Upgrade from a Truetrac - Which traction aid and why?

[V]

My 1993 XJ has been running on 33" tyres and Truetracs in each axle for 20 years. I am getting parts together for a major rebuild to make it similar to my 2001 XJ on 35" tyres which has ARB lockers in each axle. I really like the Truetracs and I am quite tempted to stay with them for the upgrade. I am interested to hear your opinion on what you would choose and why if you were upgrading an already modified Jeep.

 

I will be installing a Ford 8.8 rear axle that I have recently purchased in the UK. I will need other parts like gears and locker from the USA to complete it. The rear steer axle I had planned to build is on hold or cancelled. This is mostly due to the exchange rate for the parts I need from the USA and the additional rear wheel tub and fuel tank modifications that are needed. The total cost of completing it is now way more expensive than installing a solid 8.8 . Both of my XJs will have Ford 8.8 rears and 30-spline high pinion D30 fronts with big bearing spindle hubs 5 on 5.5" PCD, 35x12.50R15 BFG KM3 on 15x8 wheels and 4.88 gears in each axle. I should be able to swap wheels and axle parts between Jeeps if need be in the future.

 

I don't know if Eaton make a D30 Truetrac in 30-spline or not. If they don't, I will have to run 27-spline inners with a Truetrac up front which is not ideal as it makes the weakest point of the driveline the splines going into the Truetrac. ARB and OX-Locker make a 30-spline D30 locker.

 

One factor that may tip the balance towards ARB or OX-Locker is that I would like to fit a transfer-case doubler to this XJ. It didn't make it to the 2001 because of the necessary floor modifications that had a knock on effect on the Clayton rear coil conversion. The 1993 will have a 3-link long arm front suspension but the rear could stay leaf sprung as this makes it a lot easier for the doubler and the exhaust does not need modification. As the Jeep is already at 5.5" lift I only need to get to 6.5" for the 35" tyres which is easily achieved with leaf springs I already have.

 

Your thoughts appreciated.

[doodle]

I am near sure I've a True trac in my TJ.

 

I know its an auto locker. anyway..

The only thing i don't like is that, as mad a it sounds, is that you dont really know when it is going to kick in!

 

Its got me into trouble once when the locker kicked in and the back end swung out and dumped me ceremoniously off the edge of a mountain against a  tree.

I would love to get to the point where i have a selectable one but tbh it was Vs cost at the time and the amount i was doing just didn't justify it..

Maybe on a rebuild i go for something else

[UKTJ]

As far as I can see ARBs are cheaper to buy in the UK than to import from the US.  With the cost of shipping and exchange rates where they are the cost premium for selectable lockers (over TrueTracs) does not appear that great.  If I had TrueTracs already I would struggle to justify spending the money on ARBs, but starting from a position of having neither I plan to go with ARBs.

[Ludders]

Truetracs are great for daily's, locking up on damp roundabouts for example, giving improved traction is a major positive.

Detroit lockers are immense fun, but can be hard work if you drive spiritedly on the road (unlocking on a damp roundabout can be unpredictable) and if you run bigger tyres can get destroyed internally with muddy stuff that gets a lot of wheel spin.

 

ARBs are just unbeatable. Open for everyday use, locked when you really need them. What more do you need...

[V]

21 hours ago, doodle said:

Its got me into trouble once when the locker kicked in and the back end swung out and dumped me ceremoniously off the edge of a mountain against a  tree.

That doesn't sound like a Truetrac behaviour, that sounds more like a Detroit Locker on snow or ice. A 'lunch box locker' like an Aussie locker and a clutch pack LSD would do the same. If you can hear clicking when the left to right shaft speeds are different, it's a Detroit style locker, always locked until it is not.

 

A Truetrac will give you 25%/75% torque split on the rear, and 40%/60% on the front. It will kick out a bit depending on power delivery and traction available but it will usually be progressive so you get some warning. Lifting the foot off the accelerator a little is usually enough to coax it back into line at the risk of losing forward motion. It's not quite open, but also not fully locked either. The torque will float from left to right and vice-versa when the grip at each tyre differs, this will look like the axle is locked because both tyres are spinning, just not equally.

[V]

14 hours ago, UKTJ said:

As far as I can see ARBs are cheaper to buy in the UK than to import from the US.  With the cost of shipping and exchange rates where they are the cost premium for selectable lockers (over TrueTracs) does not appear that great.  If I had TrueTracs already I would struggle to justify spending the money on ARBs, but starting from a position of having neither I plan to go with ARBs.

That hasn't always been the case but I guess AUS-GBP is better than AUS-USD-GBP at the moment. It's just a shame that the diffs that I need are oddball in the UK (31-spline Ford 8.8 and 30-spline D30). Time to get some quotes.

 

My 27-spline D30 Truetrac has just over 100K miles on it. They can be rebuilt with replacement internals but I will probably keep the axle as a spare as-is. It has paid for itself in the fun I have had out of it. With all of the other internals being brand new, I would buy a new differential anyway considering the mileage already on the one I have.

 

I am still on the fence between ARB and OX at the moment. I have had a few problems in the past with unwanted air pressure in my axle housings blowing out lube which is one of the occasional faults of an ARB. I still need to do some more research, but I would consider air operated OX or cable operated OX with remote mounted air cylinders as actuators. I am happy to use solenoid air valves and electrical switching with either. I like that the OX gives you an option of installing a manual lock if the actuation mechanism has a fault in the field. With an ARB it just stays open if you have an actuation fault. With an OX you have a choice and you can revert back to open when returning to the street.

[V]

I am trying to find information on the number of degrees of rotation that a Truetrac or ProTrax GripPro rotate before the torque is sent to the other axle. It must be a function of the helix angle and I think it will have a bearing on extreme underdrive performance. I am guessing that with a 35" tyre the slip angle will translate as a significant linear distance at the tyre tread surface. A selectable locker like an ARB or OX would just have the distance the tyre rotates within the backlash of the ring and pinion. With a helical gear driven LSD I wonder how may degrees of tyre rotation have to spin on one side before the tyre on the other side starts to move. I don't know if this would be a problem on ultra slow crawling or not, I just know that it is not an issue with a locked ARB.

 

In high ratio, final drive ratio will be 4.88:1

In low ratio, final drive ratio will be 13.27:1 (4.88 x 2.72)

In underdrive, final drive ratio be 36.1:1 (4.88 x 2.72 x 2.72)

 

As the helical slip is in the differential, I think the slip distance at the tyre tread will be the same no matter what the final drive ratio is. The only way to reduce the tyre tread slip distance would be to run smaller tyres.

[UKTJ]

Way beyond my level of knowledge, but I'll be really interested to hear where you go with this.

[TimC]

For what it’s worth, if cost isn’t a problem, I’d go with a selectable locker every time. Locked when you tell it, unlocked when you tell it. So ARB…….cos ARB, or Ox locker or Eaton / Dana E locker although my E lockers don’t seem to have been very reliable. I didn’t know that Ox lockers could be mechanically selectable, that is quite appealing, the simpler the better.

[John]

I had truetracks in my tj front & rear never let me down ..didn’t have to even think about them they just worked 

 

my jk rubi has lockers that I have to switch in and out … it means I have to think about them before I use them 

 

I think if I ever broke them I’d go back to true tracks tbh … life was a lot easier with them 

[TimC]

3 minutes ago, John said:

I had truetracks in my tj front & rear never let me down ..didn’t have to even think about them they just worked 

 

my jk rubi has lockers that I have to switch in and out … it means I have to think about them before I use them 

 

I think if I ever broke them I’d go back to true tracks tbh … life was a lot easier with them 

That’s a bit like the arguments for and against auto and manual gearboxes really isn’t it John. I guess it comes down to personal preference.

[John]

9 minutes ago, TimC said:

That’s a bit like the arguments for and against auto and manual gearboxes really isn’t it John. I guess it comes down to personal preference.

 yes mate I suppose it is but don’t start me off on that one as I’ve not decided yet if  I like the auto box on the jk 

[V]

17 minutes ago, TimC said:

I didn’t know that Ox lockers could be mechanically selectable, that is quite appealing, the simpler the better.

The OX was originally only available as a cable operated mechanically selectable locker. They added actuators years later.

 

I have just sent email to Eaton but looking at the current brochure, Eaton have already limited my choice for me. The Truetrac is available for the Ford 8.8 in 31 spline and a performance model with 33 splines but then I would need 33 spline shafts to match. However, there does not appear to be a 30 spline D30 Truetrac, only ELocker.

 

Digger reminded me of ProTrax GripPro but that looks like it is 27 spline only too.

 

So, it looks like I am down to either ARB or OX.

 

My intention is to get both XJs to a point where I have a lot of common spares between them. I had an idea today that I had not considered before. The 2001 is prettier outside and inside with leather seats and should stay as the Jeep for passengers, but the 1993 is looking it's age with a few wounds and doesn't really need to stay a five seater. I could strip out the interior including the dash and centre console and make it into a two seater with an interior roll cage. Instead of having a rear tyre carrier, I could have an interior slide out cargo deck for spare wheel, tools and camping gear with a new longer, smaller diameter LPG cylinder transverse mounted behind the front seats for better weight distribution and CofG. The '93 is free of all the EU legislation, doesn't have OBD2 so can have a Megasquirt, already has a standalone transmission controller. I could replace all of the gauges and electrics with standardised generic components. I think this could become my main off roader again to last into my one-Jeep retirement years.

[UKTJ]

This thread made me think I should look again at the Oxlocker, rather than just default to the ARB.  I stumbled across a post on a US TJ forum that raised some concerns about an aspect I would never have thought about, which I thought it would be worth sharing in case others were interested.

 

As I understand it the Oxlocker requires the use of a specific diff cover, as part of the mechanism is fitted to the Oxlocker diff cover.  There was concern raised about the Oxlocker diff cover, referencing the video linked to below.  There is a caveat in that Banks are no doubt looking to sell their own diff cover, so there is an angle to be aware of, but I still thought it was interesting enough to share...

 

https://www.youtube.com/watch?v=9-yG3D3JBRs&feature=emb_logo

[V]

I've seen that video before and I don't dispute that some diff covers are better than others for distributing oil to the pinion bearings through splash lubrication. The boxy after market style diff covers are popular with pick up truck owners but not with off roaders as alloy covers are too weak to resist impact damage. It's a shame that Banks didn't make a clear plastic boxy cover for comparison to really show what happens instead of just an educated and reasonable opinion.

 

A pickup truck, hot rod or drag racer diff cover is a wasted purchase for an off road Jeep. Strength is the number one requirement, nodular iron is probably the best choice. I think all of the off road suitable diff covers have a concave inner surface that follows the radius of the ring gear more or less. The fabricated steel versions usually have three flat surfaces but they don't have the right angle that is being criticised in the video. I would guess that there is not much lubrication performance difference between a stock sheet steel Dana cover, a fabricated steel cover or one of the cast nodular iron covers from Solid, Crane, ARB, G2 etc.

 

Aeration in the lube is unavoidable by nature of the ring gear splashing through the lube during rotation. It can be lessened by using a scavenge pump if you were also cooling the lube in an external cooler, but if you were doing this you would have the pump send oil directly to the bearings first instead of relying on splash lubrication.

 

I realise that differential oil heat build up could be an issue for a tow rig but I can safely say that the only time my diffs have been hot is when I have been running them in. As a rough guide to follow this may be useful:

• Four runs of up to 25 miles under 50mph followed by a 30 minute cool down after each run.
• Four runs of up to 50 miles under 50mph followed by a 20-30 minute cool down after each run.
• Limiting speed to 50mph or 60mph until 500 miles is done on the gears with regular cool downs.
• Change the lube after 500 miles and gradually ease speed up and check diff temperature regularly until 1,000 miles done.

You will notice as the gears run in, they will run cooler. Taking good care of them in the first few hundred miles is important. I don't know what the right temperature should be as I usually just check by touch. If you burn your finger tip on the diff cover it's running too hot, slow down and have more stops on your journey to cool the oil.

[V]

2 hours ago, UKTJ said:

There was concern raised about the Oxlocker diff cover

What was that concern?

 

The OX cover has an internal web (a partition) that supports the locker's shift fork. I could imagine that the partition would restrict side spill off the toothed side of the ring gear, encouraging more lube up to the pinion bearings. I don't know if it would impede oil flow to the right side bearing. Above 15mph I doubt there is any dry spot inside the differential housing.

[V]

One thing I noticed about the Banks video showing the R&D they conducted was that it did not show any testing for steep hill climbs, for steep hill descents or for side slopes at slow speed and at high speed (banked corners). All of these vehicle attitudes affect lubrication in the axles, transmission and engine.

 

Lifting a Jeep often naturally raises the pinion angle on the axle. This also has the effect of lowering the oil fill level when using a stock diff cover. Many off road diff covers have higher fill plugs to correct this. Some people think this is for getting more oil in the housing, now you know the real reason.

[UKTJ]

7 hours ago, V said:

What was that concern?

 

The OX cover has an internal web (a partition) that supports the locker's shift fork. I could imagine that the partition would restrict side spill off the toothed side of the ring gear, encouraging more lube up to the pinion bearings. I don't know if it would impede oil flow to the right side bearing. Above 15mph I doubt there is any dry spot inside the differential housing.

Nothing more, nothing less than the shape / attached part inside the cover may affect fluid dynamics in the diff.  I am not saying it is valid (I do not have the level of knowledge to know), but shared the video in case there was something in it. But it sounds like you are all over the issue and then some.