Barrier

I changed the transmission oil in my 1993 with ZF6spd this week. Car now has 34k miles and I believe it is the first time. There was no wear on the hex plugs at all from tightening or loosening, nor indication on the threads. The was was only a problem due to location and the height I was able to raise the car for access to get leverage.
I changed to one of the recommended, Castrol 10W60 Synthetic.The Transmission feels much smoother and easier to shift and I am pleased.
I suppose 24 years does take its' Toll on oil. Next the Differential and Brake Fluid, then Clutch Fluid and continue PS Fluid exchange.
Barrier

dizwiz24

i had near disasterous results with castrol 10w-60.

at high rpm shifts, the gear level wouldnt move into the next gear.

shifting was notchier. all the problems went away when i went back to the gm syncromesh.

mine is a 93 with blue tag remanufactured for gm transmission and hurst short throw shifter

the castrol 10w-60 fluid was in there less than 200 miles and had all kinds of copper metallic flecks in it

i do not recommend it (putting engine oil into a transmission).

i am not the only one here who has had problems. that said: some people it seems to work out.

good luck !

Barrier

Thanks dizwiz24, I did read your prior posts about this.
Don't know if there is a connection, but mine is an early '93, Black Label.
I will monitor it.
Barrier

haxxx

That Castrol stuff was immediately bad in mine as well. I'm now thinking it has more to do with failing clutch hydraulics. The Castrol doesn't seem correct and the synchros do not like it. Combine this with less than ideal clutch hydraulics and the shifts become quite difficult. I think a more correct synchromesh fluid masks the failing hydraulic problem much better. The Castrol made 1st gear incredibly difficult. I ended up dumping the Castrol and switching to Pennzoil Synchromesh and I could actually get it in first. Then I replaced the clutch hydraulics with Dorman parts bled the air and now my shifts are infinitely better.

9T3VETTE

Which fluid is recommended?

dizwiz24

if you arent having any issues (do some high rpm shifts 1-2 gear) you might be golden.

also, normal shifts became real notchy - esp when cold. i had to fight the lever.
it sounds like you dont have any of those issues.

my owners manual lists a gm p/n for some kind of 5w-30 based gear oil however it has been discontinued
(note; that is not motor oil and motor oil cannot be substituted).

the chevy dealer claims gm syncromesh is the approved alternative.

ive used that with great results (i put that in after the issues with the castrol).

ive also used amsoil syncromesh with great results.

note that both of those choices yields very few metallic flakes when draining them.

the castrol chewed my synchros for some reason

woody41

I used Amsoil 5W-30 syncromesh gear oil in my 91 6 speed, shifts really smooth. I would not run engine oil in a transmission, unless you have an Austin Healey (we have 2) it calls for non-detergent 30W. ZF's are expensive gearboxes, go with the correct lubricant.

9T3VETTE

GM synchromesh it is, thanks

TorchTarga94

Another Amsoil nuthugger here. Works great in my ZF.

You could also use virgin olive oil in a pinch. Not extra virgin. Just virgin.

9T3VETTE

^LOL

Seems the he GM Synchromesh is much cheaper than Amsoil. Torch do you have a good source for amsoil at a decent price?

DGXR

There are several lubricants out there that will work with these ZF synchromesh transmissions.

The Castrol 10w60 is recommended by many and I guess if it's working well for you then go with it. That's up to you. Personally I would be reluctant to run an oil in my manual transmission that is designed for engines.

The first time I changed the oil in my ZF I used the Pennzoil synchromesh product and it worked fine, although I did not leave it in very long (8,000 miles/2 years) before changing it out. Manual transmissions typically chew the crap out of oil. So I would be willing to use the Pennzoil product again, if needed. But with these expensive transmissions I am more comfortable with a premium synthetic product like Amsoil synchromesh synthetic 5w30 which I currently run. Works great and lasts a long time.

I'm sure the GM synchromesh product is good too.

TorchTarga94

Yes sir, contact Brad. Used to go by the name Subdriver but now is C66 Racing:

https://www.corvetteforum.com/forums...66-racing.html

He will have it to your house in a couple days, knocks a good percentage off. Remember you only really need to swap this stuff out every couple years or so. I do it once a year cuz i'm weird like that (it's also easy). I would suggest getting the amsoil hand pump too makes it really easy, attached right on to the amsoil bottle.

I have the severe gear in my rear diff, also no complaints!

Nothing wrong the GM or Pennzoil stuff, I just feel like the Amsoil gives me that slick gear selection that I like compared to the others (I've tried them all).

edit- I wouldn't even consider the Castrol Garbage. Maybe 10 years ago when it was all the rage and you HAD to use it to be one of the cool kids.

70ZZ3 96LT4

I have owned my 1996 LT4 since it was new. Have not changed the transmission lubrication. I am going to drive it and not change it until it meets the requirements of the 1996's owners manual. Shifts great for 21 years now.