putting 3 speed gears in a 4 speed case...

[Cirbo]

I've done some searching and haven't found a good answer.

Obviously the intermediate cluster must be changed and shimmed properly to account for the different internal dimensions inside the newer case.

Do both gears from the three speed output shaft need changed?

Does this swap need the special cross-over input gear (36212-60030) to make it all work correctly as well?

TIA,

Jim

 

[Cirbo]

Wow, 59 reads and nobody has put 3 speed gears into a 4 speed case that can chime in on the correct process?

 

[crushers]

i have installed the low range 3 spd gears into the 4 speed cluster. i made a custom idler to make it work.
worked very well and lasted till long after i sold the truck.

 

[Pighead]

I've done it, twice. But both transfer cases were the transition transfer case, out of 12/'74s. You don't mention which transfer case you're working with...

 

[Cirbo]

Working with a '78 case. I have both a '72 and '67 to steal parts from.

Do I need the "transition" input gear?

Do I need to move all gears from the output cluster as well?

TIA,

Jim

 

[Cirbo]

i have installed the low range 3 spd gears into the 4 speed cluster. i made a custom idler to make it work.
worked very well and lasted till long after i sold the truck.

Custom Idler?

 

[crushers]

i took the idler from each and mated the 4 speed high range to the 3 speed low range.
the shop charged me $75 to machine and weld and remachine the two together.

worked well.

but i am guessing this isn't the answer you were looking for.

 

[Poser]

Do I need the "transition" input gear?

Yes.

Do I need to move all gears from the output cluster as well?

Yes.

You will need to use the high and low output gears with the corresponding idler assembly and input gear no matter what gear set you decide to use.

Curious, why not purchase a known good four speed transfer case and install that, opposed to trying to build this?


Surely this cannot be strictly trying to gain .314 in low gearing?

 

[Cirbo]

Yes.
Surely this cannot be strictly trying to gain .314 in low gearing?

Um, actually it is. It's one of those exercises where you have all these parts and wonder what it would take to make it work.

 

[crushers]

actually, if you run the figures the change in low range works out to the same as changing 4.11 gears sets for 4.88 ...
so yes, for some that seemingly minuscule amount makes a difference.

 

[Cirbo]

i took the idler from each and mated the 4 speed high range to the 3 speed low range.
the shop charged me $75 to machine and weld and remachine the two together.

worked well.

but i am guessing this isn't the answer you were looking for.

So you chopped the Idler gear into two pieces and welded old low range gears to new high range gears?

(this does ring a bell...)

 

[crushers]

that is correct. if you have a decent machine shop near you then it is easy enough for them to do.
3.55 X 1.99 X 4.11 = 29.03
3.55 X 1.99 X 4.56 = 32.21
3.55 X 1.99 X 4.88 = 34.47

3.55 X 2.31 X 4.11 = 33.70

the nice thing about this is you can retain your highway speeds using the 4.11 diff gears and yet have the similar off road performance as if you swapped the 4.11 for 4.88.
when i ran the FJ40s way back when i would swap a H55F into the vehicle and use the 1980 to 1982 split case gears in the 1983 - 1989 t/case. this would give me
4.84 X 2.27 X 4.11 = 45.15 crawl (AND the O/D was great on the highway.)
3.55 X 1.99 X 6.44 = 45.49 crawl. (you get the idea of how good this works off road. but. on road you still have highway speeds and decent fuel economy.)

something to consider next time you are wanting to experiment

 

[kiwidog]

3 speed gears in 4 speed TC

Just put a transfer case together with the transition gear input gear part #36212-60030 $95.00 from Kurt.
Here's what I found .
Case dimension between the two thrust pads 3.513" ( 3/1978 transfer case
1963 3 speed transfer case gear set)
Idler gear width 3.150''
3 speed transfer case thrust washer 0.117" x 2
Idler gear plus thrust washers 3.150 +0.117 +0.117= 3.384"
Take this away from the case dimension 3.513 - 3.384= 0.129"
2 shim for behind the washers
Used 16 gage material 0.062 thickness to make two shims.
Cut the shims with 2.5" diameter hole saw for the outside and 1'' diameter hole saw for for the inside hole. Then filed a slot for the thrust washer tab. see picture.

0.062x 2 = 0.124" take this away from the the clearance above.
0.129- 0.124 = 0.005
FSM specifies allowable clearance range 0.0049 to 0.0187 so the clearance is within the lower end of the range.
Installing the idler gear is a little tricky Holding the shims and trust washer in place and installing the gear. Used two idler shafts to just support the shim washer set. Then installed the idler gear. Then pulled one of the idler shafts out and fully install the other one.
Using two shims ( one behind each thrust washer) put the idler gear exactly inline with the input gear when installed on the 4 speed trans.
You need to use all the gears from the 3 speed TC except the input gear. You need the transition gear. If do the welded idler gear then you are into a special, which would allow you to retain the wider 4 speed gears for high range which could give a quiet ride. Good idea from crushers.

Thanks jb

 

[jjacallen]

Input Gear conversion?

kiwidog said:
"Just put a transfer case together with the transition gear input gear part #36212-60030 $95.00 from Kurt."

Whoa! Who's Kurt? I need one! Anybody know of a place that sells these?

 

[spotcruiser]

Cruiser Outfitters http://www.cruiseroutfitters.com

kiwidog said:
"Just put a transfer case together with the transition gear input gear part #36212-60030 $95.00 from Kurt."

Whoa! Who's Kurt? I need one! Anybody know of a place that sells these?

 

[camcruiser13]

I'm thinking Cruiseroutfitters named kurt

 

[Hugh Heifer]

Pretty interesting tech.
So you gain a lower gearing of the three speed and the advantage of the higher 4th gear - kinda like an overdrive for a three speed (if I understand Crusher's post?)

 

[Cruiserdrew]

Pretty interesting tech.
So you gain a lower gearing of the three speed and the advantage of the higher 4th gear - kinda like an overdrive for a three speed (if I understand Crusher's post?)

No. You gain only at the low end. it's 1.99 vs 2.3. That's a 15% difference. Hardly worth it in my opinion, because then for the rest of time, your transfer case will make more noise. In high range, the cases are the same gear ratio, 1:1.

Any money spent trying to run 3 speed gears in a 4 speed case is wasted. Save your money for an Orion and get real gear reduction, or move up to a Toybox and split case.

 

[crushers]

and i will disagree with this statement.
that change in low is the same as changing from 4.11s to 4.88 diff gears but being able to keep the highway performance the same.

well worth the swap to the majority of off roaders. rock crawlers will disagree.

 

[climber8483]

Can you get a Toybox to go between a 3 or 4 speed FJ40 transmision and the split case?