XK BroadSheetsThe Rear Axle

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Hopefully by now youve got a good idea of how toprepare your chassis and suspension; dont forget to keepnotes on the specification of the parts you are fitting Theywill come in useful later when ordering any replacement or worn-out parts. More importantly, how will you know what to buy tomake suitable improvements if you dont know where you arestarting from?

Also at this stage the rear axle needs to be thought about. Forearly 120 owners with the ENV type axle, not too many optionsare available. The scarcity of crown wheels and pinions is suchthat what you have is what you will end up with and, if thecondition of the internals and gears is not good, it may be cheaperand easier to look for another unit altogether. This has happenedto many early cars as so many now have the later Salisbury typeaxles. If you are looking to change the disc wheels to wire wheels,you do not need to change the whole axle, as splined adapters areavailable as a simple bolt-on conversion for the ENV axles.

The first Salisbury axle was introduced in 1952. This wasknown as the 2HA type, soon to be improved to 4HA by 1953.Again, the parts for 2HA axles to convert ratios or rebuild them properly are very difficult to obtainand you cannot fit a Power Loklimited slip differential into the2HA casing. So if you are thinkingof buying a replacement axleassembly, make sure it is the 4HAtype, as this will give you all thepossible variations you might neednow or later. All XKs are the sametrack width and all the XK 4HAaxles start life the same, with onlybrackets fitted afterwards to determine 120, 140 or 150 derivatives. Also, the fitting of discor drum brakes can be done on allSalisbury type axles.

So now on to rebuilding the axleitself. This I can promise you is bestdone by professionals as you willneed special tools and measuring equipment to successfully accomplish rebuildingto factory standards. You can determine the ratio of the axle bythe small metal tag located on oneof the lower bolts holding theinspection pan to the rear of thecentre casing. If this has long sincegone you will need to remove the rear pan altogether and inspectthe crown wheel. Clean the edge of the crown wheel whilstrotating it until you can see some stamped markings. You willsee 4HA or 2HA followed by two sets of numbers, for example46/13. This means 46 teeth on the crown wheel and 13 teeth on the pinion. It now becomes a simple division sum todetermine the ratio: 46 13 = 3.54; i.e. the pinion must rotate

3.54 turns for every turn of the crown wheel. There are severalratios to choose from and they must in turn work with the type ofgearbox - overdrive, non-overdrive or five speed - and also thewheel and tyre size - 15 or 16 inch, and normal or lowprofile. Allof these variations will alter the ratio of the axle, so all must workin harmony together. Dont be surprised if, when you change to15 inch wheels, the engine suddenly revs much higher in top gearand the speedo is showing an exaggerated speed. At this stage ofrebuilding, you need to be sure of what the overall specificationof the car will be and the type of driving you will generally bedoing - short trips on local country roads or continental touring.The right combination can make the car a real joy to drivewithout putting undue strain on the engine. So, speak to theexperts and plan ahead: its a terrible waste of money to do any ofthese jobs twice!

If you intend to do any competition work at all, then fitting alimited slip differential is a good idea, but again it is a job for thespecialists. If the specification includes disc brakes or PowerLok then very close inspection of the axle shafts is needed.Original axle shafts do have a tendency to break just when youleast expect it and, if the shafts are not 100% straight, you will

have brake judder when the discsrotate and brakes are applied. Thisis not so evident in drum brakes asit is not so critical to theperformance or feel. New axleshafts are available in betterspecification material andguaranteed to be straight: this isalways good insurance at this stageas any replacement later will verymuch outweigh the extra cost now.

Always refer to the workshopmanual and factory parts book tohelp you understand the axleworkings and correct torque settingwhen assembling back into thechassis.

So, to recap for ENV and 2HAaxle type customers, only gaskets,seals and bearings are available todo a standard rebuild, but for all1953 onward 4HA type units thechoice is unlimited from 2.88:1ratio for very high speed touring to4.27:1 for hill climbs or quartermile sprints with or without limitedslip differentials. Power Lok is the

name given by Thornton, the producers of this particular style oflimited slip unit, so when you see Power Lok or limited slip,these are one and the same in Jaguar terms.

Next month I will cover the choosing and rebuilding of thebrakes - in my own opinion, the most important part of the car.

From lower to upper: ENV 2HA and 4HA.

XK BroadSheetsBraking Systems

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One of the most talked about XK subjects, after cooling, isbrakes or, perhaps, the lack of them! Making an XK doover 100 mph is easy: making it stop quickly and safelyis a whole different matter.

We will start with the 120/140 drum brake system. Whetheryou have the early 120 non-self-adjusting, or later 120/140 self-adjusting system, they all have the same basic specification,number of cylinders (4 front cylinders for twin leading shoes and2 rear cylinders), drum diameter, width and size of shoe lining.The performance of each system should be alike, but I havestrong opinions on this subject. If all the components in a brakesystem are not as new, how on earth can you complain about itsoverall performance? Too many people are quick to dismiss drumbrakes without ever having driven an XK with correctly rebuiltand, more importantly, correctly adjusted brakes. Many factorscan lead to poor quality braking, from incorrect fluid to seized wheel cylinders or wrong shoe lining material or, of course, all ofthe above.

Im always a little amused at the comments made when customers or restorers ask for wheel cylinder repair kits (seals and dust gaiters) and we ask, When was the car last in use on theroad? The normal reply is, Oh,it was many years ago, but Ivedismantled the cylinders andthey look in good condition.

Lets examine what that reallymeans. My garden hose alsolooked in good condition until Iturned on the tap and, unseen byme, a leak became evident fromthe smallest pinhole, and this iswater at only 10 to 15 psi(pounds per square inch). Awheel cylinder can hold up to400 psi with only a small rubberseal to maintain all that pressure.Any corrosion marks in thecylinder wall at all, however small to the eye, will surely leak withease. Even if the cylinder looks to have a mirror finish inside, thiscould be caused by many years use and, as the cylinders are madeof aluminium, this can mean they are now oversize by the polishing effect of the piston seal, again limiting the chances of aneffective re-seal by the kit alone. Dont take chances with brakes:do the job 100% - it is, after all, your life at risk!

Once all the hydraulics have been overhauled, you can thinkabout the lining material - this is the part that takes all the heatand the strain.

If you are lucky enough to find old asbestos material in, say,Mintex M20 or Ferodo AM 14 spec., you will have much greaterefficiency in braking, as asbestos is the best at soaking up heatand it is also kinder to the drum, both parts lasting longer andwearing better. But, as this dangerous substance has not been inproduction for some years, the old spec. linings are very soughtafter. Do try, however, as it is worth it in the long run. The non-asbestos linings available today do fade quicker with the hightemperatures that an XK can generate inside 12 inch drums and,as far as my research has gone, there is no competition spec. non-

asbestos lining on the market. So this can let the side down eventhough you have rebuilt the drum system correctly.

If this puts you off spending several hundred pounds on original parts only to be disappointed when comparing the performance to that of your modern, everyday transport, thenmaybe a disc brake conversion is the best option. For those of youwith XK150s, you can say But Ive already got disc brakes, andIm still not overly satisfied with what I have. You could also beright, as the 150 came as standard with the new Dunlop discbrakes for 1957; these early 150s of 1957 and 58 had the firstgeneration Dunlop brakes with the round brake pads that couldnot be changed without dismantling the whole caliper (not verypractical). These soon changed to the square pad type, known byDunlop as the New quick change pad type. As the disc brakeswere on front and back, they were considerably better than drumsand more than adequate for their day. But, in todays high speedmotoring conditions, with most cars in front of you having ABS and servo assistance better than ever before, you are presented with hair-raising moments when the car in front canhappily control high speed braking or emergency stops withoutspilling a drop of coffee. You, on the other hand, become white-knuckled and look for the nearest soft hedge, limiting the

possible damage, should youneed to!

For average daily driving in a120 or 140, discs on the front anddrums on the rear is adequate.For more strenuous use, discs allround is the best option. Onceagain, correct pad material andfluid will cope easily with normal driving conditions butyou may want to do some mildcompetition work and merelychanging the pads can take youfrom Sunday afternoon posing toa hardcharging front runningrally car.

In our experience, especially with 120 or 140 roadsters, on carswith drums at the back and discs on the front if you