My 1971 521

[wayno]

I would wedge it between two sawhorses and pour some gas in it while turning the pinion flange, squirt some in the carrier bearings also, squirt more on the ring gear and pinion gear, when the squirt bottle ran out I would fill it up again and do it again, by that time the pinion gear will be submerged, once I thought everything was clean enough I would dump it all into a bucket and blow it out with air, then if what Mike said is safe for the front seal put the ATF in there and spin the pinion flange some more, soak everything, pour it out and let it dry and it should be ready to go.

 

I might get overzealous about how I describe things sometimes, I just don't want d.p putting it in dirty, I believe this dropout was in the 720 diesel when it had the SD22 in it, I changed it out when I found 3.3 gears for it.

 

 

[Stoffregen Motorsports]

17 hours ago, mainer311 said:

I had the same idea, but if the dust is stuck in those rollers and caked with old gear oil, well, who knows.

Soak it in solvent (or gas if you like) and then clean it out with a brush and rinse it again. New solvent will eat even the worst of gunk.

 

Do not replace the pinion bearings if they are not bad. There are too many pitfalls. How to tell if they are bad without tearing into it? Sound and feel. A clean diff with a light oiling on the bearings will sounds like wind. It whirrs when you spin it. If there are any clicking or grinding sounds, something is off.

 

If you do have to replace bearings, check the gear lash before disassembly (should be about .006", but not more than .010"). And check the pattern on the ring gear with marking paint too. If the pattern changes on a used r&p set, there will be problems. Also, I always try to re-use the original pinion shim (between the bearing and pinion gear). 90% of the time, the original shim works fine, but if it isn't right, at least it should be close enough to get you in the ballpark for making adjustments.

 

Basically, for someone who hasn't done it before, it's a pain in the ass to re-set-up an old diff, so if the pinion bearings aren't bad, keep them.

 

Replacing the side bearings is easy though, especially if the diff has adjustable side bearing retainers. If they are shim type, it gets a little more complicated, but is still a walk in the park compared to replacing pinion bearings.

[mainer311]

Yeah, your method of checking bearings only works if the bearings are completely toast. Even moderate spalling can’t be felt at low rotation speeds. Especially when the pinion bearings are preloaded up and you’re spinning a 20lb carrier.

[Stoffregen Motorsports]

Not at all. This method works great. And you're not spinning the gears from the pinion side, your grabbing hold of the ring gear and spinning it from there. Done it probably a hundred times this way.

 

A used diff has a ton less preload than a brand new setup.

[Stoffregen Motorsports]

If you must have a visual inspection, it only takes a minute to tear it apart. But don't forget to check the pattern and gear lash first.

[mainer311]

I agree though. If you’ve never dealt with a diff rebuild, you must learn the ins and outs of how to do it properly or else it’s not going to last very long.

[d.p]

On 2/10/2022 at 4:06 PM, mainer311 said:

I agree though. If you’ve never dealt with a diff rebuild, you must learn the ins and outs of how to do it properly or else it’s not going to last very long.

 

Got to last long with how little I have been driving this fucker.    Last time I got gas on October 1st.  

[mainer311]

All it takes is one trip down the freeway.

[d.p]

Alright so going to gas his baby up then ATF probably tomorrow since the weather is supposed to be nice.  I will say that @wayno packed this baby so nice and tight.  A man after my own heart with those packing skills. 

 

 

[thisismatt]

Free bandsaw blade and T1-11?!  F yes.

[mainer311]

Man, Wayno sure is crafty. 

 

But after seeing that, no way I wouldn't rebuild the whole thing. Won't hurt to give it the solvent treatment and see how good it comes out. 

Edited February 17, 2022 by mainer311

[d.p]

Called a local trans shop and going to take it over there tomorrow and see if they can give a once over.  Save me the trouble.    

[wayno]

Just to be clear, I say that is a good gearset that just needs cleaned out.

 

If you take it to a shop and they say it needs rebuilt I call them liars, it came out of my 720 and it was fine, it is just dirty from dust.

 

The way shops work is if they work on them they need to give some kind of guarantee, they will not work on them unless they rebuild them, that is up to you, but I say that it is good, from the response on this thread from others I will not be selling anymore here on Ratsun, this is nonsense.

[d.p]

Come on my man don’t take what anyone here says seriously.  I doused it in gasoline just a little while ago and will shoot some air through it and hen ATF and let it dry. 
 

Spinning the gears isn’t quite, slight noise but nothing major. But never having spun a diff before I really don’t know what is normal and what isn’t.  
 

All I was going to have them do was clean it but if they say the bearings need to be replaced then so be it. I won’t hold it against you my dude.  You did me a huge solid and I won’t soon forget it. 

Edited February 18, 2022 by d.p

[thisismatt]

Wayno, I don't think anyone is disparaging you, just that the diff needs to be cleaned, and sometimes that's easier said than done without pulling things apart...

[d.p]

Fuck so washed it out gas, spun the gears, compressed air’d the shit out of it then dumped ATF in.  Fucker spun nice, smooth and quietly.  Cleaned up really well too and the gears look brand new.  
 

Tried to get a pick but it’s soaked in oil and draining in a bucket so I’ll snap one tomorrow morning. 

Edited February 18, 2022 by d.p

[mainer311]

1 hour ago, wayno said:

The way shops work is if they work on them they need to give some kind of guarantee, they will not work on them unless they rebuild them, that is up to you, but I say that it is good, from the response on this thread from others I will not be selling anymore here on Ratsun, this is nonsense.

Wayno, there’s nothing wrong with the diff. I’m coming from the perspective that there might be some dirt in the bearings that I couldn’t get out, and therefore (if it were mine) I would replace the bearings for peace of mind. 

[d.p]

Here she is all cleaned up...not even going to bother taking it to a shop.  Going to just throw it on and run with it.  

 

 

 

 

 

[mainer311]

Looks good to me. Flog it.

[Stoffregen Motorsports]

That pitting on the drive side of the ring gear may turn into a noise eventually, but it still looks good. You can tell visually because there would be a sort of smearing of metal if the wipe area were noisy or worn out.

[d.p]

13 minutes ago, Stoffregen Motorsports said:

That pitting on the drive side of the ring gear may turn into a noise eventually, but it still looks good. You can tell visually because there would be a sort of smearing of metal if the wipe area were noisy or worn out.

Only a little bit of pitting on that one section.   Pumped to get it installed and see what kind of difference it makes.  What kind of oil should I be putting in the diff?  Sta-lube? Same shit I have in my trans?

[mainer311]

Synthetic GL-5 in the diff is fine. 75W-90

[datzenmike]

1 hour ago, Stoffregen Motorsports said:

That pitting on the drive side of the ring gear may turn into a noise eventually, but it still looks good. You can tell visually because there would be a sort of smearing of metal if the wipe area were noisy or worn out.

 

Pitting will hold the oil better!!!!

[d.p]

One other question I have, would it make sense to throw an LSD into this thing while its out?

 

https://www.tractionconcepts.com/Datsun-521-Limited-Slip-Truck-H190-Diff-Lsd-Kit-p/tcxda5512.htm

 

For $350 I might as well no? 

[NC85ST]

Install that gear as is and make sure that’s what you’re looking for as far as your gearing. If it is then install the LSD because it’s not that hard to pull the gear back out. If it’s not the gear you want and you have the LSD installed, then you’ve spent a lot of money and it’s still not geared right.