changing gear ratios. good? bad? (1 Viewer)

Joined
Oct 30, 2008
Messages
10
Location
montana
I have a 2f motor with a '74 4sp tranny and axles. I want to increase my highway speeds a bit, nothing too drastic but i was wondering if its a good option to change my ratios in the gear boxes. does it work? do i lose too much torque? does it fail alot or is there some big problem? if you can help me out it would be great!! (oh yeah and if you know where i can find out how to do it too...) thanks
 

Josie'sLandCruiser

Stop calling it a "FJ."
Joined
Feb 4, 2005
Messages
5,207
Location
Seattle, USA
 
 
 
Hi All:

You could fairly easily swap-in a pair of 3.7 ratio third members from a FJ60 to replace the 4.1 ratio diffs your rig currently has.

You'd also need a pair of these to adapt your early drive shaft flanges to the the pinion flanges on the FJ60 thirds:

Cruiser Outfitters


Good luck!

Alan
 

Poser

Oh...Durka Durka Durka.
s-Moderator
Supporting Vendor
Joined
Oct 1, 2003
Messages
20,453
Location
MN
 
 
 
Hi All:

You could fairly easily swap-in a pair of 3.7 ratio third members from a FJ60 to replace the 4.1 ratio diffs your rig currently has.

You'd also need a pair of these to adapt your early drive shaft flanges to the the pinion flanges on the FJ60 thirds:

Cruiser Outfitters


Good luck!

Alan




01/74 through 07/84 Land Cruisers share the same drive shaft bolt pattern on the companion flange. So, if you were to find 3.70 differentials from a 01/79 and later 40/55 series or a 60 series to 07/84, they would bolt right in and not need anything other than possibly a pinion seal and some gaskets.

If you were to find 08/84 to 07/87 differentials from a 60 series, you would need to change the companion flange, or re-drill them if they are the round style.



:beer:
 
Joined
Oct 30, 2008
Messages
10
Location
montana
thanks folks thats really helpful! But if i did a 3.7 swap would i lose that signature beastly torque, and what kind of gain is it? also does anyone know a good place to get the gears? I will probably end up paying through the nose for them so if anyone knows...
 

Cruiserdrew

On the way there
SILVER Star
Joined
Mar 15, 2003
Messages
15,907
Location
Sacramento, CA
 
 
 
Suit yourself, but you can get the same net results with bigger tires for a lot less money and wrenching. You might loose a bit of mechanical advantage, but it will be just fine. My guess is you'll never even notice.

Even 31s would give you a bit more highway speed, and not require any spring lift at all.
 

Landpimp

GOLD Star
Joined
Mar 14, 2003
Messages
16,072
Location
Gig Harbor WA
 
 
 
I run 33x9.5's on my 82 with stock 3.7 gears......I LOVE it, even on the hwy I can pass on hills, sure I dont wheel it but for a driver its a great combo

someplace(god know where) i should have a set of 3.7s out of my fj60, went to 4:11's in that

thanks folks thats really helpful! But if i did a 3.7 swap would i lose that signature beastly torque, and what kind of gain is it? also does anyone know a good place to get the gears? I will probably end up paying through the nose for them so if anyone knows...
 
Joined
Oct 30, 2008
Messages
10
Location
montana
The problem with bigger tires is that right now im all drums. i have some mid 80s mini truck discs but they arent complete... I've heard that bigger tires can cause problems with drums... plus tires require money i dont have. but if swapping gears reduces offroad ability maybe i should just wait til i can afford tires?
 
Joined
Sep 3, 2007
Messages
4,432
Location
Longmont, CO
 
 
The problem with bigger tires is that right now im all drums. i have some mid 80s mini truck discs but they arent complete... I've heard that bigger tires can cause problems with drums... plus tires require money i dont have. but if swapping gears reduces offroad ability maybe i should just wait til i can afford tires?
New gears and their setup ain't free either. I stop fine on 31s with drums. I'm sure I'd stop fine on 33s with em too.
 

Cruiserdrew

On the way there
SILVER Star
Joined
Mar 15, 2003
Messages
15,907
Location
Sacramento, CA
 
 
 
The problem with bigger tires is that right now im all drums. i have some mid 80s mini truck discs but they arent complete... I've heard that bigger tires can cause problems with drums... plus tires require money i dont have. but if swapping gears reduces offroad ability maybe i should just wait til i can afford tires?

Well then anything you do will be expensive. If you buy new gearing $400, bearing kit for diffs $300, set up $300, knuckle kit $100, misc seals bearings and gaskets $100 you've spent close to $1500 and you still have little tiny tires.

Used 3rd members in 3.70 Maybe $300 + knuckle kit $100+ Gaskets$50

Set of 33 inch tires $1000

Decent lift for FJ40 $1000

Minitruck or FJ60 Knuckles/hubs/discs/calipers $300 + $100knuckle kit + $100 wheelbearings

This is assuming you do the work yourself.

None of it's cheap but in the end you have to do all of it. Just the way it is.

If it were me, I'd run what you have, upgrade the fronts with the minitruck knuckles and brakes, and slowly work my way through the truck as time and money allow.
 

kcustom73

Stretched it...
SILVER Star
Joined
Jun 26, 2007
Messages
687
Location
Ottawa, ON, Canada
 
 
You need to calculate what speeds you are really going to be driving at and what the happy rpm for the 2f is (I haven't done the research on this because I'm going diesel, but someone else on this will surely know this). My 40 will be a DD 95% of the time with some mild offroad/event once in a while, so I'm planning on putting 33" tires with 3.7 gearing behind an auto overdrive tranny. This combo will give a happy rpm of 1800 at my two most driven speeds (in third and overdrive).

I plan of fixing my crawl ratio by using a toybox from Marlin Crawler (not sure if it still offered since they went to their new website) or an Orion t-case with adapter to a GM 700R4 from advance adpaters.

Here's alink to a good gearing calculator (sorry its from a heep site):
Novak Conversions - Gearing & Gearing Math for Jeeps
 
Joined
Oct 30, 2008
Messages
10
Location
montana
what does it take to make the swap? I figure its not just getting new gears and tossing them in the diff but i dont know what else is involved. Im kinda clueless (got my cruiser in august and muddled through putting an engine in for the first time. It turned out good and i hope to drive it to college but its gonna be like two days with the 4:11...)
 

Poser

Oh...Durka Durka Durka.
s-Moderator
Supporting Vendor
Joined
Oct 1, 2003
Messages
20,453
Location
MN
 
 
 
i hope to drive it to college but its gonna be like two days with the 4:11...)


It will be a two-day drive with 3.70s as well.


You are not going to remove a day of driving, simply by changing the gear ratio in the differentials from 4.11 to 3.70. :lol:
 

Cruiserdrew

On the way there
SILVER Star
Joined
Mar 15, 2003
Messages
15,907
Location
Sacramento, CA
 
 
 
what does it take to make the swap? I figure its not just getting new gears and tossing them in the diff but i dont know what else is involved. Im kinda clueless (got my cruiser in august and muddled through putting an engine in for the first time. It turned out good and i hope to drive it to college but its gonna be like two days with the 4:11...)
There is a lot involved. If you're a college student, then just enjoy having the coolest ride on campus. Save the mods for after you get out of school. Fix the stuff that breaks, chase the girls and enjoy yourself. The Cruiser will still be there in 4-5 years when you are ready to mess with it.

The very worst thing you can to to a cruiser is half thought out mods that are underfunded and never quite get finished. Then you end up with hacked junk that doesn't work, and some future owner will curse you and all of your children.
 
Joined
May 15, 2004
Messages
286
Location
Tucson
 
 
 
I was in the same exact spot you are in when I was starting college. I had a bone stock 40 and hardley any money. The drive from home was about 300 miles and almost all 75mph traffic. I had a strict budget and I looked around town at tire shops and found a decent set of 31x10.50 BFG all terrains that were take offs and they said I could have them, mounted and balanced for $45. I found my self with much improved rpms at freeway speeds, better traction on the ice and snow around college and a better lookin cruiser than when it sported 235/75s.
I am craigslist junkie and tires are the hot ticket right now. Seems everyone is cleaning their garages and the last to go items are selling...cheap. Check it out.
 
Joined
Apr 5, 2008
Messages
527
Location
N. Van, BC / WA
 
 
I have a complete set of 3:73 axles out of a 1980 (disc front of course) I would let you have for a fair price.
I would go this route, he is asking a fair price for them in the for sale section and you get front disc brakes while you are at it. CO isn't too far from MT:)
 
Joined
Oct 30, 2008
Messages
10
Location
montana
well thanks guys, alot of good advice here. I think I'll probably follow the general consensus here and go for some 31's or maybe 33's and just suffer for the drive til i have more money. Looks like its a good thing i checked before i did anything big!
 

Users Who Are Viewing This Thread (Users: 0, Guests: 1)

Top Bottom