'tool time' story: how I recreate my MK 4

[dkp_cobra]

Short update: the speedometer works now. The problem was that my VDO Siemens hall sensor has an open collector output signal. If you connect this to the hall signal input of the Smith (CAI) stepper speedometer you have to use pin 3 (red) to pull up the signal, i.e. I had to connect the battery to pin 3. Now it works (testing this I could see that my cordless screwdriver makes 130km/h [:)])

[dkp_cobra]

Now, with the "correct" air filter [:)]
   
   

[dkp_cobra]

The car was again at the paint shop for the final polishing. I think a quite nice result:
   

[dkp_cobra]

Absolutely beautiful...will you drive it when it is done?

Now, I can give you the answer: YES. This weekend we had a constancy race in our town. We had the start number 127 (there were 130 in total).
   

   
   The race was in the evening and in the night. At the end we had the second place in our group (1980 - 1984). Quite exciting if you do it for the first time.
   
   Here you can see the course: https://youtu.be/MUb9EGaqK8c   

[1984MkIV]

Here a film of another race[:D]!
   
   http://www.youtube.com/watch?v=PFIfHI6OUPw

[nikbj68]

FANTASTIC!!!!!
   
   What a joy, to have watched all your efforts, and finally see you enjoying your Cobra.
   
   Thank you for making us part of it!!!!
   
   Nik.

[dkp_cobra]

Never ending story: "MK IV strikes back" (now, without lower wishbones).
   

   
   I had a quite big bearing play in the rear wheels (no, my work on the hubs was ok). The reason is that the lower wishbone has two bushes for the arm shaft:
   

   
   These bushes are powder coated inside. So it is not a real good idea to put the wishbones into a oven for 24 hours in order to remove the old powder coat just to make them new because the bushes are damaged after that. Here you can see inside the rest of the old powder coat:
   

   
   We made new brass bushes:
   

   
   The problem is that they were made with a quite high precision but the original bushes didn't align. Now, the arm shaft doesn't pass both bushes:
   

   
   I have to extend them a little bit by hand with a reamer.

[nikbj68]

Surprised you didn`t use Phosphor Bronze rather than brass, but those original bushes are horrible! Is it possible there is some damage/distortion to the wishbone, or do you think that the holes were misaligned from manufacture?
   I hope you don`t have to do too much reaming to get the pin through!

[Robin A Woolmer]

It might be best to have undersize bushes & get them line bored to size as reaming to fit will not give full bearing surface so will wear quite quickly, i realise it will cost but the car is worth it.
   
   Robin

[dkp_cobra]

quote:Originally posted by nikbj68
   
... Is it possible there is some damage/distortion to the wishbone, or do you think that the holes were misaligned from manufacture?
   

   
   Thank you for that thought. That's what I need to wake up screaming [:)]
   I think the misalignment is "natural". We are talking about less then 0,1°. The original bushes with the powder coat inside have a difference of the id. with and without the powder coat of 0.5 mm. That's quite a lot and I think enough to push the arm shaft with some strokes through. Now with the brass it is not possible (well, it is possible but then the arm shaft cannot rotate anymore).
   
   The reason why I didn't take something better then brass is that my turner had brass at home and said to me that this is not the best but a lot better then I had before. So we will try it.
   
   The angle the arm shaft must rotate is not very big. It is nearly 18° if the wheel springs 10 cm.

[dkp_cobra]

quote:Originally posted by Robin A Woolmer
   
It might be best to have undersize bushes & get them line bored to size as reaming to fit will not give full bearing surface so will wear quite quickly, i realise it will cost but the car is worth it.
   
   Robin
   

   
   Robin,
   
   I agree that boring will be the best result but I think this is quite difficult maybe impossible. You need a laser directed drilling machine in order to target the second hole. And I don't think that one can drill with such a high precision we need for the hole.
   
   You are right reaming is not the best solution but I don't want to increase the diameter of the bush but adapt the alignment. That will increase the hole on one side but we are talking about 0,03mm. I think I only have to show the reamer to the bush and the arm shaft will fit.
   
   Let's see tomorrow then I get the reamer.

[nikbj68]

quote:Originally posted by dkp_cobra
   

quote:Originally posted by nikbj68
   ... Is it possible there is some damage/distortion to the wishbone, or do you think that the holes were misaligned from manufacture?

   
   Thank you for that thought. That's what I need to wake up screaming [:)]
   I think the misalignment is "natural". We are talking about less then 0,1°.

   Sorry, certainly didn`t mean to cause sleepless nights! I think you are probably right about the 'natural' variation, 0.1° is a pretty fine tolerance to work to, and even jigged at 0.0°, the finished part could settle to more than that! Lineboring needn`t be laser guided, over the distance we are talking about here, but if you are hand reaming, maybe try to take half from both rather than all from one hole, to reduce the amount of metal removed to the minimum. [:D]

[dkp_cobra]

It worked. As I assumed I had to show the reamer to the bushes (both, not one side) and the arm shaft passes both bushes with some gentle strokes. Look here:
   

   
   You can see the different shine. That's what I reamed away. We are talking about something about 0.01 mm. The arm shaft cannot be pushed through both bushes by hand (well, at least not by my hands) but with some gentle strokes. I cannot rotate the arm shaft by hand but using the ratchet on the grease nipple rotates the arm shaft smoothly. Now, the wheels have no clearance except the left side.
   
   On the left side also the rose joints with the right thread is damaged. I thought "well lets buy 4 new rose joints: 2 left threaded and 2 right threaded". Today 3 left threaded arrived [B)]

[nikbj68]

Were the bushes a tight fit into the arms? it`s quite possible that such a small amount to remove was actually taking out 'compression'. You might find it neccesary to reduce your lubrication intervals as well, or maybe consider fitting 'Greasomatics' during bed-in?
   

[dkp_cobra]

Impressions of a small german MK IV meeting: