From the “now I’ve seen everything” department:
I had occasion to take off the front bumper to get the rubber plugs out of the sockets, to tighten the fog light brackets.
Here is what I found inside the right hand end curl.
Four lead weights and a rubber disc with steel washers.
Anybody seen this before? Any idea what its about?
The left side and the rears do not have anything inside the curls.
Around here we put weights on the front of tractors to prevent wheelies during pulling contests. Think this car could do a wheelie?
Harmonic bumpers Rob ! Do you have the lateral spring that runs across
the front of the chassis? The bumper works in unison with the front axle.
Peter B
Yes , I also felt that it fell into the " it must have seemed like a good idea at the time" category.
Partly because the SS100 model with the same suspension didn’t have them.
I have an article on restoring/replacing the polished end covers which is in a format t hat can’t be loaded here.If it’s any use I can email it.
I wonder what the effect on the 1/4 mile times removing them would have?
There was a time when bumper bars were such a new innovation that Swallow had a badge on them for cars so fitted. Possibly a forerunner of the disc brake warning on MK IIs
You know, Peter B, I’m half tempted to believe you.
The horizontal bumper support bars are called “Mainspring, Top (1) and Bottom (2)” in the parts catalogue.
Thinking about this for awhile, I see the 3 bars are a kind of leaf spring, supported at two points but perhaps flexible enough to oscillate noticeably at the ends at some natural frequency.
If the bumps in the road happened to occur at that same frequency, the bumper would start bouncing up and down.
So the idea of extra weights at one end and not the other must be so the two ends will have different natural frequencies. Then no matter what forcing frequency you had with road bumps, the two ends of the bumper would try to bounce at their different natural frequencies, and would tend to dampen each other out.
It makes sense now. My college vibrations class was a long time ago but I still remember some of the stuff. I’ll put the weights back in.
I don’t quite see the idea in having a bumper that bounces up and down. I’ve seen many 1920s and 30s cars that have fore-and-aft coil springs in the bumper mounting for absorbing collisions.
I must say it’s news to me [ or I’ve been innatentive] but I don’t recall that the weights were on only one end. Which would lead to… Which end? would be different in LHD cars/
And the front chassis legs on a saloon would be less likely to act as a tuning fork on a saloon than a 100. being heavier and shorter
You know, Peter B, I’m half tempted to believe you…
C`mon Rob, not everything I post takes the p----
although I do like the tuning fork connection, could be handy if
one is late for the Gig, although the tuning might be “open road” not
“open D”.
Peter B.
Ed, am I correct that the same idea is used for some skyscrapers,
giant weight on cables.
No offense intended, Peter, I assure you, but it did strike me as funny the word harmonic. Actually they are dischordant, avoiding harmonic vibration.
BTW the weights fit snug inside the curl, but do not use a socket and hammer to drive them out as you will distort the lead, instead pry the curl open a bit. I discovered that the one weight with the large hole needs to go on top, to clear the flared end under the head of the threaded spike.
My vibrations professor was an expert on earthquake protection for tall buildings, and some of our class problems involved multiple heavy floors supported on I-beam stilts. We didn’t get into counterweights on cables, but we did problems with the floors having differing weights. It does change the second and third order natural frequencies.
Draw bridges have counterweights, and in Chicago we have a lot of them. One time a repair contractor was removing decking from a bridge and forgot to reduce the counterweights, and suddenly the bridge fell UP.
None taken Rob, but I seem to recall they were /are called harmonic
bumpers, to have called them discordant striking the “wrong note”
sales wise perhaps !
Peter B.
Well, so I’m totally wrong about weights only at one end so the two ends would have different natural frequencies, and I owe Peter a double apology.
The idea is indeed to counteract torsional vibration in the chassis frame.
I’ll have to get some weights for the other end.
Looks like this thing is well known among early Rover people. http://www.rover-forum.thersr.co.uk/viewtopic.php?f=17&t=3919
The 1934 patent was held by Rover and one of their employees.
I suppose they had Wilmot Breeden make the parts, and allowed them to sell to SS Cars.
Was this what Lyons was testing that day at Brooklands?
Sorry Rob, I wrote that article on the 1st of April 1995 and of course it’s all just a load of nonsense although at the time a couple of well known SS owners did write to me challenging some of my assertions as if the article was genuine. I subsequently killed off Reg. D. Bates (or register debates) and wrote an obituary for him.
Nevertheless it was pretty funny, and not a bad looking straight eight coupe.
Back to reality, somebody would have had to test a car to determine the right amount of weights. No computer simulation in those days.
The Mark V chassis frame was designed to be quite a bit stiffer, thus eliminating the need for these springy bumpers.
Tr7/8 convertibles had a weighted front bumper, on flexible left/right mounts, with a pivoting mount in the center.
How I found out?
Removed the bumper on my 7, to detail it for a show: unbolted it, and just pulled it off the center pivot, and “caught” it with my chest…thinking it would weigh a stone or two.
Also the 38 on SS100 has the engine bolted in solid to the frame, whether for frame stiffness or, for the36/7 models, to stop the engine/gearbox moving forward on the rubber mounts when the
clutch pedal is depressed I know not.
.Someone will inform !
Peter B.
There are no rubber bushes on the front springs of Mk IV,SsSaloons or SS100s.
But there is a rubber boot that the spring goes through,and these are available from Alan Gibbins in UK
