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I have a few questions regarding changing the gear oil in my '65 manual transmission. First - when I attempted to drain the transmission I could not find a drain plug, however I did find a bump out somewhat below and to the right of the fill plug. On the bump out is the outline of a circle and it appears this is where a drain plug should go. Am I missing something? Why wouldn't there be a drain plug?
Also - what are the pros / cons using synthetic gear oil?
Forrest going from what I think I know, only the Muncie M22 "rock crusher" equipped C2's would of had a drain plug. Drain plugs were in the C3 Muncie equipped 4-speeds starting in about 1970 I "think". My orignal owner 68 with a M21 (close ratio) Muncie does not have a drain plug. I have changed the fluid twice since it was new when I had to change the throwout bearing.
Forrest going from what I think I know, only the Muncie M22 "rock crusher" equipped C2's would of had a drain plug. Drain plugs were in the C3 Muncie equipped 4-speeds starting in about 1970 I "think". My orignal owner 68 with a M21 (close ratio) Muncie does not have a drain plug. I have changed the fluid twice since it was new when I had to change the throwout bearing.
I'd be willing to bet that the drain plug was deleted thanks to the Chevy cost cutters swinging their axes. Drilling and tapping the boss and installing a plug would facilitate changing the gear lube, or you could get by using a siphon gun.
Based on singular experience, I suggest that you stay with conventional gear lube, not synthetic. I've tried using synthetic gear lube in a freshly rebuilt Muncie trans and had difficulty upshifting and downshifting it. I suspect the difficulty resulted from the brass synchronizer rings being unable to "grab" the hubs due to the improved lubicity of the sythetic fluid. Switching back to standard 80w90 gear lube corrected the condition.
I'd be willing to bet that the drain plug was deleted thanks to the Chevy cost cutters swinging their axes. Drilling and tapping the boss and installing a plug would facilitate changing the gear lube, or you could get by using a siphon gun.
Based on singular experience, I suggest that you stay with conventional gear lube, not synthetic. I've tried using synthetic gear lube in a freshly rebuilt Muncie trans and had difficulty upshifting and downshifting it. I suspect the difficulty resulted from the brass synchronizer rings being unable to "grab" the hubs due to the improved lubicity of the sythetic fluid. Switching back to standard 80w90 gear lube corrected the condition.
From 1963-69 the only Muncie transmissions that were equipped with drain plugs were the 66-69 with M-22. Beginning for the 1970 model year and the "661" main case, all Muncies got the drain plug.
Why didn't the 63-69 have the drain plug? Who knows, for sure? However, one reason may have been that there was no drain and refill maintenance schedule for manual transmissions. Plus, a drain plug represents a leak source. So, considering these 2 things, a drain plug might have seemed irrelevant. Could it have been a cost savings? Possibly, but I doubt it. Here's why: many Muncie transmissions without drain plug had a special magnet attached to the inside lower case with a special adhesive. With drain plug, the magnet was included as part of the plug and the separate magnet was eliminated. I suspect that it was more expensive to install the separate magnet than to drill and tap the case and install a magnetized plug. In any event, I would expect the costs to be approximately equal.
Why did they start installing plugs in 1970 for all Muncies? Probably, customers "bitching" about the lack of them.
As far as synthetic lube goes, my personal experience has been very positive. I installed Red Line synthetic lube in my 1969 Muncie years ago. While it's a very subjective sort of thing, my opinion was that the transmission shifted smoother and seemed to run cooler (as evidenced by transmitted heat I felt on the shifter shaft).
I have a brand new M-22 that I assembled from NOS parts purchased years ago by me. I'm using it in my "ZL-1". When I fill it with lubricant, what am I going to put in? You can bet that it's going to be Mobil 1 or Red Line synthetic lubricant.
From 1963-69 the only Muncie transmissions that were equipped with drain plugs were the 66-69 with M-22. Beginning for the 1970 model year and the "661" main case, all Muncies got the drain plug.
Why didn't the 63-69 have the drain plug? Who knows, for sure? However, one reason may have been that there was no drain and refill maintenance schedule for manual transmissions. Plus, a drain plug represents a leak source. So, considering these 2 things, a drain plug might have seemed irrelevant. Could it have been a cost savings? Possibly, but I doubt it. Here's why: many Muncie transmissions without drain plug had a special magnet attached to the inside lower case with a special adhesive. With drain plug, the magnet was included as part of the plug and the separate magnet was eliminated. I suspect that it was more expensive to install the separate magnet than to drill and tap the case and install a magnetized plug. In any event, I would expect the costs to be approximately equal.
Why did they start installing plugs in 1970 for all Muncies? Probably, customers "bitching" about the lack of them.
As far as synthetic lube goes, my personal experience has been very positive. I installed Red Line synthetic lube in my 1969 Muncie years ago. While it's a very subjective sort of thing, my opinion was that the transmission shifted smoother and seemed to run cooler (as evidenced by transmitted heat I felt on the shifter shaft).
I have a brand new M-22 that I assembled from NOS parts purchased years ago by me. I'm using it in my "ZL-1". When I fill it with lubricant, what am I going to put in? You can bet that it's going to be Mobil 1 or Red Line synthetic lubricant.
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