Re-Gearing Question

[jxb003]

I’m trying to swap gears from 3.87 to 4.38. The shop doing it says I need a ring gear spacer. Anyone know how thick (4mm?) or where to source one?

[iceman510]

Is this for your rear axle?

 

[datzenmike]

Ring gear spacer??? Unless you misunderstood what they say they don't know what they are doing. Never heard of this on an H-190. In fact the entire pumpkin can be swapped by loosening and extending the axles from their spline inside, disconnect the driveshaft, unbolt the differential and lift out. 

 

 

They are probably making a meal out of a snack.

 

 

 

[jxb003]

3 hours ago, iceman510 said:

Is this for your rear axle?

 

Yep. It’s for the H190 rear. 

[jxb003]

3 hours ago, datzenmike said:

Ring gear spacer??? Unless you misunderstood what they say they don't know what they are doing. Never heard of this on an H-190. In fact the entire pumpkin can be swapped by loosening and extending the axles from their spline inside, disconnect the driveshaft, unbolt the differential and lift out. 

 

 

They are probably making a meal out of a snack.

 

 

 

Nope not misunderstanding, I took the whole carrier in with a ring and pinion I took out of another truck. Couldn’t get the back lash right so I took another carrier that felt tight but it had some broken teeth on the ring gear so I couldn’t just swap that pumpkin in.  I can not find anything on a ring gear spacer for a h190. The truck I’m putting gears in is for a 83, I have gears I want out of an 83 and out of a 620. Not sure the gear on those.  

[wayno]

As suggested, all H190 gearsets out of a 520+ truck with 29 spline axles should bolt right in, this is the 520, 521, 620, and early 720 with an H190 axle, where did you get the drop out gear sets from?

 

Count the splines in the drop out gear set, are there 29 splines?

[jxb003]

39 minutes ago, wayno said:

As suggested, all H190 gearsets out of a 520+ truck with 29 spline axles should bolt right in, this is the 520, 521, 620, and early 720 with an H190 axle, where did you get the drop out gear sets from?

 

Count the splines in the drop out gear set, are there 29 splines?

I have the entire pumpkin out of an 82. And the carrier out of a 620 not sure the year. It was thrown in when I bought parts for my 620.  Im trying to put them in a 83. 

[datzenmike]

4 hours ago, jxb003 said:

Nope not misunderstanding, I took the whole carrier in with a ring and pinion I took out of another truck. Couldn’t get the back lash right so I took another carrier that felt tight but it had some broken teeth on the ring gear so I couldn’t just swap that pumpkin in.  I can not find anything on a ring gear spacer for a h190. The truck I’m putting gears in is for a 83, I have gears I want out of an 83 and out of a 620. Not sure the gear on those.  

 

 

Well that just leaves them not knowing what they are doing. There is no ring gear spacer. Find another 620 differential and swap it in yourself. 

 

Most 620s have the 4.375 gear set. Avoid the '74 automatic and the '79 manual gears.

[iceman510]

Not too familiar with the solid axle diffs, but in the R160/180 type independent rear ends, the ring gear/pinion relationship is adjusted by shims between the side covers/bearing holders and the diff case.  Are there shims of some type that move it left right?  Typically that adjusts tooth engagement pattern.

 

If the pinion needs to be moved fore/aft, that may need to be done with a spacer/shim.  Is that maybe what they are talking about?

[datzenmike]

Essentially this is correct between IRS and solid differentials. Again if a shop is doing this why are they asking for shims? they should know what they are doing and what parts and where they are. Also 4mm is 0.1576" That's a huge correction where usually it's only a few thousandths is needed. 

[wayno]

20 hours ago, jxb003 said:

I have the entire pumpkin out of an 82. And the carrier out of a 620 not sure the year. It was thrown in when I bought parts for my 620.  Im trying to put them in a 83. 

 

I personally would not try to set up a H190 gearset myself, I would just put the 620 gearset in the 720 without messing with it, you need the pinion that matches the ring gear, you cannot interchange parts, 4.37 ring gears need 4.37 pinions as far as I know, and it has a spacer between the pinion and the flange, I know that spacer gets crushed shorter, but I do not understand how all that works.

 

I have put together several gearsets/dropouts for guys that want to put better gearing into their 320 Datsun truck, I did this when there were 5 to 10 720s in the local wrecking yards, all I ever did was unbolt the ring gear and pound out the pin holding the shaft in place holding the spider gears in, I never removed the carrier, I have removed the carrier out of a C200 to replace it as that pin had broke in two, but you're talking about an H190.

 

You cannot just change out ring and pinions from one dropout to another, or just change out the ring gear itself, it takes someone that knows what they are doing, the shop you went to does not sound like they know what they are doing.

 

It has been a while since I have done anything like this stuff, I have forgotten most of it, I just change out the drop outs/gearsets complete ready to use.

Edited Wednesday at 08:53 PM by wayno

[datzenmike]

On 5/5/2026 at 8:38 AM, jxb003 said:

I’m trying to swap gears from 3.87 to 4.38. The shop doing it says I need a ring gear spacer. Anyone know how thick (4mm?) or where to source one?

 

There is no 3.87 differential but the closest is a 3.889 in the 720. The ring and pinion are a set. On the outer rim of the ring gear will be stamped, 35:8 or 35 ring gear teeth to 8 pinion gear teeth. 35 divide by 8 is 4.375. The 3.889 will be 35:9. An 8 tooth pinion will not mesh where a 9 tooth pinion is used.

 

 

 

This is the 37:9 or 4.11 H-165 differential in my 710

[Stinky]

What size are your tires?

 

That is a pretty big jump.

 

I have 205/75-15s and 4.11 and that is plenty low geared.  If you have 14s on, I couldn't imagine needing gears that low.  What sort of rig do you have?

[datzenmike]

Rim size has nothing to do with tire diameter. By selecting the correct tire you can change rim size but not change the tire diameter.

 

Going from 3.889 to 4.375 on the same rim/tires, that's a gear change of 12.5%. Your speedometer will read 12.5 MPH faster at 100 MPH or 6.25 MPH faster at 50 MPH. 

 

If you remove the speedometer pinion sleeve and count the teeth you can move to a pinion that is two teeth more and this will slow your speedometer. 

[RoadRace]

hi - the request for a spacer when going to a lower ratio is based on a typical salisbury-style differential. They use shims and spacers to position the ring gear carrier along the axle centerline to achieve the correct engagement pattern or mesh with the pinion. this is because there is only a limited amount of space to move the carrier, like .040" for an example. You want to use as little a shim as possible, like .012" for example.

When going to a gear set with less pinion teeth, that makes the root diameter of the pinion gear smaller, meaning you have to shim the carrier closer to the pinion than it was before to get the pattern you want.  OEMs typically use 4:1 as the change over. 2 and 3 series ratios will use one carrier, 4 series and above uses a different carrier that puts the ring gear closer to the pinion, to compensate for the reduced number of teeth, and subsequently, smaller root diameter.

When a shop sees you want to swap a 3:xx to a 4:xx, thats like a red buzzer going off and typically, with a salisbury diff, that's going to need a different carrier (not always because they do make thicker ring gears just for this type of application), BUT, you can buy a ring gear spacer, typically .125 or .188, to space the ring gear over, thus not requiring tons of shims (that wouldn't fit anyway).

 

Now, that's all for a Salisbury diff - like a chevy 10 or 12 bolt - and the Datsun uses a Hotchkiss design, like a ford 9" - the "drop out 3rd member" style, where these shims don't come into play. That's because there are really big threaded adjusters in the main bearing caps that you screw in or out to move the carrier on the axle centerline to where you want it in order to get that pattern or mesh you need. I have never set up an H190, and the pic above blocks the part where you would see the adjusters - but I feel like there is some mis-communication at the shop you are dealing with.

hope this helps 🙂

Edited 18 hours ago by RoadRace

[datzenmike]

Only the '83-'86 720 4x4 had the C-200 salisbury style axle. ALL 2wd were H-190 and had the removable 3rd member.

 

jxb003... if you have a 4x4 you should have put this in your profile so we know.