Gearbox Part 3 - Electronics!

Back in the good old days, a manual gearbox was a simple matter of some magic mechanical coggery hidden in a case, with an input shaft, an output shaft and some sort of shifting mechanism to change between the (then four) gears.

Clearly, things have moved on, and not just in the number of available gears.  After unboxing my Tremec T56 gearbox I noticed a number of electrical connectors dotted around the casing.  After some internet research, I discovered the following:

The connector at the front left-hand side of the gearbox casing is for the reverse light switch i.e it activates the reverse lights when reverse gear is selected.

Reverse Light Connector

The connector at the rear left-hand side of the casing is the VSS output (variable speed sensor) which is used to send a signal to an electronic speedometer (there is also a mechanical speedometer output on the opposite side to the VSS connector - as I will be using the VSS option the mechanical output needs removing and replacing with a blanking cover).

VSS Output Connector

Mechanical Speedo Output (will be removed)

Finally, the connector at the rear of the casing behind the shifter location is for the reverse lock-out solenoid.  This is a safety feature and prevents inadvertent selection of reverse gear while the car is travelling forward at great speed; on production cars the solenoid is automatically controlled by the car's ECU to only allow reverse to be selected when the car is stationary.

Reverse Lockout Solenoid Connector

So how to control the reverse lockout solenoid?

The reverse lock-out is apparently just a spring with a ball-bearing detent.  This can be overcome with brute force but clearly is not recommended by Tremec and could lead to damaging the gearbox.

Other solutions suggested involve the use of a microswitch on either the clutch pedal or brake pedal to operate the solenoid - on the basis that you would probably have your foot on one or the other or both when preparing to select reverse gear.  The downside is a) the solenoid would operate every time the brake or clutch pedal was pressed so possibly leading to premature wear and failure and b) if the brake or clutch pedal was pressed at 100mph (not unlikely) the solenoid would operate and so it would still be possible to select reverse gear at a high forward velocity, which kind of defeats the object of having it in the first place...

There are several aftermarket manufacturers of a small black box of tricks which simply does the job of the missing OEM ECU and, using the VSS output, will only activate the solenoid when the car is stationary or travelling very slowly (typically less than 3mph).  This would probably be the most sensible option.  The downside is that these kits cost several hundred dollars (plus good old import duty and shipping).

Fortunately, the CANEMS ECU that I bought as part of my engine package does have the ability to be programmed to operate a switched output based on the VSS output i.e to only operate the solenoid when the car is stationary.  Will need a bit of loom surgery to accommodate but in theory, all looks quite straightforward.

The final piece of this story is to obtain the various electrical connectors to join up with those on the gearbox.  I bought a kit from Bowler Performance Transmissions in the States; this included all the various connectors each with a short wiring pigtail and a billet blanking plate and bolt for the mechanical speedo output.  I ordered online and was quoted some ridiculous price for shipping (more than the price of the kit) but when I rang Bowler they were able to come up with a far cheaper shipping method.

Contents of the Bowler T56 Install Kit

So looks like I will have some fun when it comes to trying to add these into the wiring loom later but for now, I can get cracking on hooking the gearbox up to my engine and getting closer to installing it in the chassis.

 

Brake Lines Part 5 - Rear Brake Lines and Fittings

I've been putting off completing the rear brake lines as the run from the bracket on the chassis leg at the front of the car to the position of the 3-way connector at the back of the car is rather complicated; not only does it have to follow the bends of the chassis along the transmission/prop shaft tunnel, but it also needs to partially run along the top of the chassis rail and then drop down to continue along the side of the rail.  It's also a single length of pipe of around 1.9m that needs 8 bends put into it accurately so that it fits into the front union and rear 3-way connector.

The other factor was my desire to use my over-engineered brake clips to secure the pipe run and try to come up with locations where these could be installed and maintain fixing centres of less than 300mm.  There is a cut-out in the chassis rail to give clearance to the starter motor which is greater than 300mm.  I was originally thinking to run the pipe down this recess and secure with a clip on the sloping face so that I could achieve the required fixing distances; I went and had a look at Richard Chippendale's build once he had got his engine installed and I am sure there was enough space.  However, as time moved on, I became less confident that this would work (the recess is there for a reason, right?).

My original thought for routing the rear line (in red)

In the end, I concluded that I was going to have to stick with the tried and tested AK routing for the rear brake line and would have to suck up using some P-clips or similar to secure the pipe run along the top section of the chassis rail.

I also decided not to bother with my previous CAD model approach for determining the lengths/bends in the pipe run; with the number of bends and changes of direction (and my limited CAD design abilities) modelling the pipe was just going to take too much time.

Time for PAD (Plywood Aided Design)!

I clamped a piece of 600x1220 plywood to the underside of the chassis and traced the outline of the chassis rails onto the wood.  I could then offset a line, representing the centre of my brake clips, and draw out the line of the pipe run in a handy 1:1 scale!

Time for some Plywood Aided Design...

With some additional 1:1 sketches for the bends down the chassis rail, I was able to measure the length between all the bend vertices and calculate the overall length of the pipe required and the position of my marks for bending.

I cut an over-long section of 3/16" brake pipe and started with the flat bends in the middle of the pipe run, along the transmission tunnel.  This section was bent up and secured in place on my plywood template using some push-in plastic clips.  This helped secure the pipe in place so I could make sure I got the correct orientation of the next bend.

A perfect fit!

I also remembered to put the brake fitting on the rear end of the pipe prior to forming the brake flare!  

Next, I made up the short section of straight pipe at the offside rear, from the flexible brake pipe to the 3-way connector at the rear.  This was a dead straight piece of pipe with the dimensions measured from my 1:1 sketch so what could go wrong?  I don't know what I did but I clearly measured something wrong, such that the first attempt was too short by a country mile!  The second attempt was much better.

Perfect - at the second attempt...

I then installed this section of the pipe and the 3-way union which allowed me to hold the rear of the long rear pipe run in place.  I could then check and double-check the location and measurements for the pipe bends up and over onto the top of the chassis leg before tentatively forming the bends.

Pipe run held in place temporarily and bend over the chassis formed

Where the pipe runs along the top of the chassis rail adjacent to the starter motor cut-out/recess I have elected to use some plastic push-in pipe clips from Car Builder Solutions; these have a small plastic collar, which is inserted into a 6mm diameter hole, the clip then pushes into the collar and clips into place.

Non-over-engineered Plastic Pipe Clip

The next task was to bend the pipe back around to meet up with the union on the front chassis leg.  Again I was sure to install the pipe fitting prior to forming the flare on the end of the pipe and making the bend.

The last couple of bends and everything lined up perfectly!

The last pipe-bending operation was to form the section of pipe from the 3-way connector that passes over the top of the differential nose and joins to the nearside flexible brake pipe.  I had modelled this section of pipe in CAD so was able to print out a sketch with all the necessary dimensions to enable me to accurately bend this into shape.

Last section of pipe bent up and in place

With all bending done I could fix the long run in place with five of my bespoke brake clips (which will also be used to hold the fuel return line to the tank in place).  This fixed the position of the 3-way brake union and using a transfer punch I could locate the centre of the fixing hole on the plate across the rear of the AK chassis.  

Unfortunately, the centre point of this hole was not ideal from a drilling and tapping perspective.  The tubular stiffening cage of the AK Gen III chassis provides enough of an obstruction to prevent being able to use a normal drill.  I had already discovered the need to purchase a 90-degree drill to be able to drill the holes to fix the brake clips along the inner legs of the chassis so this was pressed into action again to drill a 6mm hole.  

However, when it came to try and tap the hole for an M7x1.0 thread it was impossible to rotate the tapping wrench sufficiently to get the tap to start to bite in the hole.  I had to start the tap with a pair of pliers and then do my best with an adjustable wrench to continue trying to tap the hole.  It got to the point where I couldn't turn the tap anymore for fear of snapping it and so I couldn't tap the hole to the full depth.  Thankfully I managed to get enough thread cut so that I just needed a washer under the head of the bolt to get the union tight up against a spacer and all the pipes lined up where they should be.

3-way Brake Union fixed snugly in place

The last job was to drill a couple of holes to insert some plastic brake clips to secure the pipe over the top of the differential nose.  Again this job required the use of the 90-degree drill and several 6mm drill bits and I managed to snap one of the bits whilst drilling the second hole; this left a ragged hole which simply blunted any drill bit which I attempted to use to subsequently complete the hole.  In the end, I had to give up and drill a new hole just to the side of my original attempt.  

Pipe over differential clipped in place

I will, at some point soon, remove all the brake lines, blow them through with compressed air to make sure all detritus is removed and then fully tighten up all the unions for the last time.  I will also put some thread lock on the bolts securing my custom brake clips to the chassis for added peace of mind.

But for the moment the brake lines are done!