeff: I've seen the setup that's on your car, but I wasn't sure if the upper trailing link that I have would clear the shock. As per Tim's request, I'll try to get pictures of this link when I have a moment to spare (I'm putting a steering rack in my Dad's Buick right now....a horrible job normally, and worse when done outside in the rain).

 

[Morris]

So, Aeronica, I saw your tube shock conversion article before I became a BCF member, and I have been making mental plans to give it a try on my very tame, street-only '79 midget ever since. My fornt dampers are barely damping at all. And I have changed the oil on them.

By my calculations, it is going to cost my close to $200 to replace them with good "rebuilt" shocks. Your conversion looks like it will cost me about $50.00.

So my question to you, and to anyone else who cares to chime in, is should I go for the tube shock conversion? Or blow @ $200 for shocks that will just have to be rebuilt again in a coupla years? What are the pros and cons of each choice?

morris

 

[aeronca65t]

If I had a street Spridget, I'd convert to tube shocks....I like the consistent response and the low cost of a new gas-shock (about $18 locally here in NJ).
For cars that would likely be driven in a more gentle manner and only to shows (like my brother's car), I'd stick with the lever shocks.
There are lots of opinions on this....I'm just giving you mine.

Anyway, it depends on several things:
1-Do you *care* if the car is "all original" ?(some folks do, and for some very valid reasons).
2-Do you have the skills to build the parts needed?
3-Are your original lever shock units still solid enough to use as the upper control arms?

Note: You can buy a kit to convert to front tube shocks from "Frontline" or "Winner's Circle" (do a Google search to find these) or "Peter May" ( https://www.petermayengineering.co.uk ) or "AcmeSpeedShop" ( https://www.acmespeedshop.com/products.htm )

 

[RobSelina]

Hi Nial -

My tube shock conversion is very similar to yours and I had the exact same problem, though the final damage pic didn't look as severe (the section that's sitting at a 45 degree angle in your pic was simply separated in mine). Upon inspection, there were metal fatigue cracks throughout the section in question. I welded it all back up and then cut a section of 1/4" plate to fit within the cavity in the engine bay where the bolt fits through (it was a triangular cut, basically I'm using it as a big fender washer to distribute the load). And on the other side where your photo is showing, I welded up a 4"x5" plate, then bolted the upper shock mount through it.

So far so good though this was only a month ago...

 

[aeronca65t]

Rob:
Thanks for the feedback.
It looks like I should make a note of this on my original web page.
Your repair sounds similar to what I intend to do once our race season is over. I'm going to Watkins Glen tomorrow to run a three-hour enduro.....that'll be a good test of my temporary repair. /ubbthreads/images/graemlins/smile.gif

 

[jollyroger]

Dang, I have never had any concerns with the stock swing arm units. Just install competition valves to a fresh shock. They work great. I just restored the last AH prototype sebring sprite. It had swing-arms all the way around. MGB adjustables in the back. Won it's class 69 & 70 Sebring and Daytona. In fact have a more instant reaction than tubes. No heat problems in a 20/30 min. race. I too tried the tube BS. After doing so asked myself why couldn't get a good answer. Switched back lap times didn't change

 

[JohnnyB1275]

How did your car do up at limerock?
My dad took a few laps up there in september, he had it floored around the whole track and never touched the brakes at all /ubbthreads/images/graemlins/lol.gif topped out around 80mph. We used the soft A032Rs and it took about half the tread down but unfortunately, we had a little cooling problem and the track was alittle slick from some rain showers so we didn't get in a timed run.

I've been thinking about doing the tube shock conversion, do you think some 1/8" steel the size of that area would be adequte as a backing plate for the top mount?

PS- Some pics of the car.
https://www.cartct.com/results/09-16-05a/091605L21.jpg
https://www.cartct.com/results/09-16-05/09170558.jpg
https://www.cartct.com/results/09-16-05/09170509.jpg
The tow vehicle:
https://www.cartct.com/results/09-16-05a/091605L16.jpg

 

[Bugeye58]

Roger, back in the day, the hot setup was to use the shock valves from a 'B' on the Bugeyes, before we were allowed any significant suspension changes. Those valves, and heavier oil, (such as STP!), made the Sprite handle very well, thank you. A heck of a lot cheaper than remote reservoir Penske's at all four corners, too!! /ubbthreads/images/graemlins/cryin.gif
Jeff