Escort Transmission

Escort Upgrades - Transmission

Mobirise

Left - Mk3, Right Mk4

The mk3 & 4 Escorts came fitted with either a manual or an automatic transmission. Early manual transmissions were four speed but the majority were 5 speed. The extra gear lives inside a bolt on extension on the end of the main casing as can be seen in the picture above (both are 5-speed transmissions).
I have no details of the automatic transmission, sorry.
The manual transmission uses the fully synchro-meshed Ford BC type gearbox. All models used the same basic gearbox but with variations to the final drive ratios.

The sporty models final drive ratios were:
XR3i - 4.29:1
RS1600i - 3.84:1
S1 RS Turbo - 4.27:1
S2 RS Turbo - 3.82:1

There are differences between the mk3 & 4 gearbox cases though due to the revised method of gearbox mounting in the mk4 car.

The Mk3 gearbox uses a cast alloy arm bolted onto its forward face that attaches to a rubber mount on the LH forward suspension mounting plate and a bracket attached to the diff housing that attaches to a rear mount at the bulkhead. As can be seen in the photos below, the attachment point for the forward mounting of the Mk3 gearbox is not present on the revised Mk4 gearbox. Apparently some very early Mk4 gearbox still had the mounting platform in place on the casting though without the four holes drilled and tapped. These were probably end of line Mk3 units that were carried on into the new Mk4 production and with careful drilling and tapping could be used in the Mk3. I have not however seen any of these boxes myself so cannot say they definitely exist. If you do find one and decide to drill and tap the unused mount then be sure not to drill too deep or you'll puncture the casing.

The Mk4 car's gearbox is supported by an additional bolt on cross-member running from front to back of the engine bay at the bellhousing position. This bolt on cross member, incorporating two rubber mounts and known as the gearbox cross member, is fixed in place to the shell by four bolts (two in the front cross member and two at the base of the bulkhead) and to the gearbox by lower bell housing bolts. Due to the fact that it locates onto the gearbox by utilizing the bell housing bolts it is possible to fit a Mk3 gearbox to a Mk4 car.

Limited Slip Differential

Mobirise

A limited Slip Differential unit (LSD) was fitted to the top spec Series 1 & 2 RS Turbo cars to try to control wheel spin and improve traction. Fitment of these gearboxes is a good idea for high performance cars and there popularity and the fact that they were only fitted to one model makes them rather sought after so they command higher prices than the other gearboxes. However, there are no external physical differences between the LSD equipped gearbox and the standard gearbox. So how can you tell if the gearbox you are buying actually does have an LSD fitted? If the gearbox is still fitted to the car then jack the front end up so both front wheels are clear of the ground. Turn one of the wheels by hand and watch the opposite wheel. If it turns in the same direction then the gearbox has an LSD fitted. If it turns in the opposite direction then the gearbox has a standard differential gear fitted. Use the same method if the gearbox is removed from the car but still has the drive shafts or C.V. joints fitted.

If the gearbox is on it's own with the drive shafts removed then you obviously aren't going to be able to turn anything. However, you can still check the LSD is present as you will now be able to see it.
If you look through the output/drive shaft holes in the diff housing of the gearbox you will see one of two possible things:
If you see a metal bar across the hole as shown in the view below then the gearbox has a standard open differential fitted (the bar can be at any angle as it rotates with the differential gear).
If you see no bar present but what looks like a thick washer deep inside then you have an LSD equipped gearbox!

Standard Open Diff.

LSD

Standard Open Diff

LSD

There are differences between the Series1 (Mk3) and Series2 (Mk4) RS Turbo gearboxes though that go beyond the mounting differences detailed above.

The Series 1 RS Turbo was a proper homologation car with true motor sport routes and received the LSD as a result. The LSD unit could be harsh in operation and the final drive ratio was lower geared. The series 2 RS Turbo however was not a homologation car so it was toned down and re-tuned to be more civil for everyday driving. Therefore the LSD unit was altered to be smoother in operation and the final drive ratio was revised to give it longer motorway cruising legs. The other change was the way in which the crown wheel on the LSD unit was secured in place. On the Series 1 gearbox it is held onto the LSD by six bolts whereas on the Series 2 gearbox it is secured by eight bolts. Therefore the crown wheels cannot be swapped between the two LSD unit's. This means that if you whish to fit a Series 2 LSD to a Mk3 gearbox you also have to fit the crown wheel and final drive pinion. In the same way, if you wish to fit the Series 2 crown wheel and pinion to your Series 1 RS Turbo to get the higher gearing then you also need to use the Series 2 LSD unit.

Upgrades

Apart from complete gearbox swaps for either 4 speed to 5 speed or for different stock ratios, there's not a lot that can be done transmission wise that I know of except for the fitting of a limited slip differential.

Changing from a 4 speed to a 5 speed should as far as I know be a simple task of swapping the two complete gearboxes over. You will of course also have to swap across the gear selector linkage, though chances are your original 4 speed linkage is probably pretty worn out by now anyway. I don't know for definite but I seem to recall hearing somewhere that the gearbox and engine mounts might have been tweaked slightly when Ford started fitting 5 speed boxes to the Escort in order to move the whole engine and transmission assembly closer to the drivers wing. This would make sense as it would provide a little more clearance for the 5th gear housing of the 5 speed box. However, I have not yet had this confirmed. It is just something to bear in mind. If you do carry out such a conversion and discover that this is or is not the case then please do let me know so I can amend this page of the site.

Fitting an LSD

Mobirise

Fitting a limited slip differential gear to your gearbox might sound like a bit of a daunting task and many might argue that it would be easier to simply fit a gearbox from a Series 1 RS Turbo that comes with an LSD already fitted and bolts straight into a mk3 Escort.

However, the Series1 RS Turbo has a relatively low geared final drive which isn't ideal for higher speed motorway cruising etc..
The Series2 RS Turbo had a higher geared final drive for more relaxed high speed driving making it the preferred choice. Unfortunately, as already covered in the compatibility section, being a mk4 car the Series2 RS Turbo's gearbox won't fit into the mk3 Escort.
There are two way around this problem. The first is to simply fit the mk3 gearbox outer casing to the Series2 RS Turbo gearbox allowing you to mount it into the mk3 shell, or remove the required innards from the Series2 RS Turbo's gearbox and fit them into your own mk3 gearbox.
The first option is the easiest option and will work fine as long as the donor gearbox is in good condition. However, many RS Turbo gearboxes have led a hard life and the gearbox is known to be the weak link in the performance Escort.
My original gearbox has been recently reconditioned when bought so I knew it's internals were good. I therefore opted to take the second option, keeping this known good gearbox and transferring the required internal parts to my good gearbox.
This was achieved in the following steps:

Parts Required from the donor gearbox:
LSD assembly
Bare main-shaft with final drive gear (single piece unit)
New:
Gearbox rebuild kit (gaskets, seals, bearings and spring rings)

As this is a rather complex in-depth job I have broken it down into more manageable chunks.

Mobirise

Gearbox Strip

Mobirise

Main-shaft & Input shaft

LSD Prep

The LSD has a tapered roller bearing on each end. These mate with the corresponding bearing races in the gearbox casing halves. As you are fitting the LSD to another gearbox, you will be mixing the bearings with other races which is not good practice. As the gearbox is totally stripped, now is the time to replace bearings with new. Problem is, the bearings on the LSD aren't very enthusiastic about being removed and there isn't enough space to get a bearing puller in underneath them.

The only option is to destroy the bearing carrier and then carefully grinding the inner race off.

The inner race should be ground through on two opposing sides to split it and relieve the clamping pressure it is imposing on the LSD.

The inner race removed.

The new bearing can then be pushed into place.

The other bearing may well need similar treatment to remove it. Or you might find that a bearing puller will do the trick as there is a bit more space to play with. However, you must take care not to damage the nylon speedo drive helical gear.

Bearing and speedo drive helical gear removed.

Nylon speedo gear in place.

Tapered roller bearing being pushed into place.

All ready to be installed (after cleaning and removing the black tape).

Mobirise

Gearbox Rebuild

Mobirise

The contents of this website are purely a reflection of my own experiences and knowledge gained whilst working on my various projects. Anything you do based on what you have read here is done so entirely at your own risk.
Personally I wouldn't trust someone like me with a lawn mower! You have been warned! Flapper-bat!

Made with ‌

Easy Website Builder