Brakes - Part 2 - Front

I'm planning to run 16" rims on Project Snake so I went with the smaller option of the AK Big Brake Upgrade kits which is suitable for 15"-17" rims.  The kit includes two vented front discs (335mm diameter by 32mm thick), two bells for the front discs (discs and bells came pre-assembled), two 6-pot calipers for the front, and two 4-pot calipers for the rear. The kit uses the standard Jaguar rear discs.  I also elected to upgrade the brake pads supplied with the kit from EBC Green Stuff pads to Ferodo pads.

The front calipers are not a massive difference in size from the original Jag twin-pot items, althoigh they are a lot slimmer and in fact, the brake pads are practically the same size as the Jag originals.  However, with three pistons per side, the braking pressure will be more evenly applied to the pads (and to both pads) providing superior stopping power.  The other massive difference is in weight.  The original cast iron calipers weigh in at a hefty 5.2kg.  The AK items, being billet, are a svelt 1.9kg, which provides a huge benefit through the reduction in the unsprung mass of the car leading to better handling on the far-from-smooth UK roads!

Gratuitous Brake Porn...

Looks far more attractive than the original...

...with 3.3kg of added lightness and 6 pistons of (stopping) power!

New pads (bottom) are similar in size to the originals (top)

Original front disc dwarfed by new shiny monster disc!

The kit comes with some new brackets and bolts to fix onto the front uprights onto which the calipers are attached.  I fitted these and torqued up the mounting bolts to 100Nm/74ft-lb.  The new discs were placed over the studs on the front hubs and secured with a new retaining screw (P/N SF605047 from British Parts UK).

New caliper mounting block and bolts...

...installed onto front upright

Before installing the calipers, the brake pads need to be installed (technically this can be done later as the pads install from the outer side of the caliper).  This required removing two threaded pins, allowing the pads to be slid into place.  The pins and spring clip were then reinstalled, the caliper placed over the front disc and then secured to the mounting block with two Allen-headed bolts.

It is recommended that a smear of copper grease is applied to the rear of the brake pads to prevent brake squeal.  This is something I have made a note to do later.  I have not removed the protective coating from the brake discs yet as I don't want them to start flash rusting while I finish off the rest of the car.  So the calipers will need to come off again at some point.  For that reason, I also haven't torqued up the caliper mounting bolts to their final spec - 60Nm (44lb-ft).

Starting to look more like a proper car!!

 

Brakes - Part 1 - Decision Time

My original intentions for the brakes on Project Snake were always to refurbish and reuse the original brakes from the donor car.  As Jon at AK told me "if they are good enough to stop a 2.5tonne Jag, they're good enough for a 1.4tonne Cobra".

When I sourced the donor parts from Simply Performance, they suggested that getting the biggest brakes possible from the outset would be the best path to take.  I wanted vented discs on both the front and the rear and Ben at Simply Performance suggested using a car with the larger XJ twin-pot calipers at the front.  Seemed like a good suggestion at the time and that is what I went with.

So the brake discs and calipers I got with the donor vehicle are summarised below.

The eagle-eyed amongst you will spot that the rear disc diameter is larger than the front, which is unusual.  Usually, under heavy braking and weight transfer towards the front end of the car, it is the front brakes that do more work in bringing the car to a halt, and hence traditionally they are larger.  I assume that the use of the twin-pot caliper at the front provides enhanced braking performance over the larger disc / single-pot caliper arrangement at the rear and allows a slightly smaller disc to be used. But who knows what was in the mind of those engineers at Jaguar?

It seems however that those twin-pot front calipers are a bit of an enigma.  Whichever of the usual Jaguar part suppliers I looked at to try and find service parts for these calipers, they didn't seem to exist.  Even typing my donor car VIN number into various parts websites still kept on bringing up the single-pot caliper.

Twin-pot Front Caliper

Single Pot Rear Caliper

Disc Thickness (Thicker Front on Left)

Disc Diameter (Smaller Front on Left)

Front disc 10mm smaller diameter than Rear...?!

I contacted Ben at Simply Performance and he suggested that maybe if I measured the piston diameter in the caliper then I might be able to find suitable replacement piston/seal kits from another caliper option.  No joy there; the diameter of the twin-pot pistons is smaller than any of the other standard front (or rear) pistons in the various calipers over the years.

I did find a couple of places online that claimed to be able to refurbish the calipers, but given my failure to find any semblance of service parts for these unicorn calipers, I wasn't convinced.  I did eventually discover that Ward Engineering in Colchester, which is a specialist in the supply of reconditioned Jaguar axles and brakes, did offer a reconditioning service for the twin-pot calipers.  However, by then, my plans had taken a slight change.

Switching from an LS3 engine to an LS7 with close to 660hp got me thinking that, despite Jon's adage above, rapid and stable deceleration was going to be a top priority.  The oddity of the smaller diameter front discs compared to the rear on my donor vehicle was also starting to perturb me; I didn't want any unexpected twitchiness under heavy braking.

So when the UK taxman gave me a very unexpected but very well received tax rebate, my mind was made up.  It was time to buy an AK Big Brake Upgrade Kit!

Differential - Part 5 - We need to torque!

 There were a couple of small jobs that I needed to do to complete the installation of the rear differential.

The first was to cut down the 7/16UNF bolts securing the tie bars to the differential and the chassis.  The threaded length of these bolts is much greater than actually required and the protruding length looks a bit odd (to me anyway).

The second was to actually torque up all the various differential mounting bolts.  I didn't do this at the time of the original installation as, quite simply, I couldn't find the details for the necessary torque settings.

An offensive amount of bolt sticky-outedness...

I reckoned about 10mm off the end of the tie bar bolts should suffice.  Before cutting I wound a 7/16UNF die onto the bolt a) so that I could make sure the threads were intact after cutting and b) it made a handy brace to help support the bolts in the vice while cutting!

Die used to help keep bolt in place while cutting

I cut down the bolts with a hacksaw and then reinstalled them into the tie bar mounts, with a further liberal application of copper grease, adding a 7/16 washer on each end and 7/16UNF Nyloc nuts.  The final result was far more pleasing to my eye!

Much better - no unnecessary protrusion!

Now to finish tighten up all the differential mounting bolts.  You would have thought it would have been a relatively simple task to find all the necessary torque specifications, but oddly enough it took me a fair bit of searching before I was sure I had the right values.  This is complicated slightly by the fact that the AK mounting arrangement for the differential is of course not quite the same as the original Jaguar arrangement but my research was also hampered by the various Jaguar service manuals not calling any of the parts/bolt descriptions by anything remotely helpful!

I finally stumbled across a version of the Jaguar XJ40 Workshop Manual on the Jaguar UK forum.  This has a very handy series of diagrams at the front which show the various assemblies throughout the car and the necessary torque settings.  I almost missed this as I initially scrolled straight to the Final Drive Chapter (where of course everything was not called what I expected it to be).  Fortunately, I spotted this section as I was trying to refind the index!

The necessary specifications are as follows:

I was then able to finally tighten all the differential mounting bolts to the required specification and mark them as tightened with my favourite shade of blue nail varnish.

All torqued up and ready to go!

Handbrake Part 1 - Blue Suede Shoes

Once the backing plates were reinstalled back onto the rear hub carriers, but before the carriers go back onto the car, it's time to get the handbrake shoes and associated bits fixed in place (I also figured it would be easier to carry out this operation before the hubs themselves are reinstalled).

It goes without saying that for the rebuild I purchased a new set of handbrake shoes for both sides of the car; also if you recall the old shoes had disintegrated to dust when I disassembled the rear axle originally.

I was going to re-use the adjusters and the handbrake levers from the donor car.  But after several attempts to try and clean them up, the residual caked-on brake dust seemed reluctant to give up its grip on these parts so I gave in and ordered new parts and new brake shoe springs at the same time.

The handbrake shoes are fixed to the backing plate with a spring-loaded pin; these have a T-shaped end that passes through the backing plate and is locked in place by turning through 90 degrees.  Those following the story closely will recall that the T-slots on my donor backing plates (even the replacements from Simply Performance) were shot and I wasn't convinced that there was enough metal left to provide a robust anchorage point for the brake shoe fixing.

That well-known auction site came to my rescue again and I managed to buy a set of replacement pins - these were basically a long M4 bolt with a Nyloc nut.  Using three M4 washers per bolt, one on either side of the compression spring and then one between the M4 Nyloc and the backing plate (to further assist in the prevention of the bolt pulling through the backing plate) a suitable replacement fixing was achieved.

My total shopping list for the handbrake rebuild was as per the Table below.  I have to admit the cost of the replacement adjusters and levers was slightly eye-watering but at least being brand new parts I can be assured that these will (hopefully) move freely and work as planned.

Advance warning - installing the handbrake shoes is a pig of a job.  There seem to be many ways to do it, including the method outlined in the Haynes manual, which frankly, due to the tension in the lower spring, strikes me as impossible!  I did wonder whether it would be easier to have actually done this with the hub back on the car, with the rest of the chassis acting as additional ballast to help when trying to stretch the springs; however, for me, I think it was easier (?!) doing this operation on the workbench rather than trying to do it sat on the floor.

So this is how I did it (other methods are available).

New parts for handbrake rebuild

There are six small raised pads on the brake backing plate that the handbrake shoes rest on and the first step was to put a small amount of copper grease onto each of these.  You need to take care not to put too much grease on (as with all the following steps) as brake linings and grease do not mix.

Location of raised pads on back plate

I then disassembled the new adjusters and gave the screw threads and recess a generous smear of copper grease.  The brake shoes also got a strategic greasing, where the upper and lower tension springs hook into the shoes and also where the adjuster and actuating lever locate onto the shoes.  Finally, I put a smear of copper grease on each side of the mounting block on each of the back plates.

With the brake shoes on the bench, I wound down the adjusters to their shortest length, placed them between the tops of each pair of brake shoes, and then inserted the upper and lower tension springs into their respective holes.

I then placed the brake shoe assembly over the hub carrier and onto the backing plate.  At this point due to the tension in the lower spring, the bottom of the brake shoes will be too close together to fit either side of the mounting block on the back plate.

There then ensued a short wrestling match as I tried to keep the brake shoes flat against the back plate (to stop the tension springs pinging out of their locating holes) while at the same time trying to pull the bottom of the shoes apart sufficiently to get them to sit either side of the mounting block.  Oh and while all this is going on, I was trying to avoid getting all that grease that I had strategically applied to all the contact points ending up getting smeared all over the brake friction material. 

And the winner, with two falls and a submission...

I was pleasantly surprised that once the shoes were in place, the installation of the replacement spring-loaded pins was very straightforward; I anticipated further wrestling to get the holes to all lineup, but everything seemed to line up straight away.

I was initially a bit perturbed that the upper tension spring doesn't sit straight and clashes with the adjuster.  However the adjuster still seemed to move and the proximity of the spring does have the added advantage that it helps to prevent any rotation of the adjuster cog under vibration, so it's staying as it is!

The actuating levers then received a generous greasing of all the moving/contact surfaces.  The new AK handbrake cables were then passed through from the rear of the hubs and fixed into the new levers with the studs from the original levers.  Thankfully I had not thrown these away, the new levers do not come with a new stud and the part is not available for purchase. 

Lubricated lever and the donor stud for securing cable

The levers can then be installed between the lower ends of the brake shoes.  This needed a bit more wrestling and the gentle application of a small pry bar just to ease the shoes apart sufficiently to allow the lever to drop into place.

Completed handbrake rebuild

Job done - and frankly not one that I would be in a rush to want to have to repeat!  Now I can finish off the rear hub installation onto the chassis.

Rear Axle Reassembly - Part 9 - Hubs On....Finally!

Finally, the day has come when, having messed around for so long, I am hoping to get the rear hubs onto the car at last.  I had already purchased some of the new parts required for this momentous day from SNG Barratt many moons ago, as per the table below:

The first operation of the day was to secure the brake shoe mounting blocks to the backing plates using some M6x10 screws with spring washers.  I added a dobble of Loctite to these for good measure.

Brake shoe mounting block...mounted!

My new spacer tubes were inserted to place, the backing plate placed over the hub, and secured using new fixings all around.  Each plate needs two M10 screws and two M6 screws; the M10s come with thread lock compound already applied to the threads, I added some extra to the M6 screws.  These were tightened evenly using TPS45 and TPS25 bits until the backing plate was snug against the hub carrier.

Lower M10 Mounting Bolts with factory applied thread lock

I then spent some considerable time grappling with the installation of the handbrake shoes and springs (Handbrake Part 1) before it was time to reinstall the hubs.

These were given a liberal application of grease before being pushed firmly into place.  The hubs were then turned over and the ABS ring tapped onto the back of the hub using a large piece of timber as a suitable drift and a large hammer to provide the force!

Hub greased prior to insertion...

...ABS ring tapped firmly back into place...

...and one completed hub ready to go onto the car!

Finally, it was time to get the hubs on the car!

First step - install the hubs onto the lower wishbones.  This required the use of two new spacers per hub, which were installed on the face of each of the fulcrum bearings with a good smear of copper grease to hold them in place during installation.  I just ordered four new 3.955mm spacers (the same size as my donor spacers) since (according to the AK gospel of Jon Freeman) the shimming / preload of the lower fulcrum bearings is not important so long as the wishbone bracket is pulled tight against the hub.  As it was, the new spacers were just about the right thickness, and just needed a gentle tap with a soft mallet to ease the lower part of the hub into the wishbone bracket.  I gave all the contact surfaces a light smear of copper grease prior to installation.

The lower fulcrum bolt was given a very liberal application of copper grease, tapped gently through the lower wishbone mount, and secured with an M14 Nyloc and washer - just snugged into place for the moment.

The driveshafts were then installed onto the differential and held in place with plain 7/16 inch nuts.  I installed the driveshafts without any shims/spacers between then and the differential flange; the camber will be checked and the required shim thickness worked out next.

The drive shafts were then installed into the hub, which required a bit of manipulation to get the relative angles correct to allow the shaft to slide into the hub, before securing with the original cone washer and drive shaft nut.  The cone washer, drive nut, and differential flange nuts will all be replaced with new items once the camber has been set and final shims installed.

Hub and spacers tapped into lower wishbone mount

The last time I can say it - a heavily greased shaft!

Differential flange set up with no spacers/shims

Hub installed - it feels like a major milestone!

The final finishing touch was to make some plates to cover the hole for the ABS sensor in the top of the hub carriers.  Most people seem to leave these open but that just offends my sense of perfection!  

I made up a greasy finger paper template, stuck this to a piece of 2mm sheet steel, and cut/filed this down to the required profile.  The fixing hole locations were marked out and drilled with a 6mm drill.  The plates were of course treated to some candy red powder coating (as with all the other bits that won't be seen on the final car...).  I also cut out a couple of gaskets from rubber sheet, to match the outline of the plates, and then these were fixed in place with some stainless steel M6 button head screws with spring washers.

Greasy finger paper template

Powder-coated plates and rubber gaskets

Cover plate fixed in place

A very productive day - time for a well-earned beer me thinks!

Rear Axle Reassembly - Part 8 - Tubeway Army

 With my rubber gaskets sorted, it was time to get the brake back plates bolted onto the hub carriers. 

Although as I was mocking up the parts for reassembly, I noticed that the brake back plates are not particularly stiff where the handbrake cable passes through them.  The AK handbrake has come in for a bit of stick on many forums for its rather marginal performance.  My thought was that if the back plate flexes from the applied tension in the handbrake cable then this could be a factor in reducing the efficiency of the system.

The original Jaguar setup had a small spigot tube bolted to the back of the backing plate, through which the handbrake cable passed, and then a plastic clip between this tube and the hub carrier to hold the handbrake cable in place.  It is conceivable that this arrangement could offer some sort of limited bracing between the hub and the back plate (although that's possibly wishful thinking).  In any case, this option was not available to me as my original spigot tubes are now a fine lacework of rust and replacements are not available.

A small spot of tin worm...

My solution was to make a couple of spacer tubes to sit between the hub carrier and the backing plate that would serve to brace the backing plate and reduce any flex during application of the handbrake and also protect the exposed part of the handbrake cable from the elements.

This was an opportunity to press my "new" lathe into action.  This is a story in itself, but the short version is I foolishly put a bid on an old Myford ML7 lathe on the well-known auction site thinking that I would be outbid...and ended up winning the bid.  To be fair, it was in pretty good condition and came with lots of tooling, so it was a very reasonable (if unexpected) purchase.

I made some measurements and knocked up a quick CAD sketch of my intended solution, being a tube with a flange at each end to bear onto the hub carrier at one end and the handbrake mounting block at the other, with a small stub at each end to locate tube in position and a hole large enough to allow the clevis on the end of the handbrake cable to pass through.

Original Design Sketch

The spacers were machined from 25mm aluminium bar stock, faced and turned to size, a 12mm hole drilled down the middle, and finished off with a boring bar (twist drill bits do not produce a true circular hole).  I made the stubs at each end slightly longer than my original sketch (to facilitate machining) and I also machined a groove in the hub carrier end to allow the use of an O-ring to fully seal the tube to the hub carrier.

Aluminium bar after initial facing and turning - with tail support

Machined down for stub at one end

Location of flanges marked out

Spacer waisted out between flanges and larger stub formed

Drilling 12mm dia hole after 6mm pilot 

Completed Spacer Tube

Spacer in place between hub carrier and back plate

And to finish off this completely over-engineered component that will probably never be seen by human eyes again, I powder-coated it in the obligatory metallic red that I have chosen for all such parts on the car!

Further unnecessary bling!

Now I think the hubs can finally be fully reassembled.