Dana 30 Reverse Cut or Not?

[barillms]

I have an 1985 XJ Wagoneer Limited, 2.5L, 909, 229 - my Dana 30 front axle is the Non-Disco type. I want to replace my 3.73s with 4.88s, how do I know whether it has REVERSE CUT gears or not?

 

[Eagle]

It is probably reverse cut.

Look at the location of the pinion shaft relative the the centerline of the axles. If the pinion shaft is above the axle shafts, it is reverse cut. If below, it is straight cut.

All the early XJs were reverse cut, high pinion. However, this far down the road it's never safe to assume, because axles sometimes get replaced.

 

[noresttill]

Dide all the D30's come as high pinion stock before 2000?

I was searching and found that fact and dont know if its true
sorry to bring this thread up again

 

[sidriptide]

Dide all the D30's come as high pinion stock before 2000?

I was searching and found that fact and dont know if its true
sorry to bring this thread up again

true. but leave it to AMC to have built some sort of bastard XJ that will prove the theory wrong for some silly reason.

 

[barillms]

I've done more D30 research, I do believe all Dana 30s are reverse cut and all are considered high pinion, disco or not, before 2000.

 

[noresttill]

Thanks, I start my search for 4wd conversion today, and want to consolidate my knowledge.

Jesse

 

[Eagle]

I've done more D30 research, I do believe all Dana 30s are reverse cut and all are considered high pinion, disco or not, before 2000.

This is true for the XJ, but the ZJ and TJ front axles were all low pinion, straight cut, and are direct bolt-ins into an XJ. That's why unless you absolutely know that the axle was never changed, it isn't safe to assume anything.

 

[noresttill]

This is true for the XJ, but the ZJ and TJ front axles were all low pinion, straight cut, and are direct bolt-ins into an XJ. That's why unless you absolutely know that the axle was never changed, it isn't safe to assume anything.

I did not know that.

 

[falcon556]

It is probably reverse cut.

Look at the location of the pinion shaft relative the the centerline of the axles. If the pinion shaft is above the axle shafts, it is reverse cut. If below, it is straight cut.

All the early XJs were reverse cut, high pinion. However, this far down the road it's never safe to assume, because axles sometimes get replaced.

A low pinion diff is called hypoid. What is an HP30 called, hyperoid maybe?

 

[Eagle]

A low pinion diff is called hypoid. What is an HP30 called, hyperoid maybe?

They are both hyoid. The term has nothing to do with high pinion or low pinion, it just means the gears are spiral cut rather than straight cut.

"Hypoid" is not really a question of oil, so much as a question of
gearcutting. Old (1920's) rear axles used straight bevel gears to form
the crownwheel and pinion. These had two disadvantage, the pinion
shaft meets the crownwheel on its central axis, and the straight cut
gears are noisy. By using a more complex "hypoid" gear tooth shape (if
you look at a pinion, the teeth appear twisted) these problems can be
addressed. The more gradual engagement of the teeth along their length
reduces noise.

 

[falcon556]

They are both hyoid. The term has nothing to do with high pinion or low pinion, it just means the gears are spiral cut rather than straight cut.

OK, I was under the impression that hypoid means centerline of pinion not at center of ring gear.
Of course it is a hypoid gear even if it is HP, just kidding.
BTW this might be a good time to mention that a friends diff got fried because he used gear oil instead of GL-5 which is hypoid rated.

 

[Eagle]

OK, I was under the impression that hypoid means centerline of pinion not at center of ring gear.
Of course it is a hypoid gear even if it is HP, just kidding.
BTW this might be a good time to mention that a friends diff got fried because he used gear oil instead of GL-5 which is hypoid rated.

Yes, part of the hypoid thing is that the pinion centerline is not the same as the axle centerline. But that still applies to both flavors of the Dana 30s. The high pinions have the pinion above the axle centerline, and the low pinions have pinion below the axle centerline.

Where did he find a gear oil that isn't hypoid rated? Axles have been hypoids since the 1920s. I can't recall ever seeing a can of gear oil that didn't say "Hypoid" on it.

 

[falcon556]

Where did he find a gear oil that isn't hypoid rated? Axles have been hypoids since the 1920s. I can't recall ever seeing a can of gear oil that didn't say "Hypoid" on it.

Manual transmission gear oil. He thought it was ok because it was high quality,
imported I think, the diff didn't last very long.

 

[AJPulley]

I have an 1985 XJ Wagoneer Limited, 2.5L, 909, 229 - my Dana 30 front axle is the Non-Disco type. I want to replace my 3.73s with 4.88s, how do I know whether it has REVERSE CUT gears or not?

Read: http://www.naxja.org/forum/showthread.php?t=70422.