Gear Lube GL4 vs GL5

[Dmichels]

There is endless reading on the internet regaurding GL5 rated gear oil being bad for yellow metals (syncros) I am looking for facts here from people with real firsthand knowlage. I asked Jamie at Pasion Performance and I remember him saying it does not make a diference. Things I have learned so far that I think are right
GL4 is fine but getting hard to find
Most GL5 is "buffered" to prevent yellow metal damage
GL5 is a better oil from a gear and bearing standpoint but may cause some shift issues?


Whats the real scoop?
Dave

[A383Wing]

GL5 replaces GL4....yer gonna be hard pressed to find GL4 if that's what ya really want..just use the 5 or go full synthetic

Bryan

[Dmichels]

Thats waht I figured I can not imagine major oil manufactures upgradeing oil and have it destroy syncros. I picked up some Valvolene 80/90 and it says it is for gl5 and gl4 aplications.
Dave

[66FBCharger]

I was not able to find much talking about GL4 vs. GL5 using the search function.
My wife had been complaining that her A833 was hard to shift particularly into 2nd.
Her car is a '73 'Cuda 340. The trans. that was in it was junk. I had Passon build me a transmission and rebuild the Hurst shifter. Since I do not have a lift I had a buddy who runs a repair shop swap the transmission in for me. I put the shifter, new rods and levers in. The clutch, pressure plate and throw out bearing was changed when the trans. was being replaced.
So everything was new or rebuilt. I got to thinking was the shifter adjusted wrong. I checked and it was fine. I decided to buy GL4 gear oil and change the oil. I assume my buddy put easy to get GL5 in the trans. I bought Brad Penn 80w90 GL4 from Summit. I changed the oil the other day. I test drove it yesterday, and what a difference! It shifted so much easier and smoother.
I am going to change the gear oil in my 69 Charger next. It shifts OK, but takes quite a bit of muscle to shift.

[c00nhunterjoe]

Gl5 would not speed shift in my 833, normal driving was very notchy. Swapped to gl4 specific, can yank gears without clutch.

[John_Kunkel]

GL5 is more of a hypoid gear (rear end) lube, too slippery for synchros. Think of synchros as brakes to slow down the spinning parts when shifting, you don't want brakes to slip.

[66FBCharger]

Gl5 would not speed shift in my 833, normal driving was very notchy. Swapped to gl4 specific, can yank gears without clutch.

That's the word I was searching for, "notchy". It's nice and smooth shifting now.

[Charger-Bodie]

I use Brad penn gl4. Works awesome.

[c00nhunterjoe]

I ran the redline mtl in mine. It really doesnt matter as long as it says gl4 only

[Chargerguy74]

I've only used Redline MTL in my 833 after I rebuilt it, no issues.

[toocheaptosmoke]

It really comes down to how each specific oil is formulated.  GL5 oils can have additional EP and friction additives, certain ones are what harm the yellow metals.   Not all GL5 oils are safe, yet some are, and others are made specifically for use in transmissions.     

Years ago I contacted Valvoline and Pennzoil about using their standard GL5 gear oil in a transmission.  Valvoline stated their product was safe and would work fine.  Pennzoil said nope, don't use it.   Wait until you try and buy real Castrol Syntorq for an NV4500 tranny... 

[66FBCharger]

My opinion on this is, GL4 is what was originally used and with very little effort I can buy GL4 online. I have seen first hand how the trans. doesn't shift very well on GL5 and shifts nicely with GL4. To me, it is a no brainer. 

[cdr]

ATF

[PlainfieldCharger]

When I purchased my car and got it running the 4 speed had gear lube in it from the previous owner. After driving it I felt the trans needed to be rebuilt as it shifted like @#$*. Read about the GL5 being too slippery for the sycro's. I switched over to the Bran Penn GL4 as I felt I had nothing to lose, and the trans is working fine now...I would go with what the trans had been designed with what was available back then..

[A383Wing]

[c00nhunterjoe]

ATF

I tried atf in mine and it was nice for normal and even "spirited" drivng. But all out speed shifts, only the mtl gl4 specific oil fit the bill for me personally. The atf would cause noticable hard and frequent missed shifts.