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I never read the entire patent. It's interesting that they found that 20w (200 cSt)-120w oil was found to work well as listed on the patent but elsewhere someone had mentioned that the old Hydradrive oil was between 2000 cSt-10,000 cSt in weight. I don't know what cSt 120W oil comes in at but 80w is around 1000 cSt. It seems that the oil that it ultimately came with or was offered as options was thicker than the range listed on the patent. We've got oils going up to 500,000 cSt today so I'm curious how or if it could work with no friction slipper? If it isn't free spinning through the oil, it isn't building up heat in the oil at the same rate either. It may or may not be viable with today's technology but I do think it's at least worth a revisit.

Going back to the viscosity range listed on the patent, those numbers are consistent with the oils that were run in the one off hydraulic direct drive here. He was limited to shock oils. At the time I believe the best he had was the Losi Silicone with a limit of somewhere around 70w to 80w. I believe he even tried motor oils but everything suffered from too much viscosity loss through heat. I also don't know if his leaking problem was due to faulty o-ring materials or just through wear. Probably both. It was still neat and a tribute to home engineering of the 80's.

Any quick way to test to see if the hydra-drive has the oil in it still and is working ok without alot of work (taking things a part)?

Just pull my JRX-Pro SE out of long storage (~12 years). It seems the front shocks are dry (or super light oil) but the hydra-drive I can't figure a method of checking without too much work.

Please go easy on me it's only been 20+ years since I built the buggy and upgrade drive.

If I recall, you filled it by removing the white nylon plug screws on the outboard side. Putting fluid in one opening until it ran clear and bubble free through the other. Then you reinstalled the scews/plugs. Could you simply remove one plug and elevate that side of the "disc" and observe either air space or fluid to determine if it was full?

OR:

Remove it from the transmission then re-assemble it on the input shaft and engage it slowly by hand and listen for air bubbles. Similar to checking a shock after rebuild?


Just brainstorming. I ran one on my Traxxas buggy bitd. Still have it but that rotating mass and the frankenstein gear cover kill me.

Really? With the patent? Buncha nerds in here. I love it!

Mark