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Minitruck Disc Conversion

Tech information furnished by Bob Firestine



Disc brake conversion:
Additional information

This is the account of my experience doing a front disc brake conversion on my son's 1972 FJ40 Land Cruiser. According to sources on the Land Cruiser Mailing List, the same conversion can be done to an FJ55. The basic idea is to swap everything from the steering knuckles & outward with the same parts from a straight axle ('79 thru '85) Toyota Hilux 4WD pickup or 4runner, including the steering arms and tie rod assembly.
The info I used and recommend everyone to read before beginning comes from the following two sources:
http://www.geocities.com/Baja/Dunes/6948/ (Look under "Technical")
http://www.off-road.com/~beck/tech_docs/brakes.html

In my case I decided to do it as "right" as I could, so I added brake calipers from an IFS (independent front suspension, '86 & later) Hilux and Land Cruiser '81 & later vented brake rotors. These parts were a straight bolt up with no modification necessary, but I will suggest that if possible, use a hydraulic press instead of a hammer to remove the wheel lug studs when replacing the rotor. I don't like using a hammer when more gentle means are available. When replacing the lug studs, I found that by using the lug nuts turned around backwards, the studs can be gently pulled into place as the nuts are tightened.

The two biggest problems encountered were: 1. Properly setting up the steering knuckles, and 2. Dealing with the tie rod problem. For the steering knuckles, a friend gave me an SST he built and that helped a bunch. It can also be done by trial and error without much trouble. You should replace the knuckle bearings and races since they're probably almost 30 years old by now. Warden's sells an excellent kit that contains the knuckle bearings, all necessary seals and gaskets, and the shim assortment for setting the steering knuckle preload (4-5 lbs. measured with a pull scale before installing the wiper seal assembly). Keep track of the way the shims are installed on the mini truck axles and the drum brake knuckles, if they are basically equal thickness top & bottom, you should be able to split the new shim packs and be O.K. with the axle alignment.

The tie rod situation is as follows: The steering arms on the mini truck are much beefier than the L/C and not interchangeable. The tie rod on the mini truck is weaker than the L/C, and the L/C tie rod ends do not fit the mini truck steering arms. I sent the mini truck steering arms to Warden's, where they were welded up and re-reamed to accept the L/C tie rod ends. This allows keeping the tie rod ends stock L/C so there won't be as much confusion in the future when buying steering parts. There was some discussion on the LCML about using 60 series tie rods & ends but I didn't pursue it since I had already had the steering arms modified. This avenue leads to another problem in that the mini truck steering arms narrow the steering geometry by 7/8". This means that the tie rod must be shortened by 7/16" on each end to maintain the proper range of toe-in adjustment. And while we're doing things right, the drag link should be shortened by half the tie rod length, or 7/16" in order to keep the steering symmetrical. These modifications would involve re-tapping the three trimmed ends, which would require three different taps (M17x1.5 RH or LH, depending on which end of the drag link was cut, M21x1.5 RH and M21x1.5 LH for the tie rod) which adds up to about $400.00!!

Fortunately for me, Jack Rice from Oregon on the LCML contacted me and offered to build me custom "Battleship Steering Linkage". These rods are 1-1/8' O.D. with ¼" wall thickness. The ends are secured by ½" thick jam nuts, after the wheel alignment is set. All of this was done for WAY less than the price of the taps.

The only other real hang-up was in connecting the flexible brake hoses between the L/C axle housing and the mini truck backing plates. The mini truck brake hoses needed to be modified to attach to the bracket on the L/C axle housing. I used a Dremel® type tool to machine the bottom half of the split hex-type flange to fit the round hole in the bracket. It looks like factory !

I used a band saw to cut the boomerang portion from the left mini truck steering arm. I also found a tool at Auto Zone that worked very well at disassembling the steering linkage. It's called a pulley puller, and if you plan to re-use the linkage end pieces, this tool won't tear up the rubber boots like a pickle fork type tool will.

All the mini truck parts were painted before the L/C teardown began.

I was not able to use the "pipe method" to separate the short side axles from the birfields. I had to drive the birfields off with a VBFH and LARGE drift while holding the axles pointing downward in a vice. Be sure to place the LARGE drift against the flat spots of the inner race and between the hammer. Do not strike the birfields anywhere but the flats on the inner race. Like I said before, I don't like to use hammers unless absolutely necessary. But when it is necessary, be sure to use a big enough one. For this job I used an eight-pound sledge.

I came up with a good idea to assist when re-assembling the axle halves. They are held together by snap rings that must be compressed to slide the halves together. I used a "zip strip" tie to compress the snap ring. After the birfield pushes the zip tie down and is itself compressing the snap ring, the zip tie can be cut off. Bill Jackson has a clip compressor recipe on his web page:
http://wjackson.freeservers.com/clipcompressor/birfieldclip.htm
I also installed the axles before torquing the kingpin nuts, as the torquing can compress the housing to the point that the flats on the birfield don't fit the same as they did when you initially machined them out.

Cost Breakdown

Mini truck donor parts $200.00-$350.00
New vented rotors $120.00
Rebuilt calipers with pads $90.00
Knuckle rebuild kit $125.00
Battleship Steering Linkage $125.00
New tie rod & drag link ends $80.00

Total cost after incidentals is very close to $800.00

I purchased a disc conversion parts set from T.A.P. Recycling in Sacramento. They charged $350.00 but they substituted IFS calipers at no extra cost. Be sure to get the flexible brake hoses and the hard lines from the body attachment points to the calipers. If you buy a complete mini truck front end and want to upgrade to vented rotors, just buy the IFS calipers rebuilt and turn in the straight axle calipers as cores. In this case you may have to get caliper attachment bolts for the IFS calipers, I think they may be a little longer than the bolts for the solid rotor calipers.

Addendum: I saw the knuckle rebuild kit for $110.00 at www.allprooffroad.com


Posted January 8, 2002




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