Ford Capri Mk3 Track/Race Car Project

[fingers99]

There is another (less common) set up you can use for the rear suspension called a "woblink". Should give a lower roll centre than a Watts linkage (used by Arthur Mallock, who persisted with live axles when everyone else had long moved on). This does look a little like your upside down Watts linkage, but isn't quite. Details in Staniforth's books (for example).

I'd be inclined to forget bench experiments (after all, you can't be sure they're reproducing the forces you'd encounter on track) and just wander round the paddock at a race meeting where you know folk are racing Capris or cars using a similar axle. If you don't catch people at a bad time, they're usually happy to give advice.

[Will01]

Hi fingers, I have noticed a few people mention a woblink before, although I have to say I know very little about the setup. I do however have reservations about the woblink as technically you can reduce the roll centre height alot lower than you can with a watts linkage. I think really from what I have read that it is best to have the rear roll centre higher than the roll centre at the front? Although my real concern is the fact that you can have the roll centre below ground height with a woblink, this would cause more force to be applied through the mechanical setup, axle and suspension. It maybe ok if running 4 link bars, however I am sticking with the leafs for now.
It maybe deserves more looking up and I think I will get myself a copy of Alan Staniforths book.
Unfortunately there are not alot of people out there who make or at least publicise race modifications to Capri's. There is alot more info with group 4 escort rally cars running watts linkages, although most of these have the diff cover plate fixed type watts linkages that I am trying to avoid. Thanks for advice I am sure this will all take some time to sort out but I will try to keep the info coming. Will

[Will01]

So i managed to find a copy of Engineer to Win on a well known auction site this week and only paid a few quid for the book so i can't wait until it arrives. I am really enjoying reading through the books and looking at where i am in our own project. There are always little things that you overlook when building from a bare shell, but this is where the fun is. At least i enjoy it anyway.

So i have contacted a few parts suppliers recently about sizes or parts e.g. master cylinder size etc so i can build up my own bias box. This weekend should see the brake pedal reinforced ready for machining and making up new solid metal bushings to allow adjustment of the pedal ratio.
The same person who is making the modifications will also be given the job of machining up the aluminium plates which will be used to make the main structure of my pedal box. The material we have chosen is 8mm thick HE30 (6082) aluminium, although we may end up using HE15 (2014) if it prooves to be better suited to the application. Either way both of these materials are ideal for making up plate structures and are also alot lighter than equivalent size steel plate (obviously).
I have also started asking about if there is a local water cutter as at a later date i could get a few boxes made up.
I feel quite confident about this as many of the parts for the setup will be bought in from well known companies and because of its design will be very simple and effective and easy to maintain.
I still can't look at reservoir or actual master cylinder (bore) sizes as we have still not chosen exactly what brakes will be fitted. Obviously this is quite an important area to get right. Also i can't order reservoirs until i know the total volume of the piston sizes in the system. This is important to make sure i have enough fluid available to pump around the system with enough spare to prevent air inclusion from hard cornering and braking etc from fluid slosh.

[Will01]

So i only got a little bit of work done on the weekend and decided to take a rest from cutting and treating rust. Instead i had a look at the spare brake pedal i had off my old White Capri.
As mentioned earlier i decided to strengthen the sides of the brake pedal in order to allow more holes to be drilled in order to change the pedal ratio.
I used 3mm thick plate to match the thickness of the material the brake pedal is already made out of. First job was to remove the nylon bushes and measure everything up.
The brake pedal as standard in a Mk3 Capri (most likely the same in Mk2's also) is a pressed component and has another strengthening piece tack welded in the bottom of the pressing. Before i could put plates down the side to reinforce the pedal i first had to grind these tack welds flush, this was done very carefully with a grinder and a metal file.
The rest of the brake pedal at this time was then cleaned back of all paint to allow plates to be welded in as clean as possible.
Then using cardboard i made up some templates for the strengthening. This was then measured out on the plate and cut out with a hacksaw and finished with a file. Because the tops of the plate and sides of the pedal would be flush i decided to chamfer the top edge to allow the weld to penetrate into the material and leave a good finish. The rest of the plate was clamped and gradually welded around completely, being very careful not to damage the brake pivot mounting holes.
After welding the welds were ground back where needed so it looks neater and gets rid of unwanted sharp edges etc, then the whole pedal was again stripped back of paint and disclouration from welding in order to be primed up ready for paint. Finally primer was applied, this is just to stop the pedal rusting up whilst i send it off to get machined for new mounting holes and bushes.

Next job was to measure up the mounting point of the original brake servo. In the Capri the servo is mounted to a couple of metal brackets. In time i will strengthen these brackets up. The holes were measured to be equally spaced in a square pattern of 90mm. A few other measurements were taken of other nearby components to make sure the bias box doesn't get in the way of other much needed parts.
I will update more on this later once a design has been mocked up and priced in the chosen material.

[Will01]

So i have carried on trying out ideas of my Bias Box, i thought i would post a picture of the original servo mounting location on the Capri.
On the car this is located on the right hand side of the vehicle (RHD car) mounted on the bulkhead near the top, also at an angle. See pictures.
After having a good look, i may make some new brackets so as to mount the bias box horizontal-ish. Either way however the bias box i have designed will fit nicely.
The first design is just a prototype to see how everything would roughly fit together, after some basic FEA simulations there are many areas which could do with some improvement. However as it stands the original design looks to work ok. The design is very similar to others on the market, but to be honest i think i can manufacture for a little less money, plus it would be custom to my vehicle. Also i am using this car to practice what i have learnt over the years and put it into practice. All good fun and learning.
I spent quite a few weeks looking online for information on Brake Pedal forces, there was a little bit of information from Racing Driver forums which were saying about the maximum pedal effort an average Man or Woman could achieve, this was in the range of 80-150lbs force (350 - 670N). I also found alot of information in the form of old USAF papers on optimum pedal layout for foot controls in aircraft, and also looked into the change the drivers knee angle would influence on the maximum and continuous effort a Pilot could achieve.
This was very informative reading and has helped me to calculate basic forces that may be transmitted through the Bias Box.
I have updated my previous excel spreadsheet to include forces i have calculated from Pedal Ratio, i have to say i am a little shocked! A few years back i did a very similar exercise at university where i had to sit in a fixed chair and press on a load cell, at the moment i cannot remember the figure but i did write it down. It would be interesting to see how this force compares to what i have found from my research. It is a little shocking as i thought i may get to a maximum of ~3500N acting from pedal ratio, but in actual fact on max pedal effort it could be ~4700N, this is why i really need to check back if these figures are representative of me.

[Will01]

After carrying out simple FEA analysis i have found that i need more detail of yield strength of materials used in the bias box because the forces are soo high.
I have been looking into the maximum recommended bending strength of different Aluminimum grade plates.
At the moment it looks like the 2014 T6 (HE15) heat treated plate is the better option as it has a higher yield strength ~414MPa compared to 6082 T6 (HE30) heat treated plate which is ~250MPa. It is well known that 2014 is normally used to replace steel construction components due to its high yield strength. Plue the bonus is that this material is normally cheaper.
With this information i can also calculate a safety factor once the FEA analysis is complete.
From the first model as seen in pictures above the displacement of the aluminium bulkhead is about 0.12mm at maximum 4700N force, with the Von Mises stresses that are seen in the model are about 103MPa. This gives about ~2.4 safety factor with HE30 & ~4 safety factor with HE15 aluminium plate.

I reckon the weight of this first prototype bias box is in the region of 4.5kg, although with these first calculations complete, i will be modifying the box to use less material and increase the strength. I imagine that i will have more deflection of the actual vehicle bulkhead when braking than the bias box deflecting, but there are areas which can be greatly improved. Due to plans of engine choice still undecided i think it is sensible to make this Bias Box as compact as possible.

[fingers99]

From memory, the blue book specifies 6mm aluminium alloy for seat rails, so 8mm should be well over what's required for a pedal box.

Of course, although there's a weight issue, you could cheerfully weld up a steel one, without worrying about further calculations.

I think I'd be inclined to go for aluminium alloy pedals in a steel box, but.................

[Will01]

I think 8mm is good although i have seen that others on the market are 5-6mm thickness?
For my application i don't think 5-6mm is good enough from the forces i have calculated, maybe i have calculated with too much force?
Anyway in a weird type of way i actually like calculating and designing these sorts of things and its a good bit of fun, which is what its all about.
I made some more improvements last night and this lunchtime with making the unit more compact and have found that i have reduced the stresses to around 80MPa which gives a higher level of safety. I did this by simply moving the strengthening rods closer to each other and the lower ones inside the fixed mounting bolt position. I have added a picture so you can see clearer.
The weight hasn't reduced that much only ~250 grams, plus the manufacturing shape seems simpler so should help reduce cost also.
Before i go any further i now need to get hold of the balance bar and master cylinders etc and model them up also and then refine the design to suit if required.

[Will01]

So today the Brake pedal went of for modification to drill in extra holes for varying pedal ratio. At the same time i also put together a quick CAD drawing of bushes for brake pin to be made out of brass or bronze. I am leaving this to the Engineering shop to advise what is best.

I have also shared with him my plans for the Bias Box and we have now started to get the ball rolling to cost it all up. Balance bar and adjuster etc will be in the post, so as soon as these arrive i will model them up and check my Bias Box assembly.

As a next step for the Capri shell, i have strated to look into ordering 2mm thick-ish mild steel sheet which i can make up Gussets out of for strengthening the shell. Also i will be using this aswell to make up a bracket for a hydraulic cylinder to connect to the standard handbrake. I not sure i really will need this, but since i am completely building a brake system from scratch i may aswell add as they are cheap enough to make up.

[TomLouwrier]

hi Will,

Nice bit of engineering going on there!
I've come across the same question you have: how much force on a brake pedal? My assumption was that it would be around the same value as when I'd be standing on one leg, ie giving it all I've got. For me that would be a solid 100kg's on the foot-end of the pedal. Of course that is not entirely correct, since we're not actually standing on the pedal and so pedal force <> gravity. On the other hand: most people can generate more or less enough force to do a knee bend on one leg, thus giving their maximum capacity for stamping on the brakes. Being horizontal and jamming yourself between seat and pedal wouldn't increase the force in your leg.

As for choosing a suitable material for your pedal box: yes, alloy is about 3x lighter than steel but most qualities have about 3x less strength. Of course you already did your homework and came up with the 2014, but still.
I've found alloy is good for situation where stiffness is more important than strength given the same weight. Air planes are all about that with load carrying skins and quite slim innards (spars etc).
This means for compact and force-bound applications it is often easier and cheaper to use good old steel. It's much better for fatigue resistance too.
But prove me wrong by all means. I'd love to see your FEA results!

regards
Tom

[Will01]

Hi Tom thanks for your input. I like your thought process and i completely agree that 100kg's is a good number. I myself weigh about 81kg's and can easily support and squat on one leg and lift myself back up again, but then again i can only do this a few times without falling over. I think i will re-visit my numbers and re-calculate just for my own piece of mind.
As for the FEA results i will try and upload some simple FEA models and some basic figures, i don't really want to upload FEA animated simulations as they would be quite large files. Do you have much experience of FEA? I myself have only had a brief introduction and little experience of using FEA, at uni we used IDEAS to create mesh and simulate forces on components. However i am currently using Inventor which is a completely different program, if actually easier to use.
As said before i like this sort of thing so its keeping me occupied in the downtime from the garage.
Will be updating again soon after i have some feedback form the engineering shop.

[TomLouwrier]

Hi Will,

Just out of curiosity I did a little experiment: took the wife's scales and set myself up between 2 walls. Then tried to push one foot on the scales as hard a I could, mimicking a load cell. To my surprise I got to just below the 100kg's though it certainly felt like a lot more effort compared to standing on one leg and doing a knee bend.
Obviously I need to get back to the gym again....

My experience with FEA is very limited and old. I moved away from full time engineering some 15 years ago, so I missed most developments as far as 'hands on' is concerned. Same goes for CAD: I was there when 3D entered the office (actually I was the one who pulled it in) and worked with it for about half a year, then my career took a turn towards IT and management (yes, became a suit'n'tie...)

have a good one
Tom

[Will01]

Thanks for the info Tom that is interesting. I need to find some scales and try it myself.
On another note, I decided to start cleaning up the interior foot well inner sill areas today. To my surprise, I shouldn't be but I found alot more rusty holes where the inner sill joins the floor! I thought I was finished with this. In the end I cut out what I could and welded some patches in, they dont look pretty, but are nice and strong.
Anyway I also made a start with making up strengthening gussets out or card to get the correct shape. Just need some thicker mild steel sheet now. Hopefully tomorrow I will get lot more measurements taken and make up a few more models. I may even spend a bit more time stripping the paint inside the car ready for primer.

[Will01]

So as mentioned i did find more welding to carry out on the weekend, i don't want to say the welding is finished now, but i am hoping.
Anyway after this was done i did make a start cleaning up and measuring parts on the shell.
The front leaf spring mount bolt has access panels underneath, since these always rust away and allow crud into the sill, i decided to make little closing panels which will be screwed into place. Removable if required.
While i was at it i also looked at removing the cruddy old rubber bump stops, and try to release the plates from the shell. In the end i had to use mole grips, but with a bit of patience i got the bolts out. I will clean these plates up and modify them to allow polybush bumpstops to be fixed in position. I also found a few stainless fixings in the garage which could be used to fix back in place. I have made sure the threads are greased up as the difference in Stainless to Mild steel can cause garring(think thats the word) and i don't want the fasteners to weld themselves in place.

Another job which i managed to get on with was drill out the spot welds on the Battery tray in the engine compartment and remove. Eventually this will be re-used as a battery tray, but with some modifications to allow fitment inside the cockpit area. This will nto be fixed until i have had a chance to get the car assembled and work out rough corner weights. At a guess i think the battery will either be in the boot, or in rear passenger footwell(which i think is preferred choice).
I also decided to measure up and take note of the standard rear ARB mounting and connection to the rear axle. Because the live axle is a heavy unit, i will be making the rear ARB mount on the chassis and connect to the rear axle with droplinks. This should allow a reduction in un-sprung mass, which means the suspension may cope better? To be honest it is more to counteract the extra weight put into the rear axle as it will be braced. In suspension terms it is best to get as much weight out of the live axle as possible, but it still has to cope with the stresses.

Another thing i noticed while i was measuring up parts on the shell, the front ARB off the current shell has angled ARB mounts and the bar is not straight from side to side, whereas the old ARB off the previous scrapped shell has straight ARB mounts and a straight bar! Personally i prefer the straight bar for my plans, but i may be using a DIY blade type front bar on custom mounts. But i am at least going to keep the ARB mounts in situ as they help to strengthen the lower chassis rail to cross member area.

I also made some more measurements of the standard servo position and the angle (i forget at the moment) is too high. Therefore i need to get hold of some 3mm flat bar and make up some new mounts. I will make the setup as close to Horizontal as possible as i don't want to have issues with reservoir placement.

Whilst i was inside the car i made a few measurements of panels to be made up in order to help seal off the rear boot area. I am still planning on fitting a new tank, but i want to have separation between the fuel tank and cockpit area. In place of the standard fllor shelf, i will most likely use some chequer aluminimum plate with some strengthening ribs. This will be tied into a rear frame that will have a large fixed cross welded in between the strut tops, this will then extend down to the rear of the chassis legs in the boot.

[Will01]

So not much to update on the Capri, however i have just received my new old book from a well known site which i have got stuck into reading. It is the Race and Rally Car Source Book by Allan Staniforth. From the little i have read already, it is a great book on par with the 'To Win' series of books written by Carroll Smith.
Thanks to those of you who pointed me in this direction, it is very much appreciated.
My main area of interest at this current moment apart from sorting out the brake system is getting the rear suspension sorted. As i may have mentioned already i do want to rig up an adjustable roll centre watts linkage to help control the lateral movement of the rear live axle setup. It is probably flogging a dead horse with using leaf springs, but i want to be able to keep as much as the base type of the car as possible. I know that if it doesn't work and i am not happy with it, i will move to a better 4 link setup in conjunction with the Watts (6 link), but at the moment that is for another day.
Nix has kindly reminded me about a book i completely forgot about, which is Fred Puhn's book 'How to make your car handle'. It does have a lot more in depth info on setup of Watts linkages, which is the right sort of information i need at the moment.
Its not tha i don't understand how the Watts linkage works, it's just i want to try an understand other engineers experience with using a Watts link on a track car. I must be missing some simple tricks somewhere, that i hope these books might unveil? The geomtery of the Watts setup does look incredibably simple, because i have ready access to CAD it is even more simple to model and simulate the movement and the effects of crank, arm length, fixed pivot location and roll centre location can have on how the axle would behave.
I am hoping to get hold of some simple tube sections and weld up a basic Watts system with one of my spare axles. I need to try it out on the car and get some more measurements so i am sure i can order the correct dampers for the rear. Once i know the design we will build it up properly.

On another note, the first bag of 25kg worth of Glass bead will hopefully arrive before the weekend. Therefore i may be able to try out my Pot Blaster, which my wife kindly bought for Christmas. I have high hopes, although i am sure it will be very messy and take a long time. I may have to look however into upgrading some of my PPE (personal protective equipment). For the time being i may see if i can get away with welding gauntlets and goggles and see from there.