I want to share what I have done to my manual 6 speed. Lately it has been difficult to get into 1/2/R especially when cold. There does seem to be some clutch plate grab when idling in neutral and shifting into gear when ready to go. So after talking with my local diesel guy ( who changed to Duramax but thinks Cummins still best engine) he told me the synchros are the weakest part of this gearbox. So here I think I am in to a big bill for new synchros and bearings/seals. We talked about changing the oil and he said that could help. Folks you would not believe that probably 90% of tranny service shops have no clue that these boxes use special oils and it is about bearing lubrication. So I actually went to the local Mopar dealer and paid $200 to get the gearbox and transfer case changed as they both use ATF+4 and I even made sure they know what to use. Now it shifts into reverse easy and yes it still has to really warm up for nice shifts in 1/2. But I had 75000 miles 126000kms on it and had never changes the oil and it should be changed out at 50000/80000k. Also my local guy said you will thrash out the synchros prematurely if you install a short throw shifter.
Sorry to be so long winded but I wanted to pass this on to you stick shakers.

 

I have that issue sometimes, only seems to be when warmed up and sitting in traffic though. I just hit 3 or4th gear first then drop into 1-2 or R.
Yes fluid makes a difference. As well it's reported that the OE fill level is too low.
On advice from a long hauler on here years ago with a fleet of G56 trucks, fill to fill hole with ATF and then add extra qt of Lucas trans fix juice.
Have had that recipe in the truck for 100k miles, 80kmi service interval and so far so good.

 

the maker never intended to have atf+4 used in the g56. a blend of royal purple syncromax and 50 wt delvac synthetic syncromesh transmission fluid two quarts over full is what you should run.

 

IIRC Standard Transmissions recommend using synchromesh fluid in the G56 and that's what they are using for their rebuilds.

 

standard transmissions use penzoil synchromesh, it has higher levels of some anti wear additives that the others do not have. they also overfill to lube and cool the front bearing. Mercedes designed the g56 to use a 50 wt high additive synthetic oil but none is available in the US the delvac mentioned is to thick by its self for about half of the united states. using oil analysis the royal purple syncromax has a additive package similar to the delvac and meets the original oil, most are blending a 50-50 mix, the syncromax is about a 10w 30 oil so the mix comes out about a 25 wt motor oil equal witch should be about a 60 wt gear box rating. the atf+4 was a really dumb Chrysler's idea to use one fluid for all things except the differential. while you are at it, change the transfer case out to the straight delvac. delvac was mentioned because you can get in gallons from ww granger. we use delo or castrol but is only available in 5 gallon pail or 55 gallon drum
Delo Synthetic Transmission Fluid SAE 50
Delo Synthetic Transmission Fluid SAE 50 delivers exceptional all-climate, year-round performance in heavy duty truck transmissions. A unique additive package can protect gears without using the “active sulfur” agents commonly found in automotive axle oils. This results in little to no corrosion and long life for copper-containing parts, such as oil coolers, bushings, and thrust washers. Good pumpability in extreme hot or cold temperatures promotes smooth shifting and efficient power transfer. It is specifically formulated to meet the latest extended drain requirements for Eaton transmissions, with drain intervals of up to 500,000 miles.
Synchromax is recommended for manual transmissions
that specify an automatic transmission fluid or motor oil.
It is also ideal for transfer cases and 2-cycle motorcycle
gear boxes.
Synchromax is formulated with Royal Purple’s synthetic,
proprietary Synerlec additive technology, offering
improved shift quality over a wide temperature range and
reduced gear noise.
Synchromax is fully compatible with all types of friction
materials and offers excellent corrosion and oxidation
protection without affecting the soft metals commonly
found in manual transmission synchronizers.
Performance Advantages
• Greater wear protection
• Smoother shifts
• Excellent rust / corrosion protection
• Reduces friction for more power
• Lowers operating temperatures
Delvac from ww granger
Castrol 50 wt is syngear CD50 o’rileys p/n syn 50-5
Amsoil FT F05-EA

 

^^ IMO, that is a terrible mix of G56 trans fluid.

As Carl mentioned ATF is much too light to use in the G56 and why add Lucas Trans fix? Who knows what is in that?

 

Great info carl. Thanks!!

 

I've used Carl's formula substituting Amsoil 5-30 for RP. I'm in San Diego and the trans is still a bit stiff for a mile on surface streets. I wouldn't want straight Delvac.
I used Pennsoil Synchromesh before the smf conversion. The marbles in the trans resulting from the conversion prompted me to go with Carl's recipe.
He operates a fleet and has posted pics of the internals of G-56's with various fluids.

 

Well point taken. Only got about 130kmi on Amsoil ATF + Lucas. Hope the trans lasts. Changed at about 80k interval and not much metal in it and pretty clean fluid. Info above seems logical too.
I did get this info from a guy on here with a fleet of high mile hotshot Trucks, like 500k on some of them.