Rzeppa joints and rear pinion angle

[SpookyXJ]

My rear UCA's should be here tomorrow and I'm wondering if rear pinion angle matters and what the optimal angle would be with rzeppa joints? My current thinking is that since it's a CV joint I should set it so the coil buckets are level at ride height.

Also anyone know what the max shock length is before there is potential to tear the boots on the rear driveshaft joints on a 2 door auto Jl? I've seen 29" for the front but no info for the rear.

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[gpurp]

Free bump... because I'd like to know the answer too. I have a 2-door JL also and am curious about what the pinion angle should be.

 

[RenoMD]

Try this video, go to 23:33 he goes over the concept of rear drive shaft pinion angle

 

[SpookyXJ]

Try this video, go to 23:33 he goes over the concept of rear drive shaft pinion angle

That is the correct procedure only for a double cardan shaft. From what I have read you don't want to do that with the factory shaft. The rzeppa joint needs some angle on it or it will not self lubricate. Zero degrees on the rzeppa is bad.

FWIW Other stuff I have read mostly on jk forums and a few white papers:

It's ok for the 2 Rzeppa joints to operate at different angles they don't have to match angle or be in phase like a single u-joint driveshaft.

Exceeding 7 degrees on the rzeppa joint at ride height will lead to accelerated wear.( Only found one source for this)

JK rzeppas are stronger than 1310's and about as strong as a 1350(can't find any JL specific info as the joints are supposedly different than JK's)

Unlike u-joints Rzeppas keep the same strength throughout their operating range.

JL rzeppas operate at a higher angle than JK's before tearing the boot

Still can't find any info on recommended rear pinion angle range with the factory rear driveshaft.

 

[gpurp]

SpookyXJ that's good info. For the rzeppa, I wonder if any DS angle is acceptable short of it making contact with the pinion flange.

RenoMD thanks for the vid link. It was really helpful to see how the replacement is done but left me with some questions. When running double cardans I thought the pinion angle and t-case output angle were supposed to be parallel. Or is that only in the front?

 

[RenoMD]

That is the correct procedure only for a double cardan shaft. From what I have read you don't want to do that with the factory shaft. The rzeppa joint needs some angle on it or it will not self lubricate. Zero degrees on the rzeppa is bad.

FWIW Other stuff I have read mostly on jk forums and a few white papers:

It's ok for the 2 Rzeppa joints to operate at different angles they don't have to match angle or be in phase like a single u-joint driveshaft.

Exceeding 7 degrees on the rzeppa joint at ride height will lead to accelerated wear.( Only found one source for this)

JK rzeppas are stronger than 1310's and about as strong as a 1350(can't find any JL specific info as the joints are supposedly different than JK's)

Unlike u-joints Rzeppas keep the same strength throughout their operating range.

JL rzeppas operate at a higher angle than JK's before tearing the boot

Still can't find any info on recommended rear pinion angle range with the factory rear driveshaft.

Thx man for the info! I didn’t know myself.

 

[SpookyXJ]

SpookyXJ that's good info. For the rzeppa, I wonder if any DS angle is acceptable short of it making contact with the pinion flange.

RenoMD thanks for the vid link. It was really helpful to see how the replacement is done but left me with some questions. When running double cardans I thought the pinion angle and t-case output angle were supposed to be parallel. Or is that only in the front?

Yeah I'm wondering what the real limit is myself. Only saw the 7 degree thing mentioned once and it was on the [Banned Site] forum.

Parallel is for a single u-joint on both ends of a driveshaft.

On the factory front driveshaft with a u-joint on one end and a rzeppa on the other I don't know for sure. I figure you just dial in whatever gets you factory castor and the rzeppa takes care of any vibes.

On a double cardan front it will be a compromise( unless you cut and turn the knuckles) between pointing the front pinion at the tcase output and setting the correct castor angle. Since it's a part-time case you can get away with unoptimal driveshaft angle and more driveline vibration since the Jeep will probably not see highway speeds in 4wd.

You only need the double cardan shafts if you need more droop than the factory shafts allow. The limit is supposed to be about 29" long shocks on the front Before tearing the boot on the rzeppa. Don't know on the rear I'm ok with a 30.5" rear shock.

 

[gpurp]

Our factory drive shafts have rzeppa (CV) joints at both ends of the shaft. I'm guessing that is why the t-case output and pinion angle don't have to match. I've been unable to find anything authoritative about a max operating angle.

On the other hand the double cardan is also considered a CV joint. The replacement shafts I'm seeing only have the double cardan joint on the end connecting to the t-case. That explains why the pinion needs to be in perfect alignment with the drive shaft on the axle end.

There's a good drawing at 4xshaft.com under the JL link.

 

[SpookyXJ]

Thx man for the info! I didn’t know myself.

Sure. First time I crawled under the Jeep and looked at the driveshafts I was like WTF is that and is this better or worse. I miss my XJ

 

[No IFS]

Good info ,
I have a two door with a 2 inch lift thinking about doing rear upper control arms bringing my Pinon up a little bit maybe not zero angle but less than I have. This should also help my transfer case angle.

 

[MattT69]

Good info ,
I have a two door with a 2 inch lift thinking about doing rear upper control arms bringing my Pinon up a little bit maybe not zero angle but less than I have. This should also help my transfer case angle.

Did you ever change your UPPER control arms.
I also have a 2 door JLR and wanted to see if helped the drive and was it an easy modification. Im running a 2.5 lift with adjustable LCA front and back.

 

[No IFS]

Did you ever change your UPPER control arms.
I also have a 2 door JLR and wanted to see if helped the drive and was it an easy modification. Im running a 2.5 lift with adjustable LCA front and back.

No, It’s been working so great don’t feel the need. I did adjust my front lowers to give me a little more castor. But the rears been great.

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