Driveline

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In this section, i will cover info regarding Driveline upgrades on my build, and relative to many who mod/build their jeeps. 

My driveline upgrades were selected with the idea/end game of running 37" tires, and being able to tackle some gnarly trails. 

it might be easiest to break drive line upgrades into separate sections.

  • Driveshafts

  • Axles

  • Axles Shafts

  • Diff. Covers

  • Re-Gearing

 

driveshafts

First off, let's talk about the basics of lifting a JK(U). It's widely excepted that with any lift up to 4", stock driveshafts can be used. Keep in mind we are talking about the front driveshaft. The caveat here is if you are wheeling your vehicle, i.e., flexing it out. If that is the case, you will be putting a lot of stress on your stock rzeppa joint. The stress I am talking about is operating the driveshaft joint at an angle it was not designed to work at. When we lift a Jeep, the angles on the driveline are increased. We try to rectify this situation by using adjustable upper and lower control arms to adjust pinion angle, but the fact remains the driveshaft joint angles increase as we lift the Jeep. This will cause it to fail sooner rather than later. If your Jeep is just seeing pavement, or perhaps fire trails, you can most likely get by for a good long while with the stock unit. My experience was this, with my 3.5" MetalCloak lift (I netted nearly 4.25") I ran my stock driveshaft for nearly 20k miles. This included a trip wheeling in moab. This is what happens to the stock rzeppa joint on a 3.5" lift after wheeling.

My stock rzeppa joint after ~20K miles running 3.5" MetalCloak lift...

My stock rzeppa joint after ~20K miles running 3.5" MetalCloak lift...

You can see where I was making contact with the exhaust crossover...

You can see where I was making contact with the exhaust crossover...

So, what to do? Replace the stock driveshaft with one designed to work on a lifted jeep. After doing some research, talking with guys who lift, build and wheel their jeeps, I chose to run an Adam's Extreme Duty 1310 CV solid u-joint with an american made pinion yoke. This driveshaft is designed to run at the steeper angles on the u-joints, the kind of angles we get when we lift a Wrangler. Here's a look...

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Compared to stock...

Compared to stock...

American made Spicer u-joints and yoke...

American made Spicer u-joints and yoke...

Another look at the yoke that replaces the Rzeppa joint at the T/C.

Another look at the yoke that replaces the Rzeppa joint at the T/C.

And here is a look at the new adam's driveshaft installed...

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You can see that the Adam's is smaller in diameter than the stock unit. This will provide much needed clearance at the cross member/exhaust loop when the suspension cycles downward (droop). This was a pretty straightforward bolt in swap. The new driveshaft runs silent and vibration free.

Front Axle

We have a few choices when it comes to upgrading the front axle on our Jeeps. Let's cover why we might want to upgrade our axles. Typically on a Wrangler we will find one of two axles. The dana 30, or more robust Dana 44. These axles were designed to handle the tire size that the jeep came with from the factory. When we bolt on larger tires, the bigger size/weight will be putting forces and stress on the axle that the stock axle was never intended to cope with. We begin to see increased wear on ball joints, and in some cases, bending of the outer C's.

We build for specific qualities that we want in our Jeeps. My Hard Rock came from the factory with the strongest axle I could spec from Jeep, the Dana 44. While it was strong enough to wheel 35" tires, when I was ready to make the move to 37's, I had two choices available to me. I could gusset my stock D44 to add strength, or I could look at replacing/upgrading to a new front axle. After spending a lot of time evaluating the pros and cons of new axle versus building up my existing D44, I decided to source a new front axle, deciding to go with TeraFlex. 

One of the biggest factors in this decision was I could get my front end geometry back within factory spec, for my lift height. The new axle takes into account things like revised pinion angle, correct caster, beefed up everything, etc.. I had TeraFlex build me a complete axle in house. Here's a look:

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Forged C's and a beautiful powder coat...

Forged C's and a beautiful powder coat...

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Tera44 R44

Tera44 R44

Tera 44 compared to stock...

Tera 44 compared to stock...

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Time to uncrate the beast...

Time to uncrate the beast...

Axle specs:

- Tera 44R replacement axle 

- Forged heavy duty knuckles

- 3.25" x .25" axle tube

- 1/4" thick cnc laser cut axle brackets

- Pre-installed TeraFlex HD ball joints

- Proper pinion angle for lifted JK

- Reinforced front track bar mount

- Hi Performmance axle seals pre installed

- Pre-taped hole on spring perch for bump stop install

- Stamped spring perches minimize spring bow

- Pre -drilled holes for limit straps and lower spring retainers

- Heavy Duty ductile iron diff. cover

- Premium UV coated triple stage powder coat

- Ductile cast iron housing with increased rig gussets

- Smooth radius bottom design to glide over rocks/obstacles

- Bottom oil drain hole

- Integrated factory location upper control arm mounts

- Compatable with factory jk rubicon locker (r44 model)

- Retains all JK esp, abs and speedometer sensor capability

- 100% designed, engineered and built in the usa

- 100% new components

- 1 year unlimited mileage warranty

When TeraFlex built the axle, I had them install 4.88 Motive gears, and an OEM E-locker. I really like the ease of the factory (Rubicon) push button axle lock.

Here's a few additional shots of the Hi-performance axle seals and HD ball joints. I chose to run the Hi-Performance seals for the great protection, keeping mud and water out of the axles. They feature a triple O-Ring design, and allow for a grease barrier that provides lubrication for the seals as well as mud and water protection. These are the same seals developed, proven and currently being run in Nascar applications.

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Hi Performance axle seals...

Hi Performance axle seals...

TeraFlex HD greasble Ball Joints...

TeraFlex HD greasble Ball Joints...

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The HD ball joints are engineered to handle the increased load of oversized tires and offset wheels. they are rebuildable, greasable, and feature a magnesium phosphate coating to resist corrosion.

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Here's the axle getting installed .

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At MaxItOutOffroad for axle install...

At MaxItOutOffroad for axle install...

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Axle Shafts

As part of my axle build up, upgraded axle shafts were going in. Teraflex recommneded running either RCV, or Ten Factory. Trying to stick to some semblance of a budget, I chose the Ten Factory axle shafts. I did an informal survey with the guys at Northridge 4x4. They all wheel their jeeps, and are available and willing to spend time talking with you. For my use/purposes, they recommended the Ten Factory 4340 chromoly shafts. They felt going with RCV's would over kill, and the money saved I could put towards re-gearing my rear axle to 4.88's to match the new Tera 44R. 

Remember, the Tera 44R allows for direct parts swap of my existing Rubicon parts, however, I wanted more strength, that is why I upgraded my front axle shafts. Northridge describes the Ten Factory shafts as "axle shafts on steroids". 

Ten Factory 30 spline 4340 chromoly shafts(front)...

Ten Factory 30 spline 4340 chromoly shafts(front)...

I am still running my stock rubicon rear axle shafts. I was told by the crew at Northridge 4x4 that my stock rears would be fine for what I want do. We'll see, so far so good!

Diff. Covers

Ok, upgraded differential covers...yeah or neah? That would depend on how you will use your Jeep. If it's mainly treading paved roads with the occasional foray onto simple dirt roads or fire roads, the stock cover has you coverd so to speak. 

The stock diff covers are made of a pretty thin/soft metal. They are not designed to take a hit, and if you were to get your diff hung up on an obstacle, you can peel back the edge pretty easily resulting draining the fluid. 

Upgrading our diff covers is not difficult, and we have a lot of choices available to us in the marketplace. However, diff fluid and service is not cheap, so maybe think about doing this upgrade when it's time to change the fluid, or when your ready to re-gear etc..

My first foray into upgraded covers were the G2 aluminum covers. I chose these because I liked the design and looks. G2 says the aluminum will dissipate heat well, not sure if that actually occurs in a beneficial way or not, but they are cool looking, and undoubtedly stronger than stock.

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When I upgraded my front axle, that came equipped with TeraFlex's HD diff cover. 

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The TeraFlex cover is cast from Hi-Strength Ductile-Iron and is 3/8" thick. They also feature easy access fill holes, as well as a bottom drain hole.

I upgraded to TeraFlex's HD diff on my stock rear Dana44 to match the front...

I upgraded to TeraFlex's HD diff on my stock rear Dana44 to match the front...

Here's a shot showing contact to the front diff/cover. I was running Kane Creek in Moab. If that had been my stock diff cover, not so sure it would have survived...not so sure I make back in...

Note the contact on the diff/cover...

Note the contact on the diff/cover...

Re-Gearing

Why do we need to re-gear our Jeeps. The answer is if you are running stock size tires, you don't need to. As soon as we begin to add largers tire, say 35's and 37's, we begin really effect the performance. Here's why, Jeep engineers the axle ratio, and shift points to be effective and efficient based on stock tire diameter. when add larger tires, the jeep is no longer operating as intended. Think of it like this, if we were to move a ten pound bowling ball using our arms, that would not be too tough. Make the bowling ball much bigger, weighing 500 pounds, and well, now we need some sort of lever and fulcrum to move the giant bowling ball. Our arms alone are no longer going to get it done. So it is with our Jeeps, add large tires(mass), weight from armor and accessories, add the gear we load up to do the things we love, and your Jeep now feels underpowered, like our arms against the 500 lb. bowling ball. Re-gearing our Jeeps is like reaching for the lever and fulcrum so to speak.

 

Which Gear Ratio?

Here is a chart to assist us in picking the right ratio for our jeep, based on tire size and performance characteristics we may want. I've included both auto and manual transmissions. To use the chart, simply locate your tire size you are running(left side), decide which of the three performance colors pertain to your build(upper top) and locate your gear ratio up on top.

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For my build, I'm 37" tires, automatic transmission. I chose to run 4.88's. This has proved to be a great choice. It restored the power and acceleration to stock levels, and allows me to cruise comfortably at 80mph without having my engine over-reving. I could have gone with 5.13's for a little low end power/acceleration. However, that would have sacrificed my ability to cruise comfortably at interstate speed.

One thing to remember when we re-gear, we need to re-calibrate the transmission shift points. This re-calibration will allow the transmission to shift at the proper shift points. The transmission will no longer lag in the wrong gear and/or hunt during downshifts for the proper gear. 

I used the AEV ProCal to accomplish this. I really like the ProCal for it's simplicity and ease of use. You can also do cool things like add daytime running lights, adjust TPMS, etc..

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Here's look at my re-gear. Remember, I upgraded my front axle and had that built with 4.88 gears. So this is new 4.88's going in my rear axle. I had Max It Out Offroad do this install.

Tear down...

Tear down...

Checking run out...

Checking run out...

I used Motive Gear ring and pinion set for the rear, same as the front.

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While we had it all apart, I had the shop install a new bearing kit.

Stock E-Locker and ring gear out...

Stock E-Locker and ring gear out...

New pinion and bearings pressed on...

New pinion and bearings pressed on...

Pinion gear installed...

Pinion gear installed...

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New 4.88 ring gear and E-Locker ready to go in...

New 4.88 ring gear and E-Locker ready to go in...

Putting it back together now...

Putting it back together now...

Set-up...

Set-up...

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After this got all buttoned up, filled with fresh diff fluid, a 500 mile break in is required. This involves no towing and operating the vehicle at various speeds. At this point, I planned a weekend get away that took me to many different driving environments, including gentle hills that allowed me to easily load and unload the gears for proper break-in.

Back for fluid change and inspection at ~ 500mi....

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All looks good...

All looks good...

As you can see, proper re-gearing is no small thing, and not cheap. It is however a necessary part of Jeep modification to restore proper performance.

Steven TalleyComment