Project BMP

Page 10


Rear Suspension

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This weekends goal was to get the rear suspension fabricated.  I had gone round and round trying to come up with an easy to fabricate link mount that I could setup the tabs on the bench to accurately set the angles.   This is what I came up with.

This is the upper link mount for the rear axle.  The first step was to plasma cut the rough shape, next I used a hole saw to drill two openings above the heim joints.   The last step was to draw in the desired link angle and cut from the hole to the end of the part.  The next two pictures show the bench assembly of the lower link mount, same concept as the plate above just different angle and heim spacing.

Here's the lower link mount assembly for the frame.  I tack welded it to a scrap piece of tube to grind the tabs to fit.  Once they fit I lined them up with the cutout and tacked them to the plate.  Repeat for the second side, then remove it from the scrap tubing and position it on the frame. The logic for the openings above the heim joints was this: the plate is designed to mount on top of the cross member so it won't effect belly clearance.  The cross member is 1.62" thick.  The link tabs that will weld to the plate are 1.5 wide by .25" thick so they won't hang down below the cross member.   So far so good, now the heim joint is about 1.75" in diameter, this means it will hang down below the cross member if I centered the mounting hole in the link tab.  Instead, the link tab mounting hole is slightly offset, this moves the heim joint up above the bottom plane of the cross member but requires a clearance hole in the mounting plate.

We used some homemade plumbobs to position the rear axle housing and make sure it was square to the frame.  We also had to position the front axle housing to verify the wheelbase.  This is the most tedious aspect installing the suspension but you can't overlook it, measure once and then measure again just to be sure. We spent a lot of time lining things up and verifying before welding it on.  Another thing to keep in mind is that you really need all the link tabs and brackets done to start positioning components.  Pretty much everything needs to be mocked up so having one or two tabs not done means you can't properly position everything.

My friend Scott had come over to lend a hand, he was working on bending the tubes we needed for the rear axle bridge and I was working on tacking in the link mounts.  While we worked a nasty dust storm blew thru the area.  The wind was blowing buggy parts all over the garage so we called it a day.

It was really rainy on Sunday, must be a late monsoon.  The rain poured down hard enough at times I had to close the garage door.

I gusseted the link mount tower on the rear axle housing and mounted the airshocks.  The lower links are angled 20 degrees and are 33" long, the uppers are also 33" long and are angled 15" from the centerline of the chassis, both sets are made from 1.50 x .25 wall DOM and have threaded tube inserts installed at each end.  The airshocks are made by Fox and have 16" of travel.  I plan on adding a stiffening rib along the top side of the lower links just like my last rig (1 x .38 material).  This modification allowed me to run smaller links which held up well to a year and a half of use.  The old links will be cut down and used for the front suspension. I was going to go with smaller diameter upper links but couldn't find a suitable material for them when I bought my steel.

Update 11-12-04 - I have decided to sleeve the lower links with some 1.75 x .120 DOM tubing.  I made this decision after discovering my old lower links had bowed slightly inward, possibly a result of previous rolls?  Sleeving a link is not as strong as having a link with a heavy wall thickness but at this point it will have to do.  

Since the Toyota axle housings are not made from very thick material it is a good idea to spread the loads out as much as possible. As you can see, the gussets on the link tower are welded to the rear housing at several points and then terminate at a tube that we wrapped around the rear housing. I also plan on fabricating a plate that will weld to the upper link mount and extend down to the top of the housing.

Here's a picture of the lower link mounts on the frame.  I am trying a new type of heim joint this time around.  They are made by FK, #KMX12-10, they are a 3-piece, design made from alloy steel, heat-treated, and have a nylon race instead of a teflon race. They are rated for just over a 23k lb static radial load which is considerably more than the 16k lb rating of the Aurora rod ends I used previously.  Best of all the are a little cheaper and look nicer (chrome plated).  Time will tell if they work better.

The last thing I wanted to get done on Sunday was to re-mount the radiator.  I had to remove the original mounts due to an error in my measurements, I designed the front end around an axle that was 4" wider, so I wasn't going to have enough clearance between the airshock and the framerail on full droop.

The solution was to remove the radiator mounts and narrow the frame in front of the engine mounts.  I actually got the frame mods done on Friday night so I just needed to  re-mount the new radiator.   This time I angled the radiator back a bit to ensure the bottom was above the frame rails and the top was below the cross bar for protection.  This change also allows me to move the winch back another inch.

Part Numbers

The Frame Works Racing

#KMX12-10 - 5/8 x 3/4-16 Rh Heim Joint

Coleman Racing

#15589 3/4-16 Threaded Tube Insert (for 1" ID tubing)

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