PDA

View Full Version : High Pinion Diff Question


Air Randy
12-12-2009, 10:17 AM
I have a chance to pick up a stock 4.10 high pinion front diff. I checked and the ARB part number for a standard front diff and a high pinion diff are the same, so I can re-use my current ARB.

Question: Will I be able to use my current 5.29 ring & pinion and just move it over to the high pinion diff? I was reading on Trail Gears website and they offer a high pinion conversion kit that includes R&P, etc so I'm wondering if they are different?

AxleIke
12-12-2009, 11:13 AM
No. HP front diffs are reverse cut gears so that when you are driving forward, they are running on the drive side of the gears. The low pinion gears will not work, because, IIRC, the pinon and ring gears won't even mesh due to the pinion being on the high side of the diff. I could be wrong about that though.

In the front, a normal, low pinion diff, runs on the coast side of the gears when driving forward.

HP diffs are 30% stronger. In practice, it seems to be a wash, and people do just fine with low pinions up front all the time.

In your case, I'd go for it, simply because you have the room, and it will help your pinion/driveline angle, and give you better clearance.

Red_Chili
12-13-2009, 01:34 PM
Isaac is right EXCEPT... Marlin discovered, by running HPs in the REAR as an experiment, that running backwards is much weaker with a HP (if you run that way a lot/all the time on the end of the truck that bears the most burden). You are not doing that, but just to let you know that the ~30% stronger figure (never heard that, but makes sense) is true only in forward running, in the front.

I suppose applying force backwards up a hill pulling out the errant stuck 80 could expose a possible weakness in the R&P. OR... putting one in UB's 80 and asking him to make it jump could possibly lead to a failed stress test... :lmao:

Air Randy
12-14-2009, 04:25 PM
Bill,

So is it worth the expense to convert the front to HP? I can buy a complete, brand new HP housing with new 5.29 R&P, bearings, etc (everything except the locker and I can use my current ARB) for $499.

If I get a used HP housing on my own it is $300 for R&P, bearrings, setup kit, etc.

Besides getting the increasded ground clearance I would end up with my current diff and 5.29 gears for a trail spare.

Red_Chili
12-15-2009, 09:33 AM
Bill,

So is it worth the expense to convert the front to HP? I can buy a complete, brand new HP housing with new 5.29 R&P, bearings, etc (everything except the locker and I can use my current ARB) for $499.

If I get a used HP housing on my own it is $300 for R&P, bearrings, setup kit, etc.

Besides getting the increasded ground clearance I would end up with my current diff and 5.29 gears for a trail spare.
$499 set up?? :eek: :eek: :eek: That is a discount of a grand! Do it.

If not set up it is still pretty darn good. $199 for a brand new housing. Marlin wants $349. TrailGear wants $249 but it's a knock-off. Not sure I would count that as a real $100 savings personally.

I would go TrailGear R&P, they set up nicely and are much cheaper than the prices on the old stand-bys. $129 setup kit and they are the same parts as everyone else.

High pinion on a mini results in excellent clearance and a fantastic driveline angle. And they are stronger (in forward).

DaveInDenver
12-15-2009, 10:06 AM
High pinion on a mini results in ... a fantastic driveline angle.
This has always seemed to me to be the best reasoning for a HP front diff. The downside IMO is that you sorta lose the front to rear interchangeability (this universality of thirds in Toyota solid axles to me is attractive since we travel alone a lot). Although in reality there's not much question if the alternatives are walking home or driving with an eggshell under your right foot.

Red_Chili
12-15-2009, 12:33 PM
Well, there is that... although I can tell you that, given the choice last Cruise Moab between driving home in front wheel drive (even towing a trailer) versus pulling both diffs and swapping them, I would have chosen enjoying the front driveline angle all the way home.

Actually it is a fine argument for a full floater axle if you ask me. A TCase rear disconnect would be even finer. But lacking that, eight bolts to pull and four to replace (if I need my tcase ebrake) is not so bad.

DaveInDenver
12-15-2009, 01:12 PM
Well, there is that... although I can tell you that, given the choice last Cruise Moab between driving home in front wheel drive (even towing a trailer) versus pulling both diffs and swapping them, I would have chosen enjoying the front driveline angle all the way home.
No argument, since FWD would be the only option on my truck now anyway. But having the option of putting the good diff in the back half way through Hole in the Rock or half way around White Rim would make it easier to complete the trip. Driving home from Moab on pavement with FWD is different than even finishing a relatively easy trail with only the front wheels pulling. Like trying to climb Murphy Hogback or Schafer switchbacks without rear drive might be fairly frustrating even though it's normally they're 2WD section with a locker maybe if it's really dusty or muddy. You know, what with the weight transfer onto the rear tires and all.

Red_Chili
12-15-2009, 01:30 PM
A strap would be less work even on the White Rim! :lmao:

Assuming you had a friend to strap to... of course... :eek:

DaveInDenver
12-15-2009, 01:33 PM
A strap would be less work even on the White Rim! :lmao:

Assuming you had a friend to strap to... of course... :eek:
Exactly, been solo sag wagon for bikes a couple of times on WRT and I don't have a winch... Driving up backwards might be an option, which is what I would have done with my junk most likely in the case that the front wheels don't bite. Doesn't solve the weakness in reverse issues, though.

Bikeman
12-15-2009, 01:53 PM
It is known that pulling someone's rig out of a jam (backing up) using an 80 with low gears in the HP third is a recipe for breakage.

Red_Chili
12-15-2009, 03:21 PM
True dat, r & p or birf will let you down in a Yota or a Yeep (u joints obviously) for that matter