It's me again. The guy with the Trabant 601. OK in the time I have been testing different oils, I could have removed my gearbox and replaced the freilauf (freewheel device) ----> and had it back in the car. However I was told by some people not to give up on it just yet because these things can gum up. And I was told you couldn't fix a worn sprag by using a thinner gear oil as well. So at this point I'm not sure what to believe. I also wanted to see if using the correct lubricant made any difference than any other type of lubricant with the same viscosity grade. There does seems to be a difference. Either that or by giving the gearbox a diesel fuel flush between different lubricants is washing out any buildup that is clogging up the freewheel device. I have seen what looks like metal particles suspended in the oil after draining the oil but I'm not sure if this is from worn metal parts or zinc compounds (anti-wear additives). But I did not see any in the diesel fuel. So I suspect it's the zinc compounds in the mineral oil. First of all. This really only applies to folks living outside of Europe. This HLP 68 oil is basically a mineral oil containing zinc compounds. In the United States it goes under the desgination AW (anti-wear) tractor hydraulic oil. And according to the MSDS, Mystik's VG 68 is the same thing as Liqui-Moly HLP 68 (Tractor Supply two gallon jugs). And Mobil DTE 26 VG 68 ($40 a gallon from Wal-Mart). I'm never seen it at Wal-Mart but there website says they carry it. I tested different lubes. Although usually the thinner the lube, the better the freewheel device engages but what is weird is despite one lube being thinner than the other does not nessessarily it works better! Here is a chart of various oils and their viscosity grades. Not all of these lubes I tested are in any particular order. These tests were all done between 32F/0C and 50F/10C. SAE 30 engine oil: I used this oil for awhile until I started having issues one summer. Then switched to Dextron which worked fine until this past fall. The three lubes that peformed the worst: 75W90 gear oil, 0W20 motor oil and Interlube VG ISO 46 turbine oil. With these lubes the freewheel device would seldom engage even after being driven for several miles. I tried 10W30 motor oil which worked so so. By all accounts the 0W20 should have worked better than 10W30 but didn't and I don't know why. Also as to why the VG 46 Turbine oil which is basically hydraulic oil did not work as well as the VG 68 mineral oil I got from Tractor Supply I can't explain that either. The only thing I can think of is I typically did a diesel fuel flush after testing each oil. Not to flush out the previous oil but any junk that might be clogging up the freewheel device. I found that the freewheel device works flawless using diesel fuel. Although an oil it's not a lubricant so it should not be used as one. Mercon/Dextron ATF and the Mystik VG 68 seemed to work about the same. Occasionally failing to engage. The ATF is about a 20 weight oil where ISO VG 68 is around a 30 weight oil. I decided to try Tractor Supply's Traveler universal tractor hydraulic oil. This oil is a multi-grade hydraulic oil (32/46/68) or (10/20/30 weight). This lube seems to work the best although I have not tested it on a cold transmission or in subfreezing weather. Here is a couple of viscosity grade versus temperature charts I found: Based on these charts it seems to indicate it's safe if not better to use a thinner oil based on the operating temperature of the equiptment. I aimed one of those infared heat pens at the gearbox immedietly after doing a 5 mile test run at 55 MPH using the AW 32/46/68 multi-grade mineral oil. The gearbox measured 108F/42C at an ambient temperature of 50F/10C. So based on that, looks like I could use an AW 22 as long as the gearbox does not get above 131F/55C. But that is probably cutting it too close. AW 22 is typically used as hydraulic jack oil or used in hydraulic systems in very cold climates. I'll have to do a temperature test this summer to get a real world reading. Would it be safe to say that operating temperature and ambient temperatures are linier? So if the gearbox temperature was 110F at 50F ambient, then at 95F ambinet the gearbox temp would be 155F ? Concerning HLP 68. I was told by someone that this was oil was selected by the engineers at IFA/VEB/Sachenring for the transmission. But I wonder if this was the "best" oil or the only one available during the DDR era? Since the Soviet Union supplied the DDR with their petroleum products. Well at least petrol. It's probably safe to say they did not have multi-weight hydraulic oils in the DDR. Or a mineral oil with a VG of 32 was no available. Below are a list of oils from various Eastern Bloc countries where the car was sold in. I assume these oils are defunct, are basically the same (mineral oil) just a different name. Just like HLP 68 does not exist in the United States but AW 68 does which is exactly the same lubricant. DDR : HLP 68 CSSR (???) : PP 80 Hungary : C80 Romania : T 90 EP 2 Bulgaria : M 10 C Poland : Hipol 10 or 15 Yugoslavia : SAE 80 (gear oil) All others : SAE 30 engine oil can be substituted.