Stall RPM increase? I like that.

I have not done synthetic ATF in the C3 yet (plenty of other cars, though). It seems I should record some numbers an look for a change

 

stall could be more clutch slip fooling me?

 

I'll take it if it gets me through the summer! The 79 is a dog with the stock low-stall TC. The TH350 is not long for this world either way.

 

I put Royal Purple synthetic GL-5 gear lube in one of my fresh built Muncie 4 speeds. The transmission made more noise (seemed like bearings were slightly whiny, not like gear mesh M22 sounds) and shifting quality was reduced. The synchros were not doing their job well.

I drained it out and saved it. Put in the cheapest car parts store GL-4 conventional gear lube I could find in the Muncie and we were right back to where the transmission was designed to perform. Quiet and smooth.

The reclaimed Royal Purple gear lube was used in my 2010 Blown Camaro SS rear end differential. Works great there.

I also use Mobile1 synthetic Dexron 3 ATF in my Tremec TKX and my SS factory 6 speed manual. Rather hard to find this fluid but it REALLY works great to improve shifting.

On flat tappet engines I use only conventional type high zinc oil. Only 1 time I ever lost a new cam was after a break in with conventional oil and a switch to synthetic. My best guess is the synthetic was too slippery to keep the lifter spinning. There just isnt any valid reason to try it again in any flat tappet engines.

 

Been a while, been researching, a lot.

OK, synth by itself is not bad unless,,,,
the seals in the tranny are worn and hold their leak prevention from basically dirt.
Like a plumbing pipe that has a little drip when assemble and will seal up from particles over time.
The syth fluid acts much like synth motor oils. Remember when people complained about leaks when they switched to synth motor oils?

For our old trans and the need for fluid,
I researched what was a problem and what wasn't.
Dexron 6 is not good for original trans.
There are arguments about this but the changes in the fluid needed for the new trans
won't do our period trans any good.
Basically the viscosity is lower in 6 when cold but does equal Dex 3 when hot where Dex 3 is cold. And it is full synth I believe.

Then friction modifiers that allow new lock up torque converters to slip when locked up, because of problems with engine misfire codes cause by computer engine control
and "service" eng light which people didn't like, plus a "shudder feel" in lockup while driving made a need for a new fluid. The solution is to allow the lockup to "slip" 20-50 rpm, a cushion for the eng control.
This slip causes heat and carbon fiber clutch wears so dirt in the filter although Dex 6 claims 50-100 thousand miles life.
Dex 3 "H" version was made to allow this slip, real close to Dex 6 but not syth , DEX 6 syth which is Dex 3 "J" I believe.

So, in my opinion, Dex 3 "G" type is the latest and greatest fluid for our trans.
Dexmerc is Dex 3 "G" type.
Read the bottle.

Hope that helps

 

Tremic recommends MTF synchromesh for their manual trannies. So I use this and change it every time I have the tranny out. The idea of using ATF with friction modifiers in a manual bother me and other people that have to rebuild them.



As to Rear end Differentials in our C-3's. The higher the numeric ratio number like my 4.11 creates more heat. The amount of motor TQ also increases heat. So I use the best gear oil.




It's also smart to install a diff drain plug like mine. I just got done painting with black epoxy paint. I have two rear ends 3.55 for road racing and 4.11 for everyday street use with TKO 600

 

Lets give some additional context. Most GL5s will substitute for a GL4 sanz the yellow metal issue. There are yellow metal rated GL5 oils though. GL5 has a much higher pressure rating but many manufactures load it with a very high sulfur content (thus the nasty smell). This sulfur will attack bronze, copper, and brass components which are prolific in older hydraulic and gearboxes. This isn’t a big issue in most modern stuff though because yellow metal isnt as common in gear drives and the invention of better hytran fluids has pretty much eliminated mass usage of gear oils in large equipment.

This is something Ive had to contend and watch for on the old Ford farm tractor my granddad had that my mom now uses to mow 7 acres with. On that tractor the gearbox and the hydraulics share the same oil sump and the hydraulics are loaded with yellow metal parts. Samething on an old square baler gearbox.

There are GL5 oils rated for yellow metals like Schaeffer 293 GL5 but your gonna spend alot for them and probably have a hard time finding them. If GL4 has a pressure rating that is suitable for your application and you have yellow metals, use it and be happy. The oil I listed is something you typically find in the final drive of something really big but has a shared sump for either gearbox or hydraulics and needs the additional pressure rating. The oil I listed is about $20 a quart……. Imagine the cost having to change and replace a 5 gallon common sump.

 

Thanks for the clarification. I didn't want to go down that rabbit hole, since this is the C3 section of the Forum, but yes. There do exist GL-5 synthetics that DON'T eat yellow metal. But then you have to be really careful about shopping for them.

GL-4 synthetics don't eat yellow metal (AFAIK), and GL-4 is specifically called for in my C3's shop manual. So I use GL-4 synthetic, and it seems to do okay.

On other, more modern stuff, I use GL-5 synthetic, or match whatever specification is called out in the manual, with synthetic. Sometimes the diffs, transfer case, and manual transmission can all have different specifications, so I end up buying 3 different types of synthetic gear oil. Fun times.

I prefer the simplicity of the C3s.

 

I use only red line lubricants if I have a question on suitably I call them , and always find out more than I expected.​​​​​​