Trans fluid in 3 speed Saginaw

[83Stepper]

Ok guys, need some help from the guru's here. Looking to swap the fluid in my trans this weekend. But unfortunately the owners manual and the interwebs haven't been much help tbh. I know some of the older trans use to run 80w-90 gear oil and some of the 4 speeds at one time were using Dexron II. The truck has the stock running gear from when it was still the 4.1 I6 afaik. Definitely has the stock Saginaw 3 speed and what appears to be the stock 8.5" 10 bolt rear, leaky pinion diff seal included that's getting swapped this weekend as well.

TLDR; What are you guys using in your 3 speeds and anything I should stay away from?
Some of the GL-5 80W-90 gear oils say they're API GL-5 but say non-syncro'd manual trans GL-4. Wasn't the GL-5 and GL-4 eating yellow metals such as brass etc?

Thanks in advance!

 

[Sad Sack]

Research shows it needs to be API MT-1 rated.

You must be registered for see images attach

 

[xm20k]

Only stuff I know of made for old school trans with brass syncros. I haven't played with a Saginaw/Muncie/T-series 3 or 4 speed in probably over 25 yrs.

Pardon Our Interruption

Pardon Our Interruption

Local tractor supply place may carry something but might have to buy it in bulk like the 5-gallon bucket of Mobil Delvac tractor oil I use for my powerglide.

 

[Ricko1966]

Ok guys, need some help from the guru's here. Looking to swap the fluid in my trans this weekend. But unfortunately the owners manual and the interwebs haven't been much help tbh. I know some of the older trans use to run 80w-90 gear oil and some of the 4 speeds at one time were using Dexron II. The truck has the stock running gear from when it was still the 4.1 I6 afaik. Definitely has the stock Saginaw 3 speed and what appears to be the stock 8.5" 10 bolt rear, leaky pinion diff seal included that's getting swapped this weekend as well.

TLDR; What are you guys using in your 3 speeds and anything I should stay away from?
Some of the GL-5 80W-90 gear oils say they're API GL-5 but say non-syncro'd manual trans GL-4. Wasn't the GL-5 and GL-4 eating yellow metals such as brass etc?

Thanks in advance!

You are right some GL4 Gl5 will ruin your synchros. Summit sells 80/90 ,for brass syncros.

 

[77Dmax]

You want GL4 or GL1. Napa carries both. GL5 is no good.

 

[Ricko1966]

You want GL4 or GL1. Napa carries both. GL5 is no good.

Not all gl4s are good anymore either.

 

[DoubleDingo]

90w mineral oil for the win

 

[83Stepper]

You want GL4 or GL1. Napa carries both. GL5 is no good.

Seen a few GL-4's that are for non syncro trans as well, which I though was kinda weird. But it was also a synthetic instead of conventional. Then again pretty difficult to find a decent conventional gear oil anymore it seems since like everything is a blend of synthetics.

Only stuff I know of made for old school trans with brass syncros. I haven't played with a Saginaw/Muncie/T-series 3 or 4 speed in probably over 25 yrs.

Pardon Our Interruption

Pardon Our Interruption

Local tractor supply place may carry something but might have to buy it in bulk like the 5-gallon bucket of Mobil Delvac tractor oil I use for my powerglide.

Thanks! And I've tried Tractor Supply up here and yeah, all has to be ordered because it's not a common item for them to carry anymore Yeah, a tractor supply store that doesn't carry oil for tractors ‍

You are right some GL4 Gl5 will ruin your synchros. Summit sells 80/90 ,for brass syncros.

Appreciate it @Ricko1966

 

[77Dmax]

You need a GL4 that is GL4 only. Sta-lube is about the only source. Most companies make GL4/GL5 mix in the same bottle.

 

[83Stepper]

Seems like the most readily available stuff, well at least anything that can be shipped to me or able to be picked up before this stupid Nor'easter shows up on Sunday, is some Valvoline Syncromesh. Anybody have any experiences with it?
Valvoline Syncromesh MTF

 

[DoubleDingo]

90w mineral oil for the win

@Sad Sack
Not sure what's funny

https://www.napaonline.com/en/p/NHF65201

 

[Sad Sack]

@Sad Sack
Not sure what's funny

https://www.napaonline.com/en/p/NHF65201

I just liked your answer and phrasing

 

[DoubleDingo]

I just liked your answer and phrasing