Build an out of car test stand for swing axle gearbox?

[roundpotwoman]

Thinking of building a test stand for swing axle transmissions using a bare 63 chassis attached to two pads with double rollers on brackets for under the rear wheels. Power to input shaft would be from an adaptor made from a used clutch disk turned with either an electric drill or motor. Two questions- how do I approximate working load as if it was in a car being driven and would an electric drill/motor turn too fast and damage the gearing? In a pinch I could set up pulleys with different circumferences to change rpms but would rather not. How much weight is on the two back wheels in a standard bug and would it being piled just ahead of the frame forks be close enough to approximate real world weight distribution? Its going to be some work to set this up but I want to weed out the definitely bad units and I have probably 15 or more to check. Thanks for any input

[Dan the workingstiff]

I wouldn't think weight is your issue, you need to have brakes to supply rolling resistance. An electrical drill isn't going to be enough if your trying to load to real world testing. Maybe some sort of side shaft 4 stroke motor.
_________________
'69 Beetle
'66 FG buggy
My other air-cooled's
'76 IH 1200
'75 IH 1200

[viiking]

I think the problem is that your drill or electric motor will burn out before you can get up to speed. That is the starting torque required in quite large.

A 240V electric motor runs at 1400 or 2850 rpm or so from memory so with that input rpm, I'm sure the transmission can handle it. But I doubt you can simulate real world conditions because the load will not be the same. So if you want to differentiate between good and bad transmissions, you want to have the maximum load on the transmission to see if it pops out of gear etc.

IMO with a fixed speed and a direct drive you won't be able to get it to shift easily as the synchros will not slow down the transmission like you do when driving.

The only way I can see you do it with a motor is to set up a clutch system, start the motor, then slip the clutch until the transmission starts to turn but not to reduce the RPM of the motor too much.

If you could find a DC exercise treadmill motor, you could start the motor up at very slow speed and turn the wheels of the car to get it to start moving and then slowly increase speed. In industry we would be using a large electric motor with an "inverter" to change the speed of the motor but you are talking several thousand of dollars.

A great idea, but a lot of problems to overcome.
_________________
1968 1500 RHD Lotus White Beetle since birth. In the hospital for major surgery
1966 Lancia Flavia Pininfarina Coupe - in the waiting room
Discharged: 1983 Vanagon, 1974 1800 Microbus,1968 Low Light,1968 Type 3

[slayer61]

Only "kinda" on topic, but years ago I worked for a company that installed a tank transmission dynamometer at the Marine Core logistics base in Barstow, Ca.

5KV DC motor used to supply input power to the tank gearbox and a hydraulic "brake" of sorts to supply the load.
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[roundpotwoman]

Okay. Obviously need to do some more thinking. Any idea the range of needed RPM as you go up through the gears? Also smallest HP moter that would be needed? Am confused by comment that would need braking to approximate real world load as you only use brakes if your slowing down/ down shifting. Do some problems show up when downshifting only? Starting to sound like it might be easiest to bolt up an 1200cc engine for the 6V boxes and 1600 for the 12V boxes. I would still need to load the chassis to approximate the rolling resistance of going from a stand still to moving, correct or not? Thanks

[Dan the workingstiff]

Brakes would approximate rolling resistance.
_________________
'69 Beetle
'66 FG buggy
My other air-cooled's
'76 IH 1200
'75 IH 1200

[viiking]

I assume that you want to actually weed out the boxes that are damaged without installing them in a car. That's obvious.I think you need to load up the gearbox to put it under strain. Just running it and shifting gears is not going to show you much.

You want to simulate heavy loads like starting off on a steep hill and putting the gearbox under the worst conditions. Under these conditions a bad set of gears may "pop out" which is what you want to know.

My physics may be a little rusty now and the physics in this is complex, but as an example (admittedly neglecting a lot of things like friction etc). I have to do it in metric terms as that is the only correct system in science..

Assume the weight of your car plus occupants is say 1000 kg. To lift the entire car and contents up into the air with something you need to exert a force equal to

Mass x gravity. This is ~ 1000 x 10 = 10,000 Newtons

The force to push this same weight up a "hill" is equal to

Mass x gravity x sine (angle of hill). Lets assume a very steep hill of 30 degrees then the force will be

1000 x gravity x 1/2 ~ 1000 x 10 x 0.5 = 5000N.

This force is what will be acting on your car to try and push it in the opposite direction i.e. downhill.

So to get it into the ball park you need to connect the mechanism to some sort of constant resistance weight of 500 kg (5000N/gravity) and keep it there. A big strain gauge comes to mind but that would be very expensive. Maybe dynos have this facility?

That is going to be your challenge and not something I think you can do easily or cheaply.

The real rough method would be to tie the mechanism to a tree and slip the clutch enough to put a strain on the gearbox, but that is fraught with problems like burning out the clutch etc. However it would put the gearbox under significant strain.
_________________
1968 1500 RHD Lotus White Beetle since birth. In the hospital for major surgery
1966 Lancia Flavia Pininfarina Coupe - in the waiting room
Discharged: 1983 Vanagon, 1974 1800 Microbus,1968 Low Light,1968 Type 3

[Slow 1200]

all good points....and still that would only check the transmission under load, not coasting!

[Nate RS]

Many good points above! Question for me is “what usually goes wrong?” Do they pop out of gear? Synchros die and they shift poorly? Other? The test setup will differ depending on this. If “pop out of gear” is the most common it’s also the easiest to test. Usually a very high load slowly will do the trick, something like using the tranny to lift a large weight. This can be a stinker for a V8 tranny but for a tiny VW it shouldn’t be too bad. Brace the thing up in the upstairs of a barn or garage. Bolt on some rims. Run a rope through the tire valve holes and knot it. Drop the ropes downstairs and attach to something large, like a buick. You’ll want an old engine to bolt to the tranny so you can mate to the clutch and put a wrench on the crankshaft bolt. Then, with pipe on wrench, crank away and lift the Buick through the tranny. You’ll need to find a way to hold the crank pully so you can re-position the wrench. If the tranny likes to pop out of gear it’ll do it. Go in both directions to catch the downshift pop-out.

Make ABSOLUTELY certain no one can or will get near the thing you’re lifting because you’re gonna drop it. Especially with 15 trannys to test.

[roundpotwoman]

Hmm. Unforetunetly I don't have a second floor so if I were to test for popping out I would have to use one of my taller industrial storage racks and have the load directly below so the weight wouldn't cause the rack to tip over. Any idea how much of a load to use to mimic what the trans has to pull? The whole car is only 1600 lbs and is on wheels so it must be some fraction of that and I don't have much in the way of compact heavy stuff to use as a load. Will have to save this idea for those trannies that feel and look like they may be good- IE those that don't have chunks of metal laying in the bottom when I drain out the old gear oil, do not have excessive sidewise wobble when you grab the input shaft( if that is what you call the part that meshes with the clutch plate and rides in the engine gland nut), engages and turns the wheels when you use a vice grip to grab the hockey stick to put it in the gears, and is quiet if spun over quickly under no load. Is there a check list for how to check trannies that are out of the car as to what is normal as far as play between the various components? For instance how much circular wiggle is normal from the input shaft before the wheels visibly move? Other things to check by feel? A description of relative motion of the hockey stick would also be helpful as it can be confusing which direction is which gear- sort of like having to remember that when your turning a nut on the backside its the opposite direction. Also is manual transmission oil hydroscopic? Some of the transmissions have compromised boots and while stored inside they have been in non climate controlled conditions so if the oil absorbs water vapor has it lost its lubricating ability? After initial clean up I plan to replace the torn boots before changing out the oil for testing and continued storage. As I store them upright on the bell housing is it better to use regular gear oil or synthetic? Am concerned about the gears and syncros draining dry over time or in this case should the boxes actually be overfilled? I know a lot of questions that have probably been answered in other posts but not in one place and not for the lay person. I got reallly confused reading them.

[viiking]

Oil is not hygroscopic. It is hydrophobic i.e. afraid of water. As long as there is some oil in the transmission the vapour will keep everything oiled up. However if rain water has got into the transmission then it will sit at the bottom and start it’s nasty habit of corrosion. This will be evident if you drain the transmission.

If you are worried about it I’d drain each one. If oil starts draining, plug it back up and leave it alone. If water comes out first, mark that one as potentially suspect and work in that first.
_________________
1968 1500 RHD Lotus White Beetle since birth. In the hospital for major surgery
1966 Lancia Flavia Pininfarina Coupe - in the waiting room
Discharged: 1983 Vanagon, 1974 1800 Microbus,1968 Low Light,1968 Type 3