Recently I’ve been trying to figure out how to measure bump steer, there’s a number of methods I’ve found on the web using a laser level, the issue is though that any point on the outside of the wheel describes an arc when the suspension is moved through its range.

This arc needs to be cancelled out before the underlying bump steer can be revealed.

Then I had an idea, which I doubt is original but seemed a neat way to get around the issue and still give accurate measurement without a high precision set up being required.

So what I did was set a laser level on top of the suspension upright at basically 90 degrees to the rotation of the wheel, hence when the suspension is moved up and down the laser should describe a straight line on the surface it falls on, in this case it was a piece of cardboard some 3.4m away, the further the distance the greater the applification on any bump steer present.  The vertical movement on the cardboard is not important neither is getting the laser level as its only the left – right movement that’s of interest.

So a vertical line was drawn on the card board the laser lined up on it and measurements taken at 10mm intervals from full drop to beyond full bump.

Below shows the set up, the laser doesn’t need to be fixed very well in position providing you don’t touch it during the operation.

Here’s the numbers on the wall…

Which with a bit of math turns into:

Or looks like this as a graph…

The most common opinion I can find is that zero bump steer in the ideal, what is a practical target though is not very often mentioned the closest I’ve found is this:

“For reference, current Porsche 997 GT3 cannot obtain zero bump steer. In order to do so, the rack would have to be relocated and it’s simply not possible given the packaging of the front tub section. The baseline set-up these cars use for almost all tracks seems to be 0.5 mm static toe out per side in front and 2.5-3 mm static toe in per side at the rear. Front bump steer can add typically as much as 1.5 mm per side under full bump while the rear adds roughly 0.5 mm.”

Which comes from here which leads me to think what I’ve got is not bad and I’ll wait until the final car set up before trying to tweak it to be any better than current.  What I don’t like about the current set up is that it generates roll toe-in, but is the movement enough to worry about?  I’m not sure at this stage, neither do I know what direction to move the rack in to fix the issue, I suspect its forward though.

I realized there’s a couple of things that I’d not covered in yesterdays post…

firstly I’ve bought another set of instruments, these are from a Mazda 929 roughly 1995 vintage, new old stock and an eBay bargain at $25!

Previously I’d bought a set from a BMW Mini however, cars in the 2000′s use a bus system to drive the instrumentation, which means there’s 5 pins to drive 100 functions, so unless you are an electronics guru you’re not going to be able to make them work.

however the stuff from the nineties has lot and lots pins, a set for each function, so they can be dealt with one at a time, so there is some hope of getting this to work.

Also the front top shock mounts I felt were too narrow, and as I had not got perfect alignment of the shock when it was installed I decided to widen the mounting area.

this meant slicing of the back mounting tab, and attaching a C section 17mm wide cut from 25mm SHS, to do this I used the band saw in the upright position and I also used it this way for cutting out the new mounting tabs, for these goods it was great!

Below are a couple of pics of the finished job:

It’s been close on 5 months since the last post, so I should have something to write about!

Since the last post the last set of wheels were sold through eBay, and another set were bought on a family trip we did to the USA, these ones actually look much better I think and the main thing is they fit!

The fronts are 18”x9.5” and the rears are 19”x11” which is 1” wider at the front that I wanted but without spending at lot of money for custom wheels you gets what’s on the shelf!  Also the rears have 10mm more offset in them that I was hoping for, so the clearance is tighter to the rear shocks than I’d like.  On the other hand the plan is to use a 285 rear tyre which is narrow of an 11” rim, hopefully it won’t be an issue, I guess in time I’ll find out.

From the rear…

And at the front…

Note calliper on wrong side.

Also you may notice some of the parts have been painted.  I’ve used the KBS coatings Rust Seal paint which is bizarre stuff to use, but apparently very tough once applied.  I’m not happy with the finish achieved on the parts to date, it is apparently possible to brush the stuff on and it should self level etc.  So far I’ve not been able to get the stuff to look nice, having said that it was 40c+ when I was doing this so that might have had an impact on the result.  The intention is to spray the next batch and see if the result is any better.

Next, the steering rack extensions have been completed, the hardest part of this was getting the 14×1.5mm die which took weeks to get hold of.

Then there’s been the 40 yes 40! little spacers turned up for the top wishbone inner joints and for the damper ends.  Aluminium would have been lighter but I’d did these in stainless steel out of preference.

The old square harness tubes have been removed and replaced with 38×2.5mm tube to wrap the belt around as per the previous post

I’ve also got the shifter design basically done, I went and got the parts laser cut, now I need the bearing etc to assemble it.  This is the design in place, the supporting frame work is not yet thought out.  I wanted the shift lever relatively close to the steering wheel to reduce the hand movement required.

Also laser cut were the brackets for the toe control links and some big numbers for the front of the house!

So the last progress report for the year…

As I left it last time the rear top “A” arms did not fit due to interferences with the rear shock, which again was entirely my fault due to not modelling the springs in the CAD model.

Below shows the revised version bottom V the original top…

Thankfully the wheels don’t interfere with the springs with a bit of room to spare at full droop which is a bit of luck, the wheels on the rear look pretty good…

However here is the next self inflicted stuff up.  The wheels are from a 2008 C06 model which I thought would work with the Z06 big brake kit I have, however they won’t and it would take about 20mm of wheel spacers to get them to work, which I’m not happy about so the wheels will go on eBay soon and a set of Z06 wheels will be sourced.

With the rear suspension assembled I could try the CV joint for a fit, as expected the CV Boot interferes with the shock unit and shorter boots will need to be sourced.  At least this is how I expected it to be and not a surprise!

Also on the suspension I’ve made the 16 spacers to go either side of the rod end joints on the top “A” arms (which give some castor adjustment if required) and the 8 spacers to go in the dampers to bring the bolt size down to 12mm from the delivered 15mm which I thought was a bit excessive. This leaves another 16 spacers to make to go either side of the shocks

Now having the Ultrasheild 5 point harnesses to hand which I am going to use, I’ve been able to trial fit them and finalize the 5^th mounting point.  Below you can see the floor parts of this all tacked in on the passenger side.  Now it’s done I realize I could have done away with the diagonal tubes holding the seat bracket and combined them with the tube which supports the fifth point mounting, but that can wait for the MkII car.

The next realization was the shoulder mounting points as installed don’t work with the harness I have.

I was going to use eye bolts with clip in ends, but there’s not enough room between the back of the seat and the roll frame for this and the 3 bar length adjuster, the result is the 3 bar adjuster either ends up against my neck or further down on my chest, niether of these I like the idea of.

So they’re going to be cut out and I’ll go back to the idea of a round tube welded into the roll frame which the harnesses wrap around.  The picture below show how the harness gets wrapped on the tube to prevent slipping (from Schroth)

Next was dealing with an issue that I had been aware of for some time which was that to get the engine in and out the adaptor plate and flywheel had to be removed from the engine, which long term was not going to work, so the offending tube needed to be removed and replaced with a bolt in version, for this I made the brace and brackets, welded on the brackets and then cut out the tube.

I hoped to heck that the frame would not spring too much in any direction after the tube was cut out and sure enough it moved a little as is inevitable but I’m still able to get the brace to fit.  The 6 bolts in it are overkill I suspect but it’s done now.  And the aim was to get a joint that would resist bending and get more than one or two of the bolts working in shear.

Yesterday I dropped the engine and trans back into the car, the aim being this time to get the exhaust mostly sorted and to have a go at getting the thing to fire up, just so that I know it’ll run in the end.

The original headers are fairly horrid but by swapping their sides and re orienting some flanges they now basically fit but there’s a bit of work to do to get the original cats fitted up, this is all being done to keep the engine and emission systems stock, which should help with registration.

The idea is the exhaust will look something like this when done…

The next thing I’ve started is the front steering tie rod extensions these are made from ¾” hex steel, the Ford steering rack is threaded at M14x2 and I had thought that the GM steering ends were also M14x2 but that’s wrong and now I think it’s M14x1.5, anyway the ends not being machined to final size until I know for sure.

One last thing I’d previously bought an Ozito cold cut saw well this worked well for a time until the blade went and the vise broke, so I took it back (thankfully there’s a 3 year replacement waranty on their stuff) and got my money back.  Then I replaced it with the saw below from Hare & Forbes which was basically $25 more than the Ozito device and so far I think the thing is great.  The blade that comes with it is rubbish, but good replacements are $11 each.  I wish I’d has this thing at the start of the project, oh well.

Some stuff ups and progress to report this time…

The lower A arms have hade the ball joints fitted, this was not cheap, but I know the job was done properly.  Apparently the Moog parts were sufficiently different in size that each part needed to be bored uniquely.

Now that was done it enabled the first trial fit of the suspension to the frame…

Below is the front left, which looks good to me.

With the damper out the suspension is able to drop some more so one of the worries I had on running out of travel in that direction has been overcome at least.

I would show you a picture of the other side except, I made two left hand side upper arms, Doh! At least I can count that as a spare and not scrap.

Next is the rear, which looks good except the damper interferes witht the top A arm so it can’t attach to the upright! Doh!

I had not modelled the springs in the CAD model and this has come back to bite me, sure enough now I’ve put them in there’s an interference in the model just like the real thing.  I should have known better, luckily the fix is quite easy, just to cut of the brace tubes and move them out 20mm should do fix the issue. (Note the upright is on the wrong side, the tie arm will be to the front when the right part is on there).

So moving on, I’ve also begun the steering rack support, below is the MkI version…

This one I got carried away with and fully welded off of the car, which meant it warpped like hell, then when it was offered up to the frame I realized I’d read the drawing wrong, so a few wasted hours there then.

When I’d done it I didn’t like the design anyway so back to the PC to redo the design to use angle rather than box for the vertical tubes.  Then I got lucky and found an even better piece of steel in the scrap bin of a local steel fabricators, so the MkII below was made…

Note its just tack welded, then it was tack welded into the frame…

And with the rack in place…

Or not as the case may be the CAD, predicted the rack would interfere with the two outer frame tubes, which it does and the next job is to recess and reinforce those, this I’m not worried about as the 50mm wide tube was a convienient size for construction but is excessive for the load on the tube, and I’ll be taking 15mm out of it at most.

Lastly I’ve made the required threaded inserts to support the the seat harness eye bolts.  Again these are way excessive strength and weight wise but its not that much weight in the grand scheme of things.

These started off as 40mm steel bar, the eye bolts are 7/16″ UNF this and some other parts have shatered the dream of having the car fully metric.

Over the last week I’ve had some time to do some concentrated work on the car, the main thing is finishing the suspension ‘A’ arms, all 8 are done now I’m guessing there’s roughly 8 to 10 hours work in the fab of each one.

Maybe I’m slow maybe TIG welding is that slow compared to MIG in a day I can got 2 welded together having prepped the components previously so there’s 3 or 4 hours in welding one together when all the stuffing about is taken into account.

Then there was all the lathe work for the various tubes and fittings at the corners of each one.

Next for these is to take the lowers to have them bored for the lower ball joints and get those pressed in, a good wire brushing and painting is in order as well.

I’ve also got a few other bits tacked onto the frame, below is the beam which will act as the support for the upper harness mounts, through the holes there will be top hat section bosses inserted into which the eye bolts will thread.

A recent business trip to the USA enabled me to retrieve some parts piled up at a buddies place…

These are Corvette C5 axles the inner is no use to me and the shafts were too short, so for ease of transport they were cut down to just the parts I need.  These are stupidly expensive to buy new just the bits I needed, so this was the best way to go.

These are the parking brake assemblies, they fit inside the rear discs, as the stock Corvette solution its too easy just to follow, finding the parts for sale was the hardest part.  I expect most of these get trashed when the cars are broken up.

The 1UZFE motor often came with a hydraulic pump to power the cooling fan, to ditch this another pulley bracket is required to keep the serpentine belt routing usable, the old pulley won’t fit either, so a new one of these is required.

That’s it for the moment, at least I’m home for a little while now, so hopefully some progress can be made.

By way of experiment I’ve decided to enable commenting on the blog.

To do this you will first need to register via the ‘Register’ link on the right hand side column.

If the spam or commenting in general gets out of control, I reserve the right to turn it off!

If you wish to register please use your real name i.e. the one given to you by your parents.

Also I may be slow to respond to any comments as I don’t spend all day watching this thing.

Since the last update the 4 upper suspension ‘A’ arms have been completed and one of the lower ‘A’ arms has also been completed.

Also I got the point where both seats are mounted, the drivers being adjustable which is a legal requirement here in Western Australia.

I finished fully welding together the box structures which form the base for the engine mounts in the frame and these are now tack welded into the frame also the transmission mounts are finished as well.

Since the pictures below were taken the engine and seats have been removed and the car is now back on the rotisserie to complete the welding on the engine mounts and a few other identified pieces.

Whilst the engine is out I’ll be making the stock headers fit by swapping their sides (minor tweaking required), which means between the air box and cats the engine will be entirely stock, which should help getting the thing on the road.

Beyond this 5 point harnesses have been sourced, so have C5 Corvette drive shafts and parking brake assemblies.  They’re all in the USA still at the moment which is not helping but at least they are bought.

The MDF box is the mockup for the fuel tank…

A few things happening lately have prodded me to do a quick update on the project.

After making some mods to my tube notcher I got the last of the fish-mouths cut, the most extreme angle to cut was 26.1 degrees, so then it was time to see all these notched tubes would fit together…

The next job was then to manufacture the jig for welding the A arms on, this was made using some 50 x 50 X 5 EA with 5/8″ locating  drilled in it, stick welded (horribly) to a 50 x 50 x 5 SHS, the last hole in that being drilled after the two parts were welded together so as to make sure it was in the right place.

The picutres below show some of the process of putting the first 2 A arms together and the final results…

That’s a bit of luck, it fits!

This end was cut using the tube notcher and offsetting the part to the tool.

First tube tacked on and now for the second…

The finished results.

I’ve also got onto assembling the engine mounts from the laser cut parts.  These more or less work but they’ll need adjusting as the engine mounts on the engine I think have turned out to be further apart than I had initially measured, but it should not be too much of an issue to fix the brackets.