VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1937-1945 Past Approaches to Dubonnet Repair/Rebuild

I've been tearing down and prepping for rebuilding a couple sets of '37 Master Deluxe Dubonnet pods.

The first pod was just a little cantankerous coming apart, and I ended up having to mill and waterjet some tools to get the plug out etc. Once apart it had apparently original needles in the crank-arm bearings and a certain amount of slop but no real damage beyond wear.

On the second pod the upper spring seat was rusted on to the spigot of the lower seat, I had to make a tool to compress the spring back down into the housing and hold it free of the upper seat while I worked on it. Neither heat nor a week of soaking in ATF/acetone helped. Ended up destroying the upper seat getting it off but at least the rest of the pod is usable.

The third pod's interesting, and the real source of the question. It came apart fairly easily and when I tapped out the trailing arm cross-shaft and the needle bearings fell out it was obvious it'd been worked on before.

The arm-side of the unit had fewer and much larger diameter needles - around 3/16in - than the stock arrangement. The cap-side of the unit had two rows of small needles, with each set running in its own race a little like an open-ended U-joint cap.

Anyone ever seen anything like this before? Was it a kit produced at some point or something cooked up by some machinist out of what he could get his hands on?

Thanks.

It was probably rebuilt by a rebuilder that used larger rollers to make up for the material removed from the arm/housing surfaces. Some rebuilders used bushings and some rollers. There were many shops that rebuilt the units and not all were of good quality. I discovered that years ago whe when working on my 1934. Some of the rebuilt units I found were junk.
Thesize of the rollers was increasedin 1936 or 1937.

Thanks. I have *no* idea when these were rebuilt, but they'd come off a running car sometime in the past four-five years whereas the other set had been sitting around rusting for...who knows.

I'll do one good set with bronze bushings and Toyota lip seals for now.

I wonder how long these components lasted in a new Chev from the factory?

The knee-action units would last the life of the car as long as they were kept filled with fluid. The were supposed to be checked and topped off every 1000 miles. Usually after the cars were a few years old the owners never had them topped off and running dry would cause them to wear out in a hurry. Also the cork seal they used was of poor quality. Same story with the open coil spring front shocks used from 1939-1948 (and many other years on othe GM cars and some independents)...If they were kept filled they would last for ever....if not would require replacing by 40,000 miles.

...and another curiosity as I start to examine the parts:

The trailing arms are different. The first set are round around the pressed-in stub axle pin, while the second set have a square flange and a backing plate attached with four rivets.

It'd appear from browsing the various manuals and parts books on the 'net that the square-headed version with the rivets is an earlier design, while the round-headed version with just the pressed-in pin came later but I can't tell when the change took place.

Both sets were supposedly off '37s and have the same type axle beam, if the round-head design was in use by that time, would indicate that the second set (with the larger rollers) were rebuilt replacements from an earlier model at some point

The 1936 was the first to have the pressed-in spindle stub. The 1934 and 1935 were bolted and the 1935 had larger bolts.
The rebuilders rebuilt any unit and sold them for any model.
The best units were the 1937-1938. They had all the improvements. They would fit back to 1934.

Thanks again for filling in the blanks in my knowledge here.

My understanding was GM originally specced a 2000-mile maintenance interval, then cut this to 1000 miles when they realized they were leaking too much.

Neither one of my sets had anything in them that looks like GM shock oil, one had what seemed to be motor oil and the other clearly had 90W gear lube.

Any thin oil is OK. I used ATF in mine and hydraulic jack oil is OK also. The shock fluid originally used was about as "thin" as you could get back then, especially in cold weather. The heavier oils would not pass through the shock valves, especially when cold. Other than that any oil would be OK for general lubrication.

When I look at the pod guts, I end up thinking, if one wanted to go all race-car on the things (my application isn't a restoration, it's a '30s-ish sorta-Brooklands roadster):

a) The big springs are very close in inside diameter to 2.25in coilover springs and while they're pretty stiff I think there's some race springs at the high end of the rate charts that would work and provide some tunability.

b) The shock valve design is very simple and alternative poppet-valve-spring rates and orifice sizes wouldn't be hard.

c) Alternatively, the design would permit replacing the stock valve with a one-way flapper to permit refill of the cylinder while plumbing an external valve into the other end of the cylinder as sometimes used on racers and off-road trucks.

The shop manual says the wheel-to-spring ratio is 3.52:1, I haven't calculated/measured the shock piston travel yet.

The seal-less design of the piston probably limits the total hydraulic pressure possible (and you don't want to stress the things too far beyond the original design anyway.)

Just random thoughts...still dreamworld at this point.

Will the brake flange plate from a 1934 or 1935 car with mechanical brakes fit the wheel spindle on a 1937-1938 knee action unit?

Yes. The part that fits on the spindle is actually the large replaceable brass bushing.
You can install a 1938 unit on a 1934 and 1934 unit (knee) on a1938.

Thank you, Gene.

While were on the subject of, Dubonnet rebuild, doe's anyone have the #s for the upper and lower shock valves for a 37 MD? Also, is there anyone out there that makes the bigger springs for these? Any help will be appreciated. Thanks,
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Joe's 37

valve relief 2-be
valve rebound 1-bx
The above MAY be for the rear
valve rebound 1 -b
valve compression ?
There were some softer valves available for 1938.
What numbers are on your valves?

Hey Gene, thank's for the reply! When I had mine re-bushed, I put them back together myself. Now I'm wondering If I may have put the rebound and compression valves in the wrong place. This is what Id like to find out. What would be the # or, letter, for the one on the top and bottom, in the little round housings, on the front of the main unit. Thanks,
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Joe's 37

The number should be stamped into the little spring loaded valve....You mentioned heavier springs. There is no such thing but the spring height is adjustable.

Thanks Gene.