What weight Gear oil is best for 31 tranny

I used 600w in my 32!

I use modern 85-140 multipurpose gear lube in a 28, 51,53, and in the rearend of the 68, along with everything else requireing a multipurpose gear lube. I buy it in 5 gallon buckets at Tractor Supply Company.

Thanks for the info

Thanks for the info, Mr Mack and Steve

You can still get the 600W. I got mine from Little Dearborne here in Minneapolis. They are a Model A **** supplier. It is available elswhere as well.

Ya, the Filling Station sells 600W as well.

Isn't 600W and SAE 160 the same?

Its close but 160 has not been available for years.

I placed this post a while back on this subject:
I don't know anything about these gear oils but Mobil still makes 600w which is a steam cylinder oil. This has a similar consistency as 140W. The tech rep from Mobil said that this was fine for our tranmission/rearend applications. He stated that some of the new gear EP oils use sulphur base additives which can react with brass and bronze bushings.
I called Lubriplate some time ago and talked with their tech rep and they said that they have a gear oil SPO-277 which is comparable to today's 140w or Mobil 600w. It is a modern oil that doesn't contain the animal fats of the 600w. He and Their website literature says it is safe for bronze, brass and silver alloy. He also mentioned the SPO-299 but said the literature didn't mention about other metals. http://www.lubriplate.com or Technical Service Center:800-347-5343

I checked some of the 600 wt. oil that some old car vendors sell for as much as $7.00 a Quart with my kit used to find the wt./ unit of volume and vis. it checked exactly the same as 140 wt.all multipurpose gear oil and also smelled the same, and had the same color, so ...that was the end of that story for me, no more $7.00 a quart gear oil for the Wacky one.....just be sure not to use a mineral based gear oil in a hypoid rear end.
PS
I don't have harden valve seats in my old Chevrolet engines ,nor do I use any "Lead supplement" in my unleaded regular gas either in my four, in my sixes, nor my 327CI 275 HP SBC.

No snakeoil or such .....
I just use Walmart Pennzsoil or Quaker State 10W 40 or 30 wt. single vis. when I can get it. change the oil every 1500 miles or at least twice a year. Squirt a little MMO thru the carb. in spring and fall, put half distilled water and half Zerex or Prestone or Peak, which ever is on sale in the radiator. Then I drive them, and drive them and then drive them some more. The more they are driven it seems they better they like it!

If you are worried about the correct additives find a brand thats rated for GL-5 service.It will contain no sulfur additives.The additive package in GL-5 will offer better protection than a product not intended for transmissions and will lubricate better than some overly heavy unknow oil.- including 600-W.A straight 140 will do fine..85W-140 for cold weather operations unless your intentions are to cover worn parts problems with and extra heavy lubricant.

Macky Wacky is correct.....hardened valve seats and lead additives are not necessary in these old cars.

i too went into the viscosity and additives contained in modern oils,compared to old oils it is a lot better but sulphur is added to some,i used my 31 as the actual test bed,gear changes with a straight ep 140 were rubbish with lots of noise from box,rear axle leaked everywhere,got some ep160 equivelent better but still noisy and bad changes when cold,mobil 6oo next still available cured everything could now change gear without nearly coming to a stop.fuel i just use unleaded does not seam to be a prob but do check all your rubber hoses and diaphrams it can rot them,just change for modern stuff,happy motoring