521 disc upgrade - complete parts list, ball joint swap

[datsunrides]

Ok, after hours of searching, I think I've decided on how I want to upgrade my 521 to front disc brakes. Please advise if you see something that is wrong or will not work, and most importantly, tell me if I'm right!

 

83'-86' 720 will supply the following, either new or used

 

front rotors/calipers/brake hoses/spindle/porportioning valve

 

78'-79' 620 will supply the following, either new or used

 

hub/wheel bearings and seals/lower control arm/ball joints/upper cross shaft and bushings

 

Beebani's upper control arms

 

The only thing I did not clearly find is if the T/C rod needs to be changed when going to the 620 LCA. Oh, and what is the best option for a non power master cylinder? Thanks for any insight.

 

*EDIT*

 

Ok, here is what you will need to convert your kingpin 521 to ball joint disc brakes, at least the way I did. Most of the info above is correct, but I wanted to clarify since it seems the info is out there, but scattered. I don't know how many hours I spent searching for this info, and did not find everything I was looking for. Not sayin' it's not there, but I did not find it. Anyways, here goes,

 

Upper control arm: You will need Beebani's arm (or make your own)and the 78'-79' 620 cross shaft/bushings/ball joint. The 521 bolts are a smaller diameter than the 620 bolts so you need to either drill and tap for the larger bolts or do what I did and install bushings to take up the slop.

 

Lower control arm: Use 78'-79' lower arm. I did find after some head scratching that supposedly the early 78' trucks used a different control arm than the late 78'-79' arm. I am pretty sure they will interchange, but for my swap, I had the one that uses the bolt on ball joint. The early one looks to take a press in ball joint. Along with the lower arm/ball joint, you will need the torsion bar anchor arm, as the 521 will not bolt up to the 620 arm. You will also need to change the frame bushing to the 620 one as the 521 bushing is slightly shorter. As an alternate, you could shim it with washers as some others have done. Not a fun job to change the bushings. The 521 torsion bars will fit the 620 anchor arms.

 

Spindle/rotor/hub/caliper/brake hose: 83'-86' 720 This will net you the vented rotor and better caliper design.

 

T/C rod: 78'-79' 620. You will need to slightly bend it to fit the 521 frame brackets or cut off the 620 ones and transplant or cut off and relocate the 521 brackets. I put mine in a press and bent a little kick in it, about 2". Use the 620 T/C bushings and modify to fit.

 

Misc notes: 521 tie rods will bolt to the 720 spindle. I used a 7/8" 280z master cylinder and am happy with the pedal feel. You will need to bore out the firewall slightly for the master to fit and elongate the mounting holes on the master. I used the stock 521 push rod. You will need to rework your brake lines since the 280 master is a tandem and the 521 is a single. I ran a new rear channel line to the original rear brake line under the hood and connected it with a coupling. For the front channel, I ran a new line to a tee connector and then from there to the front wheels. As of right now, with minimal drive time, the brakes seem to work fine with no porportioning valve (I did not see one on the 720 I took the front brakes from), but it would not be difficult to cut in an aftermarket one if it does end up needing one. I also cut the brake pedal pad part off the 521 pedal and welded on a brake pedal pad from a automatic 510. The only thing I have not verified yet is if the 78'-79' 620 sway bar will bolt on. It probably will, but I have not confirmed this. I do know the 521 is a little short reaching the 620 lower arm. It will probably work, but it leaves the end links at a bad angle. For pics of most of the install, check my Project FTO build thread. I may have overlooked a few things so please let me know if I forgot a piece of info and I wil get it added. I hope this helps future swappers with a comprehensive list of what will be required to add ball joint type disc brakes to your 521.

 

 

 

Mark

[nismo dr]

the master you want is 7/8” or 15/16” bore from any year 280zx with vertical mounting tabs.

 

I got mine from a '78

[yello620]

Yes, the TC rods have to be changed when using the 78/79 lower arms. IIRC i had to have mine shortened as well.

 

Your list of parts should work fine, except i think that you need to use 720 hubs with 720 rotors, or 620 hubs with 620 rotors. But why use the 720 stuff when you could use HB stuff from a v-6 truck. Larger rotors, twin piston calipers.

[datsunrides]

the master you want is 7/8” or 15/16” bore from any year 280zx with vertical mounting tabs.

 

I got mine from a '78

 

Sweet. Thanks

 

 

Yes, the TC rods have to be changed when using the 78/79 lower arms. IIRC i had to have mine shortened as well.

 

Your list of parts should work fine, except i think that you need to use 720 hubs with 720 rotors, or 620 hubs with 620 rotors. But why use the 720 stuff when you could use HB stuff from a v-6 truck. Larger rotors, twin piston calipers.

 

So, if the T/C rods would need to be modified, could the 521 ones be used if modified? As for the rotors, I'm pretty sure I saw somewhere (probably a MKlotz thread) the 620 and 720 hubs are the same, except the 720 hub would need to possibly be machined to fit the wheel hole. The only reason for the 720 stuff is economics. :lol: I have located the parts cheap! I would imagine the 720 stuff is still a light year ahead of the drums! :thumbup:

 

Mark

[yello620]

The front rotors are the same part number from 78-82, for the 620 and the 720. Then the 720 rotors are the same part number from 83-86. Memory makes me think that the hubs have to match the rotor used. Let us know if you find differently.

 

It is just a lot simpler usually if all the brake parts come from one vehicle.

 

No, the 521 TC rods will not attach to the 78/79 lower control arm, different style mounting.

[datsunrides]

Does anyone have a good pic of the stock 78/79 upper and lower control arms? I looked and could not find a clear pic. I think the yard I got mine from sent 720 stuff. With that said, would a 720 lower arm work with the conversion? I am under the impression the 720 lower arm is longer?

 

Mark

[yello620]

I thought that they were the same, sorry i dont have a picture.

[datsunrides]

The reason I ask is there is a pic in the disc brake upgrade sticky and that looks different than what I have. Also, since I'm on the subject, and it may be related, does the 521 torsion bar anchor arm thingy work on the 78/79 620 lower arm? It does not work on the arm I have. May be a clue?

 

Mark

[jay520]

the 521 torsion bar anchor arm thingy

 

what thingy?

 

the back end of the torsion bar, that the bolts go through?

 

[datsunrides]

Other end, where the torsion bar connects to the lower control arm. There is a "thingy" that bolts to the control arm.

 

Mark

[jay520]

this thingy?

 

[jay520]

maybe this thingy? #52

 

[datsunrides]

Yea, #52 is the "thingy" :lol:

 

Mark

[jay520]

Now that we've gotten that straightened out. You're wondering if the 521 works on the 620? I think I remember them being slightly different. I know the other end of the torsion bar (the first picture I put up) changed with the 620s.

[datsunrides]

Yeah, I'm trying to figure out if the lower control arms (ball joint type) I bought are 620 or 720, or if it even makes a difference. I know the 521 thingy does not fit the arm I have. Here is a pic of the arm I have.

 

 

What do I have?

 

Mark

[jay520]

Your work cut out for you? Honestly, I have no idea. Hopefully, someone else can clear it up for you.

 

All I could find is this picture from lowdatsun's Project Sic Sic 620:

 

 

(It looks vaguely similar. I can't tell from that angle.)

[]2eDeYe]

You will need the splined lever arm (thingy) that comes with the 620 control arm. I can get a pic tonight if I remember.

[datsunrides]

So, is the lower arm I have for a 620 or if it's 720, will it work? Is the only difference between the 521 and 620 lever arm the shape? I.E. the torsion bars are the same spline?

 

Mark

[]2eDeYe]

I've never compared the splines.

[mklotz70]

I guess I should have subscribed to this forum awhile ago! :)

 

IIRC, the splines between the 620 and 521 are the same. We used 620 lower control arms for the ball joint mod I did for Bre620. I think the only thing posted on ratsun about that is the pics of the upper control arm build. I think the NWDE archives might have the rest of the info. Anyway....

 

As for the hub/rotor match up....you can mix and match them, but the rotor needs to match up with the spindle it's with. IIRC(been a couple of years)...the calipers are the same between the mid 720's and the late 720's and hardbodies. The rotor top hat height is different...so the difference must be handled by the mounts on the spindle. You could actually use '85 and earlier hubs...including 620 disc hubs...so that you can fit small hole rims, but you'd have to use the rotor/calipers that go with the spindle. Any of the hubs will fit any of the 620, 720, HB spindles. But, you need the rotor/caliper/spindle to match up. You could put HB hubs with 620 rotors/calipers on a 620 spindle, but you couldn't fit small center hole rims.

 

My opinion.....if you have any desire to lower your rig, go with the HB setup. You can buy lowering spindles for the HB stuff. If you go with pre-'86 720 stuff and want lowering spindles later, you'll need to buy HB rotors/calipers. As far as I'm concerned, there's no reason at all to put 620 stuff on a ball joint mod...waste of time/effort/money!

 

Time to hit the shop!!

[datsunrides]

To add to the clarifications, here is what I found so far. Evidently, the pic I posted up above of my lower control arm is indeed from a 620. There does seem to be 2 different lower arms, which led to my confusion. There is a arm that uses a press in type ball joint, which I think is for the early 78' models, and the bolt in ball joint type that seems to be for late 78' on. While this late 78' style looks just like the 720 arm, I do not know if they interchange. The 620 anchor arm has the same splines as the 521. I have not gotten to the point of installing the rear adjuster, so I don't know if the overall length will work, but it looks like it will. The 620 T/C rods will fit the 521 frame mounts with a little modification. I used a small press to put a slight kick in the bar, about 2" roughly. Also had to modify the rubber 620 bushing slightly. I'll get pics up later today. Easier to show a pic than explain. The upper contol arm cross shaft holes are bigger than the 521 bolts, so I had to source some bushings to take up the slop. If the engine were out of the truck, I would have simply drilled and re-tapped the holes for larger 620 bolts. One last possible issue is the sway bar. I may need to use a 620 one as I think the 521 will be too short to reach the 620 lower arm location. Will find that out hopefully today. Oh, and I am using a complete 85' 720 splindle/hub/rotor/caliper assembly. Not running the small hole rims so no need to use the 620 hubs.

 

Mark

[datsunrides]

Ok, pics of the installed T/C rod and the bushing setup.

 

 

 

 

 

For the bushings, I used stock replacement 620 bushings. I cut one of the bushings in half and installed it in the back as there was no way to fit the stock bushing without a whole lot of preload. I put the other half of the cut bushing up front with an uncut bushing. It was a little sloppy on the stud, so I happened to have a sleeve that matched the OD of the stud and the ID of the bushings. Obviously had to cut the front washer and bushings to clear the clevis mounting bolts. I don't know if the clevis was necessary as I could probably just put a washer there and it would have been fine.

 

Mark

[mklotz70]

The clevis is there to make sure the TC rod can't drop out of the slot under the hole.

 

If I remember right....I turned about an inch of the shoulder back on the TC rod when we did the setup for Bre's truck. I vaguely remember doing another set for someone else.....yello620 maybe? I did the same thing for my NL, but that was to get more caster :)

[hardslammed]

i'm not sure if it was mentioned but with this swap does the suspension travel change at all? basically will it affect the amount you can lower the truck without further mods...notching, etc?

 

i want to do exactly what you did but i do not want it to affect how much i can lower the truck.

 

nice informative thread BTW