Project Mini - Reworking the Rear Suspension

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Project Mini - Rear Suspension - Part 1

Http://www.4x4wire.com/toyota/tech/mini_rearsusp1

Short Cuts

Author: Jay Kopycinski May 2000

The plan for this truck is to eventually run 35" tires for rock crawling. With that in mind we wanted a suspension that provided 4 to 5 inches of soft, flexy lift. Our plan was to use my proven Mazda spring swap which allows running long spring packs for greater travel and better articulation. More details on this type of conversion can be found on my Toyota tech page.

The hybrid spring packs we will build will be fairly flat. Lift will be added by relocating the forward mount, adding welded lift blocks to the axle housing, and swapping to longer shackles. This combo has proven to work well for desert rock crawling. In this first segment I detail how we installed the forward spring mounts, and added shock and track bar mounts.

Adding New Forward Spring Mounts

New forward spring mounts

The first step in our suspension setup was to add new forward mounts to accomodate the longer Mazda springs. Before beginning, we removed the bed from the truck to make the work a little easier. We chose to use '89-'95 model forward spring mounts for our added mounts. The advantage of these over the '85 ones, typically used in the past, is that the newer ones hang down below the frame a little less and are about 25% cheaper. The '86-'88 versions are bulkier and not as good for our purposes.

Part numbers for the various stock rear forward spring mounts are as follows:

The new mount welded on Rock ramp plates added

'85 48414-35080 (left and right sides same)

'86-'88 48414-35091 (left and right sides same)

'89-'95 48414-35120 (right side)

'89-'95 48415-35050 (left side)

After grinding the mounts and the frame areas clean, we butted the new mounts up next to the old mounts and welded them in place. To complete the welds inside the frame on the passenger side we removed the gas tank. Also, in preparation for changing over to the Mazda spring packs, we drilled the holes in the mounts to 5/8".

Once the mounts were installed we added some 3/16" thick steel plates to the forward edge of the new mounts. The plates were welded to the new mounts and to the bottom side of the frame rail. These should help with scraping over rocks and prevent hanging up on the mounts.

New Upper Shock Mounts

Front of upper shock mount

With the new spring mounts on, we moved on to adding new upper shock mounts. We will be running Rancho 9012 shocks and change the mounts so that the shocks are in line, and parallel, to the axle.

Rear of upper shock mount

As seen here, we used a piece of 2" x 1/8" wall box tube that we cut down to fit over the stock round crossmember under the bed. We added 5/8" i.d. tubing for extra strength and 3/4" hex nuts to serve as standoffs to space the upper shock eye away from the mount. Our shock eyes will mount to the rear side of the round crossmember, and will be separated about 3 to 4 inches in this configuration.

Adding Lift Blocks and Shock Mounts

The welded lift block

For this project we had a spare rear axle, which allowed us to do a lot of work without having the truck torn apart for an exteneded time. We made a few mods to this housing. We are using a '86-'95 style axle, which is 3" wider than the pre '86 rear axle. If you are using a pre '86 axle, this is good time to upgrade to the wider one. Otherwise, the inside edges of the tires will rub the frame rails with the increased articulation offered by these mods.

Part of our lift will be gained by adding 1" lift blocks to the axle housing. We took 2" x 3/16" wall box tube and sliced it in half to make our lift blocks. These pieces were welded to the top of our stock perches and small end plates were welded on to box the ends. New spring center pin holes were drilled in our blocks. However, you may want to recheck you axle positioning prior to drilling these to see if you may need to relocate your axle forward or backward a bit. We'll look at this a little more in Part 2 when we mount the springs and axle.

Taller blocks can be used, but note that blocks taller than 1" and shorter than about 3" will place the emergency brake cables where they interfere with the spring packs. If blocks taller than 1" are used, you can add extenders to the e-brake levers to help the cable clear the springs. For best results, blocks no larger than about 1.5" are safest.

New lower shock mount

We'll be using Rancho 9012 shocks that are nice and long (almost 14" of travel) and adjustable. The stock lower mounts are on the lower spring plates. In Part 2 we'll be swapping to flipped u-bolts for greater clearance, so we need to add some new shock mounts to the axle housing.

We used a piece of 2" x 3/16" wall box tubing we sliced up as shown in the photo here. We drilled a hole in this box section and used the stud included with the 9012 shocks to build our mount. The short threaded end was put through the hole in the box stock and the supplied nut tightened down. The stud was then welded to the box stock as shown in the picture here.

Track Bar Axle Mount


Track bar axle mount	Track bar mount & trussing

Closer side view of mount

We will be adding a two-link track bar to help control the axle wrap that may be present due to our relatively soft springs. The mount shown here was made from 3/16" plate. Hole separation is approximately 5" center-to-center. The two plates are spaced apart to accept Rancho poly bushings that we will be using to mount up our track bar. Hole size is 1/2".

The mount is welded to the sheetmetal axle housing and is designed so that the portion mating to the axle housing is fairly long. This is done to spread the load across as large an area as reasonable. We also added some 1" x 1/8" wall box tubing to add some supprt to the track bar mount and serve as some trussing to the axle housing.

Track Bar Front Mount

The forward end of the two-link track bar will mount up near the horse collar crossmember using a rod end and a short shackle. The rear will mount to the mount we welded to our axle housing. The track bar itself will be built during Part 2.


Forward track bar mount	Welded to crossmember	Shackle added to mount

As seen here, we made the forward track bar mount from two pieces of plate and a short piece of tube. Pick tube that will accept a shouldered poly bushing snugly. The tube we used was about 1.5" i.d. Once these three pieces were welded together, we welded the assembly to the horse collar crossmember. Note how the two plates are welded at an angle to each other so the the tube rests horizontally once the mount is welded to the frame.

With the mount welded on, we installed two poly bushings and our short shackle. The shackle was made from 1/4" flat bar and is braced in the middle with a short piece of box tube. Spacers will be needed to center and retain the rod end within the shackle. Shackle length is about 5" center-to-center. Holes were drilled in one end to match those in the poly bushings and 5/8" holes were drilled in the other end to mate to the rod end shown here. I have had fine results using standard duty 5/8" rod ends, but do not use ones with a zerk fitting. It is not necessary to grease the rod end and having the rod end drilled for the zerk makes it weaker.

Part 2......What's next?

In the next segment we'll mount up the hybrid springs and our modified axle housing. We'll add the shocks, track bar, flipped u-bolts, and may relocate the rear shackle hanger to optimize our shackle angle and spring travel. Stay tuned for the rear suspension completion.

Click here for Part II