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.

Rear Axle Reassembly - Part 5 - Rear Wishbones

 With the hubs done and ready to be installed, I turned my attention back to the chassis and the installation of the rear wishbones.

The rear wishbones are new items supplied by AK.  I bought new inner pivot bolts from SNG Barratt as I ended up "slightly" damaging the original ones whilst stripping down the donor axle/rear sub-frame.

The AK setup also requires the use of a spacer tube; these didn't come with my X300 axle but I managed to source a spare pair from Ben at Simply Performance.

Looking at the AK Build Manual, the installation of the wishbones is fairly straightforward.  The (new) outer pivot bolt is passed through the rear of the new wishbone, through two washers, through the rear differential tie bar, through the spacer tube, through the front wishbone mount, through two more washers, and finally, through the differential pendulum mount before being secured with a final washer and bolt.  The pivot bolts were given a liberal coating of copper grease prior to installation.

Simple.

Wishbone, new pivot bolt, washers and spacer tube

Well, it was simple, apart from a couple of small issues.

First, the AK Build Manual calls for the use of 1 1/2" by 7/8" washers.  But for some annoying reason, they don't supply these washers.  This is a complete pain because despite exhaustive internet searching I could not find this size washer outside of the US of A.  Fortunately I was prepared.  Having read Richard Chippendale's blog and his solution of using M22 washers instead, I had already pre-ordered a pack of suitable replacement size washers.

Close-up of wishbone mounting configuration...

...and view of installed wishbone.

The second issue is that the AK Build Manual suggests the use of an M12 is needed for the end of the inner pivot shaft.  This is incorrect.  Had I read/remembered Richard's blog better, I would have already known this.  But I was not prepared for this eventuality, and so there was a short break in the proceedings for another order with SNG Barratt.

(I couldn't actually find the original fulcrum nuts from my donor axle.  But even if I had, they were so rusty from when I removed them, that I wouldn't have wanted to re-use them in any case.)

The nuts are actually I believe an M14 thread.  However, the proper Jag nuts have a bit of a skirt on them.  This helps spread the load more evenly onto the washer on the end of the fulcrum bolt; this washer bears onto the metal sleeve in the bushing in the pendulum mount and a "normal" size bolt might cause some distortion of the washer when tightening.

Nice flange...

Once these arrived it was a simple job to pop them onto the end of the fulcrum bolt, along with an M14 washer and fasten up hand tight for the moment.  I will torque these up fully to around 70-75lb-ft / 90-102Nm once the wheels are on and the suspension is partially loaded.

Next step is to get the drive shafts reassembled before I can refit the hub carriers.

Rear Axle Reassembly - Part 7 - Pig Pen, this here's Rubber Duck...

Before the rear hubs can be reinstalled into the carriers the brake backplates, which hold the handbrake mechanism in place, need to be fixed to the hub carriers.

In my view, there is a distinct flaw in the Jaguar design for this set-up.  The hub carriers are aluminium and the brake backplates are steel.  Fixing the two dissimilar metals together results in a chemical reaction, known as galvanic corrosion.  This accelerates the breakdown of the natural coating of the aluminium and produces aluminium oxide (remember all that white crusty crud under the backplates when the hubs were stripped down).

This process is exacerbated by moisture and salt (like er...road salt) and so to ensure that the conditions for this galvanic corrosion are fully optimised, the Jaguar engineers decided to leave the aluminium mating face of the hub in a rough cast form to really allow the ingress of water, dirt and salt to take place, and then to ensure that it remains trapped in place to do its evil deed. 

A haven for dirt, debris and road crud!

A number of solutions have been proposed on the various build blogs that I have perused; including just bolting it all back together, a liberal application of copper grease, or the use of the dreaded RTV silicone sealant.

I decided to try an alternative solution and go with a rubber gasket.  This should keep the two metal components separated to reduce the opportunity for galvanic corrosion and also, hopefully, keep water and crud out of various nooks and crannies resulting from the rough cast face of the aluminium hub.

I made up an initial paper template. The centre hole was sized by placing the backplate on a sheet of paper and simply running a pencil around the edge of the hole.  This was cut out using a sharp knife and placed onto the hub.  Using a suitably greasy finger, I rubbed over the paper to trace the shape of the edge of the hub and the screw mounting holes.  The template was then completed by trimming the outer edge and screw holes.

Why you shouldn't wash your hands.....

Final template

I then stuck the paper template down onto a sheet of 1mm thick rubber sheet (purchased from that well-known internet auction site).  I used a scalpel to cut around the edges of the template and create the rubber gasket.  The template was stuck down a second time and the process was repeated to create a second gasket.

Template stuck down onto rubber sheet...

...and trimmed to create gasket.

A perfect fit!

Now I have sorted this issue I can press on with reassembly...

Update - Project Snake is still alive (again....)

So in May 2021 I put up a post of hope - hope that I would get some serious work done on the Cobra.  It didn't happen...

I did a few bits here and there (some belated posts to follow) but I had a major distraction with the decision to remove some existing timber decking in my garden and replace it with some stone paving.  As always, the project spiraled and took about 10 times longer to complete than planned (actually at the time of writing it is still not technically complete as the lawn still needs to be relaid...).  Still, my wife is now very happy so maybe, with what is left of this year, I will be able to crack on with the Cobra!

Update photo - the eagle-eyed will spot that it looks almost exactly the same as the update from last year - just wearing slightly more dust!