Thoughts on a steering rack

There have been many threads on the 308 steering rack, including this rather good documentation of a rebuild.
https://www.flickr.com/photos/moseley_ferrari/sets/72157602899521527

I thought I'd share my experiences and thoughts on what is, in my opinion, one of the weakest components of the 308.

I have been through a few steering racks, different suppliers and different components and now have an excellent steering mechanism that is not excessively heavy and has zero measurable play at the steering wheel. Really - nothing you can feel by hand. Go and check yours now, if you can feel any free-play you're not enjoying the steering as it should be.... and it could be worse than you think.


Why is it weak?
Every car has to have its weak-points. On the 308, the steering rack comes straight from a mini - a car that comes in around half the weight of the 308, has a tyre contact patch which is very much smaller and generates lower forces on cornering (and on turning the wheel of a stationary car if you're that way inclined).

What are the weakpoints?
1. The near-side rack bush / guide.
2. The lubrication.
3. The leaks.
4. The appalling quality / tolerances of new rack components, from racks to pinions to bearings.
5. The rack itself.
6. The adjustment mechanism.
7. The splined "adaptor" (did you even know you had one?)
8. The rack mounts and their bushes.
9. The steering column and universal joints (and the bulkhead bush on 328's).
10. The person turning the wheel.


One by one, here are observations, suggestions for improvement and things to think about during a steering rack rebuild or replacement. If you already know lots about rebuilding steering racks, then 2 and 7 might be new to you.

1. The near-side rack guide bush is a well known weak-spot and is more often than not the reason that a steering rack comes out for a rebuild. The rack guide is not particularly great, even on a mini. On the 308, it gets worse because not only are the steering loads higher and the radial load on the rack bar higher too but the rack bar is longer in the 308 when compared to a mini, giving a higher moment on the bush, yet the bush remains in the same place. Some people have replaced the bush with bronze which is fine if it is accurately reamed but ideally the bush should be further toward the end of the rack. This is not possible with the original design as Ferrari lengthened the rack casing using riveted on ends. One nice solution is to remove the riveted end from the near-side and to lengthen the steel tube that separates the aluminium housings for the pinion at one end (the off-side) and the rack guide at the other (near-side). It is a small improvement, not one I've tried, but it would help.

2. When these cars were new, they used 80w gear oil for lubrication. New steering racks come with grease. One is better than the other. Oil quite simply provides better lubrication and a more freely running mechanism. It will last longer if you use oil. New racks come with grease, the new ones from TRW come with 0w self-levelling grease and yes, TRW do know what they're doing....... but they make steering racks for the mini, not the 308. Nobody makes a new, fully built-up 308 rack although many people adapt new mini racks for better or for worse. The fact is that a self-levelling grease is just fine for the vast majority of mini uses and will cause no problems; on a 308 it exacerbates the weaknesses. I know that not everyone will go along with this and opinions on lubricants are almost as diverse as opinions on timing belts..... but I think it's an important point and makes a big difference.

3. Oil in the 308 racks is held in by poor little seals and poor old rack gaiters. So, yes, it's tempting to use grease to make sure that some lubricant stays in there......... but checking the level on service (which is part of the 308 service schedule) is a small price to pay for rack longevity.

4. Beware new components - look at them very carefully and critically. I have shortened my experiences here into a few lines but I have seen a lot of new rack components now, none of them much good. There are various suppliers claiming to sell new steering racks. I bought one from a well-known supplier. What was delivered was an adapted mini steering rack. I have seen ladies underwear of greater structural integrity.

Rather than use a longer rack bar, this supplier increased the length of the bar by adding two drilled and tapped steel bars. Then, rather than extending the rack housing, the movement of the rack was limited by the addition of two, free-floating aluminium cylinders, hidden in the rack boots. The original rack boots were then over-stretched.

I cite this as just one example of poor quality new parts - be aware! More common is the next experience I had. I decided to buy a quick ratio rack and pinion and to rebuild these into my original housing. I won't debate the pros and cons of a fast ratio rack here but I will say that I bought it from what I believe is the engineering company who has been making these for the 308 for longer than anyone else and who supplies almost all the marque specialists advertising here with both normal and fast rack components. Upon installing the rack and pinion into my housing with new bearings and to all the tolerances given in the 308 workshop manual, I decided to check the contact patch between rack and pinion. See results in the pic below.

New components give a contact patch which is poor, it is too small, wrongly positioned on the rack tooth, different from one side to the other. The teeth of the rack also bottomed out, despite being correctly adjusted for play.

The result was so poor that I decided to check the new, adapted rack I mentioned earlier (despite all the issues, it was based on a brand new TRW rack and pinion). It fared slightly better but not much.

Intermediate conclusion - new steering racks suitable for the 308 are of terrible quality - they are built to Austin Mini quality not to Ferrari standards. Do not fit one to your car unless you check how it is made, how it is lubricated and the nature of the rack / pinion contact patch.

Intermediate solution - I de-burred everything, radiused all teeth edges, bought new bearings and used fine grinding paste, working the rack back and forth, until I got a reasonable contact patch. I rechecked that no teeth were bottoming out, finely polished all the teeth, retested the hardness of the rack and put it all back together to factory specs....... This took an absolute age! Really an age with all the cleaning between each strip-down.


(apologies for image quality, taken with an old phone since the dog chewed my camera to bits)

Proposed long-term solution - get someone to make a properly engineered steering rack to the same dimensions as the original. I'll keep you updated on this but it won't be quick! If anyone wants to step up to the task, PM me, I have some ideas.

5. The rack itself is not a beautifully made gear mechanism. Its teeth are crudely hobbed and the heat treatment is not well applied. I think that no final honing or checking is done after heat treatment. The rack is also under-dimensioned.

6. The mesh of the rack and the pinion is controlled by spacers / gaskets and a pad which prevents movement of the rack bar away from the pinion. Overall it's not a nicely engineered solution and using the available shim thicknesses is not sufficient to achieve the nirvana of a freely moving rack bar with no play at the wheel. An easier way of achieving this is to drill, tap and counter-bore the pad cover so that a fine bolt acts against the pad. I used a 8mm fine pitch cup end allen bolt and a ball bearing as an adjustment mechanism. See image below. It's just a nice refinement to make while you're there and means that you can adjust with more precision than gasket sizes allow although I still recommend that you use the gaskets to adjust as close as possible.



7. From the factory, the mini steering pinion has a splined input shaft. The universal joints on the steering column use a different spline size. To adapt from one to the other is the shaft which also passes through the bulkhead but, if you look carefully, the construction is surprising. From the factory is a male splined shaft which fits into a female / female splined shaft and the two are welded together with 3 small welds. See the image below. See also that on this one, all 3 welds have cracked and failed completely so that all force is on the splines. Be careful to watch out for this during servicing and when your rack is out. Left undetected, this could lead to wear and a sudden failure. I cleaned this one up, checked it for further cracks and then re-welded it, adding a hole and a plug weld for good measure.



8. Early dinos have solid rack mounts. Later cars and all 308s have very similar mounts but they are rubber mounted to the chassis. Various people have debated the wisdom of each type of mount but I certainly prefer solid mounts and find that there is no downside in terms of refinement but the upside is significantly sharper steering. In my opinion, the chassis is more than strong enough to cope with the additional loads. The rubber mounts degrade rather quickly and this is a source of sloppy steering. It is also worth noting that if you consider using a quick ratio rack, the solid rack mounts help keep steering effort lower. On the move I don't find that the 308 is too heavy but if you really do need to turn the wheel at rest, there is a lot of stiction. Solid mounts seem to help this and my experience is that if you have a fast rack, you really want the solid mounts first.

9. The universal joints and the steering column splines are a common source of wear. Make sure that the universal joints are properly mounted on the splined shafts, that the correct shank bolts are used and that all, including the sliding joint nut is correctly torqued. Make sure that the universal joints are frequently lubricated too. Note that cars like the 328 have a rubber insulated bulkhead bush through which the adaptor passes. I don't like this as much as the earlier arrangement and when you move the steering wheel, you can see this rubber move too........ it all adds to steering inaccuracy.

10. Having got to 9, I really thought this list needed 10 points. The driver is of course the main source of steering inaccuracy. Next next time you're in the car, see how much free-play you can feel and measure it at the wheel rim. It really can and should be zero.

Other things to look out for in a rack rebuild:

The pinion can eat into the pinion bearing spacer - see pic below.

The inner track rod tends to touch its housing which can create stress-raisers such as these - see below.