BE 646

[lew]

Hi Robin,
   Diff sorted,had to use a combo of new cupped thrusts and new flat wheel thrusts to get is right(flatted for size).
   Thanks for all your help
   Lew

[BEX308]

Peter,
   If you can open an AutoCAD file I can send you a drawing of the suspension dimensions I took off of 308 and the resulting instantaneous centers for various suspension positions. The analysis returns results for rack length very near what Ben Yates provides and I wound up using one of his kits on 308. The original long track rods on a worm and sector Ace are not even close to eliminating bump steer which is, of course, the position Shelby American came to when they convinced AC to change over to R&P. Tojeiro had it about right if you eyeball his original chassis design with the short rack.
   If you think of the Ace front suspension as an equal length parallel arm design you are not far off; which means the rack length has to be just about the dimension between the lower wishbone pivots and the rack height needs to keep the tie rod parallel with the lower arm to effectively minimize steering input on suspension deflection.
   Pete
   
   P.S.: As an ignorant young man I tried a rack from an MG Midget in the early 70's and it was too long; but at least the car didn't wander all over the road!

[dkp_cobra]

Thank you for all the input. I went on vacation for a quite long time but now I'm back in this theme.
   
   After reading Ben Yates comments about his conversion kit I think that the Morgan rack will not be a good solution because of the quite long steering arms. The original steering box had already too long arms.
   
   Pete, I can read Autocad files. It would be nice if you can send them to me.

[dkp_cobra]

I have no time to work on my car but other people have. The old seats:
   

   
   and the new seats:
   

   

[dkp_cobra]

The car had a r&p conversion and a new bracket for the rack was welded to the front cross beam:
   

   
   I decided to go with Ben Yates conversion kit so I removed this bracket:
   

   
   The original steering arms are extended:
   

   
   One can see the weld seam quite clear:
   

[Robin A Woolmer]

I would suggest you have the material checked as the Iron welding may be questionable, new caliper mounts are available from Gerry Hawkridge.

[minimans]

Hi I just wanted to say thank you for the wiring diagrams you posted for the wiper motor wiring, i used then today to sort out the wiring on bex740 I'm rebuilding it for a client up here at Infineon Raceway in Sonoma! Thanks again...........Paul....

[AC Bill]

Is there any way to determine the strength of the main frame tubes, if rusting on the inside was prevalent? Perhaps some sort of density measurement tool..or scanner perhaps?
   
   Certainly a tremendous amount of work involved, and "good at you", for having the determination to do it!

[ACOCArch]

Originally posted by AC Bill
   
Is there any way to determine the strength of the main frame tubes, if rusting on the inside was prevalent? Perhaps some sort of density measurement tool..or scanner perhaps?

There are a number of Non-Destructive Examination techniques which could be employed. A starting point would be a good visual inspection, using a remote camera for the internal surfaces, to look for obvious high-corrosion areas and pitting.
   A more rigorous examination would require ultra-sonics or similar for a general thickness survey of the main tubes. This could probably be be done from the external surfaces. Dye penetrant examination of welds would identify any surface-breaking cracks, and radiography around the important welds such as the suspension pivot points would give a volumetric survey of thickness and identify any non-surface breaking defects or otherwise poor welding.
   
   This would all need to be preceeded with thorough clean up including the removal of all paint and corrosion.
   
   An operation for the professional NDE specialist with good equipment calibrated on the correct material/configuration, and certificated training.
   
   Probably quite costly but, as the basis for an expensive restoration and with longevity and safety in mind, it would be worth it!

[ACOCArch]

quote:Originally posted by Robin A Woolmer
   
Peter
   I have spent a great deal of time investigating what racks are suitable

   One very important safety factor is to ensure that the articulation of track rods in the end of the rack, and ball joints at the track-rod ends, do not reach their full limit at the extremes of suspension and steering movement. If they do, stresses go through the roof and the result can be catastrophic steering or suspension failure.
   
   Although I have not seen AC Cars' design sheets for the Cobra R&P set-up, on the 3000ME there was much design work on this aspect. As a result, the 3000ME steering racks (Triumph 2000 pattern) are modified by AC, who designed, manufactured and fitted stops to limit the steering rack travel thereby preventing this problem and also wheels/tyres fouling bodywork.

[ACOCArch]

quote:Originally posted by BEX308
   ... Shelby American came to when they convinced AC to change over to R&P.

   With respect, I would be very interested to see any evidence that Shelby American had to persuade AC Cars to fit R&P steering. It is more likely, in my view, that the changes came as a result of professional engineering discussions and an agreed programme of progressive improvement.
   
   Well before the Cobra, AC Cars had significant experience of the use of R&P, even as early as their first 4-wheeled car in 1911! The general motor industry understanding of the workings of independent front suspension and different steering systems had moved on leaps and bounds since the days of the Ace design in the early 1950s, and the evidence points to AC being very well aware of any limitations in the cam and peg steering design and, perhaps more importantly, the transverse leaf suspension design, when work started on the Cobra.
   
   There are a number of factors which lead to this point of view.  In the 8-year period between Ace and early Cobra designs, AC had completed at least two new "clean sheet" road car designs. Both designs had R&P steering and much more sophisticated suspension than the Ace/Cobra. The 1959 AC Greyhound was in production well before the start of Cobra production, and the early 1960's MA200 was almost certainly designed and probably built some time before the Cobra R&P update. In the case of MA 200, the steering design was completely different, at that time an innovative solution to the inherent problems of R&P.
   
   The earliest Cobra was of course a rapidly introduced update of the much earlier mid 1950s Ace design, which was quite possibly due to be superceded when Carroll Shelby knocked on Thames Ditton's door. But, Shelby and Ford were in a hurry and changes to the old Ace design was probably the best solution for a number of reasons. For the earliest Cobras, in order to get series production underway quickly it is reasonable to assume that the minimum changes necessary were introduced, and perforce concentrated in areas other than the steering type.
   
   As can be seen from the posts on page 2 of the 'Cobra (Thames Ditton) Forum mk1 cox and cob', the later conversion of the Cobra to R&P required AC Cars to undertake a major re-design of the front suspension, front uprights, steering and brakes, and other changes to the spring tower and main frame. For series production this required modified jigs and tools, possibly including forging tools, and testing. This was a considerable amount of engineering work with significant production lead times. The changes were so extensive they formed the basis for what is euphemistically, but incorrectly, termed the 'MKII Cobra'.
   
   Chronologically, this all followed the AC Greyhound and probably the AC MA 200 design. No doubt, the Cobra re-design benefitted accordingly. Even then, the fundamental change to a more sophisticated suspension design, more akin to the Greyhound and MA 200, was not introduced to the Cobra line until AC's next major design change, the 1964 MKII coil-spring chassis used for the Cobra 427, the AC 289 Sports and, with a 6" longer wheelbase, the AC 428.
   
   One final question. Is R&P so superior? Currently there are plenty of manufacturers out there who choose not to specify that system.

[B.P.Bird]

A Tale of Stupidity: Since finishing a rebuild of 2033 I have been subject to some criticism from Ashley, number one son, to the effect that the steering and road behaviour was execrable. Whilst being entirely unreceptive to criticism I do have to admit that he was right, although I resisted any revision for 19,000 miles. Veiled hints were dropped that a conversion of the cam and peg steering to rack and pinion was essential. When I finally considered the matter properly, a month ago, I had to admit that the Cobra was a poor comparison with my dear old Aceca Bristol which followed my steering commands around both roads and tracks and never led me astray. By comparison 33 tried to leave the road and head for the nearest field every inch of the way.
   There had, I reasoned, to be an explanation and, as there was no free play anywhere in suspension or steering and the Bishop cam and peg steering box was smooth, precise and fitted with the competition brace the only possibility was an incorrect caster angle. As this is not adjustable and has to remain as Thames Ditton machined it there remained only one possibility - some pratt (me) had reversed the front uprights port to starboard. Removing a wheel I had a look: Sure enough there it was: The caster angle was negative (steering swivel inclined aft) instead of positive (inclined forward.)
   So I swopped the uprights side to side, making no other changes and, as you would expect, the car was transformed.
   I wonder how many Ace/Aceca/Cobra with cam and peg steering are out there with the front uprights reversed side to side? Or with an incorrect upright substituted for some reason - two of one side or the other on one car. Well one is never too old to learn and in my experience there is nothing wrong with the cam and peg steering system and conversions to rack and pinion may be a completely unwise departure from original specification. If the cam and peg is not working properly then there is a reason. Look for it.
   Why then is Alan Turner's rack and pinion chassis better ? Well it is not just a rack and pinion addition. He revised the whole thing: Wishbones, wishbone mounts, uprights and steering swivels, steering column and spring. Nothing is the same.
   One of the great virtues of the cam and peg system is the quick steering - 1 3/4 turns lock to lock.Even Alan Turners proper rack and pinion system had to sacrifice that.

[ACOCArch]

quote:Originally posted by B.P.Bird
   
A Tale of Stupidity:

   
   Great lesson Barry. Reminds me of one new car my father had, not an AC, which was delivered with a disc brake on one front wheel and a drum brake on the other!!
   
   I suspect that the principal consideration for many main stream manufacturers is a cost advantage offered by the simpler R&P system. I ran Vauxhall Carltons and Omegas for about 20 years. These had a form of worm and peg  with  a drop arm each side linked by a track rod across the car.  The car ran true, the feedback was great, and I was always confident I knew what was going on under the front wheels.

[dkp_cobra]

Originally posted by Robin A Woolmer
   
I would suggest you have the material checked as the Iron welding may be questionable, new caliper mounts are available from Gerry Hawkridge.
   

   Robin, thank you for making me these kind of headache [xx(]. But seriously, it is not a nice thought that your steering arms broke during driving.
   
   I removed the extentions. You can see that the fusion penetration is about 3 mm.
   

   
   Ok, time to make a nice picture. Say "fromage":
   

   
   Well, this picture is not well-focused but the x-ray picture shows clearly that the steering arms are in a perfect condition. No cappilary cracks, no inclusions.
   
   Unfortunately, the x-ray apparatus is not big enough for the frame. I will start there with a visual inspection.
   
   The restauration will take some years. So for the meantime I bought a second Aceca which is already finished:
   

[dkp_cobra]

In the meantime Ben Yates r&p conversion kit arrived. When Ben promises you a complete kit it is really a "complete" kit. See what you get for your money:
   

   
   Drilling four holes to mount the rack is an easy and fast job, but it takes some time to find the correct position:
   

   
   But at the end it looks good:
   

   
   Well, currently it has a slight toe-out [:I]