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disc brake swap 76 cj 5 what year front axle's can i use

18K views 20 replies 10 participants last post by  MikeMCJ 
#1 ·
what years can i use on my 76' cj to swap to disc on front? and how do i identify them if they are out of jeep...
 
#4 ·
They say a 77-78" d30, because it has the 6 bolt caliper bracket and thicker rotors. If you find one of these you dont have to swap the knuckles... you just have to grind a little to clear the calipers. I have been searching for one for a while and no luck where i am at.
 
#8 ·
True so far,

If you have drums, and you go to '77-'78 brakes,
You will have to change the spindle, outer axle (Stub Axle) to work with the 6 bolt calipers,
That and a hand grinder and you are in business.
Once the stub axle and correct spindle are on, you can slap on the caliper bracket, then the hub, rotor, caliper, ect.

You WILL have to clearance the steering knuckle to clear the caliper, but that is just a little grinding with a 4" angle grinder.

Rotors are usually 1-1/8" thick, and despite what everyone thinks, there really isn't any difference in breaking power between the 'Thick' & 'Thin' rotor versions.
Since they both have the same brake pad swept area on the rotor, all the larger rotor does is resist warpage better if you constantly ride the brakes.

Since both versions were on the 1/2 ton pickups, your light weight, low speed Jeep isn't going to overheat the rotors unless you are retarded on the brake pedal.

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If you go later, '79-'86, you will have to change outer (Stub) axle, Steering Knuckle, and put the later stuff on the steering knuckle.
This will be a two bolt caliper bracket version with the 7/8" rotor.

This rotor is lighter weight, and has better cooling fins so it doesn't have to be as thick & heavy to do the same job.
Same swept area on the pads as the thicker versions,
But lighter and we all know that Unsprung weight is bad, so when you can drop weight on the rotor and bracket without loosing any breaking power,
It's always a good idea.
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Around '83 or so the Dana 30 in CJ's went to a 5 bolt lockout on the hub, and that means the hub only has 5 bolts instead of the earlier 6 bolt hubs/lockouts.
You can get replacment hubs with the 6 bolt variety to solve this problem, but it's more money on the conversion.

Personally, when I'm looking for a conversion set, I look for an axle from '79 to about '82 so I get the two bolt calipers with 7/8" rotors and 6 bolt lockouts/hubs.
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You WILL need to modify your current master cylinder or replace the master cylinder with one for disc brakes.

The drum brakes use a 10-15 lb. check valve that holds back pressure against the wheel cylinder in the front wheels.
It's there to keep the brake shoes in close contact with the drums so you don't have to pump the brakes to get the vehicle to stop.

You will need to extract that check/back pressure valve from the bottom of the master cylinder so the front discs don't drag all the time.
It's in the tapered fitting that seals to the front brake line, and you can extract it by threading a metal screw into it and pulling it out...
Some brake lines won't seal after the valve is pulled out, so you may have to hunt around for a 2 lb. valve to put in that hole.

Right now the correct master cylinder for that set up is $19.95 at Advance Auto with no core charge!
I stocked up with a couple for myself, one extra for manual brakes, two for power brakes while they are so cheap!

You will have to change the 'Soft Lines' between frame mounts and brake calipers.

Most of the ones I do, I go to braided stainless lines of smaller diameter than the factory 'Fat' lines.
I also get them 3-4" longer than stock so the front axle can flex a little more without the brake lines limiting articulation.

The smaller diameter, steel braided lines don't 'Swell' as much as the fiber/rubber (Stock Type) lines do, so you get a firmer brake pedal and better pedal feel.

Since disc brakes don't take near the volume of fluid to get the same stopping power, the smaller lines are appropriate.

They also help with front/rear bias, keeping the fronts from locking before the rears apply since with 4 wheel discs you normally don't have a 'Proportioning' valve, and the smaller lines will help delay the fronts a little so the rears have a chance to keep you in a straight line when braking hard.

Anyway, just some thoughts that might help the swap...
 
#10 ·
The 'REASON' you have to change the Stub Axle is the drum brakes used a different one.
You will find a bronze or brass spacer in the drum brake spindle to stub axle junction,

Where the disc brake versions used a 'Plastic' spacer that was impregnated with graphite lubricant and doesn't need greased.
The disc brake version is thinner, so the axle doesn't need as much turned down surface on the 'Stub Axle'...

The spindles use a spacer between stub shaft and spindle.
The spacer is different on drum brakes,
And when you switch over, it won't work correctly with the disc brake spindle.
The axle will move In/Out too much.

When changing spindles, it's ALWAYS a good idea to replace the INSIDE bearing that is in next to the axle 'U' joint.
The 5 piece kit is NAPA p/n BK1 and comes with dust cover (metal) that slips on the stub axle,
'K' seal which slips on the dust cover/axle with lips facing the spindle,
Graphite lubricated 'Plastic' spacer, beveled side towards U joint,
Grease seal, lip faces IN towards the bearing to keep grease IN the bearing,
And the bearing which press fits into the spindle.

DO NOT hammer the bearing all the way to the bottom of the spindle bore!
You only need to counter sink it enough to slip the grease seal in behind it!

If you hammer on the bearing, you will deform the metal carrier down on the needle bearings and the bearing is shot, so don't think you have to bottom it out.

If you go to this thread, you will find a way to improve the water resistance of your hubs/spindles and see pictures of what I'm talking about...

LINK: http://www.jeepforum.com/forum/f8/water-proofing-ignition-axles-hubs-ect-675585/#post6395695
 
#11 · (Edited)
I have two sets of discs (1982 Wide Track "2 bolt caliper bracket" and 1978 "big brake" or "6 bolt caliper bracket"). The brake caliper on the big brake version has a larger piston area than the later caliper (w/2 bolt bracket). This will result in more clamping force even though the pads have the same surface area, so less pedal effort. While I don't expect a huge difference going with the big calipers and thick rotors, more is better here. Plus I can use my knuckles, which are in great shape. I found someone parting out a 78. Picked up the axle, a partially hacked up harness, distributor, module, and coil for $150. Same gear ratio, but my axle is in much better overall shape. I'll get around to installing the brakes and swapping over the Prestolite (with help from JH) when it warms up.

JH, can't you use the drum outer (stub) axle, the drum spindle, and the drum hub if you are using the big brake and 6 bolt calipers? Just knock the drum studs out the the hub, and install the disc studs? I have both and the only difference in hubs I see is the inner bearing is larger on the disc. IF your axle bearings, hub bearings, seals, ball joints, u-joints are all in good shape, wouldn't this be the easiest way to do it right? The only thing you'd be giving up is the larger inner hub bearing and marginally larger outer axle.

If I did want to use the disc spindle, I would have to change the outer axle, but I've seen discs mounted on drum spindles, so why bother?
 
#12 ·
I've heard the larger piston argument before,
but if you take a look at the '77-'78 master cylinder,
You will find the bore larger also.

SMALLER bore master cylinder with the larger pistons will give you MORE clamping power,
So if you went with the '79 master cylinder and the '77 brakes,
ONLY THEN would you get more clamping power out of that larger piston...

1/8" larger master cylinder bore means you have the same clamping power with larger pistons as the 'Smaller' brake calipers,
Same pad size means same swept area on the rotor,
Same pressure and same volume ratio with same swept area means...
No advantage unless you are going to overheat the he!! out of the rotors, then go with the larger/heavier ones, they take longer to heat up to 'Critical' levels where they will warp and heat check.

If you are going to overheat/ride the he!! out of the brakes, then an aftermarket set would do better than a Jeep swap.

The way it is right now...
There are more '79 to '86 vehicles available for salvage.
There is no perceivable difference in breaking power between 6 bolt caliper arrangements and 2 bolt caliper arrangements,

And the '79-'86 are lighter in weight, parts still available for them right over the counter without having to order anything in... (all common 1/2 ton Ford stuff)

With that being said,
You will notice I recommended the '79 CJ brake master cylinder for a replacement unit in either case.
Works with either type of brakes you find,
And adds some clamping power if you have the older 6 bolt calipers with larger pistons.

The issue with the '77-'78 master cylinder is they used pretty much the same master cylinder that was used with the drum brakes (different back pressure valve for the front),
And the bore is larger to supply more volume, not pressure...
Larger bore means your hydraulic leverage is reduced at the piston...

Better brake lines will deliver slightly more pressure to the caliper instead of 'Absorbing' the pressure by swelling. That will give you a little more braking power, and anyone with a lift can use longer lines anyway.

In the End, I don't think it matters which set up you lay hands on, they both work fine in a CJ.
Just that the '79 to '86 calipers are more accessible since there were so many more of them made and you can still order all the parts from the Jeep supply companies.

I find it easier to get parts for the '79-'86 set up...
Use '79-'86 two bolt knuckles, bracket, calipers, stub axle,
And if you lay hands on 5 bolt lockouts/hubs,
Switch to the 6 bolt hubs/spindle/lockouts.
'79 Master Cylinder will deliver more pressure than the earlier master cylinder,
That's if you want to play 'Mix-N-Match' to get the 'Best Of Everything' approach...
 
#14 ·
I used the 1981 Corvette master cylinder on my 1976 CJ front disk swap out(power Brakes). It has a 1 1/8 bore, so larger bore than the CJ bore. So to me that means less pedal travel for the same pressure as it is moving more fluid per unit traveled. So to me it had a much better pedal feel, I like it much better than the CJ master cyclinder feel. The Corvette master cylinder bolted up to my stock power booster and brake lines, and the brake line ports are on the correct side. Van at Vanco recommended this cylinder for this CJ Dana 30 disk swap upgrade.

I used the 77-78 big brake version as donor on my 76 CJ. I mounted the calipers to the rear of the wheel, not the front so that is maybe why I did not have to grind any clearance with the steering knuckel, but I did have to swap left and right calipers to do that. Worked out just fine and I gravity bleed them.

My 76 CJ came with drum brakes all around, but ironically the front the Dana 30 came with disk spindles and disk inner bearings, so go figure. Jeep was famous for just putting on what they had at the time, so make sure you measure things up first before your start buying parts. I bought a set of spindles I just did not need.

Jim
 
#15 · (Edited)
Well,I just started the disc brake conversion on my 74. The donor axle is a 79,and I have some of the parts I need.I will be taking pics to document it,and to help others identify the parts,and maybe someone can coach me along. Here's what I have so far. Steering knuckle with 2-bolt caliper bracket,6-bolt 7/8" rotor,and disc brake spindle,all from a 79.If I understand correctly,I'll need to swap the outer axle for one that came from a disc brake? I'll be working slowly on this,since money is tight right now,but if anyone is interested,I can post the part numbers to complete the job. Possibly make this a sticky,since JeepHammer has put so much info in here already?
 

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#19 ·
I had considered not even running stone shields,but I do have some I could use. The pic I posted is of the knuckles,caliper bracket and spindle from the 79,already mounted on the 74. Am I understanding JH's post correctly,that I need to swap the outer axle(stub shaft),also?What is the difference between the drum and disc brake stub shafts?
 
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