Atlas axlesThe Atlas is still the axle of choice if you’re building a rally car or

big-power street weapon. Here’s all you need to know about them.

Definitive guide to

he idea of these features is to bust myths, uncover secrets and, most importantly, simplify subjects

that might seem confusing. So a prime candidate for a definitive guide is the big power classic Ford favourite: the Atlas axle.

There seems to be so many variations, types and sizes that many people are left

dazed, confused and blinded by names and figures. And then there’s the ongoing debate about how much power they can take, for how long and whether you need 18-spline this or fully floating that. So we decided to tackle this one head on by going to see the most respected Atlas experts in the country, Fostek Engineering.

TWords Simon Holmes Photos Jon Hill

They’ve been building, uprating and even engineering their own parts for these axles for the last 13 years, so it’s fair to say they’ve got the knowledge when it comes to definitive answers.

Armed with a notepad, a head full of questions and a camera, we borrowed them for a day. We interrogated them and they gave us the facts...

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Contact Fostek Engineering 01670 734594 www.fostek.co.uk

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definitive guide: Atlas axles

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“THE MOST COMMON TYPE OF ATLAS WAS STANDARD IN

ALMOST ALL MK2 AND MK3 CAPRIS, WITH A 1600CC OR

2000CC PINTO ENGINE”

CFTECH definitive guide: Atlas axles

he Atlas axle has come as standard fit in a few different models over the years, which means there’s a variation

of suitable sizes and types. But there were also a few unusual applications which can only be used for parts, so here they are explained. These measurements are taken across the casing from flange to flange.

Full-width Atlas — 52 inchesThis is the most common type of Atlas as it was standard fitment in almost all Mk2 and Mk3 Capris fitted with either the 1600cc and 2000cc Pinto engine, or any variation of V6.

Narrow Atlas — 50 inchesThese came only in the Mk1 3-litre Capris, which makes them a little rarer. They have a slightly different pig’s head (the main body that houses the diff and CWP), smaller wheel bearings and slightly thinner shafts. This doesn’t effect their initial strength though as the end parts are the same size.

Baby Atlas — 48.5 inchesSome very rare European Mk1 Escorts came from the factory with what is known as a baby Atlas, which measures the same size as the common English axle and fits

straight under the standard arches of an Escort. These are not to be confused with the Koln/Cologne axles though, which appeared in some European cars. These look very similar to Atlas axles from the outside, but have English axle internals and are useless in terms of big power. You can tell one from the back plate which has a non-symmetrical bolt pattern and straight side edges. The OthersThe Cortina Mk3/4/5 2000cc, 2300cc and the estate model came with an Atlas axle. But due to their more modern, trailing arm rear suspension set-up, it makes only the middle pig’s head section useable, which is only ideal if you need to shorten an axle in the first place.

The pig’s head is also slightly different, having void-bush

lugs cast into the top of them, to cater for the Cortina’s upper swing

arm suspension.A variation of Atlas came in the Ford

Transit right up until the late 1980s, but it used a five-stud bolt pattern, is much wider and has a different hub arrangement, which again means only the centre pig’s head section is of use. Be careful though as other Transit axles look very similar to Atlas axles, but aren’t. So you need to have a good idea of what you’re looking at.

On the same note, P100 pick-ups also came with a similar axle, but only on the later

Sierra-based examples. They have a different heavy-duty casting, but again the stud pattern and hub arrangement means only the centre sections are useable. They do come with the desirable 4.6:1 or 5.1:1 ratio CWP (crown wheel and pinion) though.

What different types of Atlas are there?

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Full-width, narrow or Baby — how do you need yours?

What lengths are used for what cars?

Mk1/Mk2 Escort on standard arches with a 7J wheel?A Baby Atlas at 48.5 inches is the size of the standard English Escort axle, but Fostek prefer to play it safe when using standard arches and wider wheels and recommend using a shortened axle to 47.5 inches to ensure room. This is especially important if you’re changing to a disc brake set-up as this will space out the wheels by a further 8 mm each side.

Mk1/Mk2 Escort on bubble arches or Forest arches?Ideally, use a 50-inch narrow axle from a Mk1 Capri, as they were the original fitment to the arched works rally cars and most historic rally cars still use them. It allows 9- or even 10-inch

wide wheels with the right offset. A 52 inch can be used and are a lot easier to get hold of, though Fostek say it restricts you to an 8J wheel.

Anglia 105E?An Anglia needs an axle smaller than even the Baby Atlas, so nothing will fit straight in, meaning you will need to fit new shortened tubes and shafts to match. If you are going to the hassle of fitting a custom width axle then it makes sense to make it smaller still to give some space to fit wider wheels, so Fostek supply a 44- or 45-inch axle to cater for this. Standard shafts can be shortened to suit by having them cut and friction welded. But there’s not much difference in price to new upgraded shafts which can take more power.

The axle first appeared in the 1960s in Mk1 Transits and Capris, as the heavy duty alternative to the English axle needed to cope with high performance engines or heavy load lugging. They used bigger internal components that were ideal to ensure reliability, which is why they were used for rally cars too and they proved to be so strong the rally teams didn’t even carry a spare! Ford continued to use them in their commercial range right up until the early 1990s.

The History of the Atlas

HubsThe outer hub arrangement is the same for most types of Atlas, unless it is a Group 4 fully floating axle.

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To put it simply, they are stronger in every way. They use a bigger CWP, with bigger teeth on the gears, which allows for more contact area — the most important factor and where English axles are heavily let down. Atlas’ also have stronger diff housings and stronger tubes, making them an all-round heavy duty axle.

Why are they better than an English axle?

Pig’s headThis is the name given to the centre section of the axle which houses the crown wheel, pinion (CWP) and differential. There are variations of this with slight differences to the castings, to cater for other models.

TubesThese fit into the pig’s head and house the shafts themselves. Bracing can be used to increase strength.

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CFTECH definitive guide: Atlas axles

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How much power can axles take?

How to improve them

What’s the weakest part of the Atlas axle? Why do CWP ratios matter? Why is grip the most important factor? And, how to buy an axle secondhand...

Differentials, casings and shafts... what you need to know.

90 August 2011

he most important factor here is grip, as the more you have, the more likely you are to break

something. Generally speaking though if you were to start with a totally standard Capri axle in good working order and drive with moderate care, then they are usually fine until about the 300 bhp for a fast road car. After that, it depends largely on how much you abuse the car and if it’s being used for drag racing or rallying — if so, the shafts will start snapping.

However, with the right uprated components fitted they’ve been proved reliable on 500 bhp YB-powered fast road, track and strip cars. There are a couple of points worth knowing about though...

DifferentialThe first thing to do, if you haven’t already, is fit an LSD, as the standard open diff isn’t ideal for putting down any kind of decent power. For a road car, Fostek suggests using a Quaife ATB as it’s easy to maintain and kind to halfshafts. But they do advise it’s considered to be strictly a road-going diff and not suited to track or for harsh driving (which includes burnouts and doughnuts). If that’s more up your street, or the car will be spending time at the track or the strip, then a plated diff is better suited to your needs. They are motorsport orientated items and although they lock both wheels for traction in a harsher way, they can be adjusted through ramp angles and preloads, to suit a less aggressive road going application. Fostek prefer to use the Gripper diffs, which cost around £900, as ZF items. They were very popular but are no longer available new. Be aware that the P100 came with an open diff in a heavy duty casing which looks like an LSD to the untrained eye, so be careful when buying secondhand.

ShaftsAll standard shafts are one-piece 16 spline and quite small in diameter, which makes them the weakest link, so the first thing is to upgrade to larger two-piece 18 spline shafts. To fit larger shafts the casing doesn’t need to be modified, but the side gears that connect them to the diff will need to be changed or machined to suit. Normally,

an LSD will be fitted already at this stage and the side gears needed to fit 18 spline shafts cost about £150 for the pair. For the shafts themselves there are quite a few different brands available, but Fostek have had good results from using two piece shafts from Phil and Mick Squires at Rally and Competition Equipment (01782 523664) which are about £125 each. These are known as Group 1 shafts but are in the fact the same diameter and spline count as what would be used for a Group 4 axle. The matching outer flanges, to make them a two piece shaft, are £70 each and the new bearings to go with them are £40 each. New wheel studs will also be needed for around £20 a set. The shafts come in the most common sizes to cater for baby, narrow and full-width axles off the shelf and for more bespoke or custom applications such as the slightly shorter 47.5-inch Fostek prefer to use in un-arched Escorts can also be supplied. The quality is outstanding and will cope with most high power applications. But Fostek do sell an even heavier duty, gun-

drilled, rolled-spline version that come with an unbreakable guarantee for £1200 a pair, and can be done to any length required.

CasingFor the average fast road car no more needs to be done, or can be done, to increase the strength of the axle internals in terms of power than a good LSD and a set of uprated shafts. However, as soon as you start to use a car in harsh conditions, rough terrain on a rally stage or the extreme cornering forces of a track, thicker tubes and extra bracing is needed to stop any flex or twisting of the tubes out of the pig’s head.

Fostek have just had some brand new castings done for the pig’s head in high grade, high strength iron, which are even better than the original Ford item. They are the first company to successfully do this and will only be supplying them with their own axles, so will not be sold separately. Alloy ones are in the pipeline too, which offer a big weight

saving.

What CWP ratios are available?3.09:1 These are the highest ratios available and came in most V6- engined Capris. They are very common, but generally useless, as they are deemed too ‘lazy’ for the road.

3.22:1This was a ratio found in some Mk1 3-litre Capris and is very rare. But sadly, again, pretty useless in most road cars as they are too high.

3.44:1Ideal for big power or big torque YB-engined cars that won’t find the slightly high ratio a problem. Originally came on 2-litre Pinto-powered Capris.

3.75:1The most desirable of all the ratios for a fast road car, as it offers the best compromise and is ideal for the average YB-engined car. These were fitted to the 1600cc Pinto-powered Capris.

4.1:1This is a rare Ford Motorsport item and wasn’t fitted to any road car as standard. It’s ideal for an NA-powered car and they have since been reproduced as an aftermarket item by various companies.

4.6:1Common on P100 pick-ups and some Transits, there’s a steady demand for these from the rally boys who regularly use them, as they are too low for the road.

5.1:1These were the rare standard-fit Transit items for special vehicles, such as Ambulances or even ice cream vans. There’s a high demand from the rally boys. They’re available as reproduction items.

ShaftsThese are the weakest points of the Atlas. If you’re using standard shafts, source some from a low mileage car — ones that have been marked to indicate what side they come from, as shafts twist marginally over time and tend to set into position, like a corkscrew. They are at their strongest once set, as they become ‘work hardened’, which means if they ever swap sides for whatever reason then they’re more likely to break.

CWPOut the box these are very strong and rarely break. However, the lower the ratio, the weaker the pinions become as the amount of extra teeth that physically have to fit to decrease the ratio makes them smaller and therefore weaker. It’s also worth noting that the

original Ford items are stronger than reproduced items and as a result

command more money.

AdvantagesOver something like an English, they use a bigger CWP, bigger tubes, bigger bearings, have a stronger casing, use bigger wheel bearings and there’s lots of potential to improve them to near indestructible levels. Also sometimes an English axle isn’t wide enough to fit a wide arch car and finally, now everything has been re-produced a brand new axle can be built up from scratch.

DisadvantagesWeight is the main one and the significant one; they weigh a fair bit more than an English axle. There’s some work and expense needed to fit one, as there’s no readily available off the shelf item for most cars as it has to be modified. Due to their bigger size, a diff tunnel may be needed if the car is running extra low. Also, in comparison to the rear loading English axle, the front loading Atlas is harder and more time-consuming to work on, which comes into effect if you want to change ratios often.

Once the correctly uprated parts have been fitted to suit the intended use, they are very strong, reliable axles. This depends if they have been built correctly in the first place, as it’s important to check what’s known as the backlash clearance to ensure it’s within its tight tolerance. If it hasn’t been done correctly it will create excess heat, noise and wear. It needs to be carefully adjusted, using shims, to make sure there’s good contact between the teeth and similarly the pinion needs to have a good mesh with the crown wheel. This ensures the longevity of the components and through this kind of clinical preparation Fostek have seen axles cope with over 5000 race miles between rebuilds.

Atlas pros and cons

How reliable are they?

Ideally get one with as low mileage as possible and in good working order, although it’s hard to tell from the outside, so here are some pointers. If the oil inside the diff is clean and full to capacity it’s generally a good sign; the back plates tend to corrode, leak oil and then they run low on lubrication, which causes excess wear to the internals. It’s best to spend extra time and money looking for the right size and ratio for your application, rather than buying any old axle that comes along and having to spend money adapting it. Expect to pay around £150 for a 52-inch Atlas without an LSD and £500-plus for the rare Capri Special axle which had a plated ZF LSD in it. A narrow 50-inch Atlas from a Mk1 Capri will normally go for around £300 as it’s more desirable for the wide arch cars and rally boys.

BUYING SECONDHAND: what to look for

CWPThe crown wheel and pinion ratio can be changed to give different acceleration characteristics.

Plated DiffsDesigned with motorsport in mind, these are ideal for big power cars.

Open DiffsStandard in most axles, these are the first thing to replace.

1Atlas axles won’t take

big power? False. With the right parts fitted they have been proven on big power and big grip cars.

2Group 4 floating axles

are stronger? False. The differences are only on the hub arrangement and not the pig’s head internals.

3Ford never made a Baby

Atlas for the Escort? False. They are very, very rare, but they were fitted to some European cars.

4An LSD is stronger than

an open diff? False. They are as strong as each other.

5 A standard axle can cope

with 350 bhp? True. This has been known with gentle road driving and, importantly, lower grip levels.

MYTHS

Run by father and son duo John and Tom Foster, the company started out around

13 years ago when they were building themselves a rally car. When it came to the axle they found no one could supply them with one. Taking the initiative, they read a few books and had a go at doing it themselves, with good results. They were soon doing another for a friend’s car and word spread. In the early days they had to machine and adapt standard parts, as very little was readily available. But they now make their own parts, redesigning items along the way to be both stronger and lighter. Over time they’ve learnt what works and what doesn’t and now turn out hundreds of axles a year for customers all over the world for road and competition use. They quickly established a reputation as being the leading force and experts in Atlas axles and their latest development of newly cast pig’s heads means they can now supply a complete brand new axle from scratch. So if you’ve got a big power engine and need an axle, Fostek are the ones.

ABOUT FOSTEK ENGINEEERING

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his is something you hear being banded about a lot within rally circles and it

relates to the strength of the hub arrangement, rather than the power it can cope with. The heavy duty upgrades to the hubs allow for sustained shocks and harsh use over rough ground such as rallying. The centre pig’s head section, including the CWP, diff and shafts, is virtually the same as any other Group 1 or fast road uprated item, but the tubes are thicker and heavily braced. They also use a stub axle arrangement and bearing carrier, so the hub itself is designed to spread the load onto the tubes and axle. On a normal axle the shafts and bearings have to transfer the torque of the engine as well, taking the wheel load, but this way its role is reduced to just transmitting power. This is done by anchoring the hub, using two tapered roller bearings, which stops wheel movement no matter what the wheel encounters. It also means that even under very hard cornering the wheels will always point in the same direction, which is ideal for track or circuit based cars too. As it’s a fair amount of work to machine the necessary end parts, and different shafts are needed, it’s not something that can be done as a kit or as an after thought once the axle’s been built.

What is a fully floating Group 4 axle?

Fostek is a family run business which caters for everything Atlas related.

Only the outer hubs and shafts are different. On the left is a Group 4, next to a normal axle.

Fully floatingThis is something we hear being used a lot, but it only relates to the hub arrangement, to give extra strength.