Jul 152016

I’d been lucky to have an opportunity to drive an unmolested E-Type while on my recent travels (Sydney in an E-Type) and wanted to return the favour when the Christopher was next back in the UK. Not least because he would be able to give valuable feedback, good or bad, on how the two cars compare.

Crossing the Sydney bridge in an E Christopher’s original S2 FHC

I had experienced slight gear selection issues with mine when changing from 2nd to 3rd and from 3rd back down to 2nd – something I might cover in a future post. Although these were more due to being used to modern gearboxes and resolved by adopting a more sympathetic technique changing gears.

I had decided to keep reasonably close to the original spec. The most noticeable differences are the EDIS electronic ignition system and the Mangoletsi cable throttle linkage. The EDIS system hasn’t been properly mapped yet so the only real difference between our cars was the throttle linkage.

Christopher’s visit coincided with the car’s trip up to the trimmers to fit the hood. It had been up with Suffolk & Turley for a lot longer than expected and so the only opportunity for a drive was on the day he was returning to Australia.

This would have been fine had the MOT not expired while it was up at the trimmers. It had been there so long I hadn’t had an opportunity to organise a test since getting it back and now the speedo had seized. It might be possible to get away with a broken speedo on a modern car as the MOT tests are all static and the brakes tested on rollers.

However due to the limited slip differential, the E-Type had to be tested out on the road whilst travelling at 20mph. Braking efficiency is measured using a calibrated decelerometer. Therefore it would be glaringly obvious that the speedo wasn’t working. So it was a race against time to get the car road legal before he left. No pressure then!

To make matter worse, I’d noticed the ignition warning light wasn’t going out indicating the battery wasn’t charging. I had a matter of days to resolve both issues and get the car through the MOT. Things weren’t looking too promising, especially when I contacted Speedograph Richfield as the speedo hadn’t turned up as expected. I had specifically asked for a 24 hour delivery but they had forgotten, sending it out 2nd class and without the ability to track it. Aaaaaah …. and relax!

I was more concerned about the charging system since I had modified my alternator to a more modern design. This eliminates the 3AW and 6RA relays so the only two things that could be wrong were the 4TR voltage regulator or the alternator itself.

Modified alternator doesn’t need 3AW
and 6RA relays … less to go wrong!
Three additional diodes (trio) have been
added to self-energise the field coil

A failed 4TR regulator is fairly easy to diagnose. The unit is simply removed and a jumper lead used to link its connector’s F and – terminals together. Essentially this just puts the full battery voltage across the field winding and removes the feedback loop.

Alternator components

As the alternator starts spinning it’s output voltage increases. Without the feedback, the increased output increases the current in the field coil which, in turn, increases the alternator output voltage.

It would quickly reach a run away situation and burn out the alternator coil. Therefore, as soon as you’ve registered that the output voltage is increasing, you need to immediately switch off the engine.

I had pre-ordered another 4TR unit as a precaution but it wasn’t found to be faulty. It was the alternator. The modifications I’d made to the internal electrics and external wiring give it a ‘soft start’. The voltage across the field winding starts at approx. 1.5v rather than the full 12v battery voltage.

This is because the battery voltage is applied across the ignition warning light bulb (approx. 300 ohms) in series with the field winding (approx. 4 ohms). Hence the lions share of the voltage drop is across the bulb rather than the field winding.

The measured voltage without the engine running was 2.74v which seemed a little high. I incorrectly deduced this would result in an increased current flowing in the field coil, which wouldn’t be a bad thing. Once the engine was started, this voltage only rose to 6.36v rather than the expected 14.4v.

The rotor field coil voltage was
higher than the expected 1.5v
With engine running, the field coil
voltage should rise to 14.4v

A reduced output typically points to failed diodes in the rectifying bridge. This became my main focus. The bridge needs to be removed from the 3-star stator windings in order to test the diodes. So the alternator had to be taken apart and it revealed some interesting problems.

The AL post’s insulating piece had disintegrated. I wasn’t able to source a new one and had to rebuild it as best I could, with araldite making up for the missing bits! Not ideal but it should do for now.

Pulling the pulley wheel AL post insulator had disintegrated Temporary fix – rebuilt with araldite

The original slip rings piece was found to be cracked so I had replaced it when the alternator was rebuilt. The replacement has raised sections between the rings but, as the brushes sit either side of them, I thought nothing of it.

These raised sections had been in contact with the brush holder and had worn a groove in the nylon housing. The slip rings looked clean enough but I gave them quick polish with wire wool.

Difference between slip rings Signs of rubbing on raised sections Groove worn in brush housing

My multimeter has a diode checking function so it was easy to check the diodes once the bridge had been removed. My suspicions were that one or more of the additional three diodes I’d added for the alternator modification had failed. They hadn’t and all the diodes were fine.

Removing the rectifying bridge Diodes can now be tested

The other standard checks were made; the resistances of the rotor field and stator windings and the insulation between the rotor coil & rotor and the stator winding and stator laminations. All were fine … and I was stumped.

The alternator was rebuilt and put back on the car to test but there was no change. The ignition warning light stubbornly refusing to go out. I was getting fairly despondent. It was lunchtime, the alternator was in pieces on the bench yet again, there was no sign of the speedo, the car had no MOT and Christopher was due to turn up first thing the following morning!

For some reason I decided to measure the combined resistance of the rotor field winding and brushes. The rotor winding should be around 4 ohms. With the brushes included, I would have expected something in the order of 5 to 10 ohms (max). It varied between 30-40 ohms depending on the rotational positon of the rotor. This was way too high and would result in a significant reduction in the current in the rotor winding and therefore the output of the alternator.

Slip rings required light sanding Checking coil to rotor insulation

As a last resort and even though the slip rings had initially been cleaned with wire wool, their surfaces were sanded down with a fine wet and dry sandpaper. The combined resistance dropped to only 7 ohms. The alternator was quickly rebuilt and tested. Eureka – it was working!

I’m fairly sure the cause was due to the slip rings impacting the nylon brush housing. The resulting friction had melted the nylon to form the groove and some of the molten nylon had formed a glaze on the slip rings. The sharp points of the multimeter’s leads would penetrate the glaze to give a false impression of the resistance seen by the brushes.

I was expecting an initial voltage across the field winding of 1.5v rather than the measured at 2.74v. The higher voltage was due to a high combined resistance of the field coil and brushes compared with the 300 ohm bulb.

Refitting the alternator
… for the 4th time!

In total I had removed the alternator, taken it apart, tested each component, rebuilt it and retested it four times to get it working!

It was such a relief to get to the bottom of the problem and things started to look up when the postman arrived clutching the speedo. The garage kindly rescheduled things and its second MOT was passed late in the afternoon.

The following morning Christopher and I headed off for a drive and dropped in on his parents. His father had also had an E-Type years ago so it seemed fitting to vacate my seat so he could also go for a spin.

The feedback on how the two cars compared was positive too. The driving experience was very similar which was pleasing as there’s always a fear a restoration could change things for the worse.

Chris takes his father for a spin

One item that got the thumbs up was the PD Gough exhaust which has a lovely throaty roar from 2,500 rpm.

Something I can thank the administrator of the E-Type forum for as his advice was to stick to the standard cast manifolds, avoid the big bore systems and fit 1.75″ tubes with straight through silencers and straight through resonators.

Jul 052016

The joy of finally having the hood completed was short lived. I had hoped for at least a reasonable period of trouble free motoring. Alas, as the speedo had packed up on the way to the trimmers, I now found myself having to take things apart and rather urgently. Its 2nd MOT is overdue.

There are two issues to address; firstly to investigate why the wretched thing has stopped working and secondly to have it re-calibrated. It was reading a mere 56mph whilst following a lead car travelling at 70mph – 20% too low. The suggestion from the E-Type forum was to send it to Speedograph Richfield for the recalibration. So that left just tracing why it had stopped working.

The cable was detached from the back of the speedo in order to see whether the inner cable was rotating whilst driving. It was not. So this pointed to issues at the gearbox end. Most likely a failed angle drive, which is a known weak spot if everything isn’t operating smoothly. I didn’t want to contemplate if that wasn’t the cause. The only other option would be the speedo driven gear, which would require the engine & gearbox to be removed due to the lack of clearance.

Location of angle drive. Unfortunately the trim
had been put back in place since this was taken
A faulty speedo driven gear needs engine &
gearbox removal, as it’s removed sideways

Even so, accessing the angle drive is not easy, let alone getting it off once you have! The transmission tunnel is so close, the gearbox needs to be levered to the left side in order to withdraw the angle drive. The two options are from above, removing the seats, radio & centre consoles and gearbox cover or attack it from underneath.

It was almost possible to get at the angle drive from below with a very small pair of mole grips when the rear was raised on ramps. However the grip’s handle impacted the gearbox mount. At least it confirmed that it should be possible from below.

Exhaust was lowered to gain
access to the angle drive

The plan hatched was to lower the exhaust by undoing the mountings rear of the front downpipes rather than removing this whole section of the exhaust. The gearbox would be supported in order to remove the gearbox mounting.

In my haste I’d completely taken leave of my senses. Even though I had supported the gearbox, I’d forgotten that the supporting spring in the gearbox mounting was still under considerable compression.

I merrily set about undoing all the rear mounting bolts a bit at a time. As soon as the third of the five bolts was removed, the spring suddenly ‘let go’ with an almighty bang, pressing the gearbox mounting against the bodywork on one side and the dropped exhaust on the other.

Fortunately there was no damage but it was quite a shock and I was cursing myself for not reading the manual first! By trying to cut corners and not remove the rear exhaust section, I had created another issue. I now had to find a way of pushing the rear mount back into position in order to remove the last two bolts. However the exhaust was in the way and was now supporting one side of the rear mount that had been pushed down by the spring.

By chance I found a thin block of metal which fitted in the narrow gap between the silencers, enabling the bracket to be jacked back into position. Phew, but it was a nervous time removing the last two bolts. The angle drive was then unscrewed with mole grips and removed, while levering the gearbox over a few millimetres with a short length of 2″x4″.

Supporting the gearbox while
trying to jack the gearbox mount
to compress the support spring
The driven shaft from the gearbox had
been pulled out of the faulty angle drive
Note: round shaft, squared at one end

On initial inspection the angle drive did appear to be broken. The square shaft that engages with the driven gear in the gearbox was detached from the angle drive. Although this could have been caused during removal. This shaft looks a though it is made from a very tightly coiled wire which gives it some flexibility and is squared off at the output end. The internal end is left rounded and is simply held in place by an interference fit and it was this that had failed.

SNG Barratt didn’t have any in stock and wouldn’t for several weeks. So I called Speedograph Richfield to see if they had any available. They didn’t but during this conversation I found out that not all angle drives are equal. The correct one for E-Types has a ratio of 1:1.27. Other makes and some other Jaguar models had a 1:1 ratio. Externally they are identical so I needed to make sure I sourced the correct ratio.

Searches on angle drives in the E-Type Forum confirmed the variations. Hmmm …. could it be the angle drive causing the low speedo readings rather than my speedo needing to be re-calibrated? The test reading of 56mph multiplied by a ratio of 1.27 gives 71mph. Too close to the speed indicated in the lead car to be a coincidence.

Sure enough, the ratio of the old drive was found to be 1:1. A rolled up Post-It had been inserted into the old angle drive to check the rotation of the output drive for one revolution of the input shaft. The same test was repeated on the new angle drive to confirm a correct 1:1.27 ratio before it was installed on the car. The replacement angle drive had a shorter drive shaft so it should be easier to fit as it won’t require the same amount of clearance.

Checking the ratio of
old angle drive
Exercise repeated for new
drive before fitting
Newer drives have shorter shaft
– much easier to fit!

I still hadn’t got to the bottom of why the old angle drive had failed. Did it just fail or was it caused by other components? The cable was removed from the car and all appeared to be in order. There were no kinks and it was operating reasonably smoothly by hand.

It was a good opportunity to clean and re-lubricate the cable and the inside of the sheath. I wiped the cable with some silicone lubricant as some advised that grease can cause binding problems further down the line. Grease or oil will also have a tendency to migrate up the spinning cable which acts as an Archimedes screw, potentially causing damage to the speedo itself.

The cable was reattached to the speedo to check it could still rotate freely and not bind. It couldn’t be turned at all! The speedo’s input drive had seized. This explains why the weakest link in the chain had failed – the interference fit of the round shaft into the angle drive.

The conclusion is the seizure in the speedo would have stopped the cable from rotating. This in turn would have stopped the output of the angle drive from rotating. With the angle drive locked and the input shaft still being driven from the gearbox, the round end of the input shaft would have failed rather than the square end.

With the cause identified, the new angle drive and cable could be fitted back on the car. The exhaust was removed first so the gearbox mounting bracket could be easily jacked into position. It was also a good opportunity to finally fix my wonky tail pipes.

Something I should had done at
the outset – remove the exhaust!
Access to the gearbox mounting
bracket is much easier
Jacking the mounting bracket
into position to fit the bolts

All the instruments and gauges had been professionally restored many years ago and safely put in storage until needed. So I was rather disappointed the speedo had failed after only 500 miles. It will now have to been sent off for repair.

The input drive into the speedo performs two tasks; i) driving the needle and ii) driving the odometer/trip distances. At the internal end of the input shaft is a worm drive and an input disc containing permanent magnets.

The worm drive simply rotates another gear wheel which then drives gears for both the odometer and trip distance mechanisms.

In close proximity to the input disc is a similar sprung disc containing magnets to which the speedo needle is attached. As the input disc starts to turn, its magnets attract those on the needle disc causing it to turn. The faster the input disc rotates, the greater the torque on the needle disc due to the magnetic attraction.

Brass worm gear turns nylon gear
that drives odometer/trip distance
Input disc rotates within the
needle disc

A hairspring on the needle disc counters this rotational force, stopping the needle disc from free wheeling. The amount the hairspring coils is proportional to the rotational force and therefore road speed.

Speedograph Richfield can either calibrate the speedo back to the factory settings or calibrate it to your specific vehicle. I’m fairly sure the new angle drive will resolve the fact that it was reading 20% too low and so the factory settings would be fine. However I’ve also provided the measurements for it to be calibrated to the car, so they can determine if there is a discrepancy between the two.

To do this, they need to know the type of tyres in order to calculate the rolling circumference and the number of revolutions of the speedo cable for 6 revolutions of the driven wheel. The tyres were checked to ensure they were the correct pressures and a chalk line put on the rear tyre to aid measuring exactly revolutions.

To help count the revolutions of the speedo cable, I cobbled together a pointer made from matchsticks which slid onto the square end of the cable. All very high tech! The car was pushed forward with one person counting the wheel revolutions and the other the cable pointer. The average of three measurements was 8 full turns and 290 degrees (+/- 5 degrees) for six revolutions of the rear tyre.

Mark to accurately a full revolution My matchstick speedo cable pointer!

It is now with Speedograph Richfield who have indicated it should be returned within the week. A pretty good turn around. So fingers crossed this will be the end of my speeding troubles.