VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1937-1945 Is anyone driving a car with DuBonnet Shocks?

I am a new member and a recent purchaser of a 1937 Master Deluxe 4-Door Sport Sedan.

One of my surprises on this car was the issue with rebuilding the front knee action shocks. With a cost of about $1,100 per pair for rebuilding, I am wondering how long can you expect these shocks to last?

My goal is to keep the car as stock as seems prudent. It won't be a "show" car, but rather just something that I wanted to be able to drive around in sometimes. It needs to be safe and reliable, but, as much as possible I want it to be stock. That being said, I am likely to replace the 216 with a '56 235 that I have already located. I have seen the Mustang II front ends that would not cost that much more than the rebuild cost for the DuBonnet's.

I would appreciate any comments that anyone might have on this subject.

Thanks,

Rich

I have a 1939 Master Deluxe 2-Door Sedan that I've been driving for about six years.
I have knee action shocks, but don't know the type. All I know is I've only serviced them with lite oil thru a plug on the top.
I can tell when to check the oil by the way they ride. The oil has to be added very slowly. Hope they keep working good.
By the way, I just installed a 261 last year that's running great. Now I wish I had disc brakes when somebody pulls out in front of me.
39 Den

Ken,
Your 1939 has the open coil spring susprnsion which was all new for 1939 and continued unchanged through 1948. The 1934-38 cars had the enclosed coil spring Knee-Action, a very different animal. Was very large and contained over 2 Qts. of fluid.

I have a '37 Sports Coupe with the DuBonnet shocks and have been driving it 2-3k miles a year for 15 years or so. I don't have any idea if they were ever rebuilt before I bought it, but the car now has about 80k on the clock. The DuBonnets started leaking a year ago, just before a 3600 mile trip to S. Dakota. Not having time to do much, I filled them up and went on the trip. They are still leaking, 20 nmonths later.

I plan to look at them this winter. I saw the $1100 cost from Apple Hydraulics, so I decided to try and rebuild them myself.

the 35 on the members photo has dubonnet front supention . they are not hard to work on . there is some real good pictures in the parts book . i repaired these about six years ago . no problem . i found a factory rebuilt one at chic. oklahoma took it apart they removed the needle bearings and installed bushings so that is what i did also machined the housing installed modern lip seals on another one i used o rings instead of the packing . the rub comes in when the shaft is worn that is when it gets complicated. you have to excuse me sometimes i get carried away most do not have the tools out in the shop especially machine tools but usally in town there is a machinest that do the small stuff . hope this helps

Rich:
New member to VCCA? Welcome!
You don't say what's wrong with the units you have, but presumably you have some leakage. Re-seal kits are available and frequently appear on Ebay. A full rebuild typically usually includes replacing the needle bearings with ball bearings and replacing all the seals.
Keep them topped up with fluid and you should get many miles of smooth driving.

I may be wrong, but it seems to me that I read somewhere, that the later DuBonnet units ('37 & '38) had bushings instead on needle bearings.

All year Knees had needle bearings.
The 1934-36 king pins had rollers instead of bushings.
The 1937-38 had king pin bushings.
After 1937 the new king pin sets came with bushings and covered 1934-38.
The rollers were not a good idea for the king pins either.

Simply put, my shock absorbers don't absorb any shocks. Also, when I got the car, they were dry as a bone. I did fill one shock with a couple of quarts of ATF and this made no difference in the dampening action. The good news is that that oil has been in there for a couple of weeks with no sign of a leak. From what little I know of the history of my car, it was last driven in the 70's by the "little old lady" that we have all heard of. I doubt that the car had any maintenance on the shocks during the latter years. I would rate my mechanical skills as a 5 on a 1 - 10 scale and quite frankly would be a little hesitant to rip them apart. While I am not looking forward to dropping a big chunk of change on them, at least a pro rebuild would give me lots of miles on the units.

I want a "stock" car as much as practical. If the rebuilt units have a decent life span, that would be great. If they are only good for a few years, I am not going to get them rebuilt. From what I am hearing is that they are good units when properly maintained.

Thanks for the feedback.

Rich

if you are not absorbing any shock both have to full of oil . i use hydraulic jack oil if they are full of oil then the valves in the shock part are stuck or the mechanical parts are broke that operate the shock cylinders this includes the springs . operating them with no oil can do a lot of damage from bearing failure to the cylinders freezing up and breaking . most all of the parts inside are harder than wood pecker lips so they wear really well . i have some that are over ten years old never added oil work fine . but the other thing is i dont put very many miles on a year . another tip is every now and then i take the bottom bolt out and check to see if any water has collected inside . you can drain the oil and take the cylinder covers off and check the valves for trash in them . every now and then there is gaskets and the seals for the bolts on e bay hope this helps pushrod

Well, you are right, I only have oil in one shock. I will put oil in the other one and see what happens. The car has zero miles on it since I bought it. I have just grabbed the front bumper and bounced it up and down a few times to see how the shocks were working. When you release the bumper, it takes about 4 bounces before it stops. I figure that to drive this car the way it is you would get motion sickness and puke on the new upholstery.

I too have seen the rebuild kits for the shocks and may give this a try. I just don't want to invest in the rebuild kits, do a bunch of work and then find that I haven't solved the problem.

Rich

This web site explains about Dubonnet front suspension.
<http://home.znet.com/r1937/Knees.htm>
I'd shy away from the Pinto (AKA: Mustang II) front end. They may be cheap but they never tracked too well when new and will never parallel a trolley rail like the Dubonnet. . .
. Good Luck, Lou

Chevy's of the 40's sells a reseal kit for $70/each. From what you can see in their picture, there is not much "stuff" in the reseal kit.

Has anyone installed these kits? Did it solve the problems?

Thanks,

Rich

Most inits will need more than a reseal kit due to wear on the shafts and needle bearings.

Can any of the worn parts be easily replaced, or do you need a machine shop to take care of worn parts?

Thanks,

Rich

http://www.antiqueautoarchive.com/folders/Restoration/kneeaction/kneeactionpdfcompressed.pdf

This site has some great Knee action rebuild info.

Merry Christmas to all!

Thanks, this is a very well written article. Now I have to decide if I want to tear into this myself or take the easy, but not cheap, way out.

Rich

Even sending the units to Apple Hydraulic would still require a fair amount of work (like removing front fenders and removing the units), not to mention the shipping cost as these guys are heavy. You would still want to renew the king pins while the knees were off. I would try to enlist a buddy to help and take a copy of the article to a local machinist so they can better estimate machine work and if they want to do machine work. I have yet to do mine on my 38 coupe project. I did manage to find a nice tool to unscrew the spring top tension plugs and have the gasket set. When they dampen the bumps right, these knees do make for a very nice handling and riding old Chevy. At least this is how I remember mine when it was last in one piece many years ago. Converting the front end to a straight axle or hot rod suspension would (in my humble opinion) be a real shame.

It is not necessary to remove the front fenders to remove the knees. The two major parts to remove would be the king pins and radius arms, both of which are usually also worn out. These parts should be replaced also.
I still don't understand what the dampenining means.....The front suspension will be softer tha any present day cars. If the bumper bounce test is done it will be possible to bounce the car quite frrely. The test is how long it continues to bounce after you stop appling pressure. Should level off after the last "push"...The real test is when driving, the front end will bob up and down when coming to a fast stop when the shocks are not working.....The shocks are only a small part of the knee action units and can be inspected by removing the two round cups on the front of the knees. Be careful when removing as they are SPRING LOADED....There are the shock pistons and valves under the round covers. They are the parts that offer the resistance or dampening, not the spring inside the unit. If the knees do not leak when filled they probably do not require rebuilding. The other problem would be their being very stiff (no wheel travel) which could be caused by stuck shock pistons or a stuck coil spring guide. If this were the case most likly one side would be stuck (stiff) and the other side normal.

Gene,

It is quite likely that my expectations are way off. I am thinking this car should respond similar to a modern vehicle when you try to bounce it up and down. I am not all that far from being able to do a road test. Perhaps the best thing would be to just fill the shocks and see how it drives.

With a little luck, I can be on the road for testing in just a couple of months.

I really appreciate all the good advice I am getting on this site. I started to repair antique radios about 8 years and found a good local support group and a forum quite like this one where some very smart people have provided many hours of time teaching dummies like me how to do things that they were never trained to do.

Rich

Soon, I will be getting my shocks rebuilt. Chev's of the 40's does it as well as Apple Hydraulics. I do know that Chev's of the 40's does it locally and does not send it on to Apple Hydraulics.

Cost is about the same, shipping to Apple would be a little more for me, but I was wondering if anyone has any experience with either of these companies with this type of rebuild.

Thanks,

Rich

Have you checked the Mr. Goodwrench Forum on Tech Talk on this site? There is a site identified there as having info on knee action work. Beamer

Yes, I have checked this site. I have read the instructions on rebuilding the units. I am very tempted to try to rebuild them myself, but I don't want to screw it up.

In the rebuilding instructions, I don't really see where the "shock" itself it repaired. Needle bearings are replaced with a bushing and a bunch of seals are replaced, but I don't see how the shock is returned to function. Since mine is a '37, it appears that the needle bearings are already replaced by a bushing. That should make rebuilding easier.

Rich

If your 1937 knees were never rebuilt it will have rollers. If it has aftermarket rebuilts it will have busings. If it does they probably don't need rebuilding. If leaking around the big arms probably just seals. Most will leak when wheels are raised off the ground and hanging down.There isn't much to rebuild as far as the shocks go. There is the large shock pistons (two, an upper and lower in each unit) and some times the pistons get rusted in place. This will make the front end very stiff. The only other part of the shock area is the valve and I have never seen one give trouble. If the shocks are not working the front end will hit a bump and keep bouncing. Or if you bounce the car from the bumper it will keep bouncing rather than make one dip and then stop. Will be much easier to bounce than a modern car. If all is OK and you want a firmer ride a heavier fluid can be used.If they are working and the unit is at least 3/4 full of fluid this will not happen.(the continued bouncing)

Gene,

You sure are right about the increased leaking when the car is up on jacks. I have that situtation now. I have no idea if they have been rebuilt or not. However, there is NO dampening action at all. The left shock was dry when I got the car. I filled it with ATF and there was no difference at all in the action. The right shock did have fluid, but no dampening action. Since the front end is not stiff, and filling them with fluid did not make any dampening action, should I remove the two pistons on the front of the shock to see if something obvious is wrong?

Thanks,

Rich