Thursday, 29 March 2007

Up to the front ... Continued

I have still been thinking about how stiff the suspension is. I hadn't really got any helpful replies from the Cobra Club forum so I decided to build up the other side. I made sure that everything that should be greased was greased and assembled as before - the result was pretty much the same. I had improved things slightly by adding another camber shim. The original donor parts had 3 shims each 1.6mm thick - total 4.8mm. For some reason I had but back four new ones each 1.0mm thick. This results in the upper wishbone arms being 0.8mm closer together and therefore distorting the bushes slightly. So I added another one which makes things 0.2mm over size - much closer. (4 to the front 1 to the back).
I am now two short for the other side so I need to order some more!

I had therefore concluded that things should be this stiff - I'll just have to slacken the nuts to check the bump steer - more on that later.

Having checked the camber of the off side hub the next thing was to check the castor. This is why I haven't fitted the front callipers yet. The hub carrier has two lugs where the brake calliper fits (see below)
These lugs have a machined flat on them so that the two flats represent a line parallel to the steering axis. So measuring the inclination of the these lugs will give the amount of castor. I did this using a homemade template I knocked up on Autocad:You can see that the off side castor is exactly 5 degrees (measure with the top wishbone horizontal). This should be OK but can only be confirmed with a test drive - so that'll have to wait then!

If this may be of any use then click on the image below for a copy - print it out and stick it on a piece of MDF and used some black cotton with a plumb bob.
So I need to order a couple more shims before I can complete the near side and check the set up there.

It's starting to look like a car now (if you squint really hard!)

Monday, 26 March 2007


Having seen Picassa Web Albums (Thanks Andy) I've moved all the photo galleries over - it is much easier to use than Fotki and does some pretty good slide shows .... so what are you waiting for?..... give it a go and right click the link below:

Up to the front

Having had to leave the rear shocks and dampers until I iron out a couple of probs I decided to start putting together the front suspension. The lower wishbone was fitted relatively easily remembering to apply copper grease to to all the faces of the polyurethane bushes. The upper wishbone was bolted into place with 1/4" camber spaces as a mean setting. The upright and hub was then fitted and the ball joint nuts torqued up. The wishbone nuts were then torqued and the camber was then checked. It was found to be 1/4 of a degree negative which was within the specified range of 0 to 1 degree negative - the important thing is that both front wheels have the same camber.

You will notice from the photos that the hub has been fitted without the brake calliper. There is a good reason for this - all will become clear with time!

One thing that did strike me was how stiff the bushes are. It took considerable force to move the suspension up and down. Polyurethane bushes don't work by twisting like normal bushes rather the wishbones move around them - the interfaces being lubricated (in this case with copper grease). I shall check out whether this is normal or not - I just expected them not to be as stiff - but then the forces I can apply compared to those exerted by the car are two completely different things!

Next jobs are to check castor and hub end float.

Something is not right?

Since posting the diagram of the rear wheel alignment I've been thinking it wasn't quite right. The total toe-in seems ok but the offsets at the front are unequal. All the measurements where taken relative to the chassis centre line with no reference to the centre of the rear axle - and on reflecton I also wasn't that happy about how I had determined the centreline of the chassis at the front - oops!

So - here we go again. First thing I did was to take a number of measurements from various points on the front suspension to the centre of the visible end of the hub driveshaft. These measurements were all to wthin less than 1mm from side to side so I can be reasonably confident that the rear axle is "square". I then set up the aluminium box section (clamped saquare across the chassis) over the rear hubs as close as possible and marked the projected faces of the hubs:
I then marked the centre of the hubs on the box section and on the chassis. I then spent some time measuring between a number of reference points to determine the physical centre of the chassis and marked that also:

Hey presto nearly 1.5mm difference!? The centre of the hubs being offset towards the off side. This actually does make some sense as there are more disc, camber and diff shims on the offside compared to the nearside (about 50 thou' or 1.27mm - this gives an centreline offset of 0.64 - the remaining 0.63 must just be normal manufacturing tolerances)).

Armed with this invaluable information I moved to the front of the chassis and carefully marked the centre point of the front crossmember relative to the wishbone pivots. I then set up the box section with the chassis centre line marks lined up. I could the project the laser forwards to measure the projected face of the hubs relative to thier marked positions on the box section from the rear - thus measuring the actual toe in of each wheel directly:

I repeated this three times - each time setting everything up from scratch! The end results are shown in the diagram below but are:

Toe in - 0.6mm total (almost equal between rear wheels).

Line of thrust 0.25mm off centre toward the nearside.


So that's the end of that saga. I thought I'd finish off the back end by fitting the shocks and dampers -however I hit two snags:

1) The lower shock shaft safety washer (jaguar item) has too big an outer diameter and fouls the adjustment valve on the damper.

2) The upper mounting bolts appear too short and when done up no thread protrudes beyond the end of the nyloc insert in the nut.

I shall have to enquire about these.

P.S. They really must make millimetres a bit larger so I can stop using a magnifying glass!

Sunday, 25 March 2007


As promised yesterday - here's a diagram of the final measurements.


Saturday, 24 March 2007

Good Day ...... Bad Day ...... Good Day

On with rear axle today. The next job was to install the drive shafts into the rear hubs. This done using loctite on the splines and remembering to insert the brass spacer ring first. The castle nut on the drive shaft needs to be tightened up to 100 lb ft torque without the whole lot turning round? - put it on the floor with long piece of wood with a hole drilled in it for one of the wheel studs.

The near-side hub and drive shaft assembly was fitted first. It was necessary to fit shims between the hub and the forked end of the wishbone to take out any play and prevent the fork ends being stressed when the pivot shaft is tightened. The next job was to fit the camber spacers before fitting the drive shaft to the disc. As a first guess I was going to put back the total amount shims present before stripping. So subtracting the brake disc shims already fitted left me with four 20 thou' camber shims.
These were placed on the studs and the drive shaft fitted - as this may be a bit of trial and error it is important not to ruin the steel lock nuts by keep tightening and un-tightening them. A handy tip is to pack out with washers and use only the normal part of the nut when tightening up prior to checking - as shown below.

The next stage was to double check the diff was dead level and then check the camber of the rear hub - GD specify zero degree camber for the rear wheels. So... using a camber gauge the result was:

.... pretty damn close - each camber shim is supposed to give approx 1/4 of a degree - so there was no more adjustment that could be done here. So that's the near-side complete. Same deal for the offside only four shims this time - camber was spot on again: So here we have a near completed rear axle:

It was now time to check the toe-in. These measurements are typically small 0.25-1.00 mm over the width of a wheel. In order to make these easier to measure I used a laser level clamped onto the face of the hub to project the line over a greater distance. You can see in the photo below that the line of the hubs is project to an aluminium box section 2.0m away from the hubs.

The hub faces are then projected backwards 0.3m lining up one laser dot with the corresponding mark from the front measurement. The distance between the other laser dot and mark being the toe-in over 2.3m - this can then be equated to a toe-in over a wheel diameter. Unfortunately my hubs appeared to toe out 0.9mm!! Now without the chassis I couldn't check the thrust line so I couldn't check whether this toe-out was due to one wheel or both - Nothing for it - time to fit the chassis and check. The photo above shows the same procedure only this time the front measurement is taken in line with the front crossmember (2.4m from hub centres) and the pivot holes for the lower wishbone were used to define the centre of the chassis.

The results were mixed:

Toe out (rather than in) was 0.9mm - however the line of thrust was only 1,5mm off centre over 2.4m - well within acceptable limits.

There was only one thing for it now - I would have to add diff shims in-situ!! So the chassis was jacked up and the suspension pulled up using ratchet straps as shown below:

So the next steps were to cut the lockwire on the pivot bracket bolts - withdraw the pivot shaft (without losing all the washers and seals) knock out the distance tube - undo the bolts - insert shims - put it all back together. Would be easy if access wasn't so difficult:
I had a chat with my friend Pythagoras who reckoned I needed 10 thou' behind the rearmost pivot bracket bolt on both sides. Shims only come in 5 and 7 thou' and 10 would be the nearest for what I needed.

A handy tip to prevent losing all the washers and seal is to insert a 3/8 extension bar into the front of the wishbone as the pivot shaft is removed.........

........ and not to remove the pivot shaft fully from the other end:

As Mr Haynes would say "re-assembly is simply a reversal of the above". Although I had worried about having to do this it only took about 3 hours from start to finish. However with plenty of bumps to the head and scraped knuckles.

Everything was jacked back down and the checking procedure run through again......

Old Pythagoras had worked his magic and the numbers read:

Toe in - 0.75mm (GD advised range 0.5 to 2.0 - although as much as 2.0 is best avoided due to increased tyre wear)

Thrust line - as before 1.5mm of centre to the off-side at 2.4m from the rear hub centres.


So I dropped everything where it was and went for sit down with Mr Carlsberg (and his 5 brothers)!

Tomorrow I may post a diagram of the final measurements.

Turned out alright in the end.

Wednesday, 21 March 2007

Rear Axle Build Up (2)

Managed to get the diff onto the floor and set about fitting the lower wishbones. A relatively straightforward task if it wasn't for the 8 washers, 8 oils seals, 8 retainers and 8 thrust washers that all had to be greased and kept in place while the pivot shaft was inserted! After a bit of patience and using a handy piece of bar as a dummy shaft the job was done!
The GD chassis carrier brackets were then fitted over the ends of the pivot shafts no problem without any forcing and the nyloc nuts fitted and torqued up. Fingers crossed I don't have to take this all apart to adjust the diff shimming - now that would be demoralising!.
Out of interest the washers for the front brake calliper bolts fit perfectly for the pivot shafts - there are no washers on the pivot shaft in Jag installation so no part number to order?

Next time hubs & driveshafts and hopefully camber adjustment..... and then checking what toe-in I've got!

Monday, 19 March 2007

Rear Axle Build Up (1)

Having plucked up the courage to trust my shimming efforts I removed the diff to the bench. It would be easier to work at a height as the caliper bolts are hard to get at and there is some fiddly lock-wiring to do.

I placed the disc shims as previously calculated and fitted the calipers and discs and rechecked the centering of the disc - both discs were within 5 thou' of centre.
When complete I lock wired the bolts and fitted the pads and pad pins remembering to apply copper grease to the pins and backs and edges of the pads. Next job was to fit the handbrake calipers. These are self adjusting efforts and whilst relatively straightforward a lot of faffing about with the brass retraction fingers was needed until the balance between the two pads was even.

So.... the result of an evenings work......
Ready to go back on the floor for the wishbones and drive shafts to be added. By the way - remember the old callipers?

Friday, 16 March 2007

Diff Progress

Sat down with a bit more patience this time and a hand full of shims. After a bit of faffing I managed to get the pivot shafts to fit nicely through the pivot brackets and chassis carriers.

After a bit of trial and error I found that all I needed was two 7 thou' shims on the offside front bolt and a bit of paint removed from the back of the nearside bracket.

So next time I'll take the diff out and start building up the rear axle with this arrangement of shims. Anyone fancy a bet on how it turns out?

Thursday, 15 March 2007

Chassis thoughts

Hmmm - Still thinking about the best way of doing this.

Spoke to Craig at GD. He was suggesting that as you will have to check it in the chassis (and adjust if necessary) anyway - build up the back axle as best you can (You can check total toe-in but not the line of thrust on the axle) - fit it - check - adjust if required. I think he's right. It is probably best to get on with it and check the end result - otherwise I'll be here for weeks thinking about it!

So as the diff is in at the minute - I shall use the chassis brackets and diff brackets to make my best estimate of shims. Build up the back end, fit it and check, and then probably adjust it!!

At least this way I'll be doing something.

For those of you confused about toe in/out thrust etc have a look at:

Wheel Alignment - A Short Course

Wednesday, 14 March 2007

Toe In - Toe Out - Shake it all about??

Right then - down to business. The first job was to fit the bare diff (with only the pivot shaft brackets fitted) to the chassis and then to part fit the lower wishbones and hubs so I can check the rear wheel toe in (hopefully not toe out) and work out what shims will be needed between the diff and pivot brackets.

I fitted the wishbones without seals and washer at this stage and fitted the hubs to the ends. The end of the wishbone was packed up to give a 2" fall representing the normal running attitude. Then with a car jack under the hub, the hub was levelled vertical as shown below (this of course after checking that the chassis was level across it's width):
Once done a laser level was clamped to the hub face (and aligned horizontal) as shown in the next photo:
A piece of wood was clamped under the front cross member and the distance from the centre of the front lower wishbone pivot to the laser was marked.
I could then determine the toe-in (although measured over 2.3m (ish). This was repeated for the other side.

End result?........... offside 8mm toe-in - nearside 22mm toe out!!!

Not right - now admittedly I had the front chassis angle that takes the pivot shaft in place but the rear one wouldn't quite fit - it appeared that I would need some weird shimming arrangement to get it to fit - which is why I thought I best check.

Now Andy states that the brackets are drilled spot on. So tomorrow I will remove the pivot brackets from the diff and check the alignment with the pivot shaft angles fitted and see what that gives. If it is ok then I can leave the angles fitted - remove the wishbones and try to fit the pivot brackets using the angles to align the pivot shafts.

Might give GD a call - see what they advise?

Tuesday, 13 March 2007


At last I'm now in possession of my chassis - rather uneventful trip but good opportunity to pester Andy with even more questions and have a good snoop around. So without more ado here it is.......

I also picked up shock absorbers, springs, fuel and brake pipes, assorted brackets, bolt pack and steering rack.
Not much else to post as I'm busy reading the build manual!

Wednesday, 7 March 2007

C Day

Andy Rang me today to tell me my chassis was ready for collection - all arranged for next Tuesday (13th) so watch this space!!!

Now the plan was to use my own car and bring the chassis back on the roof rack - all I needed was the two load bars to fit on the roof rails already on the car. However.. Volkswagen wanted £165 for two bits of metal!!! So hiring a van it is - that'll cost half the price even with fuel!

Sunday, 4 March 2007

Maybe this week?

Chassis not ready last week - so here's hoping.

There is only so much tidying of the garage you can do!