Differential sounds chuncky

[boxboy]

Had a friend look at my truck the other night trying to diagnose my vibrations above 45 mph. I know I need to have the driveline looked at because I am having trouble getting the u-joints to fit properly. But he turned my line back and forth and it sounded a bit chunky. Almost like it would catch a bit and then let loose slip to the next tooth before resting firmly.

 

I am wondering, there is a parts truck close by for sale for cheep, but it is a 71 521. Would the rear end be a bolt in swap? I mean the whole deal, not just the gears. I understand the gearing might be different than my J13 set up, but would it work? Or, is there a way I can fix the one I got cheaply. I am cheap. My wife is ready to get rid of me and this truck!

[datsunaholic]

It should bolt right in, might be some issues with the brake line routing but dimensionally they're the same. Different gear ratio though, it'll be more sluggish getting up to speed but have lower freeway RPMs.

[wayno]

Hey there Boxboy, Is there less than a 1/4" of play in the rearend flange, if there is, you should check the rearend fluid for discoloration, if it is anything other than new motor oil color, then you might have a problem. If there is more than a 1/4" play, it's wore out. It can also howl, make clancking noises, vibrate at at almost any speed, but usually at higher speeds such as above 35/40ish. I also have the rearend in the truck you got the parts off of, I beleave it has 437 gears, I also have a set of 488 gears in the parts shed. wayno

[boxboy]

yeah wayno, I may need one of the two. I need to do some diagnosing. Do you know what you have is good? Mine turns way more than 1/4", and definitely shakes at higher speed. I don't know if I would be qualified to change out the gears. I know nothing about it. But I imagine the swap for the entire rear end is pretty easy.

[datzenmike]

Easy, anyone can do it.

 

Remove tires and drums. If drum sticks loosen the brake adjusters or, there are two threaded holes you can tighten a bolt in and the rims pop off. Remove the brake line at the wheel cylinder on the backing plate. Remove the 4 X 17mm nuts from the back of the backing plate that secure the axle. A few good tugs or tap with sledge hammer will drive the axle out of the housing. You only need it out about 6-8" so have something to support it's weight so it doesn't crush the rubber seal in the axle tube. The E brake cable should allow enough travel. Do other side.

 

Unbolt driveshaft, drain diff, unbolt the 12? nuts holding the diff carrier in place. Separate the diff from the axle housing. It's about 70 lb so watch it! Clean gasket surface. Use a proper liquid gasket sealer. NOT RTV silicone! This isn't a chevy valve cover, so get the right stuff. You do not want it to fall out or leak later. Permatex makes some. Very thick blue gooy stuff. Let set and instal new diff.

[boxboy]

Thanks Mike. How about Hondabond? I have the High temp stuff or the Hondabond 4. I have used this on motorcycle engines, and have heard there is nothing better for case sealer. It is pretty spendy though. But since I already have it.

 

Also, I am assuming you are talking about the forward facing section of the rear end that is what comes off, so that I don't have to do anything with the pinion/ bushings etc. Is that right? What do you think of the 521 gears? Will they make the truck worthless? I wouldn't mind easier RPM's and I am not looking for jack rabbit starts. But I want it to be driveable.

[datsunaholic]

The 4.375 rears are plenty driveable as long as you aren't climbing mountains with pianos in the back all the time. A little harder on the clutch, being you have to rev a bit more off the line, but seeing that 4.375s are the most common ratio out there they're easy to find. 4.88s are harder to come by, but that's what a 520 came stock with.

[boxboy]

I got home from work and crawled under the truck right away to check the rear end play. Wayno says 1/4 inch of play is acceptable. But where? I can turn the flange a bit, and at the very outer corner it is about exactly 1/4 of an inch movement. I can't get it to move in and out at all, or wiggle it side to side at all. What is the diagnosis from you all? Perhaps it is in fact my driveline that is at issue.

[datzenmike]

Perhaps it is in fact my driveline that is at issue.

 

 

Yup very possible. You did say the differential so I ran with it. Check the U joints, is the d/s damaged or dented, are the tranny mount bolts tight and rubber solid?

 

All drive shaft/differentials have gear lash or 'play' in them. All will clunk slightly when turning the d/s back and forth. Hard to tell if it's too much or not.

[wayno]

Hi there boxboy, What I hope I said is if there is a 1/4" or less play remove the upper differential plug, stick your finger or something in the hole and check the color of the gear oil, if it is a clean golden motor oil looking color then it is more than likely good, if there is more than a 1/4" play then likely it's worn out and the gear oil will probably be a silver or black color, it won't be a golden color. If the gear oil is a golden color then something else is probably wrong, not the dif. wayno

[boxboy]

Ya, so I did check the differential oil. I wouldn't say it looked like fresh motor oil, but it wasn't silver or black. Kind of a brown.

 

Mike, I had the tranny mount out to check it last week, and it looked okay. I don't know what they look like new, but nothing seemed torn. No dents in the D/S. But I am having a time getting the u-joints in. I will get the drive shaft in to Six States and have them put in the u-joints and balance the thing and we'll see what happens after that. I hear there is a 3 week wait though. Ouch. Good thing there is plenty to do!

[wayno]

Ya, so I did check the differential oil. I wouldn't say it looked like fresh motor oil, but it wasn't silver or black. Kind of a brown.

 

Mike, I had the tranny mount out to check it last week, and it looked okay. I don't know what they look like new, but nothing seemed torn. No dents in the D/S. But I am having a time getting the u-joints in. I will get the drive shaft in to Six States and have them put in the u-joints and balance the thing and we'll see what happens after that. I hear there is a 3 week wait though. Ouch. Good thing there is plenty to do!

If the gear oil is brown, you should change it. To me brown means water has gotten in the oil, you should be able to see threw the gear oil. The truck might have sat so long that moisture has found its way in the differential, or rust. wayno

[boxboy]

This truck has been a daily driver for the last two years. Just no maintenance of any kind in at least that long.

[boxboy]

Great news! I got my driveline back from Six States today and the truck is running smooth! Nice to have a victory once in a while. Now, on to the next thing.

[wayno]

Great news! I got my driveline back from Six States today and the truck is running smooth! Nice to have a victory once in a while. Now, on to the next thing.

 

Happy to hear the good news, smooth running datsun, the best kind.:lol: Sorry to hear about the ign. light,:unsure: but I am sure you will figure it out.:rolleyes: wayno

[boxboy]

Thanks Wayno. I have resigned myself to the fact that there will always be something to fix. I just hope it gets less frequent and less expensive! I have had a lot of small issues that have added up to way too much cash. Just slows the resto process way down. That's probably not all bad.

[wayno]

There will be a point, when you have fixed everything important, that it will just keep running like the energiser bunny, all you will have to do is keep oil in it. wayno