40 series front disc brakes: 79+ OE vs any other conversion?

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Aug 12, 2020
Northern Arizona
Hey all, I am looking at doing some front axle work and had some questions. I have a 66 and my axle is ball and claw, converted to disc, spring under. I will not be hardcore wheeling this rig, tho obviously I don't know what it has been through up to now. Apart from some breather issues and a light seal leak, they function just fine. Parts moving forward are always a gamble, so that's a risk factor that is unknowable. EVERYONE pretty much says to just swap axles vs putting any time/money into them, for a lot of different reasons. I understand the reasons and am okay with that.

My main question is: is it worth going to a 79+ front axle that has OE discs on it or can I just find any birfield (CV) design axle and do a conversion on that? I have searched for actual reviews on the later series OE disc brakes vs their aftermarket counterparts, from a performance standpoint, and have found nothing. Since I have a dual disc conversion now, I have the dual circuit master cylinder all sorted so that's not an issue. I haven't yet researched what/if Toyota still makes for the 79+ axles, so it may be that I'd have to look for aftermarket support on those anyhow. I have a line on a 79 axle, but the owner is asking $1200, plus some time to go get it and then then rebuilding it to get it functioning as well as possible. That is easily going to hit $2K. Not my preferred use of that $ on the truck, but I can wrap my head around it. Obvious slight cost benefit to not having to buy the new disc parts, but if the rotors are worn/bad then some of that goes away. The benefit from the better knuckle and birfield design would likely be had on any later model axle choice- really anything that is not ball and claw. I read somewhere that the 76-78 knuckles and studs have weak points, but don't know exactly what was entirely meant by that. Studs, I get.

Knuckle rebuild cost is a wash really between my current 66 axle and any other. Seals will be a little more, but bearings, felts, and stud upgrade will be roughly the same. I'll need to sort out that brass bushing install, but there are some good write-ups/videos on that. This is a daily driver for me, so I definitely like the ability to rebuild the 79 axle slowly and then just swap it out when it's ready, reducing down time. Would hate to get into the front axle on mine and find my axle [seal] bearing surface is out of spec, or who knows what. Then I have to do all this with a down vehicle. Sub-optimal at best. Would love to keep downtime to a week. As a side note, I doubt I'd ever put a locker in the front on this truck so that is not influencing my decision, though it may make it easier for the next person that owns it if I ever sell. Limited slip was stock on only very rare US models, so the 79 axle isn't a benefit in that way, per se.

Anyway, I'd appreciate any input on the matter. Thanks.
Finding 79+ axle may be hard I think you could get away with a 75-78 disc brake front end. One issue also will be pinion flange but you may be able to swap them ,your driveshaft may not bolt up to 75 and later pinion flange . The small pattern disc brake knuckle is fine for cruising around. I would grab any front disc axle you can find.
Just curious still runnning the 3 spd. ? Also still using the 9mm brake line fittings or have you updated that ?
Hmm, you make some good points pbgbottle. My truck has V8, H55F 5 speed combo, done by PO. I have been working on a new rear drive shaft, so pinion flanges are at the front of my brain. Weird coincidence, after changing sizes at multiple times, but the 8-78 to 7-83 trucks have the same bolt pattern on the front pinion flanges as my current rig, so that is a nice thing.

I don't know what size brake lines I have. I know they were redone by the PO, but I haven't thought to look at the size. Having dealt with motorcycle brake masters, I know they come in all shapes, configurations, and bore sizes. I was given a huge book of receipts when I bought the truck, so research on the brakes should be fairly easy. Man-a-fre did the conversion and they are helpful when I call them.

You say coming by a 79 axle might be difficult. Are they just rare because more of the trucks are still on the road? Are they unique in any way, besides OE disc brakes? One thing that is a concern is that Toyota did use some 3:73 gears around that time. I have 4:11 now, so that would up the cost quite a bit.

Thanks for your time.
A '76 and later FJ40 axle has front disc brakes. I may have one for sale this spring here in northern New Mexico from my running FJ40 with ~67,000 original miles.

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