4 Speed gear oil

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jtkaaa07

jtkaaa07

BossMan
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I know it's been brought up before, but what do the rest of you guys run for gear oil in your 4 speed's? Just about done with my 4 speed conversion, then it's time to bang some gear's

Thanks Jeff
 
jtkaaa07 said:
I know it's been brought up before, but what do the rest of you guys run for gear oil in your 4 speed's? Just about done with my 4 speed conversion, then it's time to bang some gear's

Thanks Jeff
Click to expand...

90 wt gear oil will make your trans live longer.
 
Thanks guy's, I just talked to Dan at Brewers Performance, he said 80/90 with a GL4 rating for friction. He say's guy's that switch to sythetic, usually end up with leaks. Again it must have a GL4 rating he said.
 
hi, I have ran four speeds for 33 years with mobil 1 synthetic gear oil. never had a leak from using it. also, the trans shifter easier, cold or hot. on tear down, had no wear on counter shaft. thick gear oil does not lubricat when cold, causes wear.
 
Synthetic gear oil is the way to go. Leaks from synthetic oil. LOL.
 
80/90 is too thick. Synchros will be gummy. Shifting will be slower and hard. May not stay in gear while coasting. Look at the input shaft and the gears on the main shaft/counter shaft. See the little hole every 4th tooth or so? That is a oil pump that pumps oil to the main shaft and the counter shaft needle bearings. Factory manual says ATF type A/ Dextron.
 
I had a 73 Dart Sport that was new and came with ATF and it made a lot of noise. I lived in Syracuse NY which was the home of New Process Gear who made all of the 4 speeds back in the day. My buddies there and a Chrysler Service Tech had me change it to 80 wt and the noises went away and it was no harder to ship unless it was zero degrees out.
 
I tried Mobil 1 synthetic gear oil and the tranny would grind on every shift. It lasted for a round the block drive and I drained and replaced with 80w/90 non synthetic and it was fine. I have heard this same experience from a lot of folks. Likely the limited slip friction modifiers that come in it don't let the syncros grab resulting in the gear crunch.

I have tried ATF and the shift quality is much proved over the gear oil but you do get a lot rattle from the gears in neutral. I tried Penzoil Syncromesh Fluid a couple of years ago and it's better than the ATF without the noise.
 
I see that Royal Purple has a syncromesh also, Amsoil has some manual trans fluid too. I think I'll try the Penzoil out.
 
slant6/4speed said:
80/90 is too thick. Synchros will be gummy. Shifting will be slower and hard. May not stay in gear while coasting. Look at the input shaft and the gears on the main shaft/counter shaft. See the little hole every 4th tooth or so? That is a oil pump that pumps oil to the main shaft and the counter shaft needle bearings. Factory manual says ATF type A/ Dextron.
Click to expand...

Not so. Been running 4 speeds for almost 40 years, built them too. No problems you have mentioned, unless the trans was worn badly. A trans with Auto trans fluid will be worn badly in about 100k, 90 wt gear oil will run forever with almost no wear 4 speed or OD. Never had slow shifting!!! It's your trans do what you will. At -20 degrees it was a bit slow till it warmed up, now that I think of it...
 
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