3.90 vs 4.11 - Opinions?

Stocksuspension66

Well-known member
Mar 26, 2020
79
3
California
I wonder where the number 336 came from.
I hope this magic number does include the transfer case high range ratio.
Very true. No clue I found that formula years ago when re-gearing another vehicle. I did some research via the ole inter web and it appears 336 represents fixed values including distance. Just found out now that that equation applies to vehicles with a trans ratio of 1:1. Which is every vehicle I’ve regeared. Being that disco 2s have .73 4th gear would mean rpm would be lower. Learned something new every day. I thought d2s where 1 to 1 4th gear. Back to the drAwing board
 

p m

Administrator
Apr 19, 2004
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La Jolla, CA
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Very true. No clue I found that formula years ago when re-gearing another vehicle. I did some research via the ole inter web and it appears 336 represents fixed values including distance. Just found out now that that equation applies to vehicles with a trans ratio of 1:1. Which is every vehicle I’ve regeared. Being that disco 2s have .73 4th gear would mean rpm would be lower. Learned something new every day. I thought d2s where 1 to 1 4th gear. Back to the drAwing board
Also, factor in 0.72:1 4th gear ratio of 4HP22/24; and an option of having 1.4:1 high range ratio LT230.
Some of the "old-school" formulas assumed a certain amount of slippage in torque converter (5-10%) - there isn't any with locked torque converter. So pick your equations carefully :)
 

Blue

Well-known member
Mar 26, 2004
9,072
276
AZ
I'm in the re-gear boat too.

2004 D2

Almost 180,000 miles on truck

4.6 engine - second engine in the truck, this engine has about 145,000 miles. First engine replaced due to an extreme tick...engine actually ran fine but the tick drove me nuts. I bought the truck with 50K miles and it must have gotten nice & hot before it went on the market. Reseller had head gaskets done as prep for sale when I bought it. I did head gaskets again at about 80k miles. Then replaced engine with 112K on the truck. Second engine was just a simple pull & install from a wrecked 80K mile D2 that a little old lady only drove on Sundays to the grocery store.

Stock ZF auto transmission

Stock diffs & axles

Running 285/75/16s on stock wheels, second set of same tires this size, I really like them.

Thinking about installing another 4.6 engine with a proper top-hat rebuild. Current engine feels a bit tired and I'm constantly losing coolant. May have compression tested with next oil change. Also going to have 180-degree thermostat installed at next oil change (have a 190 now). Temp is constantly creeping up, runs at about 195 on downhill highway coasting but usually runs at 210-215 around town and on highway (summer temps here now, over 100 ambient temps). Idling in traffic it'll get into the 220s on a hot day with the AC running. I monitor with a scan gauge. I'm sick of worrying about the temp.

Mechanic's theory is that exhaust gases are getting past slipping liner and over-pressurizing coolant system. Coolant reservoir (expansion tank) is consistently burping coolant when engine is hot. Replaced the last cracked plastic expansion tank with a Carrs 4X4 aluminum tank. Now coolant is escaping out the tank's pressure cap. Going to try to get a new cap sent to me just to rule that out. Engine has occasional tick when hot but no consistent or frequent.

Besides the chronic coolant issues, I've always wanted to re-gear. This thing is just a dog going up into the mountains, constantly hunting for gears. Off-road it feels underpowered unless I'm in low range.

I've been leaning towards 3.9's from Great Basin Rovers. I think 4.11 is too much. I like to run at 80 MPH on the highways (on flat ground). Opinions?
 

Howski

Well-known member
Oct 19, 2009
1,149
76
Greenville, S.C.
Blue, is the re-gear mainly drivability thing around town or are you wanting some more in low range too? I had the same setup as you on my first D2 and can attest to it being sluggish around town with stock gearing. I never felt it was lacking in low range. Lower low range gearing would be a bonus but if you’re really needing it around town why not swap in a 1.4 ratio transfer case?
 

Blue

Well-known member
Mar 26, 2004
9,072
276
AZ
Primary goal is highway driving in the mountains to achieve less downshifting and gear hunting, secondary goal is around-town drivability, tertiary goal is improved off roading in high range. I drive for miles and miles off road and it’s mostly in high range, only using low for really tough sections. You know when you’re in high range and you are trying to get up and over a small ridge or swale and the truck just revs and revs and doesn’t move? Never used to do that before.
 

Blue

Well-known member
Mar 26, 2004
9,072
276
AZ
I’ll look into the transfer case ratio change. Isn’t that really expensive relative to re-gearing diffs though?
 

rovercanus

Well-known member
Apr 24, 2004
9,363
88
I you ARE going to rebuild it, make sure you have the top hat liners installed - properly, from someone who knows what they're doing, not Skeeter's Machine Shop down the street. No offense to Skeeter, but you know what I'm sayin'.
Or just pin the liners.
 

K-rover

Well-known member
Jan 15, 2010
2,065
27
Raleigh, NC
Im running 4:11s with 35s in my D2. I originally wanted 4:37s, but there was an issue with shipping from Ashcroft.. at least according to Lucky8.
Anyway, I can run 80mph at roughly 2800 rpm. I feel like this brought it close to how it was stock. Lets me run at speed on the highway, but have no issues turning the 35s offroad. If I were to do it again, I would have waited out for the 4:37s. I think that would have been the sweet spot for a D2 on 35.
 
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CORover

Well-known member
Jun 11, 2007
719
54
Colorado, USA
I know three guys, 2 classics and a D90 that all have 4.11 gears. They wish they had done 3.90s. One had a 1.4 with the 4.11 and said it was horrible, he took out the 1.4 and left the 4.11 gears installed. The transfer case option does not give you a lower low range, just the high range, the diff gears give you both. I think the math with a 1.4 and 3.54 works out to a 4.43 overall ratio. Probably really need to turn 35s for that to work well. You should probably do the whole case, cross pins, seals etc while you are doing the work, or at least buy one that is done. These go for 1700 to 1800 and up from what I have seen. Depending on who you get to do the work, the diffs can be cheaper and are at least easier to install yourself once they are set up. The gears can be stronger than stock too. The fronts are a pain but just tedious not difficult. You really need a lift and at least a trans jack with the modified plate for the transfer case to try it at home. More space underneath the vehicle would be a huge plus for the case install, not needed for the diff installs.
 

p m

Administrator
Apr 19, 2004
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La Jolla, CA
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These go for 1700 to 1800 and up from what I have seen.
From Ashcroft: rebuilt LT230 with 1.4:1 high range 495 UKP +s&h
From Great Basin Rovers: 3.9 front gearset $349.95 + 3.9 rear gearser $349.95 = 10 cents short of 700 bucks.

Labor - up to you; local shop charged me recently 5 hours of labor for removal and installation of a transfer case.
I could never install a TrueTrac in less than 2 hours, all taken into consideration; last time three weeks ago took 2.5, and it was the rear. Front takes longer, even if you don't remove the axleshafts, and these times do not take into account setting pinion depth, only ring gear backlash.

There is an argument that you don't get a "lower low" with 1.4 high-range LT230: true, you don't. But personally I've broken enough axleshafts and CV joints with existing gearing not to want to go lower - if you do, factor in the price of HD axleshafts. It is a good investment in any case.
 

CORover

Well-known member
Jun 11, 2007
719
54
Colorado, USA
UKP. UK pounds? That's over 600 and then shipping from the UK, way over 700 total. What's the door to door cost?
5 hours to R&R the case is good, I was just quoted 6 to do it. No way I could do it shorter, but cheaper maybe if I fight it all weekend maybe.
I've got lockers so the axles are a must and already there.
The 1700 for the case was from a reputable shop in the states and they are all ready to go, gears, seals, minus the HD cross pins.
 

rovercanus

Well-known member
Apr 24, 2004
9,363
88
There was a thread a while back discussing rpm and gear ratios. I'm running 4:12 with a built 4.6 and have no problem on the interstate. Somewhere in that thread I listed rpm to speed.
With 4:12's I have ...
 

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p m

Administrator
Apr 19, 2004
14,621
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La Jolla, CA
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UKP. UK pounds? That's over 600 and then shipping from the UK, way over 700 total. What's the door to door cost?
<skip>
The 1700 for the case was from a reputable shop in the states and they are all ready to go, gears, seals, minus the HD cross pins.
Still a far cry between ~800 and 1700 for the case. And I assume Ashcroft cases are all ready to go as well.

I also mentioned my other concern elsewhere - if you bust a stock R&P, you can get one from many junkyards around. With a custom set, you're subject to availability in stock where you bought one, +some wait.
 

Tugela

Well-known member
May 21, 2007
4,349
176
Seattle
Still a far cry between ~800 and 1700 for the case. And I assume Ashcroft cases are all ready to go as well.
The rebuilt Ashcroft option is looking more appealing. I had been contemplating buying a second LT230 from a parts truck and rebuilding it at my leisure - Ashcroft sells a rebuild kit for GBP 95 (excluding shipping), which seems like a good value. This makes a stronger case for buying the finished unit. My Disco is my only car, so if I rebuild the transfer case I'd need a second unit - I can't have it out of action for the time it would take to do this job. Here's a rough cut at a cost comparison.

DIY
  • Second LT230: $200 (just guessing here, I haven't priced these out so can't be confident in this figure)
  • Rebuild kit: $119 + shipping
  • Tools: $150. I don't have a transmission jack and don't know anybody who does.
  • Time: some people don't put a value on this. I know this project would take me a long time. It would be a valuable learning experience. There's a chance I'd screw something up. And I'll be honest: I'd rather be mountain biking or driving my Rover somewhere cool instead of working on it. Can't put an exact figure on it, but it's worth something.
  • Total: let's call it $500 plus however you value your time.

Ashcroft rebuilt case
  • Price of unit: $622
  • Shipping: I can't tell from the Ashcroft website with the info I have, but it can't be cheap. Wild guess of $178.
  • Tools: $150
  • Time: same situation as above, sort of. Using the 5-hour shop figure from a previous post for remove and replace, that would be about $660 in my local market. Or do it yourself.
  • Total: somewhere between $800 and $1,610 depending on your choices and needs.
On the low end, the DIY option saves $300 over the rebuilt option. On the high end, the savings is $1,100. If the savings was $300, I'd opt for the rebuild over DIY. That's worth it to me for the time and peace of mind knowing Ashcroft did it right.
 

_ExpeditionMan

Well-known member
Dec 11, 2017
181
16
Fort Worth, TX
From Ashcroft: rebuilt LT230 with 1.4:1 high range 495 UKP +s&h
From Great Basin Rovers: 3.9 front gearset $349.95 + 3.9 rear gearser $349.95 = 10 cents short of 700 bucks.

Labor - up to you; local shop charged me recently 5 hours of labor for removal and installation of a transfer case.
I could never install a TrueTrac in less than 2 hours, all taken into consideration; last time three weeks ago took 2.5, and it was the rear. Front takes longer, even if you don't remove the axleshafts, and these times do not take into account setting pinion depth, only ring gear backlash.

There is an argument that you don't get a "lower low" with 1.4 high-range LT230: true, you don't. But personally I've broken enough axleshafts and CV joints with existing gearing not to want to go lower - if you do, factor in the price of HD axleshafts. It is a good investment in any case.
That GBR price is just the R&P kit though, not complete diffs right? Youd still need to set them up yourself or pay someone to.