Yeah manuals suck to drive with a heavy load, the 1st gear ratio is extremely long so lots of clutch slip required, and reverse gear is an even longer ratio again (what were they thinking?) so reversing a trailer is no fun and you will smell your clutch burning (I sometimes chuck it in 4 low to reverse).
Also the manuals will hugely benefit from having the correct diff ratio relative to the rest of your built (tyre size, weight, tow weight). You'll need to get this right, otherwise it will be a pig to drive.
The stock dual mass flywheel and clutch don't last long at all if towing or your Jeep is loaded. Despite the required clutch slip to get the JK moving, its quite often the dual mass flywheel that fails before the clutch wears out... The fix is to replace the clutch with a NPC solid flywheel (single mass) and heavy duty clutch, then you will have no probs ever again, these clutch kits go for around the $2k mark but is cheaper than a stock replacement, and if you wear your clutch out again, your only need to place the clutch not the flywheel as well.
The autos in the earlier JKs have the 545RFE trans, its a decent trans on paper and will be so much nicer to drive when towing etc and I think the greater majority would prefer auto (I personally prefer manual). Will also be more forgiving with gearing being not quite right so you can save money by not re-gearing (depending on your choice of tyre size and loads etc).
BUT the autos like to overheat and quite often by now need to be rebuilt, if not already, because they've most likely run hot all their life... The stock trans cooler is shared with the AC condenser (stupid design) and needs to have its own separate aftermarket cooler. This is a must do mod. After you've done this, the auto will be fine. Also your engine coolant will run lower temps cos the auto trans isn't pumping as hot fluid into the radiator area anymore.
Manuals don't really have any overheating issues, and on average their coolant temps sit about 10 degrees lower that the autos. But an auto with a aftermarket trans cooler will run a lot cooler as well and overheating will not be an issue (as long as the cooling system is in good cond).
A aftermarket heavy duty clutch fan (approx $80-100 shipped) is highly recommended to help keep everything cooler too.
2007 model JK's had 4.1 diff ratios and LSD in the rear diff, and apparently small brakes (need to confirm this).
MY2008 onwards had 3.21 ratios (and no LSD) for manuals, and 3.73 ratios for autos, and apparently bigger brakes (but they're still on the small side).
But you might also get lucky and find a JK that was optioned with the 'full tow package' from new, which meant it came with 4.1 ratios regardless of manufacture year (and obviously a tow bar).
Depending on your intended tyre size, 4.1 ratios might be perfect or they might be too high and therefore not very economical. But 3.21 ratios for a manual is an absolute joke, for anything other than a stock JK carrying zero weight they are terrible to drive (re huge amounts of clutch slip required to take off etc). 3.73 ratios in the autos is fine up to a max tyre size of 33", possibly 35".
I have 4.1's in my JKU CRD manual, I run 35" tyres and I feel this is perfect for me. At 110kmh in 6th my revs are 2,300 rpm (peak torque is at 2,200 rpm). And when I am towing, I can use 5th (non-overdrive 1:1 ratio) and do 90kmh with revs at about 2,300 rpm as well. This is perfect for me as I use my JK to tow my drift car, and it does it very comfortably now, was nearly impossible when I had 3.21 ratios and 33" tyres.
Last edited by Turismo07; 30-01-2018 at 11:10 AM.
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