Rear Suspension Geometry

Okay, lets get technical. I've finally managed to get my suspension models working well (they're easier to use-- modify and see how it affects the suspension).

My initial design, as shown in an earlier post, was to mount the A-arms to the frame inside of the upper diff mounts. This however, wouldn't allow me to get the diff in and out of the frame. So, the following designs are based on mounting the upper A-arms outside of the upper diff mounts.

The models below are kind of a chronological progression as I worked through several different modifications to address particular issues. Each time I created a new model I gave it a letter to identify it. For sanity, I have only included selected models.

For each different model, I started with it at rest, and adjusted it until the the track width was near my target (64.5" for the rear) and the camber was near zero. Then I perturbed the model in 3 different ways: bump, droop, and roll. For each of these, I measured the absolute camber, track width and roll center position. These absolute values were then used to calculate the relative changes from rest.

rD: A place to start.

This model is based on a cursory identification of where the A-arms might have to be mounted to fit around the differential. The subsequent changes in other models are based on this one.


This model is alright. But it's got a lot of negative camber change in bump. Also, in droop the roll center follows the body up high. I'm afraid this might cause a problem with jacking.



rF: Moving the inboard lower link mount outward.

The lower link was shortened to accommodate this. The upper link length and mounting has not changed from rD.


This helped with the camber change in bump, but there is now more slightly more positive camber change in roll, and much more in droop. Also the roll center has gotten really high in droop. Neither of these is very good.



rH: Moving inboard lower link mount inward.

The lower link was shortened to accommodate this. The upper link length and mounting has not changed from rD.


This hasn't done anything to address the negative camber in bump, and has slightly increased the positive camber in roll. It has managed to stabilize the roll center though.



rJ: Increasing the inclination of the upper link from rH.

This was done by moving the inboard mount downward and lengthening the link.



This has greatly reduced the camber change in roll. But it has totally messed with the camber during both bump and droop. The negative camber change is absolutely out of control in bump. Most importantly though, the roll centers are just way too high here.



rK: Going back to rD, and decreasing the inclination of the upper link.

The inboard mounting location for the upper link has been moved upward to decrease it's inclination. It is now almost parallel to the lower link.



This has reduced the camber changes in both bump and droop. This is good. It has slightly increased the camber change in roll. The roll center is also very low. This might eliminate the possibility of jacking.



rL: Backing off a bit from rK.

Okay, so rK was looking good but this model just slightly increases the inclination of the upper link a little bit (so the upper an lower links aren't quite as close to parallel).



This model isn't as good at camber change in bump, but it is a bit better at reducing camber change in roll and droop. Also, the roll centers are nice and low (except in droop where it gets a little high).



Summary

I think I'm going to with something like rK or rL since they have low roll centers, minimal track width changes, and achieve a balance between camber change in bump and roll.

Also, none of this would have been possible without Carroll Smith's awesome book Tune to Win. If you're building your own suspension, you NEED this book.

Seats!

Ain't this seat cool? It kind of dwarfs the frame right now, but I think it'll manage to look okay once the whole thing is put together. The best part is that it fits between the transmission tunnel and the outside of the frame.



The bad news is the the bracket doesn't quite fit. Oh well no big deal, I'll just take the sliders off the bracket and make my own custom mounts for them on the frame.



The bracket (for a "flat floor pan" installation) is actually for a Porsche application. Don't worry, I won't be using these. No part labeled "Porsche" is going on this car.



I've been doing a lot of maintenance on the Jeep. What we've got here is some oil (say: eeearl).

Transmission mounts

I welded up a place on the frame to mount the transmission. There will be a crossmember which will mount to these platforms and to the bottom of the transmission. Here there are going in:





Also... I got some goodies!

Rod ends for the suspension:



A fuel cell. It's the Summit $99 special. It'll hold 8 gallons:



And brackets to mount it:



Since I ordered from Summit, I got some snazzy new stickers for my bench. "Racing season is almost here!"



I also tried mocking up a rear end. I don't think this one is going to work however. I won't be able to get the diff in an out of it. I'll have to try building the A-arm mounts a little further out.

Random stuff

Okay, so I haven't made a post in a while. Here's some random stuff that I've collected that I haven't posted yet.

Here's a close up of the turbo. I took it off so I could clean it and the engine a little bit.



I thought that I'd repaint the valve covers. Here are the coil packs exposed on the engine:



Check out my cams baby.



Valve covers and gaskets:



Cam closeup:



I also figured that I might as well change the timing belt. Here's my method for removing the crankshaft pulley. It's tough, but you can kind of see the newly painted valve covers here. They're a metallic gray. Trust me, they look way better than before (an cleaner).



The important part of removing the pulley...

A tough week.

Here's what I worked on this week... Costa Rica.

A brief note about suspension design

It's complicated.

Okay, so I need to finish building the frame. But first I have to design the rear suspension so that I know where to build the inboard mounting points. And while I do that, I have to design the front suspension so that somehow they'll work together (as if I knew what I was doing).

From what I've been reading of Carroll Smith in Tune to Win, I think my major goals for the suspension are:

1. Keep the laden (outside) wheel as vertical as possible during roll (without requiring gobs of negative camber at rest).
   
2. Keep the track width as consistent as possible.
3. Also, I'd like to be able to drive around without clipping the top of every 1/2 inch pebble.
   

I'm trying to not get too wrapped up in every possible detail that could affect the outcome of the design because:

1. I really don't have any idea how certain features of the car are going to turn out... like the weight balance. And even if I did, I wouldn't know how these would interact with the suspension.
   
2. There are just too many things to worry without going totally crazy.
   

So I just want to focus on a few parameters, build something I think might work and then try it out. Hopefully it'll be adjustable enough to work out minor problems, and if it's a total catastrophe, I can just redesign it (with my wealth of knowledge gained from having tried it once already).

Here's a sample of front suspension design layout:



Wow that image looks like garbage. I think my computer found out that I hate it.

I think I'll sleep with Mr. Smith's book under my pillow tonight-- maybe I'll wake up with the answers.

Driveshaft tunnel

Okay, check it out... some actual progress. Here I am test fitting the engine in the frame again. This time I can actually mount it to the frame though.



An engine mount close-up. Everything fits together nicely.



With the engine back out again, it's time to get it back on the table and get to work.



Here's the first part of the driveshaft tunnel-- the bottom rails.



After cutting out the center of that rear cross-member, the differential can be test fitted to make sure that the driveshaft will have enough room inside the tunnel.

It's difficult to tell here, but the input to the differential is actually offset from the centerline of the car (towards the passenger-side) by about an inch. Since the output of the transmission is on the centerline, this means that the drive shaft won't run straight back to the diff-- it will have to be run at an angle. But, I consulted the oracle and he said it was okay. In fact, I shouldn't have the driveshaft running perfectly straight. Once everything is hooked up, the angle on both the front and rear u-joints should need to be about 3 degrees.



A little bit of string where the tunnel will be makes sure that everything will fit... before I start cutting any metal. I want to make the tunnel as narrow as possible so that I'll have enough room left over to fit a decent pair of seats.



The cut pieces that will make up the driveshaft tunnel. This is 3/4" 16 gauge square tubing.



The tunnel tacked into place:



Another angle:



I've run out of gas... literally. I'll need to stop at the welding store and pick up a fresh cylinder before I can fully weld this. There are a few more pieces to cut to completely finish the tunnel. Also, I need to fit the front differential mount in here some where.

The stairs are finished!

Well, here they are. This ended up taking waaaay longer than I expected, but I think that they ended up looking pretty good. Now it's time to get back to working on the 7.



Dad, Meg and Erin-- Thanks for the HD gift cards. Here's what I got, first an 18V cordless drill set:



And also this big, honkin' drill press. It's got lasers:



And, I finally got my own engine hoist. This is going to end up being a lot more convenient than borrowing one like before. Even though it's orange, it didn't come from Home Depot. Rather it came from the made-in-China-store.