My (mostly) Toyota Hybrid Front Axle Build for FJ40

[Chris Wilcox]

This thread is to detail the build of my front axle for a 1978 FJ40 using mostly toyota parts. Intended purpose is to do some medium duty offroading with friends but also to retain road manners and be able to take my kids exploring in the woods. Mostly I enjoy a challenge and the time spent during the build.

To get this far I've spent lots of time reading threads and have collected the following parts for the build:

1. FJ62 front housing because it is setup for 9.5" and has factory stiffener on the underside of the housing.
2. 80 Series 9.5" E-Locker third member re-geared with 4.88 nitro gears.
3. Donor 80 series front axle for brakes and many small parts.
4. Hellfire knuckles with 20mm trunnion bearing as this is not the rev 2 version.
5. RuffStuff diff cover (1/4" thick fabricated).
6. Pneumatic cylinder to replace actuator.
7. Warn locking hubs (but I have some aisin on another spare axle that I may use instead).
8. Wheel spacers/adapters 2" thick, which convert to 8x6.5" to fit the oem HMMWV 12 bolt dual bead lock DOT approved wheels/tires.
9. 80 series front axle rebuild kit.
10. Still Need: custom inner axle(s).

Current status is that the 80 knuckle balls are welded to the 62 housing, however I don't know the WMS or caster/diff angle yet and may have to adjust. I bought this already welded. Welded cover has been removed to fit the ruff stuff housing.
4.88 gears have been installed in the third member.
Donor 80 front axle parts disassembled.
Time to start the real work.

 

[Bret]

I have an 80 e-locker in the front of my 40, would be interested in which actuator you are using for the locker (mine is cable for now). I had looked at using air or direct electric actuator but that was quite some time ago. On my 40 axle with 30 spline axles the next week link was the hub studs. I drilled the hub body and hubs for 4 pins and it has worked well so far. Based on the other cool stuff in that axle it may be worth it. Sounds a step or two past "medium wheelin"

 

[Chris Wilcox]

Bret I'll detail the Festo ADV-25 later. Search Festo on the forum for other peoples installation of this cylinder.

The first thing I am concerned with is the upper trunnion pin. On the following thread there is discussion on posts 166 & 167.
https://forum.ih8mud.com/threads/fj80-high-steer-anyone.384101/
I'll quote some of the discussion

"The only issue I wonder about is the tiny bit of sideplay created by having an adjustable trunion pin. The factory cap/pin is locked in place by the two bolts through its flange and can't move axially or radially, but a floating pin only loaded axially (the bearing preload) will be able to wobble by the tolerance between the pin and its bore in the steering arm.

On a trail rig this play will be insignificant compared to all the slop in the suspension system, just wondering how it will hold up over time. Could the minor radial movement slowly wallow out the hole and wear the pin, or will a thick grease film provide an adequate cushion? Or are there a pair of perpendicular lock screws that come from the side of the arm to lock the pin in place after the preload is set?

For the record I'm not worried about the pin play, just pointing it out to keep those of you with unbridled OCD awake at night. =^)"

"I'm glad you brought this up. you have a very good point, and i have put a lot of thought into this. first off, the pin goes up into the arm 1/4" and is a press fit. the bore in the knuckle is 1/8" longer than a stock knuckle since there is 1/8" of added material up top, so there is more holding it from wobbling, and it is a snug slip fit. there wont be enough movement for it to hurt anything or wear anything prematurely.

if you look at the stock knuckle and the stock upper cap, you'll see how the cap is thin on top with only 2 bolts. this can allow for some flex in the cap plate as well as flex in the bore since it isn't that long. i am confident that this will hold the pin more securely than the factory design."

I do worry about the long term reliability of a loose upper trunnion pin with poor aspect ratio. Also my parts did not come with a press fit but rather a slip/slightly loose fit between the pin and both the arm and knuckle.

Additionally having the steering input at the top adds load to the upper trunnion bearing and pin. My plan is to make a new pin, incorporate the 25mm 30205 bearing and weld the pin into the arm. Utilize shims under the bearing to adjust preload. Unfortunately I'll have to grind the hellfire knuckle to permit assembly of the birfield through the knuckle.

First I have to mockup the axle under the 40 and to do that the 20mm pin and adjuster setscrew will work fine.

 

[Tapage]

I have an 80 e-locker in the front of my 40, would be interested in which actuator you are using for the locker (mine is cable for now).

would be nice to see your cable setup .. any buildup thread..?

 

[Bret]

I am using the old Downey conversion. I will try to get some pics. If you PM me an e-mail I will send them to you so we don't clutter up this thread.

 

[47coeman]

I sure would like to find a Downey conversion set up to copy I have two "E" Thirds that I am thinking I would like to make into mechanical set up for one of my rigs..

 

[mookie]

very nice pile of parts! Is this the hybrid axle that Eric Hagen started a few years ago?

 

[Chris Wilcox]

mookie, some parts are from dr_dobro https://forum.ih8mud.com/threads/redesigned-xtd-40.783827/

I contacted Billy, maker of hellfire knuckles to ask him why the knuckles were smaller at the spindle bolt pattern which prevents the birf from passing through. Reason is to reduce a machining step which makes sense to me. Anyway I ground away enough of the ID of the lip so you do not have to use the camo method for birfield installation. You can see the modified one above the original hellfire knuckle. OEM 80 knuckle beside it for comparison. With about half the lip remaining the birfield and axleshaft pass through without interference.

Mockup to see where stock 80 series axles land in third member housing and to measure preliminary WMS.

Performed some QA/QC on the hellfire vs the Toyota knuckle. Using my mitutoyo digital level, digital calipers and by bolting parts to it I have come to the conclusion that Hellfire Fabworks has done a VERY good job at recreating the toyota knuckle but with added material and high steer. One thing that really concerned me was the angle that would set camber but they measure equally.

Also considering using the toyota e-locker actuators to save work. I can always change later.

 

[Gumby]

I'm using an Ox locker lever and cable for my e- lockers.

 

[47coeman]

Hey Gumby where can I see or get info on these cable lockers. Best

 

[Chris Wilcox]

Are you guys hinting that I should choose cable lockers? haha

 

[Chris Wilcox]

Today I was able to measure the hardness of the Hellfire and OEM Toyota trunnion pins. I will say that Hellfire is essentially the same tensile strength as the toyota unit. This was measured on a calibrated tester at a University. I took 3 readings on each and they were all very close.

Hellfire upper trunnion pin

Toyota Lower arm

Conversion of hardness to Tensile Strength

This information indicates that the trunnion pins are probably 4340 Q&T having a Yield of ~124 ksi. Toyota may not be this particular material but it is close in yield. Regardless this information is important to the design of my upper trunnion pin.
Chris

 

[Chris Wilcox]

I'm always busy with 3 kids under 4 but made some progress. Installed the axle under the 40 using engine hoist legs as a ground to preload the springs to ride height and measure caster and diff angle. This also enabled me to check shock, steering and tire clearances. Next I tacked nuts to the housing to allow the ruff stuff diff cover bolts to hold. This was a 62 front axle and had the front cover welded on. Previous owner cut it off and bought the 1/4" thick diff cover. I then cut and turned housing. I believe most people use a bar through the axle with spacer pucks in the empty diff. I could have done this but considering the camber is positive 1 deg and I couldn't figure out how to accurately angle down both spindles 1 deg while maintaining a straight bar through all I elected to use bearings and a dial indicator to measure runout. I got it down to about 0.008" TIR and then checked the kingpin angle. It measured exactly 13 degrees and the hellfire trunnion axis vs spindle face measures 14 deg. Therefore I'd have my 1 deg camber (OEM Spec) and also have nice true knuckle balls. Not sure if others do it this way or not. Pictures below.

 

[J Mack]

What caster angle are you shooting for?

 

[GLTHFJ60]

 

[Chris Wilcox]

3 degrees, Factory 80 series is 3 deg +- 1 deg. My 37" tires are larger therefore more mechanical trail so there should be more stability. People have lots of opinions, in the end I just picked 3deg. My brother has an 80 with 37's and stock caster and camber and it drives great.

 

[Chris Wilcox]

Been travelling more than preferred for work so progress has been minimal however i've been working when I can.
Today I cut a second groove 8mm back in the birfields. These are HARD! First try HSS was a huge fail. Second I ground a carbide insert brazed to a steel holder. This half cut it but was really jumping up over each spline. What worked was a 4.5" grinder makeshift mounted to the toolpost with a 0.062" thick zip disk. This setup made a fairly good groove with ease.

"Toolpost Grinder" setup

Before

New Groove

 

[UZJ40]

Awesome thread and very innovative. I look forward to more!

 

[Chris Wilcox]

Not much to report as i'm helping my father build a trailer however this showed up today. Custom length front axle shaft. It looks REALLY good and measurements exactly match my drawing. Thumbs up so far for RCV. You do have to pay for it though, $290 shipped for this one axle shaft for those considering this approach. Please no cluttering of my thread with opinions on the price.
Soon I hope to finish the custom upper trunnion pins and begin final assembly.

Chris

 

[White Stripe]

So why did you go this route rather than a dana 60? I mean you do really good work, but for the same amount of work and money you could make a dana 60 that would be way stronger couldn't you? Correct me if Im wrong because if this is indeed a cheaper and stronger route you are taking I would like to know in case I want to upgrade my front axle.