Project Mini - Reworking the Rear Suspension

Project Mini - Rear Suspension - Part 2

Http://www.4x4wire.com/toyota/tech/mini_rearsusp2

Short Cuts

Author: Jay Kopycinski July 2000

As stated previously, we are building this truck to have a fairly soft, flexy suspension with 4 to 5 inches of lift. One option was to purchase aftermarket lift springs, custom or off-the-shelf. However, to get the lift and flex we wanted without spending a lot of cash, we chose to assemble our own hybrid packs, starting with a pair of Mazda 2WD main leaves. More details on building such hybrids can be found on my Toyota tech page.

Starting the rear suspension disassembly

Results may vary when building hybrid springs and you may have to play with the packs a little to get a combination that works well for you. Some people prefer not to go through the possible extra work to build such packs, but you can decide for yourself. I have found seasoned springs to flex well while maintaining height, even after being bent backwards repeatedly.

Setting Up the New Rear Springs

We enlarged the holes in the forward spring mounts to 5/8" and used 5/8" x 4 1/2" hex bolts and nyloc nuts to bolt on the forward eye of the Mazda main leaf. We retained the steel sleeve and stock bushing in the forward end of the spring.

We built longer shackles for the swap

The plan was to use longer rear shackles, so we made new ones from 3/8" x 2" flat stock. Center-to-center bolt hole distance was set to be 7 inches. Poly bushings were used for the rear hanger and spring eyes. A Toyota application set was used with 5/8" hex bolts and nyloc nuts. However, the o.d. of the lower set of bushings had to be reduced to fit in the Mazda spring eye. Pre-freeezing bushings allows for easy machining on a lathe using a relatively low turning speed.

We knew that to optimize our shackle angle we would need to relocate the rear shackle hangers. We used a circular saw and die grinder to remove the hangers and mounted up just a main leaf to help set up the hanger location. With the shackle hanger clamped to the frame rail, we tried several hanger locations. We settled on moving the hanger 2 1/2" forward of the stock location. This provides a shackle angle of about 30-35 degrees from vertical with the truck at rest. With the hanger location finalized, we welded the hangers back onto the frame.


Spring hanger clamped onto frame for testing	Exercising a rear main leaf with a floor jack	Spring hanger welded at new location

Building the Hybrid Rear Spring Packs

Hybrid spring pack mounted

We built five leaf packs using the following leaf stack:

Main leaf: 0.280" thick, 52" long

Second leaf: 0.280" thick, 45" long

Third leaf: 0.280" thick, 38" long

Fourth leaf: 0.280" thick, 37" long

Fifth leaf: 0.280" thick, 29" long

Mounting the Springs and Axle


Modified axle being mounted	Plate & bump stop for U-bolt flip

With the springs built, we mounted up the completed packs. Next, we attached our modified axle housing using an All Pro u-bolt flip kit. This kit eliminates the use of the stock lower spring plate and improves ground clearance. Also included in the kit are new lower shock mounts that can be welded to the axle housing. We built our own shock mounts so didn't use the All Pro ones. We did, however, save them for use on our front suspension. To retain the stock bump stops, we welded them to the top of the All Pro spring plates.

Once the housing was attached to the springs, we installed the third member, axle shafts, brake parts, and driveshaft to complete the rear driveline. Our rear driveshaft was a stock one-piece unit that bolted right back up with no required modifications.

If you have a two-piece version, you may want to consider having a one-piece replacement made. In stock form, the two parts of a two-piece driveshaft are straight in line. But, when lift is added, the two parts are no longer in line and this results in some vibration as the driveline must work through this angle. The truck may stutter a bit under acceleration and the rubber in the center bearing will wear quicker.


Checking articulation and clearance	Another articulation shot

Adding Shocks

Passenger side shock mounted

With the axle in place, we could (almost) install our shocks. We used 5/8" hex bolts and nyloc nuts on top and the Rancho supplied self-locking nuts and washers on the lower stud mount. The passenger side shock bolted right up to our new mounts.The driver side shock has to wait until our stock exhaust is rerouted up higher and more towards the driver side. We knew it would be that way.....

Adding a Two-link Track Bar

The last mod to the rear suspension was to add a two-link track bar to help control rear axle wrap and pinion angle while still allowing for full axle articulation.


Rear end of two-link track bar	Forward shackle end of bar

I have more detail on building two-link track bars on my Rear Suspension Tech page. For this bar I decided to make it a bit more versatile. All three ends are now adjusatable to allow for any reasonable future suspension changes. The forward rod end is, of course, threaded and the two rear legs use 3/4" bolt/nut combinations to allow for adjustment of those ends as well. (Note: one thing not shown in the photos are the 3/4" jam nuts we added to each leg.)

The front 5/8" rod end is secured to the forward shackle using a 5/8" hex bolt, tube spacers, and nyloc nut. The rear ends of the track bar use standard Rancho poly hourglass bushings in salvaged welded-on shock eyes. They are secured to the rear mount with 1/2" hex bolts in steel sleeves, and nyloc nuts.

Results

The rear suspension came together very well, and all at reasonable cost. It should flex well with good control, and have plenty of travel. Overall lift gained from the springs, shackles, block lift, and moved mount is about 4 1/2 inches. For now we're running a temporary third member. We'll be upgrading to lower gears and a locker in the near future.

Next month we'll show you the front straight axle swap. Don't throw away your stock rear suspension parts. We used some of ours on the front suspension. You might want to as well. Stay tuned as we proceed further.........

Thanks for reading!