PaulN Posted June 12, 2016 Share Posted June 12, 2016 HI Guys - I have a Def 90 with a D1 300tdi engine, g/box and T/Box and the combination works really well - except that is for the lock up speed. Really wearing where we live as often we hardly ever get to lock up! It locks at around 54mph which is naf when following a lorries at 56 or most journeys as my truck is forever bobbing in and out of top. Some roads we don't get lock up for 10's of miles!! I've read many a thread and the it is clear that we have used the wrong T/Box in that we stayed with the combo from the D1 but I cannot find how to remedy the issue..... In what to change to make her pop up like a Disco? Now in both my auto 300 D1's lock up was lovely at around 48 - 50 so I cannot understand why it's not the same except maybe the tyres are now 235/85/16 whereas Disco's were 70's profile has a bit to do with it? I do want to keep stock Defender tyres at 235. Will a change of T/box do it? Anyone advise please? Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted June 12, 2016 Share Posted June 12, 2016 Yes, it is most likely the tyres making the difference. You can drop back to a 1.4 which should help, but do check your kickdown cable adjustment beforehand, it may be that it is too tight... Quote Link to comment Share on other sites More sharing options...
PaulN Posted June 12, 2016 Author Share Posted June 12, 2016 Thanks - I will check the KD cable to make sure I have it nice and slack - iirc it's on the last hole I like the relaxed Disco set up and the longer final drive and so top speed and noise reduction. Thought maybe a Classic RR T/Box might be ever so slightly different? or overhaul with a small change of final drive? I have read that there may be a G/Box adjustment but that's a bit beyond me..... Even 50 would be better...... If all else fails I can use the disco sized tyres then but she'll look a bit naf..... Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted June 12, 2016 Share Posted June 12, 2016 There's is a TINY difference to one of the RRC boxes, but not enough to make a difference for you. No other final drive ratios available unfortunately, but for more flexibility you could look into diffs.... Quote Link to comment Share on other sites More sharing options...
Paul Woodward Posted June 12, 2016 Share Posted June 12, 2016 Mine has a 1.4 transfer box and 255/85x16 tyres. Locks up just under 50mph. That's just about right for me, any lower and I'd have to kick it down to accelerate every time. Quote Link to comment Share on other sites More sharing options...
pat_pending Posted June 12, 2016 Share Posted June 12, 2016 Mine has a 1.4 transfer box and 255/85x16 tyres. Locks up just under 50mph. That's just about right for me, any lower and I'd have to kick it down to accelerate every time. I have the same, works very well. Quote Link to comment Share on other sites More sharing options...
PaulN Posted June 12, 2016 Author Share Posted June 12, 2016 Just loosened off KD cable completely - no difference to Lock Up. Wouldn't altering diff ratios would affect all speeds and gears and I'm only keen on a lower speed lock up in top - I'm happy with everything else. With 4.10 TB revs will be too high for main road wouldn't they? Compared to a 1.222.... Assuming the engine performance is fettled - would a LT230 with 1:1.003 lock up earlier - not withstanding all the other longer cog effects? Quote Link to comment Share on other sites More sharing options...
Lewis Posted June 12, 2016 Share Posted June 12, 2016 I have no direct experience but just applying logic to the responses on this thread - if 1:1.4 transfer box equals lower lock up speed then 1:1 transfer box will give a higher lock up speed. Surely? Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted June 12, 2016 Share Posted June 12, 2016 Yep. Quote Link to comment Share on other sites More sharing options...
PaulN Posted June 12, 2016 Author Share Posted June 12, 2016 aha! Got it! Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted June 12, 2016 Share Posted June 12, 2016 Lower transfer box will also alter lower gears.... You could try the Ashcroft gearing calculator with 3.75 ring and pinion -pretty sure one of the suppliers produce those. Very small change, but could be enough, just a bit spendy, but then so is a refurbished transfer case..... Quote Link to comment Share on other sites More sharing options...
mickeyw Posted June 14, 2016 Share Posted June 14, 2016 If you compare (using Ashcroft's calculator), I'm sure you discover that the Defender wheel size combined with 1.4:1 ratio trf gears will work out very similar overall gearing to D1 tyre size and 1.22:1 gears. I found the same problem with my old V8 90 (255 tyres). Too tall a gearing meant it never locked up on back roads, and struggled on motorway hills. Changing back to 1.4:1 completely transformed the drive. Quote Link to comment Share on other sites More sharing options...
PaulN Posted June 16, 2016 Author Share Posted June 16, 2016 Thanks for everyone's input here. Mickey: I have used the Ash calculator and saved screen shots of each tyre size against each box (28D & 22D) then changed them around and - well - I can't work it out. Revs change but some ratios don't! Never mind though I can now see you guys are right that the issue is either to change to disco tyre sizes (not doing) or to change the diff back to a Def 4.10 which we will have to do. It was just that we used a Disco TB to reduce revs and noise and achieve higher speed for a more pleasurable higher open road drive. I cruise at 70/75. Am I going to lose that to achieve a lower lock up? " Changing back to 1.4:1 completely transformed the drive. " I am keen to know how bad was the high revving, the noise and top speed loss? Quote Link to comment Share on other sites More sharing options...
Disco-Ron Posted June 17, 2016 Share Posted June 17, 2016 I have a d1 3.9 and auto in my 90. I originally used the 1.2-1 box from the disco.... on 235 /85 lock up was far too fast.... changed for a 1.4-1 and its great.... due to slightly higher revs you actually need less throttle at higher speeds whichs makes it more economical. .. and less hard work to drive as i was previously constantly trying to get to lock up speed but usually failing on regular A rds. Also everything runs cooler as once locked up less temperature is produced by the gearbox. .. basically everything just works better...... Quote Link to comment Share on other sites More sharing options...
mickeyw Posted June 17, 2016 Share Posted June 17, 2016 Thanks for everyone's input here. Mickey: I have used the Ash calculator and saved screen shots of each tyre size against each box (28D & 22D) then changed them around and - well - I can't work it out. Revs change but some ratios don't! Never mind though I can now see you guys are right that the issue is either to change to disco tyre sizes (not doing) or to change the diff back to a Def 4.10 which we will have to do. It was just that we used a Disco TB to reduce revs and noise and achieve higher speed for a more pleasurable higher open road drive. I cruise at 70/75. Am I going to lose that to achieve a lower lock up? " Changing back to 1.4:1 completely transformed the drive. " I am keen to know how bad was the high revving, the noise and top speed loss? It wasn't so much the high revving. Running 1.2:1 I found that on back roads I was never going fast enough for the TC to lock up, so economy wasn't as good as it could be. On motorways I found the revs were too low when cruising. If I hit an uphill stretch the engine didn't have the grunt to keep pulling. I was over geared. As torquey as a V8 is, this was below the power band. Speed would drop right off, and a manual downshift, or flooring of the loud pedal to prompt kickdown was required to maintain speed. With the box in 3rd it would be revving silly at 70mph. By contrast, with the 1.4:1 gearing, motorway speeds and hills can be tackled with ease. I think 70 mph was a shade under 3000rpm. This might sound high, but if I wanted to overtake, or do illegal speeds, the engine was in its sweet spot, and would just get up and go. I'm sure we all appreciate that doing these kind of speeds in a Defender with its house-like aerodynamics will burn a lot of fuel, but being able to accelerate freely at those speeds is a great thing Quote Link to comment Share on other sites More sharing options...
PaulN Posted June 17, 2016 Author Share Posted June 17, 2016 Many thanks - off to hunt a 4.10 Quote Link to comment Share on other sites More sharing options...
mickeyw Posted June 18, 2016 Share Posted June 18, 2016 Just to clarify Paul. It's a 1.4:1 ratio transfer box you need. You've made a couple of references to 4.1, which is more like an axle diff ratio. Std axle diff ratio across Defender, Disco & RRC is 3.54:1. Some folk changes to custom 4.1:1 to correct gearing with 35" tyres. Not trying to teach you to suck eggs, just don't want you to waste time and £ looking for the wrong item ? Quote Link to comment Share on other sites More sharing options...
PaulN Posted June 18, 2016 Author Share Posted June 18, 2016 A much appreciated correction to my poor references Mickey. I am glad of the advice from all above. I have a 28D fitted at the mo and will be searching out a 22D (according to the Ashcroft variants list). I must say throughout all the searching on-line I still see guys changing their Defenders to 1.211 even now - guess the must have the smaller Disco wheels. Anyway I know what I have to do - looking fwd to it. Quote Link to comment Share on other sites More sharing options...
Snagger Posted June 18, 2016 Share Posted June 18, 2016 I was concerned that the 4.71 diffs on my 109 would be too low for the retrofit of a ZF and BW transfer box to work well, but this is an element that make me think it will be rather good, even though it'll be similarly geared to a Series transmission with overdrive. Anyone know if 4.1:1 diff gears have become cheaper of late, though? Last time I looked, they were horrifically expensive. Quote Link to comment Share on other sites More sharing options...
Litch Posted June 19, 2016 Share Posted June 19, 2016 I should hopefully be in a position to comment in the next week or so. I have a 300TDi 90 running 265/75x16's and a Disco 1.2 transfer-box and have run it with this set-up since the engine / gearbox were brand-new back in 2004 but am now in the final stages of fitting an Ashcroft autobox conversion. I decided to stick with the 1.2 for now as there was no point changing to the 1.4 and then thinking that I might have preferred the 1.2 after all, if I decide that the gearing is too high then I will change the transfer-box next year but that will give me plenty of time to make an informed decision. I do no towing, carry no excess weight so it will be interesting to see how it behaves. Took it for the first run around the block today (seat loosely fitted, shifter clamped to the seatbox etc etc) and it was great fun, a very novel experience being able to keep the left foot on the floor (will fit the foot-rest if I decide I need it). Quote Link to comment Share on other sites More sharing options...
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