Trans Shifting Issue

[dannystarr]

Decided to change trans fluid and put in "Amsoil Synthetic Manual Transmission & Transaxle Gear Lube"  SAE 75W-90  API GL-4.
Seem to work ok for a while then after a couple hundred miles it starts acting weird. Let me try to explain this correctly. Trans is Muncie M21.

 SO, with the car warmed up, push in the clutch and it won't go in to first without EXCESSIVE pressure. Push like hell two or three times and it goes. This happens for 2nd gear also...Then out driving when you come up to a stop sign and begin downshifting, it falls in to 3rd, 2nd, and even 1st like butter! But ONLY if the car is moving!! Once you come to a complete stop, and it's a 6 way signal so ya throw it in neutral for the wait.. light turns green, push the clutch in, won't go in to 1st. However if the car is rolling even ONE mile an hour while down shifting, it drops right in to first gear. Now, once you GET it in to 1st while keeping the clutch depressed, it goes in and out no problem. Throw it back in neutral and let the clutch out, push it back in, won't go in to first. Read this twice before ya reply... ha ha  Linkage and clutch adjusted perfectly. If it wasn't it would bind all the time? Could it be the synthetic oil? Would like opinions before I change it out.  Danny

[z28z11]

Sounds almost like the three drive dogs on the synchro sleeve are worn, or out. Give us the rest of the story - how old is the trans, ever been freshened, have you tried selecting second or third before you try to select first (from a standstill). If the other synchros are good, then it points to the sleeve for first, obviously. Brass sleeve could be heavily worn, also, causing not enough friction to be able to slow the rotating gear mass down enough to select the gear. 

Before you start ripping things apart, drain the synthetic fluid out and go back to the recommended weight of conventional oil - worth a shot. What's the old saying, the simplest solution is the best solution ?

JMO,
Steve

[L78racer]

you should be running GL-4 Gear Lube in a Muncie.

[dannystarr]

First line states...This happens for 2nd gear also... So yes, it does happen for second also. Just won't go in without a lot of effort. Trans has 55,000 Original miles and looks pretty good inside. I put in a clutch and took some pic's of the inside. NEVER apart! Original tailshaft seal/shift seals/side cover gasket etc. New seals are leaking. I KNEW I should not have used that oil. I was going to put it in the Rear Axle and Engine also. But might just forget it and send it back. $254 worth of oil and rear diff additive! I got talked into it by a friend. Is it ok to use in the engine with solid lifters, or the rear posi axle?
Danny

[dannystarr]

Got the linkage adjusted well. Even fine tuned it after this picture. So it isn't that... Danny

[L78racer]

send it back. use conventional oil and gear lube.

[Stingr69]

Synthetic oil is probably so slippery the synchros will not work.  Drain and refill with conventional dinosaur oil.

[68Zproject]

Jerry always said NEVER use synthetic in the Muncie.  I use it in my 302 engine but I add the ZDDP plus to it.  I don't know about the rear and would like to know if synthetic is ok in that as well.  BTW it's a posi if that makes a difference.

[firstgenaddict]

The synthetics don't perform the same way... we have learned, tried them in multiple different 70's and older MT's and they do not shift right... the blockers or synchros don't slow down enough, it's as though the fluid does not cause enough drag due to low viscosity.

Newer transmissions are designed for use with low viscosity lubricants as the low visc lubes enable the vehicles to get better fuel economy.

[bcmiller]

As others have mentioned, use conventional oil ONLY!

Drain out what you have and get some regular gear oil.  I get mine at NAPA. Does not have to be a big name high dollar brand.  It is $6.99 per quart around here.   PART # NOL 75210

Put in conventional gear oil and your problems will most likely go away.

[RS Copo]

Let us know how it works out. I have a friend who went to synthetic late last year and ran into the same problem.He is sure the trans has got other problems and it is not the oil causing it. Parked it,has not driven it at all this year.

[Kelley W King]

Couple hundred miles just enough to dilute or wash off the old lube from the gears. You know what to do but the symptoms sound like low lube level.

[joesauer]

Ditto on the xmsn synthetic.....don't use it.  Conventional oil is better in old cars, including engine oil.

[dannystarr]

I still can't believe I did this   I was told this 3 or 4 years ago to never use it. I bet it's in the old post from the other car? I just can't remember things since the surgery. I was under 5.5 hours, and I must have moved a little during the thyroid and 3 tumor removal. Then the surgeon must have scolded the anesthesiologist and he turned the knob and overdosed me with goop. After that, I was dizzy for 91 days! I lost a little that day 

 I KNOW it is full of oil. While filling it, it started coming out the fill hole. THEN I directed the nozzle to the tailshaft and cranked it 3 or 4 times. It was POURING out as I installed the plug.
Problem is how do I get it all out without pulling the trans? I can't get the side cover off and spray giant cans of carb cleaner in there to flush it down and out. I was going to drain it, then use the 80/90, then drive it for 10 miles, drain it again, add the 80/90 and see what happens. Or do that 3 TIMES! But won't the syn stick to everything? I better just pull it, drain it, spray it down. Flip it over a 5 gallon bucket like I did before. Rotate the assembly and keep spraying and bucket it again. Then add new oil and reinstall trans. SOB this sucks!!  Danny

[Kelley W King]

I think you are overdoing it. Just drain it overnight, put the 90 weight in it and try it. Drive it through the gears when you do and let the oil get up in all the sliders,ect.