What are JK Rubicon axle ratio?

[UKTJ]

Anyone able to confirm the axle ratio on a UK spec JK Rubicon?  If it is as per the US I think it will be 4.10, but it would be helpful to know for sure.

[TimC]

Yes, it's 4.10.

Dana 44 front and rear with elockers on both diffs.

 

I think the standard ratio was 3.73 or that might have been the "axle plus" towing package, not sure without looking it up.

 

You looking at getting a JK Terry? 

Edited August 31 by TimC

[V]

My Swiss 2.8 CRD auto JKU Sahara was 4.11 . D30 open front, D44 rear with LSD.

[UKTJ]

3 hours ago, TimC said:

Yes, it's 4.10.

Dana 44 front and rear with elockers on both diffs.

 

I think the standard ratio was 3.73 or that might have been the "axle plus" towing package, not sure without looking it up.

 

You looking at getting a JK Terry? 

Was musing about the possibility of getting JK Rubicon axles to swap under my TJ.  Not sure how often they would come around.  In the US there are loads around because so many JK owners are swapping them for one ton axles, but that doesn’t really happen here.

[TimC]

Still looking for regear options eh? I know it's a very personal thing but you'd probably be better off just finding a JK Rubicon and selling the TJ. However, having said that, I wouldn't consider selling my JKUR and buying a JL in order to get an 8 speed auto box. 

 

They do come up occasionally though. It was a few years ago but I remember seeing a JKUR at a scrappy that had had a fire but all the drivetrain was OK. Bit of a rare occurrence however.   

[V]

JK axles are 5" wider than TJ axles and have a 5 on 5" stud pattern instead of 5 on 4.5". The extra width doesn't matter much in a lot of US states with Wrangler's driving around with naked tyres but it could be an issue in the UK. You would need new wheels so there is room to increase back space to narrow the track but you also need to take into consideration the king pin angle on the front axle with the tyres you intend to use. You should work out the backspace you need for the chosen tyre diameter to tune the scrub radius to your preference.

[UKTJ]

1 hour ago, V said:

JK axles are 5" wider than TJ axles and have a 5 on 5" stud pattern instead of 5 on 4.5". The extra width doesn't matter much in a lot of US states with Wrangler's driving around with naked tyres but it could be an issue in the UK. You would need new wheels so there is room to increase back space to narrow the track but you also need to take into consideration the king pin angle on the front axle with the tyres you intend to use. You should work out the backspace you need for the chosen tyre diameter to tune the scrub radius to your preference.

I must admit I struggle with the whole concept of scrub radius, plus the baseline information dseems very hard to come by.  If you know of any good resources on it I'd love to hear about them.

 

On width I've had a quick look online, as I understand it the OE wheels on a JK Rubicon come with 6.25" of backspacing fitted with about 10" wide tyres. I have read that to run 35x12.5" tyres requires a spacer of at least 1.5", effectively taking the backspace down to 4.75". But that is due to rubbing on the frame. As far as I can see a JK frame is just under 36.5" wide at the front versus a TJ's frame at the front of about 33.2". That means the wheel mounting surface of a JK Dana 44 will be about 1.6" further out from the frame on each side than it is on a JK ((36.5-33.2)/2). So it should be possible to run a 35x12.5" tyre on a stock JK 6.25" BS wheel with a JK front Dana 44 under a TJ.  A TJ has a 60.5" wms to wms, my stock wheels have 5.25" back space, but I run a 1.25" spacer giving a net 4" of back space. My current tyres have a quoted width of 11.2", therefore, I think my current set up gives a distance between the out edge of the tyres of 74.9" (60.5-8+22.4). The JK Dana 44 is 65.5" wide, with 11.2" wide tyres on 6.25" BS wheels I make the total width 75.5" (65.6-12.5+22.4). So on each side the tyre would only be about 0.3" further out.

 

The other issue with this swap is camber.  As I understand it the TJ needs a lot more camber.  On some swaps I have seen ghey have 'cut and turned' the axle to give more camber.  If that is a necessity it wojld be more than I woild want to do.

 

As ever, this is all just about me wanting to explore all possible options.

[UKTJ]

1 hour ago, UKTJ said:

I must admit I struggle with the whole concept of scrub radius, plus the baseline information dseems very hard to come by.  If you know of any good resources on it I'd love to hear about them.

 

On width I've had a quick look online, as I understand it the OE wheels on a JK Rubicon come with 6.25" of backspacing fitted with about 10" wide tyres. I have read that to run 35x12.5" tyres requires a spacer of at least 1.5", effectively taking the backspace down to 4.75". But that is due to rubbing on the frame. As far as I can see a JK frame is just under 36.5" wide at the front versus a TJ's frame at the front of about 33.2". That means the wheel mounting surface of a JK Dana 44 will be about 1.6" further out from the frame on each side than it is on a JK ((36.5-33.2)/2). So it should be possible to run a 35x12.5" tyre on a stock JK 6.25" BS wheel with a JK front Dana 44 under a TJ.  A TJ has a 60.5" wms to wms, my stock wheels have 5.25" back space, but I run a 1.25" spacer giving a net 4" of back space. My current tyres have a quoted width of 11.2", therefore, I think my current set up gives a distance between the out edge of the tyres of 74.9" (60.5-8+22.4). The JK Dana 44 is 65.5" wide, with 11.2" wide tyres on 6.25" BS wheels I make the total width 75.5" (65.6-12.5+22.4). So on each side the tyre would only be about 0.3" further out.

 

The other issue with this swap is camber.  As I understand it the TJ needs a lot more camber.  On some swaps I have seen ghey have 'cut and turned' the axle to give more camber.  If that is a necessity it wojld be more than I woild want to do.

 

As ever, this is all just about me wanting to explore all possible options.

That should of course say caster, not camber

[V]

1 hour ago, UKTJ said:

The other issue with this swap is camber.  As I understand it the TJ needs a lot more camber.

Solid axle Jeeps have zero camber when the wheels are pointing straight ahead unless the axle has been accidentally bent.

 

Lifting a solid axle vehicle reduces the positive caster to zero or negative if the knuckles are not cut, rotated and rewelded to the axle tube to restore it.

 

Scrub radius can become a factor in the feel of the steering and overall handling. If you like how a particular Jeep handles with steering response, measure the scrub radius as that will be the size you need running that tyre. You can measure the stock setup to get an original equipment baseline. My preference is between zero and 40mm.

[TimC]

1 hour ago, UKTJ said:

As ever, this is all just about me wanting to explore all possible options.

As far as exploring options goes I can see few advantages in doing this if you are not sentimentally attached to your current Jeep. If you want JK Dana 44 axles then buy a JK R with them already under it and you get a nice JK with all the goodies as standard to boot. I have never owned a TJ and only driven one once so my experience with TJs is limited, but from what I recall, a JK, particularly a JKU and a Rubicon is a much better vehicle all round. No disrespect to TJs, as I said, my experience there is limited.

[V]

TJ wms-wms = 60.5"

TJ wheel backspacing = 5.25"

TJ wheel width = 7"

Spacer for 10" wide tyres = 1.25"

Effective backspacing = 5.25" - 1.25" = 4"

 

Stock TJ outer rim spacing = 60.5" + (7" - 5.25") + (7" - 5.25") = 64"

Stock TJ inner rim spacing = 60.5" - (5.25" x 2 wheels) = 50"

 

1.25" spacer TJ outer rim spacing = 60.5" + (7" - 4") + (7" - 4") = 66.5"

1.25" spacer TJ inner rim spacing = 60.5"  - (4" x 2 wheels) = 52.5"

 

My TJ on 35x12.50R15, outer rim = 60.5 + (8" - 3.75") + (8" - 3.75") = 69"

My TJ on 35x12.50R15, inner rim = 60.5 - (3.75" x 2 wheels) = 53"

 

 

JK wms-wms = 65.5"

JK wheel backspacing = 6.25"?

JK wheel width = 7.5"?

 

Stock JK outer rim spacing = 65.5" + (7.5" - 6.25") + (7.5" - 6.25" ) = 68"

Stock JK inner rim spacing = 65.5" - (6.25" x 2 wheels) = 53"

 

It looks like a pretty good swap. It will need brackets, coil buckets and possibly knuckle rotation.

[UKTJ]

8 hours ago, TimC said:

As far as exploring options goes I can see few advantages in doing this if you are not sentimentally attached to your current Jeep. If you want JK Dana 44 axles then buy a JK R with them already under it and you get a nice JK with all the goodies as standard to boot. I have never owned a TJ and only driven one once so my experience with TJs is limited, but from what I recall, a JK, particularly a JKU and a Rubicon is a much better vehicle all round. No disrespect to TJs, as I said, my experience there is limited.

Never driven a JK or a JKU, so like you hard to comment based on any comparative experience.  There are no doubt advantages to both, but clearly there is a tendency to 'talk your own book' - on a TJ forum you will read why a TJ is better, on a JK forum the reverse .  As far as I read one big issue is the 3.8l engine in the early JKs was not great and many seem to think it was a backward step from the 4.0l.  But it definitely was beefed up in some areas around steering and axles.

 

The JK is no doubt a much, much more comfortable vehicle to use for motorway miles and the JKU is far more practical.  But if I need to do a lot of motorway miles or to carry more stuff I have other vehicles which are better options than a JK or JKU.  The only reason I do any long trips in the TJ is to get to places to offroad, so that factor is not a big one for me.  At about 8.00pm tonight, after a 3 hour drive, when I get to Summer Camp I will be very happy to step out of my TJ.  But come Saturday morning I will be very happy to jump into it again.

 

I am sentimentally attached to my TJ and would find it very hard to bring myself to sell it.  We had lots of fun with the top down when my kids were young.  But I have also really enjoyed the last few years of picking up a spanner and working on it.  My sense is that the newer you go with Jeeps the less of an option that becomes.

[UKTJ]

9 hours ago, V said:

It looks like a pretty good swap. It will need brackets, coil buckets and possibly knuckle rotation.

Given the popularity of this swap in the US there are several options for swap kits.  For the front, from what I have seen on Youtube, there is also the option in the front to keep theJK spring location which nets about 2" of stretch without needing to move the steering box (but this does need the upper coil bucket extended outwards and custom control arms).  In the rear the extra width makes outboarding shocks possible without cutting the frame, but that may not be possible if using bigger backspace wheels.

 

Knuckle rotation would probably be a step too far for me.

[CandsEvo7]

17 hours ago, UKTJ said:

Was musing about the possibility of getting JK Rubicon axles to swap under my TJ.  Not sure how often they would come around.  In the US there are loads around because so many JK owners are swapping them for one ton axles, but that doesn’t really happen here.

I searched for 10 years for JK Rubicon axles in the UK, they never come up at a scrap yards, eventually I found a set from someone doing a ton axle swap who wanted to run 40's , BUT I would still say its the rarest part you can imagine to find. 

with regards to castor , on a jk it isn't really a problem, rotating the axle with adjustable control arms or castor adjusting bolts is an easy fix for that , I assume on a TJ the arms will be shorter so it might not be quite so easy, this swap has been done quite a bit in the states . 

 

just incase you are interested, I have a pair of axles here , D30 with cromolly shafts and Bigger UJs and stock D44 , both with 3.73 gears and ARB diff covers 

[BLUE STAR]

20 hours ago, V said:

My Swiss 2.8 CRD auto JKU Sahara was 4.11 . D30 open front, D44 rear with LSD.

My April 2007 2.8CRD Sahara 6 speed manual  same spec but rear LSD ? Don't think it has according to build sheet

Edited September 1 by BLUE STAR

[V]

There were lots of variations on the standard spec of each model between countries. My JKU was in the first batch supplied in Switzerland and it had a Diesel Particulate Filter. I don't think any of the UK models had them for a number of years afterwards. The LSD was probably an optional extra on the UK model.

[BLUE STAR]

21 minutes ago, V said:

There were lots of variations on the standard spec of each model between countries. My JKU was in the first batch supplied in Switzerland and it had a Diesel Particulate Filter. I don't think any of the UK models had them for a number of years afterwards. The LSD was probably an optional extra on the UK model.

Yeah mines got no DPF, which is good for me, as I've read on another forum that a guy had a cracked one on his JK and couldn't get a replacement (not checked myself), as they've been discontinued, but it was suggested he may be able to get it welded ! (depending where the crack was I suppose)

Less additions less to go wrong 

Makes one ponder about the longevity of the newer RHD models with all the additional electronics, without them they'll be 'dead in the water' how long are they going to be supported for ?

Can still get aftermarket TIPM's for the JK that appear to work OK, but that post on here about the failed WCM for export models is no longer available, is a concern.

I wonder if he managed to get it resolved ?

Would hate to write off a perfectly good vehicle for a 'sh**y' piece of electronics.

[UKTJ]

2 hours ago, CandsEvo7 said:

I searched for 10 years for JK Rubicon axles in the UK, they never come up at a scrap yards, eventually I found a set from someone doing a ton axle swap who wanted to run 40's , BUT I would still say its the rarest part you can imagine to find. 

with regards to castor , on a jk it isn't really a problem, rotating the axle with adjustable control arms or castor adjusting bolts is an easy fix for that , I assume on a TJ the arms will be shorter so it might not be quite so easy, this swap has been done quite a bit in the states . 

 

just incase you are interested, I have a pair of axles here , D30 with cromolly shafts and Bigger UJs and stock D44 , both with 3.73 gears and ARB diff covers 

Thanks, that doesn't surprise me, so many more people will be going to tons in the US which means there is a decent supply, but here that is much rarer.  I guess my hope was that now the oldest JKs are over 15 years old there may be more starting to be scrapped.  But having looked at the How Many Left website it seems the number of JK Rubicons sold was tiny (sales seem to be higher for JLs), so the chances of finding a set of JK Rubicon axles probably remains remote.

 

My thinking was that JK Rubicon axles would provide added strength, but also avoid the need for regearing and lockers so could be cost effective.  But none of that matters if they aren't around.

[V]

I think it is prudent to assume that as soon as a vehicle ceases production that the spare parts unique to that model will no longer be manufactured by the vehicle brand. When warehouse stock has been exhausted, those parts will no longer be available. Cars are no longer designed for long term ownership, only for leasing up to 6 years.

 

It is possible/likely that components that were outsourced to Chinese factories will continue to be available after OEM contracts have ended. There is little chance of the Chinese manufacturer being prosecuted so they continue making money from the tooling for as long as they can. Tooling is sold on to 2nd tier manufacturers when they need capacity for current contracts. This is how XJ Cherokees are surviving at the moment. A derivative of the XJ was made in China when US production ended in 2001. There are many Chinese companies still producing parts for it long after US manufacturers have ceased.

 

The key aspect of keeping a modern vehicle for 30 years is ensuring that the owner has the right to repair and that type approved components can be substituted with alternatives without breaking any law or preventing the car having an MOT. Only a handful of people in the UK are aware of this and there is very little interest to do anything about it. All cars registered in the UK after 1st March 2001 are affected. The newer it is, the more parts it has that cannot be replaced with anything other than the genuine original type approved part. If it has a graphical display panel in the dashboard as original equipment you can be certain that the software licenses that are legally bound to it will prevent those systems from being repaired with anything other than genuine hardware or software. It would be nice for FCA to prove me wrong by open-sourcing the code for DRB III and all of the DRB III configured ECUs that are no longer used in newer vehicles.

 

If you want a vehicle that you can keep for 30 years or more, it really has to have been first registered before 1996 (Pre OBD2) as that's when the changes in law started sneaking in undetected. The alternative is to build the vehicle yourself either as a kit-car or of your own design and have it pass a BIVA test. That way you control your right to repair and what components it has.

 

Edited September 1 by V
Corrected punctuation and typos

[TimC]

2 hours ago, UKTJ said:

But having looked at the How Many Left website it seems the number of JK Rubicons sold was tiny (sales seem to be higher for JLs), so the chances of finding a set of JK Rubicon axles probably remains remote.

Yes indeed, the number of JK and JKU Rubicons was very tiny. The number of JKs and JKUs in any case is pretty small, at the time Jeep had almost no marketing for the Wrangler and the only models it offered were the Sahara and Overland in 2.8 Diesel only. I think it was partly ( or maybe largely ) down to the efforts of this club, people like Jim and Stewart that they made the Rubicon available at all and then it was special order only and 3.6 petrol only. As the numbers show there were hardly any delivered here in the UK, quite a rarity. Whole different story with the JL as the numbers show, Rubicon was available and marketed right from launch and sales in the hundreds rather than the tens, which, considering the huge price hike is a bit surprising. I suppose, as V said, nobody actually pays the sales price these days you just pay the devaluation on a monthly basis to rent the vehicle so in a way they have nothing to lose by making the list price new as high as possible.