5.71/33's impressions and notes on factory 4.88 rear third Vs regular

[elripster]

Let me start this off by giving props to Mark and Progear and his crew. They do top notch work.

I love the 5.71's with the 33's. I had the rears cryo'd to enhance their toughness. The truck is so much more pleasant to drive. I would recommend this ratio. It actually has some punch in 1st gear. Now to the boring techy stuff for those interested.

My speedo is about 10% high now when one divides 31/4.88 by 33/5.71. It subconsciously makes me drive slower even though I realize my RPMs with this set up are still a bit lower at a given speed than they were with my old 5 speed/4.88/33 combo. To compare, I set up them them up as ratios of tire size/rear axle.

33/4.88 Vs. 33/5.71 equals 6.762 and 5.779 respectively. Dividing those two numbers (first/second) equals 1.170 or basically 17% (undergeared in this case). My engine spins 17% faster which might seem like a lot but...

If I take into account the OD's, this changes and I'll again compare my old truck to the current. 33/(4.88*.85) Vs. 33/(5.71*.71) equals 7.956 and 8.140 respectively. Dividing the first/second equals .977. In this case my engine spins 97% as fast as my old truck's or this truck gearing is 2.2% taller. That's fine since 33's and 4.88's in a 5 speed are about 6% undergeared anyway.

Now onto some install highlights.

My rear third I used for the regear had a wheel speed sensor in it. My truck has them on the wheels. As a result I needed to plug some holes. My friend is a whiz on the lathe and installed the 4 jaw chuck. He made a sick part.

http://sdori.com/eventimages/plug.jpg


http://sdori.com/eventimages/plug2.jpg


http://sdori.com/eventimages/plug3.jpg

Now, I know those factory 4.88 rear thirds are supposed to be different but that difference must be rather subtle because I'm having a hard time seeing it.

http://sdori.com/eventimages/third1.jpg

http://sdori.com/eventimages/third2.jpg

http://sdori.com/eventimages/third3.jpg

http://sdori.com/eventimages/third4.jpg

http://sdori.com/eventimages/third5.jpg

During the install we threw the CV hardware on the lathe and took down those splines a tad so they can be more easily removed for trail repair.

Lastly, I realized when I went to install the ADD actuator that this non-ADD third didn't have clearance for the sensor. Well, you can file that sensor and the front of the third to get it to fit. If you puncture the sensor housing, JB Quikset will do the job. I don't know about going to far into the diff housing though...thankfully.

Frank

[slosurfer]

I hate you!
:flipoff: :flipoff: :flipoff: :flipoff: :flipoff:





































:lol:J/K I'm extremely jealous. How does it pull hills on the highway now, does it stay in OD? I've got a 5.29 geared front diff sitting in my garage, I'm starting to think that I need to go to 5.71's. I realized this when I put my 31's on awhile ago and it realized that it was still bad with the 4.88's and 31's.

On another note, have you installed that body lift yet?

[elripster]

It does way better at holding OD. I made it up 163 coming out of Mission Valley but it down shifted going up 805 by Sorrento Valley. These are steep hills though.

The body lift is going on when I get back on the 19th (leaving the 2nd). I just haven't had time.

Frank

[BruceTS]

Now, I know those factory 4.88 rear thirds are supposed to be different but that difference must be rather subtle because I'm having a hard time seeing it.
http://sdori.com/eventimages/third5.jpg

Take a close look at the thickness of the ring gear. Factory 4.88 have a thinner gear, so the carrier is different. Aftermarket 4.88's are similar thickness to the 5.71 pictured....

[elripster]

Interesting. So would that mean one could run a different carrier in the factory 4.88 third housing and regear it?

Frank

[Marc P]

The factory 4.88 thing always has confused me a little. For the past 5 years I have been running the "factory" 4.88 gears with a Detroit soft locker as the carrier.

[slosurfer]

Doesn't it have something to do with the pinion being different so that they could run a thinner ring gear? I know it is a 4 pinion (don't know what that means) aren't the rest 2 pinion?

[elripster]

Typically the 2 pinion carriers are for 4 cyl's. The 4 pinion carriers are stronger and used in the V6 trucks. That said my buddies V6 4x4 has an axle code of G252 which should be a 4.56 ratio 2 pinion carrier. We don't know if it actually has the 4cylinger 2 pinion though but it's weird a V6 truck would have that code.

I didn't have my calipers handy and was too much into getting the truck back on the road to measure that closely. Now I wish I had.

Frank

[paddlenbike]

We should go sand-dragging again, you know...for comparative reasons. :D

[elripster]

I'm down! I was actually thinking of that when I got on the freeway just after the install. I had to baby it but it still got up and went on a steep on ramp.

Frank