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Manual transmission hard to shift when engine is on


sgtsandman

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I used the Mercon V replica made by Valvoline to drain and fill the manual trans about 10k miles ago. I can try Mercon V I order online from Ford. I am surprised a slightly different formulation affects performance that much in a manual transmission.
I think I tried both Castrol and Valvoline. Whatever the difference is, it shows.
 


4x4junkie

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I do not recommend Mercon V for a manual trans. I've seen it cause too many problems with shifting in manual transmissions.

Plain ol' Mercon (what was originally specified for the M5OD) is still widely available, it simply is known as "Dex/Merc" now (any auto parts store carries it).
After dealing with the issues V causes, I wouldn't take chances with a fluid that Ford at one point (correctly) said was not compatible with Mercon before changing course... Why they changed course I don't know (well, I have one theory, but it probably would get shot down as conspiracist. More likely they just failed to research or test it adequately in the real world using real transmissions). Getting rid of the effects of Mercon V requires multiple fluid changes.
 

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The M5OD I rebuilt about 6 years ago for my '88 started grinding going into 3rd last year (only in really hot weather though) and I had Valvoline Dex/Merc in it. Fluid looked new when drained, no major metal or anything, just the usual light sparkles that I would expect from 25k in a manual trans.

I put 10w40 synthetic engine oil in it about a month ago and occasionally I still get just a little "chunk" going into 3rd but never the nasty grinding noise. I "fixed" another M5OD with a 2nd gear grind with 5w30 engine oil. My suspicion is that the thicker oil makes up for a worn synchro temporarily. I don't think that I'll have oiling issues with engine oil like I might with gear lube but I guess I'll find out if I ever tear it down. Why a synchro would fail after only 25k is a mystery... junk aftermarket parts maybe.

I would like to try Valvoline Synchromesh MTF in an M5OD sometime but at $10/quart it's a high price to pay for an experiment. I really like that particular fluid for Mitsubishi transmissions.
 

sebastian323

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The M5OD I rebuilt about 6 years ago for my '88 started grinding going into 3rd last year (only in really hot weather though) and I had Valvoline Dex/Merc in it. Fluid looked new when drained, no major metal or anything, just the usual light sparkles that I would expect from 25k in a manual trans.

I put 10w40 synthetic engine oil in it about a month ago and occasionally I still get just a little "chunk" going into 3rd but never the nasty grinding noise. I "fixed" another M5OD with a 2nd gear grind with 5w30 engine oil. My suspicion is that the thicker oil makes up for a worn synchro temporarily. I don't think that I'll have oiling issues with engine oil like I might with gear lube but I guess I'll find out if I ever tear it down. Why a synchro would fail after only 25k is a mystery... junk aftermarket parts maybe.

I would like to try Valvoline Synchromesh MTF in an M5OD sometime but at $10/quart it's a high price to pay for an experiment. I really like that particular fluid for Mitsubishi transmissions.
This is the stuff I have in my car right now:
1689381090311.png

SUITABLE FOR Mercon®, Dexron®-III, Ford M2C138-CJ and M2C166-H, Allison C-4 and TES-389, and Caterpillar TO-2.

I imagine that the transmission was damaged by running for 2 years with the bad slave cylinder and forcing the gears to engage. I dont get a grinding noise at all when engaging gears but theres is a noticeable pop when engaging first gear ( and sometimes second). Maybe I can try changing the master cylinder as well (can I do this without dropping the transmission). I am up for trying out engine oil in the transmission
 

franklin2

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If the engine is running with the trans in neutral and the clutch pedal out, half the transmission is turning the same speed as the engine, the other half is not. ALL transmissions are going to balk at going into gear if you push the clutch in and immediately push it into first. The first gear synchro is trying to stop the transmission guts as it's coasting to a stop.

As you found out, as the transmission synchro gets worn, it does a less than satisfactory job at this. You can wait a little longer for it, or you can try another gear. Any of the different forward gears will stop the transmission when it's coasting to a stop. Then you can quickly shift to first.

If you push in on the clutch, wait a little bit, and then try reverse, if it grinds, stop,, and wait a little more, and try it again. If it is still grinding, you still have clutch problems. The transmission will eventually coast to a stop. If it never does, the clutch is still turning the guts of the trans.
 

sebastian323

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If the engine is running with the trans in neutral and the clutch pedal out, half the transmission is turning the same speed as the engine, the other half is not. ALL transmissions are going to balk at going into gear if you push the clutch in and immediately push it into first. The first gear synchro is trying to stop the transmission guts as it's coasting to a stop.

As you found out, as the transmission synchro gets worn, it does a less than satisfactory job at this. You can wait a little longer for it, or you can try another gear. Any of the different forward gears will stop the transmission when it's coasting to a stop. Then you can quickly shift to first.

If you push in on the clutch, wait a little bit, and then try reverse, if it grinds, stop,, and wait a little more, and try it again. If it is still grinding, you still have clutch problems. The transmission will eventually coast to a stop. If it never does, the clutch is still turning the guts of the trans.
Wish I had read this earlier. Makes perfect sense. Until I showed the truck to my freind who is a mechanic, I thought the trans needed to rebuilt ( I peeked in the observation window, and the clutch seemed to be working and the travel when engaging the clutch seemed sufficient). This makes perfect sense, and I recall my dad telling me that when engaging first you should go for second first then put it into first (he was probably rolling around on worn transmissions).
 

88workcar

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Mine is whinning and grinding going into 3rd also. Any thoughts on Terrestic 46 ? or even DTE 732?
 

Manscout

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I would like to try Valvoline Synchromesh MTF in an M5OD sometime but at $10/quart it's a high price to pay for an experiment. I really like that particular fluid for Mitsubishi transmissions.
I've been running Syncromesh in my M5OD for 20k miles over two years. It's better than ATF, but not magic. I'm still glad I went that route though.
 

bobbywalter

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that mt90 is pretty good. full syn 5 w30 mobil 1 lately. way better in winter.
 

sebastian323

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I am going to run some full synthetic 5w30 in my m50d trans next time I change the fluid.
 

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