Another Disc Brake Conversion Thread, but... (1 Viewer)

[Tecagist]

I know this topic has been discussed at length. However, after reading through many threads on this topic and the FAQ, I am still not clear what is the best option for a front disc brake conversion. I have come to the conclusion that it is best to source parts from either a 60 series or Mini truck but it is not entirely clear the specific parts or modifications that I would need to make in order to successfully convert my front drum brakes to disc on my 74 FJ40. Ideally, it would be great to produce a bill of materials with multiple options so that anyone interested in taking this route, could simply grab it and get started with at least sourcing the parts. Here are a few questions that are running through my mind at the moment:

1. Can I simply swap my front axle for a later model fj40 axle with stock disc brakes?
2a. If I use parts from a 60, will I need to make any modifications (welding/cutting) are can I simply buy the parts and install them?
2b. If I use parts from a 60, what are the specific parts that I need? Will I need to upgrade the brake booster? Which one will I need?

3. If I use mini truck parts what years are compatible and what specific parts will I need? Will I require a new brake booster? If so which one is recommended? Will I need to make any modifications (welding or cutting)?
4. Is there a donor option that you think is better that I am not considering?
5. Do you have any recommended resources that provide a step by step on how to perform the conversion on any of the options above?

I will summarize the responses and do my best to build a draft Bill of Materials based on feedback. If one already exists, that's even better.

Thanks!

 

[pb4ugo]

A complete 76-78 fj40 disc frt end will swap in. A later model will likely have 3.70:1 gear ratio, which can be changed out with your 3rd mrmber. Fj60 knuckles to lockouts will swap out. You'll need to use shims or something to address the 40 smaller tre's and the 60's larger steering arm tapered holes. 76 to 78 fj40 knuckles to lockouts will swap out. These are small pattern knuckles. Of coarse in all scenarios you want the birfs. Go to FAQ's and scroll to front ends and read the 1st two threads to learn knuckles and lockout differences.
Below is a pic of all you need except backing plates.

 

[POPO AGIE]

I know this topic has been discussed at length. However, after reading through many threads on this topic and the FAQ, I am still not clear what is the best option for a front disc brake conversion. I have come to the conclusion that it is best to source parts from either a 60 series or Mini truck but it is not entirely clear the specific parts or modifications that I would need to make in order to successfully convert my front drum brakes to disc on my 74 FJ40. Ideally, it would be great to produce a bill of materials with multiple options so that anyone interested in taking this route, could simply grab it and get started with at least sourcing the parts. Here are a few questions that are running through my mind at the moment:

1. Can I simply swap my front axle for a later model fj40 axle with stock disc brakes?
2a. If I use parts from a 60, will I need to make any modifications (welding/cutting) are can I simply buy the parts and install them?
2b. If I use parts from a 60, what are the specific parts that I need? Will I need to upgrade the brake booster? Which one will I need?

3. If I use mini truck parts what years are compatible and what specific parts will I need? Will I require a new brake booster? If so which one is recommended? Will I need to make any modifications (welding or cutting)?
4. Is there a donor option that you think is better that I am not considering?
5. Do you have any recommended resources that provide a step by step on how to perform the conversion on any of the options above?

I will summarize the responses and do my best to build a draft Bill of Materials based on feedback. If one already exists, that's even better.

Thanks!

You don't need a complete axle just replace the knuckles for a later disc version. Late FJ40s and FJ60 knuckles have a larger bolt pattern for the trunnion bearings. Newer spindles and then use the disc brake parts and it will work out fine.

I bought a set of FJ60 knuckles for my 78 FJ40 axle and reused my original 78 spindles. The knuckles are available used and NAPA sells reman calipers and rotors to save money.

 

[Tecagist]

A complete 76-78 fj40 disc frt end will swap in. A later model will likely have 3.70:1 gear ratio, which can be changed out with your 3rd mrmber. Fj60 knuckles to lockouts will swap out. You'll need to use shims or something to address the 40 smaller tre's and the 60's larger steering arm tapered holes. 76 to 78 fj40 knuckles to lockouts will swap out. These are small pattern knuckles. Of coarse in all scenarios you want the birfs. Go to FAQ's and scroll to front ends and read the 1st two threads to learn knuckles and lockout differences.
Below is a pic of all you need except backing plates.

View attachment 3840152

A complete 76-78 fj40 disc frt end will swap in. A later model will likely have 3.70:1 gear ratio, which can be changed out with your 3rd mrmber. Fj60 knuckles to lockouts will swap out. You'll need to use shims or something to address the 40 smaller tre's and the 60's larger steering arm tapered holes. 76 to 78 fj40 knuckles to lockouts will swap out. These are small pattern knuckles. Of coarse in all scenarios you want the birfs. Go to FAQ's and scroll to front ends and read the 1st two threads to learn knuckles and lockout differences.
Below is a pic of all you need except backing plates.

View attachment 3840152

Thank you for this overview and the photo. Could I simply use the steering Arm from my 74 Knuckles or is it best to modify FJ60 steering Arm to work with the 40? If so, what will that require?

To summarize:

Instead of the full axle, harvest everything from the Knuckle to the lockouts from a 76 through 78 FJ40 or FJ60 to include:
1. Knuckles
2. Backing Plate
3. Spindles
4. Rotors
5. Calipers
6. Birfs
7. Steering Arm???

 

[Tecagist]

You don't need a complete axle just replace the knuckles for a later disc version. Late FJ40s and FJ60 knuckles have a larger bolt pattern for the trunnion bearings. Newer spindles and then use the disc brake parts and it will work out fine.

I bought a set of FJ60 knuckles for my 78 FJ40 axle and reused my original 78 spindles. The knuckles are available used and NAPA sells reman calipers and rotors to save money.

Thank you and appreciate the tip to purchase the calipers and rotors from NAPA. I have a few clarifying questions.
1. You mentioned the larger bolt pattern on the knuckles for the trunnion bearing. What will this mean in terms of parts or modifications?
2. What are your thoughts on the steering arm - will the 74 steering arm work on the "new" Knuckles or should the steering arm that comes with the 60 or late model 40 knuckles be used?

 

[pb4ugo]

I think the drum arms are different. Cruiser Outfitters sells tre shims to adapt fj40 tres to fj60 steering arms, or you can try pressing in starter bushings in the fj60 hole.

 

[POPO AGIE]

Thank you and appreciate the tip to purchase the calipers and rotors from NAPA. I have a few clarifying questions.
1. You mentioned the larger bolt pattern on the knuckles for the trunnion bearing. What will this mean in terms of parts or modifications?
2. What are your thoughts on the steering arm - will the 74 steering arm work on the "new" Knuckles or should the steering arm that comes with the 60 or late model 40 knuckles be used?

The 4 bolt pattern is spread out on the later knuckles and the bolt size increased. The hole in the steering arm was also increased so the tie rod will be larger. This added strength. You would need steering arms with the same bolt pattern.

If you put latter than 1978 knuckles on the 74 steering arms wont fit. I did a high steer set up for mine with larger trunnions and bearings.

If you get 1978 and lower knuckles for disc brakes the 74 steering arm will work. You have options.

How you approach the upgrade do a through cleaning of the axle and clean up the knuckle ball and put a new set of seals and bearings in.

I found a pair of spindles for $45 each from Man a Fre and they go up from there. I used there spindles for the rear when I converted my FJ60 axle to full floating.

 

[cruiseroutfit]

Read here:

Tech Talk: Ultimate 40/55 Series Disc Brake Conversion Parts Thread (Work in Progress)

Skip anything that has you reusing course spline birfield outer axle and uses adapters to fit GM calipers and rotors. Like hard pass skip. These require you to re-use your course spline (low strength) outer birf joint and free-wheel hubs, both of which have no options for upgrades. If you have a...

forum.ih8mud.com

 

[diesellibrarian]

I just did exactly what you are hoping to do. I swapped my coarse spline drum brake front axle to disc brakes and fine spline birfs. I did not change the axle housing: just the knuckles out. Not sure of the year on the newer axle, but it had 4.11 gears, so pre-78 I suppose. I re-used my original tie rods, but installed new tie rod ends. The new tie rod ends fit perfectly in the large pattern steering arm, so I did not need to source a starter bushing or shim. The swap went very smoothly overall, and there were no other snafus that I can think of.

 

[diesellibrarian]

I just did exactly what you are hoping to do. I swapped my coarse spline drum brake front axle to disc brakes and fine spline birfs. I did not change the axle housing: just the knuckles out. Not sure of the year on the newer axle, but it had 4.11 gears, so pre-78 I suppose. I re-used my original tie rods, but installed new tie rod ends. The new tie rod ends fit perfectly in the large pattern steering arm, so I did not need to source a starter bushing or shim. The swap went very smoothly overall, and there were no other snafus that I can think of.

Actually: I realize that I used the tie rods that came with the disc brake axle. Not sure if that’s why I got away with not having to deal with shimming the steering arm holes.

 

[POPO AGIE]

Actually: I realize that I used the tie rods that came with the disc brake axle. Not sure if that’s why I got away with not having to deal with shimming the steering arm holes.

The steering arms tie rod hole was not enlarged until after 1978 when they also changed the steering arms with a larger bolt pattern for the trunnions.

 

[pb4ugo]

Actually: I realize that I used the tie rods that came with the disc brake axle. Not sure if that’s why I got away with not having to deal with shimming the steering arm holes.

Did your later large pattern knuckles come a later FJ40? Typically 78 and earlier are small pattern knuckles. FJ60 uses larger tie rod ends and the axle is about 3" wider.

 

[diesellibrarian]

Did your later large pattern knuckles come a later FJ40? Typically 78 and earlier are small pattern knuckles. FJ60 uses larger tie rod ends and the axle is about 3" wider.

hmmm. That must be the case. I seem to recall that the newer arms were a wider bolt pattern than the ones I took off the ‘72, but memory can be a fickle wench.

 

[POPO AGIE]

Using FJ60 knuckles does not widen the axle when used on a FJ40. My axle is wider because of the big brake kit I installed using IFS wheel hubs so that it would match the track of the rear axle which is a FJ60

 

[POPO AGIE]

Did your later large pattern knuckles come a later FJ40? Typically 78 and earlier are small pattern knuckles. FJ60 uses larger tie rod ends and the axle is about 3" wider.

That is correct.

 

[cruiseroutfit]

The steering arms tie rod hole was not enlarged until after 1978 when they also changed the steering arms with a larger bolt pattern for the trunnions.

Fwiw, the steering arm hole size stayed the same for 1979-1985 4x's, large pattern but small TRE hole, no shim or mods needed. We used to have new arms for that, they are discontinued so you use the 80-90 6x/7x arm and the shims.

Now we have these:

Steering Arm - LH - Fits 8/1980-12/1989 4x/6x & 11/1984-12/1989 7x Series - LH Applications (ST60060LH)

Steering Arm - LH - Fits 8/1980-12/1989 6x & 11/1984-12/1989 7x Series - LH Applications (ST60060RH)

cruiserteq.com

 

[Tecagist]

I just did exactly what you are hoping to do. I swapped my coarse spline drum brake front axle to disc brakes and fine spline birfs. I did not change the axle housing: just the knuckles out. Not sure of the year on the newer axle, but it had 4.11 gears, so pre-78 I suppose. I re-used my original tie rods, but installed new tie rod ends. The new tie rod ends fit perfectly in the large pattern steering arm, so I did not need to source a starter bushing or shim. The swap went very smoothly overall, and there were no other snafus that I can think of

Read here:

Tech Talk: Ultimate 40/55 Series Disc Brake Conversion Parts Thread (Work in Progress)

Skip anything that has you reusing course spline birfield outer axle and uses adapters to fit GM calipers and rotors. Like hard pass skip. These require you to re-use your course spline (low strength) outer birf joint and free-wheel hubs, both of which have no options for upgrades. If you have a...

forum.ih8mud.com

@cruiseroutfit do you ship to the US? If so, I'd love to find a full setup including 75 - 78 knuckles, rebuild kit, bearings, spindles, birfs, etc..Thank you for sharing your writeup, it was extremely helpful.

 

[Tecagist]

Fwiw, the steering arm hole size stayed the same for 1979-1985 4x's, large pattern but small TRE hole, no shim or mods needed. We used to have new arms for that, they are discontinued so you use the 80-90 6x/7x arm and the shims.

View attachment 3841186

Now we have these:

Steering Arm - LH - Fits 8/1980-12/1989 4x/6x & 11/1984-12/1989 7x Series - LH Applications (ST60060LH)

Steering Arm - LH - Fits 8/1980-12/1989 6x & 11/1984-12/1989 7x Series - LH Applications (ST60060RH)

cruiserteq.com

is it possible to simply use a larger TRE instead of a shim or will the entire TR need to be replaced?

 

[POPO AGIE]

There are a lot of options just do your research and find what works best for you.

 

[POPO AGIE]

is it possible to simply use a larger TRE instead of a shim or will the entire TR need to be replaced?

The threads on the TREs I have been told are the same for FJ4x/60x/70x.

You can mix and match the parts to work with your build.

I have been doing a lot of that on my build.