Syncromesh fluid in T-86 with R6 overdrive?

[Daniel Jones]

I'm getting ready to change the transmission and overdrive fluid in my 1938 Imperial with Borg Warner T-86 3 speed and R6 overdrive.  The 1938 factory service manual recommends the use of SAE 70W aircraft engine oil in the summer and 50W in the winter.  There's a warning against using lubricants with extreme pressure lubricants that contain lead soap as they can centrifuge out.  There's another statement that says other types of EP lubricants are okay.  Searching the net (and this site), there's a warning against gear oils with EP additives (which may attack brass/bronze/copper parts) unless they pass the ASTM D130 Copper Strip Corrosion Test and some are running the Ford tractor 90W all mineral gear oil from Tractor Supply.  I'm thinking about trying the GM/Pennzoil Syncromesh fluid.  I run Syncromesh in my TR8's LT77 5 speed transmission and it is recommended by the TR8 Car Club of America's.  Before I switched to Syncromesh, I polled the TR7/TR8 list for what people used.  Lots of different lubes were tried: Types G and F ATF, Dexron II and III ATF (with and without home brew additives for yellow metals), Redline MTL, Syncromesh, etc.  Synchromesh was universally recommended.  Some had used ATF with no ill effects but some of the racers had had problems.  Also, my Tremec manual specifies GM Synchromesh for 3550 and TKO transmissions and a number of autocrossers run it in their T5 5-speeds as well.  Syncromesh contains additives for protection and performance of the synchronizers and any yellow metals in the transmission and has the proper viscosity for low temperature operation and protection of the small plastic gears in the LT77 transmission oil pump.  When Pennzoil introduced their version of Synchromesh, I saved the press release:

 

 "Pennzoil has designed a new transmission fluid, Pennzoil Synchromesh, that is specially formulated to meet the demanding needs of manual transmissions used in certain General Motors vehicles. These vehicles require GM part number 12345349 (Spec. No. 9985648) Synchromesh Transmission Fluid.  Pennzoil Synchromesh Fluid is formulated with high quality paraffinic base stocks, a fluidity modifier and a multifunctional performance additive. It also has corrosion inhibitors, a foam suppressor, and shear stable viscosity index improver additives. Pennzoil Synchromesh provides excellent oxidation stability and low temperature performance. Plus, it's compatible with yellow metals, such as the bronze, brass and copper components found in manual transaxles and transmissions.  This fluid will effectively lubricate General Motors manual transmissions and transaxles from -40 degrees C to 150 degrees C."

 

One of the TR8 owners sent in a sample of the GM Synchromesh fluid (GM p/n 12345349) and it came back is a mineral as a paraffinic base stock with additives and viscosity enhancers improvers and appears to essentially be a kind of motor oil adapted for transmission use.  Similarly, a post on the message board at www.oilanalysis.com found Synchromesh to consist of a 5W30 non-detergent oil with a friction modifer and an EP (extreme pressure) additive. It is made under contract for General Motors by Pennzoil (APC 3378) or by Texaco (Code 1874 MTX Fluid).  According to Don Johnson:

 

"Synchromesh fluid was developed for use in the New Venture manual transmission used by Chrysler and General Motors. Specifically, Synchromesh is formulated for transmissions that require GM Part No. 12345349 (Specification No. 9985648), GM Part No. 12345577, or Chrysler Part No. 4874464 (Specification MS-9224). Owners of Diamond Star Motors (DSM) Eclipse, Talon, and Laser cars with MMC (Mitsubishi Motor Corporation) transaxles have reported positive experiences using Synchromesh. The same can be said for owners of the Mitsubishi 3000GT and Dodge Stealth cars with the Getrag-manufactured AWD transaxles. The main benefit to DSM and 3/S owners seems to be excellent synchronizer performance, with reduced grinding and easier shifting compared to using some other gear oils. Pennzoil Synchromesh Fluid can be purchased as that brand or as the equivalent products: Quaker State Synchromesh (Quaker State is part of Pennzoil), Texaco Synchromesh, GM Synchromesh, or AC Delco Synchromesh (part number 89021808)."

 

I have to granny shift 2nd gear on my T-86 to keep it from clashing and the overdrive is not engaging.  I've got a rebuilt T-86 with R6 OD ready to swap in but I figure it's safer to experiment on the transmission currently in the car.  Any reason why this could be a bad idea?  Loren, how did your 10W-30 synthetic motor oil work out?

[Loren]

My theory is worth exactly what you pay for it and my experience is worth a little more.

I was a Saab mechanic & racer for years. The Saab 96 has freewheeling in the form of a sprag clutch like those in Overdrives and automatics.

Two stroke engines need freewheeling because the lubrication is in the fuel and when the throttle closes the lubrication is greatly lessened.

Freewheeling was carried over to the V4 four stroke era for other reasons ( better control on slick roads for one ). Since engine life was no longer part of the reason for it’s existence drivers often shifted to direct drive and forgot about it. The crud that develops in manual transmissions likes to collect in the freewheel unit and when called upon to function they some times slip. The old timers ( like me ) observed that automatics get hotter but never develop the crud and they are as clean as a clock inside. So the idea that it was the fluid that kept them clean grew. The question became could we use temporarily ATF in a freewheel gearbox to clean it? When I found that old Mercedes transmissions specified ATF as the lubricant of choice that cinched it. When a customer complained about a slipping freewheel draining and refilling with ATF temporarily became the fix. 
The lube became a series of changes starting with 90wt. Then the factory learned that lowering the viscosity also lowered the running temperature, so 75wt became the standard. This caused distribution problems because it wasn’t commonly available here and thus the factory had to supply it. Finally the factory came to the conclusion that 30wt motor oil was just as good and they could get out of the oil distribution business.

In our off road race cars we always used freewheeling ( Saab used on center ring & pinions which were not as strong as we needed especially in backlash. Do not push start an old Saab ) thus the lube we needed had to be freewheeling friendly and high heat friendly too. Redline made the right stuff ( Redline is a brand of Conoco-Phillips ). It was designed for manual transmissions had a thin viscosity and could take high heat. The modern equivalent is Redline MTF.

So here’s my theory: When ever you plan to change lube or overhaul a manual transmission, drain it and refill with ATF ( the cheapest will work just fine, don’t over think this ) drive it a week normally and either refill it with the lube brand of your choice or remove it for repair.

Lower viscosity will lower the running temperature a noticeable amount.

Never use an EP rated lube in something that has a sprag clutch.

Many sources recommend GL-1 lube for Overdrives but I am not one of them.

You just can’t beat modern synthetic “Transmission” lubes but…when you start looking at auto maker branded or recommend lubes the price gets out of line.

Remember the last car ( or truck ) to use Overdrive 3 speed manual transmissions was about 1973 and there weren’t any wizz-bang super lubes then.

So I think you could safely use a good synthetic 30wt motor oil and it would work fine in a pinch. For my money the old stand Redline MTF is my first choice in everything. It’s Baja proven! 

[Daniel Jones]

Thanks for the reply.  I don't think I've ever seen a SAAB 96 in the wild though I have seen a Sonett III.  I did an oil change last night (6 quarts of 15W-40 Motorcraft Super Duty Diesel oil, has 1000+ PPM phosphorus in the form of ZDDP).  While I had it on the stands, I also drained and refilled the fluid in the T-86 transmission and R6 overdrive.  I didn't think about flushing it first with ATF but I let it drain for several hours.  I filled it with 4 /4 pints of Pennzoil Synchromesh fluid and checked the lubricant level in the differential which was topped off.  I drove it to work today.  I'll need more seat time but the synchronizers didn't have any issues shifting into second.  I forgot to order water pump lubricant but did that today. 

[Daniel Jones]

A quick follow up.  Shifting is much improved with a fresh fill of Syncromesh fluid.  I no longer have to pause for a second between shifts which makes keeping up with traffic much easier.  Also, I think the overdrive may be working but not the way the owner's manual says it should.  The owner's manual states that "pulling this button out to the limit of its causes the overdrive unit to be inoperative.  Do not pull this button out when going more than 35 MPH. However it may be pushed in at any speed while the clutch is disengaged."  

Mine seems to engage overdrive when the knob is pulled out, not pushed in.  Also, while the car was in motion (well above 35 MPH), I depressed the clutch and tried to push the knob in but it didn't want to move.  When I attempted to force it, I heard a bit of gear clashing and quickly backed off.  I need to get back under the car and see if maybe the control lever was flipped so that it's 180 degrees out from where it would have been originally. 

 

Edited September 11 by Daniel Jones
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