Chicago British Car Festival

Well, I made it there and back in the '38 SS, no problems. Put 40 miles on the trip meter. It was a rainy day so attendance was down. About 25 Jaguars, 200 or so other British. A lot of people said they liked the car and took pictures, and many said they were not aware of the Swallow Sidecar & Coachbuilding and SS Cars history. I won an award, People’s Choice Jaguar.

Last year we discussed the damper weighted front bumpers. There were three other cars at the show with these bumpers, two Bentleys from the mid '30s and a '39 six cylinder MG saloon.

We’ve read in some of the history books that the SS Jaguar was called the poor man’s Bentley when it came out. Here is a visual demonstration, my car with a '36 Thrupp & Maberley.

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Hi Rob,

Well done both on the trouble free run and the award.
Costing just one third of that of the Bentley I think the SS is certainly a “Bentley” for the poorer man. A comparison made at the very start of this webpage.


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Yes, in fact the Thrupp & Maberley owner commented that the Park Ward was an even closer comparison.
I think the MG at the show was a WA, also similar. I noticed it had down draft or vertical throat SU carbs and a round body fuel pump with two pumping coils, a double pumper.

That’s an SA but WA looks quite similar except that it has a dip in front bumper.



Hard to tell, precisely from a single picture, but I think I prefer the MG over the Bentley and the Jag!

Ok the pictures I found of SAs had side vent doors rather than louvers, but perhaps they have variations just like SS and Mark IV do.
Paul, perhaps this will change your mind.

Then here’s a Wolseley 18-80 to add to Peter’s comparison page.

And one as driven by Sam Stewart.

I think I made the right choice. :grin:

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I’d have to see them in person: reeeeeally like the MG!

Early SAs had letter box slots and later ones had louvres. Another way of distinguishing WA from SA is that the WA has a side mount instead of the wheel on the boot lid.


My memory could be crap but weighted bumpers were actually made by a company that claimed they harmonically reducedcertain resonant frequencies.

I often wondered if they just took the standard “tuning fork” tendencies a standard bumper had and weighted them beyond their ability to vibrate easily.

T’would be interesting to find how they determined the weight needed: I suspect they just added weight till some perceived “shimmy” decreased.

There is a detailed factory document, with drawings and description, somewhere on this forum I think, of the theory behind this intriguing invention. It does not have weight details and obviously, this would be different for different cars. It relies on the bumper being attached to the transverse leaf spring assembly and not the chassis, which is why the extra weights are not required in the rear.

If anyone has a complete assembly, I would appreciate if they could post the specifications of all the internal parts as I would like to remake them. Dimensions and weights, etc. My car does not have any internals and occasionally a slight shudder/shimmy occurs at the front with some bump conditions and I think it is because of this weighing missing. I doubt they determined the weighting factor individually by car, but standardised the set for each model and make

I also expect that less-than-honest mechanics might have removed them during service to get scrap money. Scrap lead would have been worth a bit after the war, and anyway, the owner wouldn’t know.would they? If they did complain of a shimmy, the said mechanic probably said ‘Ah, you need new shockers.’

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Yes, Lovell, it was the Wilmot Breeden company that made the harmonic bumpers, although the patent was held by the Rover Company.
The Rover patent for which I gave a link in the previous thread uses a lot of words where a picture would have helped, and sort of implies that weights were determined by experiment. They would have put a front wheel on a set of bouncing rollers and seen how the frame twisted, then added weights until it cancelled out the first natural frequency. My best guess anyway.


You’re in luck, Peter. I took measurements to see if I could duplicate them in steel. Here they are top to bottom.

Lead disc (qty 1) 2.188" OD x .375" thick with 1" hole; weight .457 lb
Lead cylinder (qty 1) 2.25" OD x 1.625" high with .5" hole x 1" deep and 1.25" counterbored hole x .625 deep; weight 2.25 lb
Lead discs (qty 2) 2.188" OD x .375" thick with 17/32" hole; weight .544 lb each
Total lead 3.794 lb calculated using lead density .410 lb/in**3

Rubber washer (qty 1) somewhat squashed out but I estimate originally 2" OD x 1/4" thick with 17/32" hole
Steel washers (qty 2) 2" OD x .062" thick with 17/32" hole; on either side of the rubber washer
There is also a thicker steel washer with one curved side to fit against the curved top mainspring bar, and the other side has a step to fit inside the curled bumper end. The stem of the top plug passes through this washer and there is a nut and lockwasher under it.

This set is from a '38 2-1/2L saloon, weight ready for the road but less petrol 31 Cwt 2 Qrs, so another model of different curb weight might take a slightly different set.
Funny the weights aren’t listed in the parts catalogue.

Apparently this idea caught on if Rover, MG and Bentley used it as well.

Convertible TR7s did, too.

Thanks Rob, that is great. I don’t know the value of the flat steel washers and they don’t seem to do anything. I assume the rubber washer should be an interference fit on the main stud at least, and possibly in the curl. It’s intention should be to stop the weights from rattling and bouncing.

It is interesting that the spares catalogue does not list these parts but does mention a rubber washer under the top and bottom caps along with plain washers, probably to try and waterproof the void in the curled end, but what do the plain washers do?

I interpreted the plain washers as giving a full bearing surface to the rubber washer, where the lead discs and the thicker steel washer on the bottom did not.
I also found that the tall lead cylinder was an interference fit inside the curl. I discovered this when I tried to hammer it out using a socket and damaged it, which was also when I discovered it was made of lead. I then used a pry bar to expand the curl a little bit so the lead would come out.
The other lead discs were slightly smaller OD, so perhaps the rubber disc is to prevent them rattling in there.