Anyone ever seen hydraulic scales ?

SVreX wrote: In reply to Knurled: OK, so explain... Assume 0psi with no load. Extreme temperature, fluid expands. What happens to psi? If the fluid has no where to go, doesn't psi increase? Seems to me there would need to be some kind of expansion chamber for the psi to remain 0.

Well, if there is no top-out stop, the scale top would rise slightly and zero would still be zero. If there was a top-out stop, the scale would be slightly preloaded and it would take the amount of PSI in weight to push the scale down off of its stop, at which point it would still work normally. The unloaded scale would register the required amount of weight to move it from the stop, and the needle would not move until more than that amount of weight was loaded, at which point it would read normally.

Used to borrow a set from my stock car buddy, early 90's. Easy one man operation. Set scales on pieces of cut pipe, bounce suspension out so no binding. Added sand bag ballast to simulate driver weight. 1000 lb. sports racer btw. Get ya ballpark but not precision like today's scales. Worked for me.

In reply to Knurled:

Makes sense. You're right.

I think you just said what oldopelguy said, in a more sciencey way!

oldopelguy wrote: Which brings up the real issue: Empty height. If there is a tiny bit more fluid or something in one stand so that they aren't exactly the same height empty that tall one would act like it was weight jacked and read a higher pressure/weight.

That... is quite valid, isn't it? If you were using them for corner-weighting, you'd need to get them micrometer-precise even with each other before use.

If the piston is free to move up when the temp goes up the pressure gauge should read the same. If its topped out because of the cylinder, yes the pressure will go up.

So, next question...

If you incorporated such scales into a lift, how would you keep the consistency according to the lift points?

When you use a set of pad scales, you are measuring the actually contact points of the car.

If you used stands like the original post, you would not put them under the tire, you would put them under the frame. Every time you setup would be different, depending on how much of the car was hanging fore/ aft.

It would still give you the correct overall, but corner weighing would be useless.

In reply to Knurled:

If you built in a screw height adjustment, then build a box or frame to calibrate their height. Just so it doesnt deform, then use a feeler gauge to gap it.

RossD wrote: In reply to Knurled: If you built in a screw height adjustment, then build a box or frame to calibrate their height. Just so it doesnt deform, then use a feeler gauge to gap it.

Right, but as I noted, there are 2 different setup calibrations that would throw the whole thing off.

The first is jack height, which you addressed.

The second is exact position on the car. This would vary every single time you set it up, both fore and aft and side to side. It would be impossible to setup consistently.

The scales are placed under the tires.

In reply to Don49:

Really? Perhaps I misunderstood the original pic. Didn't think that is what some folks were discussing.

That would make them better. (Though I'd still strongly prefer my pad scales)

If you use bottle jacks with pressure gauges (under the tires) it would allow you to level the "pads" with the jacks for precise corner weighting (and bonus you can use any surface, doesn't have to be perfectly flat). Once the car is fully in the air, jacking doesn't raise pressure, it just adds volume.

Still, bottle jacks are the wrong shape. A pad is much more feasible to actually use.

What would really be needed would be a large area short throw pressure chamber. But by the time you fab 4 of those you are better off buying the $800 digital pads.

In reply to SVreX:

We had a set. You jack up the car and lower each tire down onto the big saddle on top. Since we were more concerned with percentages on the nose, left side, and wedge it didn't matter as much if they were all off slightly as long as they were all off the same amount. Our crew chief was obsessive about always using them in the same position and on the same spots on the shop floor and they never varied too much from the electronic scales the track used.

I had a set that I got at a garage sale, they didn't really work for me. I didn't like the car sitting on them so high it would have worked better if I had a lift where I could set them down evenly but they always seemed tippy front to back.

In reply to chandlerGTi:

They were a bit tippy but at the time the price was good. Inexpensive digital scales were still a dream at that point so on a budget your options were these or large a frames and bathroom scales. Eventually we picked up a set of grain scales when a big buck team moved on to an electronic set.

Wall-E, when did they build/ sell the scales?

In reply to Donebrokeit:

They looked old 20 years ago. I'm not sure where they were from originally.