First Post - Help validate thinking on a disk brake upgrade (1 Viewer)

[MakeitWrite]

First tech post here and wanted to validate my thinking on a front disk brake upgrade for my 04/72 FJ40 (bought here on MUD a few months ago; Thanks MIKKELSEN!) –


While pouring through the FAQ here for front disk upgrade options, I stumbled on a complete hub to hub disk brake front axle from a 76 FJ40 local to me on CL. It’s a bit crusty from being stored outdoors for about 10 years but after getting it home and cleaning / partially disassembled, appears remarkable clean and completely serviceable. My thinking is to rebuild the 76 with a knuckle kit, new wheel bearings, rotors and reman calipers, brake lines, paint it and swap it directly for my 72 drum axle. I can see there needs to be some additional brake work as the brake splitter location is different, and I’ll need to get a proportioning valve, but wondering about what else I’m missing (drive shaft?)


It honestly sounds too simple a swap and sure there must be something I have not taken into consideration. I realize there is an option for using the knuckles and birfs from the 76 on my 72 axle, but not sure that’s easier. Greatly appreciate any guidance / suggestions / pointers.


All the best,


Bob

 

[FixedIt]

More info than anyone here can put in a single reply:

40-series FAQ

Just page down to the axle rebuild section. Oodles of info.

Edit: Dif flanges are different among certain years, making a driveshaft swap a bit more entailed. and if you want to add the rear with parking brake you'll have to look at a number of other things to consider (e.g. tcase)

 

[Rigger]

Take the pinion flange from your 72 and put it on your 76 axle. Then your 72 driveshaft will bolt up nicely.

I did a similar thing on my 70 some years ago. Had a lot of folks on this board chime in and help me.

Rigger's disc brake conversion

 

[Jdc1]

You are going to need to rebuild the knuckles anyways, an option would be to swap knuckles out from the 76 into the 72 housing and save yourself from messing with the splitters.

 

[GHalll]

I believe the '76 birfs are still coarse splines and the fine splines started later. But yes I agree with JDC, you'll pull it all apart anyways so may as well swap. I did the conversion in January. Used FJ60 knuckles and parts.

 

[MakeitWrite]

Thanks for the pinion flange info and a link to that thread - Super helpful - I still can't believe how much info is here! I thought I was good at searching... but hadn't run across it.

 

[MakeitWrite]

The 76 axle is 30 splines at the hub. I think my original 72 has like 6. I'd prefer to go with the 30 so I have a better choice of locking hubs and replacement parts. I think I can swap the 76 knuckles and axles to my original housing with some grinding?? Back to the FAQ...

 

[GHalll]

Huh, there was something different about the '76, if it's not the splines then I can't remember what.

 

[3_puppies]

Huh, there was something different about the '76, if it's not the splines then I can't remember what.

76-78 use a longer birf. not terrible, just different.

 

[Rigger]

I think 76 - 78 was small pattern knuckle??

 

[3_puppies]

I think 76 - 78 was small pattern knuckle??

correct.

 

[GHalll]

76-78 use a longer birf. not terrible, just different.

10-4, my mistake..

 

[77wagon]

Also you may want to consider that you might need to replace your single diaphragm brake booster with a dual diaphragm one. I did after swapping to disc brakes. Initially they were even harder and worse than with the drum brakes until I swapped boosters.

 

[FixedIt]

I swapped with an early 80 booster and master. Works great and highly recommend

 

[65swb45]

Also you may want to consider that you might need to replace your single diaphragm brake booster with a dual diaphragm one. I did after swapping to disc brakes. Initially they were even harder and worse than with the drum brakes until I swapped boosters.

YMMV. I have done a few swaps with the early boosters that worked just fine.

 

[bikersmurf]

I'd highly recommend the disc brake swap. When I did the same back in '93, I kept my 74 Center section to keep the 4.10 ratio, swapped the knuckles/hubs/birfields, removed the residual valve from the front master cylinder, and added a brake proportioning valve.

In your case I'd clean up and swap in the complete '76 axle. Add a proportioning valve from @Racer (if you may ever do rear discs). Remove the residual valve from front circuit of your current master. And sort out the driveshaft to 3rd flange issue if they're not the same.

Possible pitfalls include:
Different ratios between the two 3rd members. (To test turn one wheel on each axle a full turn and count how many revolutions the driveshaft flange turns.)

Different flanges (Cruiser Outfitters and others have replacement flanges to sort out if they can't be swapped).

If the rear brakes lock too easily, the proportioning valve needs to reduce rear braking more.

If your brake pads don't wear fast enough, the rotors tend to wear out and calipers never move enough. To put this in perspective, my first set of 'cheap' organic pads lasted 19 years and 95,000 miles. Given they still had some life left in them, long lasting, high tech, fancy pads would have worn through the rotor and would still have life... even though the caliper would've seized because it never moved.

 

[White Stripe]

I would do rear discs as well while your at it.

 

[Rigger]

I would do rear discs as well while your at it.

X2. Rear discs are easy with the Poser brackets.

 

[bikersmurf]

If your rear brakes are good, I'd not bother with them now. However, I'd do a rear disc swap if the rears need attention.

Front brakes do roughly 80% of the braking... so rear discs only make a difference to 20% of your braking. If your rear drums are working well you'll not notice a significant improvement. If not so we'll swap to discs and move on

 

[MakeitWrite]

I'd highly recommend the disc brake swap. When I did the same back in '93, I kept my 74 Center section to keep the 4.10 ratio, swapped the knuckles/hubs/birfields, removed the residual valve from the front master cylinder, and added a brake proportioning valve.

In your case I'd clean up and swap in the complete '76 axle. Add a proportioning valve from @Racer (if you may ever do rear discs). Remove the residual valve from front circuit of your current master. And sort out the driveshaft to 3rd flange issue if they're not the same.

Possible pitfalls include:
Different ratios between the two 3rd members. (To test turn one wheel on each axle a full turn and count how many revolutions the driveshaft flange turns.)

Different flanges (Cruiser Outfitters and others have replacement flanges to sort out if they can't be swapped).

If the rear brakes lock too easily, the proportioning valve needs to reduce rear braking more.

If your brake pads don't wear fast enough, the rotors tend to wear out and calipers never move enough. To put this in perspective, my first set of 'cheap' organic pads lasted 19 years and 95,000 miles. Given they still had some life left in them, long lasting, high tech, fancy pads would have worn through the rotor and would still have life... even though the caliper would've seized because it never moved.

Appreciate the info - I know what they say about people who assume, but I did assume everything in 76 FJ40 was 4:11... Maybe a bad assumption? I just ran out to the garage and checked it as 1 complete wheel revolution is 2 and a tad extra on the pinion shaft. 2 complete wheel revolutions (360+360) equal 4 and maybe an 8th (or thereabouts measured without a protractor) turns of the pinion shaft. Does that sound right? Started checking youtube and got more confused.