Quaife Automatic Torque Biasing Limited Slip Differential

Whilst returning home on a wet road from the Lancaster Bomber show the back end of my Mk3 3 litre tried to meet the front end, resulting in a minor impact with another car.

Nobody was injured but I had Theo with me and the thought of what could have happened to him was enough to prompt me into immediate action – to acquire a LSD as soon as.

Trawling for a 3.09:1 back axle would take time and likely to be expensive and with no guarantee it would be a good one. So why not convert the one already in the car. Better the devil you know……

Having had previous experience of Quaife I knew they were good, so a visit to their website revealed they make an Automatic Torque Biasing Limited Slip Differential specifically for the Ford Capri Atlas back axle with 16 splines on the half shafts. But the price nearly knocked me over at just over £900! I bit the bullet and placed an order, with it arriving a few days later.

The box contained a technical spec and a leaflet that gave some tips on installation, but even so a plan was needed to make sure everything was ready and the job could go smoothly.

This is what £900 buys you

Quaife’s technical specification

Two new taper roller bearings were also required for the installation as the old ones had done their job for 32 years. But what was Ford using for the job nowadays? Not SKF or Timken as I would have expected but Japanese equivalents at half the price. A pair was obtained and I was ready to go.

First job was to clean off the waxoyl from the diff unit back plate so I could get at the bolts for the extraction, removing the back plate slowly to give the oil time to drain into a large bowl.

Where it needed to go

Then off with the rear wheels and draw the half shafts out far enough to release the old diff unit.

With the half shafts out far enough to free the diff unit, removal of the bearing keepers was next. With these removed one would think the diff would simply slide out, but no such luck.

These had to be drawn on both sides

This was out far enough to release the diff

The yellow is foam from the oil

Empty diff housing with pinion visible

There are spacers on each end that have a triple purpose.

1. They ensure the unit is a tight fit in the housing – in fact it is under slight pressure
2. They ensure the taper roller bearings have the correct amount of free play
3. Most importantly they are used to adjust correct tooth alignment between the pinion and crown wheel

Quaife’s instruction sheet was explicit regarding these spacers. They had to be replaced on the new unit in exactly the same place and in the same order as they were fitted on the old unit. Any change here would result in a noisy diff unit.

As expected the old unit was in there tightly, in fact it required the help of a small crow bar to lever it out. Once out and on the workbench, the next job was obvious. Change the crown wheel from the old unit to the new one. Haynes manual gives the torque wrench settings for the bolts as 80 –
87 Nm.

Having got the crown wheel satisfactorily fitted to the ATB unit the next job was to concentrate on removing the old bearings and spacers, taking due note of the order in which they were fitted.

New and old units. Bearings still on the old unit

Crown wheel fitted on new unit

View from RH end showing half shaft splines

And LH end. Numbers 663 and 3.09 visible

This job was beyond my capability as I had no suitable bearing pullers. So I contacted Whitmore Engineering who I’ve known for many years and John, who answered the phone, simply said to bring the parts over and he would sort them out.

Within five minutes of arriving he had removed both bearings and freed the spacers. There were 3 of them – a thick and a thin one on one side, and a thick one on the other. After another five minutes they had been carefully placed on the ATB unit end shafts and new bearings pressed home on top of them.

While watching this process, I was thinking to myself, what if….. There’s no way we could have got it apart again without damage. Anyway, job done and I headed home to install what we had accomplished.

Fitting it wasn’t an easy job either and again I’m thinking what if……..
When lined up, it had to be driven home with a rubber hammer and if unsuccessful I would never have got it out again. There was nowhere on the ATB unit where I could have got a purchase with the crow bar to lever it out as with the old unit.

Unit fitted. It looked good when in place and torqued down. Note No. 663 on the pinion

Unit fitted. It looked good when in place and torqued down.

So fingers crossed, I drove it far enough home with the hammer to get the keeper bolts for the end caps to start. Torqueing them down did the rest. The unit was in and what’s more looked good.

The number 663 on both the pinion and crown wheel indicate they are a matched pair. The other number 3.09 is the gear ratio – 34 teeth on the crown wheel and 11 on the pinion giving a gear ratio of 3.0909:1.

Having got the ATB unit successfully installed the next job was to refit the half shafts. They slid into place like they were meant to be there. Locking plate bolts in and tightened and wheels back on.

Next was the diff housing rear cover with a new gasket and bolts torqued down. Oil was another requirement and I filled it with Castrol Hypoy LS – produced by Castrol (when it was Wakefield Castrol before BP got their hands on them) specifically for Limited Slip differentials.

There were no obvious leaks so the next thing was to take it on the road and try it. It was quiet. I ran it up to the speed limit and a bit beyond just to make sure, but it was certainly no noisier than the old diff unit had been.

Then back in the garage and check for leaks. There were none. The unit was warm, but not hot and it needed a top up as oil had no doubt worked its way inside the gear housing.

I’ve since used it in anger a couple of times, accelerating in second gear on a wet road when the old diff would have, without doubt, spun the car.
On both occasions the back end gave a slight twitch and the car then accelerated fast in a straight line, as if on a dry road.

So, job successfully accomplished and as a result I can highly recommend this particular unit by Quaife.

I’ve since discovered that Pete has the same diff unit in his track car – he kept a lid on that information. My experience of it with him on a track day was exhilarating to say the least…


Timing Gears for Essex and Cologne engines

KLCC has become aware that some members have experienced problems when replacing the timing gears on their engines with after-market steel replacement gears.

The fault is insufficient backlash (running clearance), which produces problems in service, the most noticeable of which is a pronounced whine from the gears. This can occur at specific engine revs and is caused by the gears not meshing correctly.

The Ford stated backlash for these timing gears is 0.007″ – 0.011″ (0.17mm – 0.27mm), whereas replacement gears purchased by members have had backlash as little as 0.002″ (0.05mm) – or less.

A backlash of less than the Ford stated limit will cause increased pressure on the oil film between the teeth as the gears mesh with each other. The smaller the backlash, the greater the pressure on the oil film.

With a backlash of 0.002″ (0.05mm) the pressure on the oil film becomes extreme as the oil is literally squeezed out from between the gear teeth.

When in service, the gear teeth will become eroded and pitted due to this extreme pressure on the mating surfaces of the teeth.

It should be noted that engine oil is not capable of absorbing the extreme pressure generated on gear teeth by insufficient backlash. This pressure leads to small particles of metal being torn away by a form of cavitation.

These particles travel within the oil directly into the oil pump where they cause premature wear of the pump housing and rotor lobes resulting in reduced oil pressure.

In one case, on tick-over, this caused oil starvation to the big end and main bearings, necessitating a complete lower engine rebuild.

After investigation into the problem, KLCC has found that the matched timing gears produced by Challenger Camshafts, Robert Street, Darwen, Lancs, BB31DL will solve the problem, as they have matched tooth profiles and typical backlash values of 0.010″ (0.25mm). This complies with Ford specification and also ensures silent running of the gears.

For details on all of their products visit

After three of our members experienced the problem of insufficient backlash and noisy after-market steel timing gears due to incorrect machining, we strongly advise these should not, under any circumstances, be run in the engine.

Any purchase proviso stating “no claims or refunds can be accepted for reason of excess noise,” may indicate that after-market suppliers could be aware of a potential problem. If the gears are machined correctly, there will be no excess noise – in fact, no noise at all.

Even if the after-market supplier refuses to give you a replacement or refund, your loss here will still be cheaper than a bottom end engine rebuild.

Timing Gear