Last night a neighbor and myself adjusted the clutch slave cylinder on the 74 SR-5. After more work than ever, the car started, and the wheels ran forward and backward, consistent with the what a wheel should do when in the appropriate first gear and and reverse stick **** settings.

Took the truck down off the jacks and will actually MOVE the vehicle later today.

But before it actually goes for a drive, it would be wise to check the differential fluid level, yes? It's been sitting for over twenty years, so telling what has grown inside the pumpkin.

Confirmation request: this is the differential plug and drain plug ( attached pics).

I'm 99.9% sure, but seeking confirmation. I looked in the Hayes manual for confirmation, but the drawing is different than the differential on the 74. No bleeder air valve, and the positioning is slightly different.

Fluid plug at 3 PM.
Drain plug at 5 PM, at bottom.

Also see the exhaust pic. The engine I got and installed did'nt have an exhaust attached to the flange. I put a piece I had from an 8 RC on, and it fits.

Now can I cut it to size and clamp on an exterior cover piece?
($5.99 at AutoZone.) Or must it be weld on?

What's your 411 thoughts?

 

The drain plug is at the bottom of the diff and the filler is at the 3pm spot. It will be a 22mm socket to remove the drain plug.

I'd go with a 100% synthetic gear oil. I use Amsoil for my truck.

Rick

 

Yes do change it like right away-your diff gears will say thank you. You could flush it a little by first putting a solvent in the fill hole (not much 1-2 oz's) and just let it spin slow to distribute. Wait a bit and then dump and refill with 100% synthetic 90w. If you haven't I would change out the gearbox oil as well.

Your pipe would be nicer welded, but back there a clamp on would work fine.

 

Will do!

What kind of solvent?

Then can I put the truck up on a jack, start the engine, put it in gear, and spin the tires ?

Or should I spin the tires by hand?

 

Any upper cylinder lube would do. SeaFoam or similar. Yes to both-spin by hand to check your driveshaft (see if its rotating smoothly and isn't loose at any joint) and so you can listen to and feel your diff gears moving. You should have a small amount of play going in opposite directions but no grinding or skipping once its engaged. Then yes put it in gear and run it a little (not very fast though as only one side will be turning-good time to be extra careful too) then just drain and refill.

 

MM - Thanks for the detailed response! Big assist!

Okay, so I called Seafoam regarding the use of its tranny addiative for cleaning and use. Their rep said to use 20% Sea Foam OIL STABILIZER with whatever standard transmission fluid. Same ratio for Seafoam in the oil crankcase (20% plus oil ).

Thoughts on this mixture? Yea or nay?

Also loosened the drain plug.
But I still CANNOT loosen the fill plug!

Put more Liquid Wrench, but I suspect it is still frozen.
What to do next? Heat with torch?

Thanx!

 

Okay, so I finally go the fill plug off.

I sprayed it with BB Penetrating spray and let it set for days. I took a 24 MM on a breaker bar to remove it. First tightening to the right, And then to loosen it by pushing it to the left.

Still wouldn't move or budge.

So I removed the passenger rear tire ( The truck's already up on jacks. ). Put the 24MM breaker bar on the bolt head, Put a long pipe extension on the shaft of the breaker bar. There wasn't much room in the area for the wheel, but I did the tighten/loosen sequence again. It worked! The bolt loosened.

Removed the pipe, and completely removed the bolt with a 24MM on a ratchet.

Drained the oil in the differential. It was a weird looking gritty, dark brown, not black like engine oil. I doubt it had ever been changed since 1974. The level was really very low.

So I put in a quart and a half of gear oil plus some solvent. Ran the engine for about 5 minutes. Drained the the differential again.

This batch looked much better. Close to the original color of the oil I had just put inside. A little discoloration, but to me, that's a good sign. I got out any residual crud lingering around.

Now I'm going to put in A bottle of Royal Purple Synthetic Gear Oil, then Lucas Oil Stabilizer ( Bill at the customer service line of Lucas said to put in 20% of capacity of Lucas ), and then top off with more Royal Purple Synthetic.

 

Here's The Differntial Oil - Drained Twice

Here are the pics of the first differential oil change.
When I finally got the fill plug off, I stuck my finger inside, and it seemed dry. Nothing. So like the posters said, I added some gear oil and solvent.

I turned the wheels first by hand ( No, my name isn't Clark Kent; the truck was up on jacks ), and then I ran the engine for a few minutes. I then drained the differential oil. Here are the pics of what drained out.

The stuff that drained out was really dirty, gritty brown. I suspect the differential oil had NEVER been changed in 40 years. The color was so brown gritty, I refilled the differential again with gear oil and solvent, and I then ran it again. I wanted to err on the side of caution.

Pic on the next post of the second draining.

 

Differential - The Second Drainage

So I refilled the differential again with both gear oil and solvent.

Like the previous oil change, I first moved the wheels by hand to get the oil gently on the gears, and then I ran the engine for a few minutes.

This time when I drained the oil from the differential, there was a huge difference. This batch was still a little dirty but had a color that was more amber like the oil I had originally put in for the second rinse. See the pic of my gloved finger in this rinse and the gloved finger from the first rinse.

Big difference. Worth the extra effort? I think so ...

As I left this second rinse batch to settle for a few days, there was residual "stuff" on the bottom of the container. Any ideas what this stuff is? Gear shavings? Dirt?

It's fine, black stuff that settled out from the oil.

For the final fill of the differential, I put in one-and-a-half bottle of ROyal Purple Synthetic 75w oil plus Lucas Oil Stabilizer. The oil stabilizer was recommended to keep the oil "sticky" and viscose. Filled the stuff until it started to flow out of the fill plug. Seal the plug firm and tight.

Question: is it "okay" to mix different brands of oil, i.e. Mobil and Royal Purple? Or is it better to stick to one type? (Why shouldn't the two different types be mixed?)

Thoughts?