Differential is stuck! Any ideas?

[matchstyc]

Anyone have any idea how to get a stubborn differential out?!

So the other day the differential went out on my 620. It was making clinking noises under load and I made a sharp u turn. All of the sudden the wheels locked up and the truck made a loud pop. Then there was nothing. No power to the wheels but the driveline was spinning. I towed it home and jacked it up. Spin one wheel, the other wheel does nothing. Pulled out the drain plug and put my finger up inside. There's a little gear just floating around in the bottom of the case. But, here comes the other problem. I can't get the damned differential out! I undid the twelve bolts around the case. Undid the four bolts on each axle and pulled the axle's out about two inches. Started pounding on the sucker. Used a hammer and block of wood on the little nubs. Kicked it. Cursed a lot. The usual. Tried attaching a come along to the driveline hub to see if I could pull it out that way, attaching the other side to the cross brace. The cross brace started moving a little but that differential didn't at all. Anyone got any idea how these things are supposed to come out of there little homes?

Also, anyone have any clue what gear might be floating around loose in there? I'd love to get this thing out so I can see what's going on.

[datsunaholic]

I've pulled several off. Most just fell out.

 

Either you don't have the axles out far enough or something broke inside and is holding it up, but even in those cases you'd still have some movement. I know on a friends truck he had to wail on it with a deadblow to break the seal to the housing. Of course it didn't move until he took the last 2 nuts off that he'd somehow missed...

[matchstyc]

Hah, I double checked to see if I got all the bolts out. The hubs are pulled out about 2 1/2 inches. /that's as far as the brake lines would allow. I suppose I could disconnect the brake lines if they need to come out more. There's no movement at all on the sucker. And I don't want to pry it apart because that would marr up the seal. Where did your friend hit his at when he was using the dead blow?

[datzenmike]

Even with the axles in, the case could still separate from the housing. When you get it loose the axles may have to come out further than 2 1/2".

 

I used a very blunt chisel to start the case/housing separating. Its a steel housing and a cast third member you won't hurt it. Oh yeah that sucker is heavy when laying full out under the truck so have something to let it down on.

[matchstyc]

Cool, I'll give the chisel method a try! Just wasn't sure if that'd mess anything up too much!

[matchstyc]

Well, got the differential out. Datsunmike's chisel method did the trick. Split the case and it was free from there. Once I got it out I looked in the bottom of the case and this is what I found. Looks like the whole thing just sort of exploded right in the center. Both of these little gears are missing a lot of teeth and the rod that holds them in is snapped in half! Looks like I need me a differential. Anyone out there have one they can sell? These things worth rebuilding? Can't believe this thing exploded!I know the kid who had this truck before me ran it with a dry differential for a while. Must have worn it out running without oil. Good stuff!

 

[yello620]

Good time to consider a different gear ratio. Those gears should be a 4.375 ratio. many of the later trucks(720) came with gears that are a lot more highway friendly. I have tried 4.11 gears, 3.70 gears, and now 3.89 gears in my 76 620. The 3.89 seem to be my favorite so far. And they came in some of the 720 trucks and bolt right into a 620 too.

[matchstyc]

Sweet! do all the 720's have a 3.89 ratio or is it just certain years?

[yello620]

No, not all years and not all models. Seems to change a lot with what year, motor, trans, cab they got. They have a tag in the engine bay that lists the factory gears to that truck. This has been discussed many times before, so it is time to search, there is also pictures and an explaination of the underhood tag somewhere.

[Guest Rick-rat]

Just did mine last weekend, put in 3.89 and really like this gear ratio for the highway driving

[datzenmike]

The side and spider gears do not turn when driving straight. They form a square around the thrust block with the pinion mate shaft through the center. As a unit they rotate with the crown gear. Only on a turn when the two wheels turn at different speed do the side and spider gears begin to turn and then only about a 1/2 turn on a 90 degree corner in town. As you can see they don't turn much and power is fairly light and divided more or less equally onto the two side gears.

 

Damage like this is likely from doing burnouts. With one rear wheel stopped and the other rotating at what ? 20 MPH and with the engine at full throttle for 20 seconds (or more) that little square of gears is going to turn very fast, many times and under lots of power.

 

I ran an H-190 dry and it growled. The pinion bearing went and the pinion was free to move inward and 'chafe' against the housing that holds the side and spider gears.

 

 

720 ratios:

 

'80-'83 4x4 were H-190 4.375 and 4.625, later 4x4s used the C-200 so forget it.

 

'80-'86 2wd were H-190 and ranged from 3.364, 3.545, 3.70, 3.889, 4.11, 4.375 and 4.625.

 

To narrow down your search look on the engine tag located on the inner fender, passenger side below the hood hinge.

 

 

Find the TRANS/AXLE... FS5W71B.... HF38 (the 38 means 3.889 ratio , 41 would be 4.11 and so on)

[matchstyc]

I'm pretty sure the kid I bought the truck from a few years back was quite partial to one wheel burnouts. As I recall, the rear tires were completely bald when I first took it home. And with a dry differential this makes a lot of sense. Personally, I figure. If you're gonna do a burnout. You better have at least two wheels spinnin. Each to their own I guess. Thanks for the heads up on how to find gear ratios. My search has begun!

[Braden]

Good time to consider a different gear ratio. Those gears should be a 4.375 ratio. many of the later trucks(720) came with gears that are a lot more highway friendly. I have tried 4.11 gears, 3.70 gears, and now 3.89 gears in my 76 620. The 3.89 seem to be my favorite so far. And they came in some of the 720 trucks and bolt right into a 620 too.

 

the spider gears (the gears you broke) have nothing to do with the gear ratio it is only the ring and pinion that have an effect on ratio. it looks like in the picture that your pinion gear is damaged too.

 

question for you yellow, did all of the 620's come with the 4.375???? i have a 77 620 and i was wanting to try and figure out what gears i have, i am probably going to the junkyard this friday and i could probably pull some gears out of a 720 if i had an idea of what i have and what i need. i need to inspect my rear end anyways so i might as well try some diff gears since this 4 speed is killing my ass on the highway.

[hang_510]

To narrow down your search look on the engine tag located on the inner fender, passenger side below the hood hinge.

 

 

Find the TRANS/AXLE... FS5W71B.... HF38 (the 38 means 3.889 ratio , 41 would be 4.11 and so on)

any LSD identification from the tags?

[datsunaholic]

There weren't any factory LSD H190s, so the data plate won't help. Only thing I remember having factory LSD was the Pathfinder (and quite rare) but using a H233.

 

 

For Ghetto, the 4.375 is the most common ratio for 620s. It was used on ALL '75-78 US-spec 620s, as well as manual-trans '74s and automatic '79s. The uncommon ratios were 4.88 ('73 manual heavy-duty), 4.625 ('73-74 Automatic) and 4.11 ('79 Manual). As far as freeway speeds, I run my '76 at 60-65, or 70 when heading to PDX, for hours at a time. Heck, I used to run my Mom's '73 at 70, and it has 4.88s. It sounds like it's revving out of this world, but for an L-series it's nothing. The truck 5-speed will help more than the rear gears though, and you don't lose the 1st-gear takeoff speed. Put 3.89s on a L20B and you'll lug it off the line badly.

[matchstyc]

So, from what you're saying Datsunholic. A 3.89 ratio in my 620 matched with my 5 speed tranny and my L20B with flat top pistons and race cam would be a bad idea for quick starts off the line? Come to think of it. My gear ratio was pretty decent once I put the 5 speed in. Even on the highways. Maybe I'll just look for the same differential I already had..

[datzenmike]

I've found a reference to an H-190 factory LSD in the D-21 and will explore this.

[moparvwfreak]

i just saw this post, i have a near complete KC rear axle that i am willing to part with. and i am fairly local (monroe). so let me know.

[matchstyc]

Back on the road and terrorizing the neighbos. Thanks moparvwfreak for the new diff. It's working great!