Differential fluid question, conflicting information

[MEZZZ]

I am confused and need some direction. I am in the process of tearing out and rebuilding the rear end. I have a question on the level of gear oil to put in the differential. I have read on here (yes, I did a search) and I remember reading in the past on the tech tips section of Atlantic Z...to fill the diff through the plastic tube on the top of it. I remember seeing a photo using the IV method, a hose and turning the bottle uside down.

Both that tip and some post on here read to fill it until the plastic tube overflows, or as I read it, fill up the diff with gear oil.

Mine is out of the car ( '77 280 btw) and drained, cleaned and painted. I went to put the fluid in, it took 2 quarts and still did not fill to the top of the plastic tube. At that point, I pulled out the Haynes manual and the specs call for 1 liter or 2.1 U.S. pints!

Hence, my confusion. I have 2 quarts in this thing. Should I drain and refill 2.1 pints? Should I fill to the top? I have read about a typo in the past in the Haynes manual, is this one of them? Is it a case of the more the better?

Any help is greatly appreciated.

[mlc240z]

AFAIK, you fill it until it hits the level of the FILL (upper) plug on the rear cover, not the plastic vent tube.

I think if you go thru the vent tube, you have to measure the amount and only put in that much.

You're presently overfilled, I believe.

[Carl Beck]

Drain are refill with 1.3 liter if it's an R200.

You NEVER fill to the breather!! You fill to the level of the bottom of the "fill" plug. That is about the middle way between top and bottom. You can use the breather to put 1.3 Liters in, if you can't get the fill plug to come out...

FWIW,

Carl B.

[MEZZZ]

thank you guys! I will drain and refill with 1.3 liters per your suggestion Carl. Not sure if it is a R180 or R200, it is a '77. From the amount of filth that came off of it and the entire underside, I would think its stock

I swear I had enough dirt to pot a plant just from the diff. I have pulled the entire rear including the tank and scrubbed the underside with degreaser, wire brush, wire wheels, etc and then resprayed. It had been undercoated when new and it has held up well. No visible rust anywhere including the diff, gas tank, drums, control arms, etc...just filthy.

Everything has been cleaned, repainted and ready to install. New R/T mount from Dave, brake shoes, wheel cylinders, s/s brake lines, fuel lines, poly bushings, Tokico shocks, Eibach springs, etc. I did similar to the front end last fall and have a new set of Rewinds with Toyo Proxes and a new exhaust system as well. Cant wait to get it back together and take it for a spin.

Thanks again

[MEZZZ]

I just went back and referenced the Atlantic Z tech tip. The photo clearly showed the hose going in the top plug, not the breather tube as I had thought earlier. It states to fill unitl it comes out of the top hole. I assume now thats the fill plug.

I stand corrected and I appreciate the help.

[Arne]

Guys! No where in the factory manuals does it ever say to fill until it runs out of the filler plug, for either differentials or transmissions. If you do that you will be overfilling it significantly. I'd recommend following the factory's instructions, which always state to fill with the proper (measured) amount of lube.

I know that in a Type A transmission - for example - filling to the filler hole is over 0.5 quarts too much.

[Carl Beck]

Not sure if it is a R180 or R200, it is a '77.

If it was a stock 77 4/5 spd. - it's an R200

If it was a stock 77 A/T - it's an R180

FWIW,

Carl B.

[BTF/PTM]

Stupid question, on topic; what happens if the diff or transmission are overfilled? Are we just talking about leaking past sealing lips that become submerged in fluid instead of holding back splashes, or are we talking something more severe like synchronizers that don't work properly because they're slogging through too much oil? Just curious.

[mlc240z]

That would be my guess on a tranny, could slow synchros down enough to cause bad engagement.

On a diff, probably something similar but more likely eventual seal leakage from the constant bathing.

Don't know enough to confirm, someone smarter, more experienced please jump in.

[Arne]

Leakage is definitely a possible problem (trust me, I know firsthand). Didn't have it overfilled long enough to notice any long-term issues.

[doradox]

Since the 1972 FSM maintenance schedule shows checking the diff and trans oil level every 3000 mile are you suggesting that the only way to properly do that is to drain, measure amount drained, add if necessary, and refill?

My 72 FSM gives the proper *approximate* refill capacities.

Take out the plug, stick you finger in the hole, if fluid level is at or just below the bottom of the plug hole pop the plug back in and be on your way.

Manufacturing tolerances for cast parts back in the day could lead to substantial differences in the amount of lube required to reach the recommended level. Hence the *approximate* refill capacities in the FSM.

Steve

Guys! No where in the factory manuals does it ever say to fill until it runs out of the filler plug, for either differentials or transmissions. If you do that you will be overfilling it significantly. I'd recommend following the factory's instructions, which always state to fill with the proper (measured) amount of lube.

I know that in a Type A transmission - for example - filling to the filler hole is over 0.5 quarts too much.