Escort Upgrades - Transmission

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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

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

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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

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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:

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

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Gearbox Strip

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Main-shaft & Input shaft

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Gearbox Rebuild

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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 some like me with a lawn mower! You have been warned! Flapper-bat!

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