Word of Warning Rear Toe in
 

Well Just spent this evening correcting the alignment of my rear hubs, dont know what made me think of it probably a recent post but I thought I would double check the rear toe in which I assume should be 0 degrees well the OS was + or - 1mm over a meter but the NS was well out not sure how it happened but I had fully welded the brakets and forgoten about them. Resolution was to remove one of the brakets and pack it out slightly.

Ahh yes that was me who also has that problem. i have looked at the dummy shuck and thats not the problem so will strip it all down this weekend and see whats up.

Do you mean that you cut off the mounting bracket, packed and rewelded?
The Lightning rod boys used to pack out the hub carrier with a washer or 2 to get the wheels square.

Yes cut off the mounting braket and packed out 2 mm. I also notice that there is a fair amount of movement on the actual carrier bushes so after this excercise I can still move the hub out of alignment in both directions. I was hoping if I align the upright proir to fully tightening all the bolts it would actually want to stay straight anyway.

This is why you have to work from the centre line and not just put the brackets on the tubes. You would be better to make a simple jig that sets the correct alignment of the brackets then bolt brackets to this then put the tubes on.
if you have one side toeing in or out it will cock the whole thing up and will handle like a sack of spuds on a skateboard.

tack a tube on the centre line, use a scriber to scribe centre line and always work from that;)

If a piece of tube used as a temp shock is pushing things on the piss then a shock absorber will be worse as it has a springy thing with loads pressure behind it....must some something else a tad wonky?....work back from the centre line of the car as well as check the track front to back...you will be surprised how much things can be different from one side to the other.

I had worked from a center line maybe something moved when I fully welded everything up but anyway I hadn't checked very well after welding as it was out. The welding a tube to the centre line is a good call pity I didnt think of it at the time.

Tack a piece inside so it sits at same level, that way you can measure without distorting tape or ideally a steel rule as tapes tell lies...mind you so can steel rules come to that:confused:

Make sure you check the track front to back on both sides of the car as any difference will mean weird handling, I have seen a locost with as much as an inch of difference in track :eek:

Don't forget that the face of the rear upright is determined by the bottom rail of the suspension cage, the bottom wishbone and the rear upright it's self. If all these things are even 0.5-1mm out any where the worse case you could end up being 3mm out very easily. With the best will in the world the rear suspension is made from fabricated parts welded together not CNC made and assembled production components.

It's called accumalative error, if you start with the basics, each item will have a tolerence on dimensions, then if it is a welded component, each weld will have a tolerence too, once you start to add fabricated items together then all these tolerances can quickly become a problem if not kept in check.

I appreciate that this is a home built car, so keep the tolerances in the real world, it would be impossible to work to 0.1mm for example.

The way round it would be to have a jig for the suspension pick up points front and rear firmly screwed to the table and make sure that these are in alignment, then build the chassis around these. After all, the purpose of the chassis is to join the important parts (suspension etc) together.

Thanks Guys, is the track width the same front and back ? guess I need to put all the front and rear suspension back on and check its all paralel, I never did this before I used the book jigs at the front and offerred up the wishbones at the back.

Yes front to back, not easy to measure on your own though. If you take a measurement from the rearmost front bracket to one on the rear do exactly the same on the other side. If its on wheels measure centre of wheel to centre of wheel...it MUST be the same CASTOR MUST be the same angle also or weirdness will set in.

My solution will be an adjustable rear suspension. Based on Rorty plans and suited to Roadster. I think that my car will be on wheels on summer. Then I can share my experience. Adde also a picture of 3D model.

Doesn't just apply to track cars it's a MUST for road use unless you like hedges;)

I think I'm going to uses washers/ shims on the rear hubs to correct mine

Puts me in mind of a Renault back in late 70s or early 80s .It was the Renault.5 Ithink. One of the rear wheels was about an inch forward of the other to accomodate some strange suspension idea. They made a selling point of it --Quirky/cute French "flair" or something like that( they were crap anyway ).:mad:

Oooh 70s-80s Renault 5

The first thing that springs to mind is .... Rust :D :D

Perhaps that was just Cornwall :o

No I can assure you it wasn't just Cornwall. That wasn't the worst rust bucket Renault did either. Anyone out there old enough to remember the Renault Dauphin?

Well it gets worse after measuring everything for several hours this evening it appears the wishbones and hubs introduce a little more error as stated by Talon and Trick earlier in this post as well so when there fitted I have the following errors

Front Track NS 0 Front Track OS +3mm
Rear Track NS +3 Rear Track 0

Not realy sure the best way to resolve seems I would need a lot of shims but at least it will go around left hand bends well:mad:

rust! thay would keep owners up at night at you could hear them rusting away on the drive :D

i think i sweped one up in the workshop once
for some reason my first boss had a thing for r4's and r5's the body roll was fantastic im sure you could get 30-35 deg then it would start to slide
unrollable tho?