hawaii75stingray

I'm ready to change out my fluid this week. A lot of people insist on using dino instead of synthetic and several caution against oil with limited slip additives. The most popular choice seemed to be Valvoline 80W-90 High Performance Gear Oil GL-4/5.
The problem is, here's what Valvoline says http://www.valvoline.com/pdf/high_performance_gear.pdf
"These products are recommended for conventional rear axles, limited slip rear axles, and transmissions requiring EP gear lubes under high speed, high load, high torque, and high horsepower conditions. Valvoline High Performance Gear Oils meet or exceed API Services GL-5 and GL-4*. The inclusion of Limited Slip Friction Modifier in this product makes it unnecessary to add additional friction modifier (Ford M2C118A, Chrysler MS-5630, or GM1052358) in most vehicles."
"*In synchronized manual transmission applications use:
• Valvoline Professional Series Manual Transmission Fluid or
• Valvoline Synchromesh Manual Transmission Fluid (available September 2012)"
So, if Valvoline includes limited slip additives, should I look for the GL-4 stuff for synchronized transmissions instead of the GL-5 High Performance Gear Oil?

hawaii75stingray

On the Chevelle forum comes this warning:
http://www.chevelles.com/forums/arch.../t-132531.html
"I was not aware the GL5 & Hypoid additives that contains sulphur & is very slick was harmfull to the syncros in our muncie's that are rated for GL4 80/90 LUBE ONLY. I was unknowingly running GL5 lube in my muncie for 4+ yrs and it has been shifting harder even though clutch is adj correctly. Now i know why after reading the info from the Redline Oil Site which i have LISTED BELOW FOR YOU ALL TO READ TO AVOID DAMAGE TO YOUR MUNCIE'S.

Also,i checked approx 9 auto parts stores in my area and not one of them sells or stocks any 80/90 std trans lube that not rated for GL5/Hypoid,they are all rated for GL5/hypoid use . None of the 9 stores i checked stock the lower rated GL4 80/90 lube thats rated for our older muncie std trans so beware of this as i am sure many of you are running the wrong GL5 rated lube that will eventually tear up your syncro's AND DONT EVEN KNOW IT'S HAPPENING.

I just drilled and tapped my muncie for a drain plug so i could drain the wrong GL5 lube out and replaced it with redilnes MT-90 gearlube thats specifically desigend for our trans but i think it's too late for me but i hope i can save some of your trany's if you take the time to read this great info from Redline oils listed below."

jb78L-82

I have read the same and have 2 qts of Redline GL4 ready to go in the 4 speed this spring (why tempt fate) BUT I have had Mobil 1 GL5 in my 4 speed since 1992 and the trans is perfect-no issues in the last 22 years….My thinking is that if this 1. brass synchro issue was as big as some portend it to be, there would be trashed 4 speeds all over the forums and in real life which simply has NOT been the case. 2. The engine builder who just did the short block in my L-82 and worked as a field tech for GM for 16 years up to about 10 years ago and who builds/repairs not only engines but manual transmissions and rear ends, has NOT seen this issue to be the case when he rebuilds older 4 speeds with GL-5 synthetics-I asked him!. I suspect people who have issues with their 4 speeds and are running Gl5 probably would have had issues regardless of the gear oil they are running. None the less, since Redline offers a synthetic GL4, I will make the switch-probably would do nothing if the synthetic was not available.

hawaii75stingray

It gets more interesting. Going to Redline's website and checking on applicability for C3's with 4-speeds, it recommends their GL5, not GL4. Specifically: 75W90 NS GL-5 Gear Oil (which seems to have the limited slip additive).

leadfoot4

I had a '77 Pontiac T/A, before buying my Corvette, and the T/A had a Borg-Warner T-10 4 speed in it. It developed a bearing whine, so I pulled the tranny and had it "gone over" by a local drag racer who rebuilt transmissions for some extra $$, to support the race car.

After he finished it, I re-installed it, and filled it with Synthetic gear oil, and what a difference. It never shifted as smooth, from the day the car was new. However, that doesn't help with your GL-4/GL-5 dilemma

Jason Staley

I use to use Mobile 1 synthetic gear lube in my Richmond 5 speed with brass synchro's. Several years ago, I decided I would try Redline MT-90 75W90 GL-4 Gear Oil for manual transmissions.

Even though the synchro's were in fine condition and the synthetic gear lube didn't appear to have caused any damage, there was a HUGE difference in shifting smoothness with the Redline trans fluid. The synthetic gear lubes are simply to slippery for the synchro's to operate at their peak performance.

Solid LT1

This subject has been best to death on this forum! I run Brad Penn gear lube in my old Muncies it's works well and is specifically formulated for bronze Syncro blocker rings. You need an MT-1 rated gear lube if you have a Muncie trans.

jb78L-82

Redline MT-90 is synthetic…..

resdoggie

I'm using this:

http://www.redlineoil.com/product.aspx?product=58304

Should I be concerned? It does say:

"Musclecar applications like Ford Top Loader, Borg-Warner T-10 and Super T-10, and Muncie transmissions"

Jason Staley

Yes, but it doesn't contain the friction modifiers that make most synthetic gear lubes great for rear end gears (i.e. most of the ones found at your local auto parts store). The MT-90 synthetic is specifically formulated for manual transmissions.

Jim__H

I put Ford full synthetic manual transmission fluid in my Jag. It was the only thing that quieted my noisy reverse idler. Might be a good choice for you guys with manual gearboxes:

<<Motorcraft® Full Synthetic Manual Transmission Fluid is a premium-quality SAE 75W-90 gear oil recommended by Ford Motor Company meeting warranty requirements. It is particularly recommended for 1995-2011 MTX-75 and IB5 transmissions, and is also recommended for older transmissions including rear wheel drive that recommend GL-3 and GL-4 type gear oils>>

http://tinyurl.com/lx97za5

Not cheap, I think I paid over $20 a quart but seems to be working well for me.

hawaii75stingray

The originally specified fluid for a '75 was GL-5 80W90. Most brand's GL-5 over the years have acquired a lot of modern additives, some not so good for 4-speeds. Redline's application guide for '75 4-speeds actually lists their GL-5 (synthetic) 75W90 "NS" GL-5 gear oil. They say the "NS" version for 4-speeds "lacks friction modifiers to balance slipperiness", "helps to slow synchros for easier shifting", and has "improved copper corrosion protection to prolong synchro life". Anyhow, that's what I went with and it's working great so far!

jb78L-82

Good info!

Which explains my post #3 above.. Thanks