Thread size confusion
Among the jobs that have passed through the workshop lately have been two 200Tdi conversions on short wheelbase Series III Land Rovers. I have not done one of these for a little while, so I had to remind myself of all the bits that I would need. Everyone has their own way of carrying out this very popular conversion: I prefer to use a Td5 intercooler mounted in front of the 200Tdi radiator as it makes for some very simple, straightforward pipe runs. Both vehicles were running 2.25 diesels with issues and left my workshop with, I suspect, around four times the number of horses under the bonnet that they had when they came in. This makes for a highly entertaining if slightly wayward drive.
As is usual on conversions, both vehicles arrived with a list of additional jobs to be done while they were in the workshop. The first Series III was, to put it politely, electrically challenged. I pulled out about half a mile of home-brewed wiring and random switches and relays, plus a couple of burned and melted sections of harness, without affecting the operation of a single electrical item on the vehicle. The weight saving from this exercise was probably worth five brake horsepower on its own. Some people (including Dave the landlord) regard auto electrical work with fear and loathing and see it as something akin to witchcraft. I love it and soon had the Series III electrics working as well as they had ever done, which admittedly is nothing much to boast about. Lucas electrics – Home Before Dark.
Vehicle number two came in with all its lights working, but was sitting well down at the back and had a very noticeable list to starboard. The front springs were new budget parabolics, the rears new old stock standard springs of unknown provenance. I had a play around with jacks and tape measures to try to ascertain which spring was causing the vehicle to lean so badly, but struggled to come up with a definitive answer. Given that the rears were clearly below par and the fronts cheap and possibly nasty, the owner gave me the go-ahead to change all four for British-made parabolics of decent quality.
Changing leaf springs on a Series vehicle is physically hard work, no question. It gets much harder when the upper rear shackle pins are rusted solid into the chassis bushes. Having been told that the springs on both ends were recent replacements I was hoping for a relatively easy ride. I was disappointed to find that the upper shackle pins at the back of this Series III would not shift no matter how much brute force I applied. The bodgers had been at work – grinder marks showed how the old springs had been cut off the shackles, allowing the new ones to be fitted by brute force and ignorance without having to tackle the seized upper shackle pins. So I broke out the power tools and gas torch and set about removing and replacing the chassis bushes, which has to be in my top five least-favourite Land Rover repair tasks.
The front springs were easier to tackle, having been very recently fitted by another garage. I was slightly surprised to find that the front spring bolts (the ones through the dumb irons) were far too long and had been padded out with an assortment of rusty washers to stop the nuts bottoming out on their threads. The end result was safe enough but rather unsightly. What I found next was by no means safe.
The springs are attached to the axles using four long U bolts and nuts. On the rear axle all four U bolts are identical: on the front, the offside inner has a squarer profile than the others to match the shape of the axle casing at that point. This vehicle had been fitted with four front U bolts of identical profile, which is not ideal as the offside inner will tend to loosen over time as it bends under load to shape itself to the axle profile. But that was not what worried me. I was more bothered by finding that I needed two different sizes of socket to undo the four U bolt securing nuts: three at 19 mm (M12 metric), and one at 3/8 inch BSW. A U bolt with different sized threads on each end? I don’t think so.
On inspecting the U bolts I found that three of the four threaded ends had been fitted with incorrectly-sized nuts. Those M12 nuts were slightly oversize and not quite the correct pitch, but close enough to allow them to be wound on to the ends of the U bolts and done up just about tight enough without actually stripping the threads. It was a close-run thing – the nuts were little more than finger-tight and the threads badly damaged. I suspect that much of the grip was actually coming from the Nyloc inserts. I would not have liked to be driving that vehicle when the U bolts pulled through the nuts, which would almost certainly have happened sooner or later.
Older Land Rovers are a remarkable mishmash of different thread sizes: a late Series III will have BSF, BSW, UNC, UNF, BA and Metric threads all on the same vehicle, which is why I have so many sockets and spanners in my toolbox. In some cases (such as those U bolts) the change from Imperial to Metric took place during the production run, and it pays to be vigilant in ensuring that the correct fasteners are used. Braking systems on Series IIIS present a particular hazard: the pipes and unions were partly metricated in 1980 (although wheel cylinders remained Imperial). A 3/8 inch male brake pipe union will screw into an M10 x 1 mm female, but not securely enough to make a safe and secure join. With many vehicles having had components such as hoses and T-connectors replaced over the years, it is dangerous to assume that the thread you are looking at is the one specified in the parts book.