Rear Disc Brake Conversion

Joined
Jul 9, 2021
Messages
15
Location
Blairsville GA
Has any one added a rear disc brake conversion to a 71 FJ40 from Spector Off Road? I am having problems with run out on my axle and run out with the rotors mounted. Paperwork say's runout with the rotor installed should be less tan .010 (measurements are in inches). My axle had a .035 run out on the truck so I took it to a friend with a lathe and on the lathe it was .015. He refaced the axle to where there is only .002 run out but when I put the axle back on the truck it was at .012 and with the rotor mounted it is at .019.

I am not a super mechanic and haven't worked on any thing since the early 70's and am just looking for some knowledge. Is the .019 runout on the rotor too much or can I go with it? If its not ok where do I look for the problem? I have a .010 difference between the lathe and just an installed axle and another .009 when the rotor is mounted. All of the surfaces are clean and smooth and the rotor appears to mount flush on the axle face.

Thanks for any help in advance.
 
Joined
Oct 7, 2011
Messages
1,049
Location
Austin TX
I have always wondered why people spend the time, money, and effort doing a rear disc brake changeover. Probably 65% of the braking is on the front brakes. The rears are fine with drum brakes as long as your front discs are properly working. Better to spend the effort on the fronts and let the drums handle what little braking they need to do.
 

pb4ugo

SILVER Star
Joined
May 8, 2006
Messages
2,231
Location
spay-lay-wi-theepi, Ohio
Rear drum brake adjustment effects the pedal height. Up until Toyota moved the emergency brake to the rear drums, their adjustment was manual. I trail ride a lot and I was constantly adjusting rear brakes and freeing frozen wheel cylders just to adjust them. Disc are brakes basically maintenance free.
 
Joined
Jan 8, 2013
Messages
14
Location
Pleasant Hill OR.
Assemble the brakes and give it a test drive. If you still have vibration / judder when braking then take it to a shop and have them resurfaced with an on-car brake lathe. Then the rotor is surfaced to the centerline of the axle.
 
Joined
Jul 9, 2021
Messages
15
Location
Blairsville GA
Rear drum brake adjustment effects the pedal height. Up until Toyota moved the emergency brake to the rear drums, their adjustment was manual. I trail ride a lot and I was constantly adjusting rear brakes and freeing frozen wheel cylders just to adjust them. Disc are brakes basically maintenance free.
Assemble the brakes and give it a test drive. If you still have vibration / judder when braking then take it to a shop and have them resurfaced with an on-car brake lathe. Then the rotor is surfaced to the centerline of the axle.
Thats what my friend with the lathe told me as well. Found a place not too far away that does that. Thanks for the help.
 

1911

chupacabra
Joined
Aug 11, 2006
Messages
6,677
Location
Parker County, Texas
I used to think the same thing until I converted mine from front disc to full disk. The answer is no more adjustment and much better pedal feel.

Same here. Large improvement in overall braking, especially after replacing the stock master cylinder with an FZJ80 master made for four discs.
 

merbesfield

SILVER Star
Joined
Jan 28, 2005
Messages
3,307
Location
Atlanta, GA
Same here. Given the cost of drum refurbishment, it made more sense to go disc plus the added benefits of no more adjustments and leaking wheel cylinders ever again.
 

pjohnson

SILVER Star
Joined
Jan 15, 2003
Messages
2,576
Location
Idaho
With the work you have done so far, how does it drive and stop? Do the brakes operate properly? Are they dragging a lot?

If it works properly, call it done and enjoy.
 
Joined
Sep 20, 2004
Messages
2,748
Location
here
The axle flange you had surfaced on the lathe is gonna change when you mount the wheel, bolt it up and run it, that run out will keep the pads from dragging, especially if you leave the residual valves in. I left the valves in on my 1970 mc and it works fine with 4 wheel discs and I use the larger GM calipers, not the metric ones. Does your kit put the caliper bolt right behind the leaf spring ?
 
Joined
Jul 9, 2021
Messages
15
Location
Blairsville GA
The axle flange you had surfaced on the lathe is gonna change when you mount the wheel, bolt it up and run it, that run out will keep the pads from dragging, especially if you leave the residual valves in. I left the valves in on my 1970 mc and it works fine with 4 wheel discs and I use the larger GM calipers, not the metric ones. Does your kit put the caliper bolt right behind the leaf spring ?
Yes. I need to rotate the caliper and bracket up to about the 10:30 position (looking at the passenger side) and 2:30 on the other. On the SOR kit that only allows 3 bolts on the mounting bracket. Two on the top and one one the bottom. They say that should be good. Well we will see. That is with the Old Man EMU suspension.
 
Joined
Apr 12, 2019
Messages
43
Location
Los Alamos New Mexico
Same here. Large improvement in overall braking, especially after replacing the stock master cylinder with an FZJ80 master made for four discs.
Hi. I have a 1977 FJ40 with 78 power steering. I’m converting the rear drums to disks but have no idea of what kit to use or what else I need to do.
If you can help guide me through the process I’d be grateful.
Also, fronts are discs but I want to redo them too. Should I replace or rebuild the calipers and where to get them and new discs. Thanks.
Paul
 
Joined
Jul 9, 2021
Messages
15
Location
Blairsville GA
Hi. I have a 1977 FJ40 with 78 power steering. I’m converting the rear drums to disks but have no idea of what kit to use or what else I need to do.
If you can help guide me through the process I’d be grateful.
Also, fronts are discs but I want to redo them too. Should I replace or rebuild the calipers and where to get them and new discs. Thanks.
Paul
I am probably not the one to do any guiding as I am doing this for the first time. Spector off road has a kit for the rear and should bolt up easily if you have an original suspension. As for the front I would just get the part number stamped on the caliper an buy new ones. Some one else here might be able to give you more help. Good luck
 

Blue77FJ40

SILVER Star
Joined
Nov 30, 2004
Messages
2,600
Location
MD
Check the FAQ section for this common mod. You'll find listings of parts and part numbers. Poser sells full kits. Well worth doing. The only thing I did extra was replacing the bleeder screw in the GM metric calipers with Speedi Bleeder to ease my one man bleed process. While the stock toyota bleeder screw in the front stock discs has very fine thread to ease the bleeding process because air will not slip past the tight/fine threads while loosened only a 1/4 turn, the GM caliper bleed screws are coarse thread and allow air to easily pass through, making bleeding a PIA. The Speedi Bleeders stopped that. I use the Phoenix system to bleed, and their catch bottle has a nice one way valve on it to stop backflow. You can make up your own cheaper version with a Dorman one way valve from a parts store, a bottle, and tubing.
 

pjohnson

SILVER Star
Joined
Jan 15, 2003
Messages
2,576
Location
Idaho
The TSM kit is well known, with lots of success. Many builders here use it.
 
Joined
Apr 12, 2019
Messages
43
Location
Los Alamos New Mexico
I am probably not the one to do any guiding as I am doing this for the first time. Spector off road has a kit for the rear and should bolt up easily if you have an original suspension. As for the front I would just get the part number stamped on the caliper an buy new ones. Some one else here might be able to give you more help. Good luck
That’s what my sister said. She was friends with Marv and swears by them. Thanks.
 

Users who are viewing this thread

Top Bottom