Transfer case re-gearing
- Thread starter NielsC
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iptman
SILVER Star
So doing some Interweb tire size/gear ratio calculations going from stock 270/70/R16 to 315/75/R16 on the stock 4.10 diffs you'd need a theoretical 4.59 diff ratio to get back to stock. Seems like these under drive gears are a good match for 315s then.
That seems to fit what others have calculated out. That would get your gearing back, but not account for the weight of accessories.
Would it be possible to get 37's to run like stock by regearing just the t-case? Or would the case and diffs both need to be done?
Someday I'm going to 37's on my rig and I'd like to have some kinda plan for turning them!
Someday I'm going to 37's on my rig and I'd like to have some kinda plan for turning them!
Would it be possible to get 37's to run like stock by regearing just the t-case? Or would the case and diffs both need to be done?
Someday I'm going to 37's on my rig and I'd like to have some kinda plan for turning them!
As mentioned earlier in this thread, the 10% overdrive gears will get you back to stock gearing with 315's. If you are going to 37's then you would need additional gearing. It seems that most people who go with 37's re-gear with 5.29's and call it a day.
inkpot
SILVER Star
Would it be possible to get 37's to run like stock by regearing just the t-case? Or would the case and diffs both need to be done?
Someday I'm going to 37's on my rig and I'd like to have some kinda plan for turning them!
37's and 4.88 gears put my rig about 2mph slower than the speedo reading on the freeway. So, 75 mph on my speedo shows 73 on my gps and roadside radar units. This is about as close to stock final gears your gunna git as far as I know. This rig had 315s when I bought it, and tack has dropped about 350 rpm on the freeway.
@artech
It makes no difference where along your drivetrain you choose to regear. You can do it at the differentials, transfer case or transmission.
What is important when you regear, is to get back to the OEM spec in terms of tire size, correct engine speed and velocity.
As I said above, you can alter the 2.804 first gear ration for example (will leave all others out of this conversation just to keep things simple), or the 1.00:1 at the transfer case (in HI mode) or at the diff where originally it came with 4.11
2.804 x 1 x 4.11 = 11.52444 ....... On 31" tires!!!!!!!!!!!!!!!!!!
1st gear x transfercase x diff
To maintain that ratio with 37" tires you will need 13.75497 final gear ratio
-- (11.52444 x 37)/31=13.75497
If you only regear the transfer case with 10% underdrive, you get this much:
2.804 x 1.10 x 4.11 = 12.67688
Slightly below the target gear ratio.
If you regear the x-case with 15% gears (doubt you can find them) you get a little closer but still missing the mark at 13.2531
So you will need a little extra to help out, preferable at the diff.
But in that case, you have to ask yourself why regear at the tranny and at the diffs to accomplish the same thing as 4.88 gears at the diff which will get you 13.6835?
Very close.
Well, there is a trick Georg explained here. You can get a short gear (high numerically) like 5.29 and an underdrive gear for the t-case (0.9 for example) along with a short (3.11) LO gear. Awesome combo in my view.
It makes no difference where along your drivetrain you choose to regear. You can do it at the differentials, transfer case or transmission.
What is important when you regear, is to get back to the OEM spec in terms of tire size, correct engine speed and velocity.
As I said above, you can alter the 2.804 first gear ration for example (will leave all others out of this conversation just to keep things simple), or the 1.00:1 at the transfer case (in HI mode) or at the diff where originally it came with 4.11
2.804 x 1 x 4.11 = 11.52444 ....... On 31" tires!!!!!!!!!!!!!!!!!!
1st gear x transfercase x diff
To maintain that ratio with 37" tires you will need 13.75497 final gear ratio
-- (11.52444 x 37)/31=13.75497
If you only regear the transfer case with 10% underdrive, you get this much:
2.804 x 1.10 x 4.11 = 12.67688
Slightly below the target gear ratio.
If you regear the x-case with 15% gears (doubt you can find them) you get a little closer but still missing the mark at 13.2531
So you will need a little extra to help out, preferable at the diff.
But in that case, you have to ask yourself why regear at the tranny and at the diffs to accomplish the same thing as 4.88 gears at the diff which will get you 13.6835?
Very close.
Well, there is a trick Georg explained here. You can get a short gear (high numerically) like 5.29 and an underdrive gear for the t-case (0.9 for example) along with a short (3.11) LO gear. Awesome combo in my view.
inkpot
SILVER Star
Would it be possible to get 37's to run like stock by regearing just the t-case? Or would the case and diffs both need to be done?
Someday I'm going to 37's on my rig and I'd like to have some kinda plan for turning them!
I know some folks with 37's on their rigs and they are still running the stock diff gears. Learn to control shifting in high range with the little handle thingy on your console. We wheel anywhere from 1500 to over 7000 ft altitude. They do run the low range transfer case gears, which make them pretty capable off road.
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Lots of things on my rig are not stock, so OEM spec,
, have never seen the OEM spec for a ~5" lifted, 37" tire rig?
I like the rubber overdrive of the 37"s, ~2000rpm at ~70mph is nice and quiet cruising. On the trail, it worked, but is better with the crawler low range gears.
Pardon my stupid question, but in the High Range case, don't you also have to replace the bigger gear in the idler gear ? In other words to accomplish the high range change you need to replace 3 gears ?
Thanks !
Lots of things on my rig are not stock, so OEM spec,
I like the rubber overdrive of the 37"s, ~2000rpm at ~70mph is nice and quiet cruising. On the trail, it worked, but is better with the crawler low range gears.
There is a problem with not having the engine and drivetrain as close to spec as possible.
If you are running bigger size tires, you normally want to regear to "get more power" back. Of course there is a clause here regarding power. Of course gears don't make power, etc, etc. You actually get into the designed/optimal power band the car was designed to run in.
Therefore you don't end up hyper milling the engine and the torque converter lockup will be as close to the OEM spec too.
While descending with overdrive given by larger size tires, you tend to pick up more speed then you need or want.
duggy
SILVER Star
Nobody has ever complained about too much speed in an 80 series with the 1FZ.
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My rig has a shifter, I select the gear needed for the conditions, the stock spec thing is long gone. What did you observe about the 37"s on your rig?
This should read; the 10% UNDERdrive gears will get you close to stock with 315s. The only people who will likely be interested in overdrive gears will be the H151/diesel people.
orangefj45
Supporting Vendor
Exactly.
Guys with 1FZs running larger tires and stock gears would want the UD gears. But the diesel crown likes the OD gears for obvious reasons.
We've installed about ten sets of the OD gears here at Valley Hybrids and they were all diesel 80s.
We just sent a set of the UD gears to a customer in Iceland and have a few more sets on the way from Terrain Tamer in Australia.
Georg @ Valley Hybrids & Cruiser Brothers
Guys with 1FZs running larger tires and stock gears would want the UD gears. But the diesel crown likes the OD gears for obvious reasons.
We've installed about ten sets of the OD gears here at Valley Hybrids and they were all diesel 80s.
We just sent a set of the UD gears to a customer in Iceland and have a few more sets on the way from Terrain Tamer in Australia.
Georg @ Valley Hybrids & Cruiser Brothers
@orangefj45 I messaged you a few weeks back on a quote for underdrive gears. Please let me know when you receive more gears.
orangefj45
Supporting Vendor
Thanks for everybody's patience.
Long story short ....... we have the OD and UD high range gears in stock. We've installed a number of the OD gears over the last couple of years and they've performed flawless.
But we have not installed any of the UD gears here at the shop.
I'm the type of guy who likes to know parts from personal and/or professional experience before selling them to the general public.
In other words, I'd prefer to install a set of the Terrain Tamer UD gears into a case here at the shop and drive the vehicle before I sell them ....... call me old fashioned, but to me it's peace of mind and good customer service & tech support.
Georg @ Valley Hybrids & Cruiser Brothers
Long story short ....... we have the OD and UD high range gears in stock. We've installed a number of the OD gears over the last couple of years and they've performed flawless.
But we have not installed any of the UD gears here at the shop.
I'm the type of guy who likes to know parts from personal and/or professional experience before selling them to the general public.
In other words, I'd prefer to install a set of the Terrain Tamer UD gears into a case here at the shop and drive the vehicle before I sell them ....... call me old fashioned, but to me it's peace of mind and good customer service & tech support.
Georg @ Valley Hybrids & Cruiser Brothers
that is a heck of a way to stand behind your products Georg ! I would be very interested in one of those 2 gears sets for UD gears once you have tested them out.
Thank you for all the info !!!
Thank you for all the info !!!
