Should I go for synthetic? (manual truck trans)

[SecondMonkey]

I just bought a 1979 Chevy 1 ton pickup with the SM465 4 speed transmission. This is my first manual transmission, and I'm teaching myself how to drive it.

I understand that this is a big, old, slow, heavy duty truck transmission and it's not like driving a Honda. The trans is somewhat sloppy getting into gear, but that is to be expected on something 30 years old. It's also a little hard to get into gear sometimes, though part of that is me learning to drive it.

Anyway, I haven't fallen in love with this trans. Thinking hard about swapping in an automatic. Should I spend the big bucks and get some good synthetic oil in this thing before I decide I don't like it? Can it make a noticeable difference in shifting performance? (current fluid is unknown)

 

[oilboy123]

Try it, it's cheap compared to an auto trans.

 

[daves87rs]

Give it a try-it might help.

 

[Steve S]

Redline MTF or MT90 may improve the shifting quite a bit.

 

[Nederlander75]

Ive had very good results from Amsoil's MTG 75w90 GL4. Very smooth shifting and operation.

 

[Dualie]

I would go redline MTF Don't know if HD syn 50WT would help. I have a 72 Chevy out back with the same transmission in it. The Trans is now on its 3rd frame and is SO sloppy you couldn't find the gears unless you knew where they were. Trans has 300K+ of hard [censored] work in nothing but heavy cab and chassis work trucks. whines likes its going to flail apart. Been that way the 20 years i have been around it and never once gave anyone a single problem. AS sloppy as it is if their was still any suspension left in the front end of that old bucket of bolts i wouldn't hesitate to drive it anywhere.

Gotta be one of the toughest transmissions ever made.

 

[ZZman]

Any oil change might help a little as that fluid may have never been changed or maintained properly. Syn oil would make a better change.

Just rememmber that those older vehicle transmissions were not built tight like newer ones.

 

[TallPaul]

I tried all kinds of fluids in my '95 F150 manual tranny and the Redline Manual Tranny Fluid is the best. 165,000 miles and smooth shifting. Also lots of good antiwear additives.

 

[aquariuscsm]

I`d do some research to find out what kind`ve fluid your tranny takes. It can take either an atf or a GL4 gear oil,depending on who makes it`s tranny. Try to find an fsm for that truck.

 

[SecondMonkey]

Originally Posted By: aquariuscsm
I`d do some research to find out what kind`ve fluid your tranny takes. It can take either an atf or a GL4 gear oil,depending on who makes it`s tranny. Try to find an fsm for that truck.

My original owners manual says to use "SAE 80W GL-5 or 80W-90 GL-5 Gear Lubricant". A synthetic 75w should be fine, right?

Originally Posted By: TallPaul
I tried all kinds of fluids in my '95 F150 manual tranny and the Redline Manual Tranny Fluid is the best. 165,000 miles and smooth shifting. Also lots of good antiwear additives.

Anyone know if Autozone sells Redline gear oil? I know I saw some on the shelves somewhere recently but I can't remember where... (my local oil dealer just went out of business

)

 

[SecondMonkey]

While we're talking about it, do you guys think an aftermarket shifter like this:
http://www.jegs.com/i/Hurst/530/503-0030/10002/-1#
Might help fix some of the slop in this old thing?

 

[Rob_Roy]

If you have a hard time getting it into gear, I would make sure the clutch is adjusted properly.

As for the gear oil, that transmission is a very tough unit. A 75w90 will work, or a 80w90 if you want something a little thicker.

 

[SecondMonkey]

Alright, now I have arrived back at my original problem. I went and looked for fluid locally, all I can find is Mobile 1 gear oil for $6.99/quart, Royal Purple for $17.99/quart(!), or Coastal non synthetic for $12/gallon. Looks like I'm going to need about 8 quarts to do my trans and rear end.

My only other option is to order Reline or Amsoil at about $10/quart plus shipping. I'm SO mad the local Amsoil dealer went under!

Anyway, since it's SO expensive and I have no idea what fluid is in there now, (could be 30 years old for all I know) do you think I should do a quick "flush" using cheap fluid like Coastal for a few hundred miles? Or for that matter, are there any good cleaning additives for manual transmissions? I'd be too afraid to try a cleaner in an auto...

 

[unDummy]

Use the Coastal. Give it 1yr or 10k miles!!!
And, if the truck is running good, then switch it over to a mail-order boutique oil.

75w90 blend would be a good choice. If not in stock, see if your local store can order it.
http://www.warrenunilube.com/gearoils.html

 

[mechtech2]

Some speed/high performance parts stores carry Red Line.
It's worth a few calls.

 

[SecondMonkey]

Originally Posted By: unDummy
Use the Coastal. Give it 1yr or 10k miles!!!
And, if the truck is running good, then switch it over to a mail-order boutique oil.

My main concern with this is gas mileage - especially since my truck is geared so low and everything but the tires spin fast, I'm sure a lighter synthetic would help over the regular 80w90. Not really worried about wear so much, I'm sure these big old clunky gears will last forever. It's been 30 years and they still only have 48k on them!