Monday, September 3, 2018

fj50 disc brake conversion (chevy rotors)

I wrote a short write-up for IH8MUD on doing a disc brake conversion on FJ40's using chevy rotors.

Preface: From reading numerous threads I assume folks are going to ask why I didn't go with Toyota parts as many suggest here. Simply put, these parts were readily available and I had the tools to make the conversion happen.

I know this has been covered here before, but I thought I might share my experience of putting disc brakes (Chevy rotors and calipers) on the front of my 1975 FJ40 in case it helps others. I decided to see if I could do this conversion a bit cheaper than buying the complete JT Outfitter's kit and sourcing separate parts and doing some labor myself. I'm posting here for other who don't mind doing a little work themselves and might want to price out the parts separately.

First I started with the JT outfitter's caliper bracket. I believe others here on the forum sell this bracket as well.

I made a list of several part numbers from many of the threads here on the forums to help sort through what I would need to buy. My notes are as follows:

Front Disc Conversion:
18-4071,72 (monte carlo) fronts
Autozone Part Number: C161 
Alternate Part Number: 90125 

88-91 GM, 1/2 ton, K series 1
specifically 1990 CHEVROLET K1500 PICKUP 5.0L 305cid V8 TBI
machine center hole to 4.175”
Raybestos - 5977
Napa # 85977 for rear rotor if wanting thin rotor

I also took notes on the rear conversion in case I decide to tackle that later, but this thread will focus on the front's only.
Rear Conversion:
from a 85 monte carlo autozone #p4071 68.31 
front not rears!!!

Caliper Brackets:
brackets, rotors steve aka POSER 161.00 plus shipping

Proportioning Valve:
wilwood proportioning valve jegs# 555-63020 34.99 

Wheel Studs:
as your stock ones will be short, to short for comfort for me. DORMAN 44mm long . stock is around 38mm, part # is 610-265 10 peices to a box and they are M12-1.5X44.8MM.
dorman wheel studs, part # is 610-265 $1.99 a piece at oreilleys
Napa part number for longer studs #641-2196
Longer wheel studs - Dorman 610-414

Brake Hoses:
Raymold brake hoses - 4536825
brake hoses for calipers autozone 70770 15.99 x2
Part Number: 70770 
Alternate Part Number: H381115 

Banjo Bolt(s):
autozone #13940 4.99 x2
part number 13940

New Part Number List for Front Conversion:
Then I started cross referencing part numbers on Rock Auto so i could figure out what to purchase. I came up with the following. I'm sure many of you will be able to further cross reference these parts to find sources to be able to purchase the parts you need if you decide to go with Napa, Autozone, etc....

Rock Auto:
Caliper: A-1 CARDONE 184071 Qty:1 (18-4071) $ 35.23
Caliper: A-1 CARDONE 184072 Qty:1 (18-4072) $ 35.23
Banjo Bolt: DORMAN 484205 (13940) Hydraulic Hose to Caliper / $ 2.10 (you need if the calipers do not include these, but the calipers I ordered did come with them
Hydraulic Hose: RAYBESTOS BH36825 Qty:2 $ 19.14
Rotors: RAYBESTOS 5977R Qty:2 for $ 45.58
Brake Pad Kit: RAYBESTOS SGD154M Qty:1 $ 9.86

I already had an updated brake booster, master cylinder, and proportioning valve so I was set to start work. The parts came in and I started to mock things up to see what else would need to be done.

The caliper mount is a very nice piece. Many had commented on needing to grind the caliper to fit the bracket so I was glad to see that the caliper fit without grinding. That said, it would need to have a small area ground away to clear the birfield/axle housing, so I jumped the gun a bit when I saw the initial mockup.

The Chevy rotors need to be opened up a bit to fit the Toyota wheel spindles. I happen to have a small machine shop and since my lathe has too small of a swing to accommodate the rotors, I decided to mount the rotors in my CNC mill and machine them to size. As noted above in the rear conversion the insides need to have the center hole machined to 4.175”.

I ended up just profiling the rotors rather than pocketing to make the process quicker on the mill.

The machined rotors turned out well and fit the hub perfectly when I slid them over the hub and studs with the rotor flipped inside out when I still had the wheels mounted on the FJ and just wanted to do a quick check. EXCEPT...that once I had things torn down I discovered that the hub would need to be turned slightly to fit inside the hat of the rotor.

I tore down the hubs, dismantled the drum brakes, and popped the wheel spindle off so I could machine it. I had started by just grinding the casting a bit, but decided that since I had a lathe it would be more accurate to make them fit properly.

I mounted the spindle housing on the lathe.

Now I'm prepared to remove part of the casting.

I turned away a bit of the rough casting on the outside until the machined rotor fit nicely over the spindle housing.

As noted above the caliper had to be ground down a bit to clear the axle housing. There is a small nub that can be quickly ground down with an angle grinder and flap wheel.

And here is one of many "mock-up" shots to see if things are fitting properly.

Once the caliper was mounted and I was getting ready to connect the brake hose I discovered that the casting of the caliper needed to be ground again for the hose to be connected. I popped the caliper off quickly and hit it with the flap wheel again. It was here that I saw the true benefit of the calipers in being able to service them quickly. 

In hind sight I would like a to use a different hose. I connected this Chevy hose to my existing Toyota soft line but I wish I could find a longer single soft line to connect at the hard connection of the FJ rather than having yet another connection between the two soft lines. Having some custom hoses made would solve this problem. Sorry for not posting any photos of this. I'll try to do that soon.

I bled the brakes and "WOW" what an improvement. I wish I had done this from the very beginning. I can stop quickly and the serviceability of the disc brakes is awesome (no more adjusting drum brakes; other than my rear drum brakes). I think this kind of conversion ranks up there with power steering for certain. It makes the FJ40 much more drivable here in the mountains of NC and I have confidence in the speed in which I can bring things to a halt in a panic situation. I'm not sure if I am going to bother with the rear disc brake conversion other than to make serviceability better as the majority of the braking is done with the front brakes and I am already impressed with the ability to stop quickly. Time will tell though.

I hope this short write-up helps others who are thinking about doing the Chevy rotors on the front of their daily driver and not wheeling their FJ40 in aggressive terrain and needing the Toyota upgrade. 

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