UniBrain Trust

• Parts List
• Procedure
• Pictures
• How does it drive

I decided to go with the SPComponents Ford type 9 gearbox with the semi-helical close ratio gears and a 4.11:1 differential gear.  My decision to go with the 4.11:1 rear gear ration and the SPC transmission was help by referring to a gearing spreadsheet that shows speed in each gear. With the 4.11:1 diff, the old and new transmission give about the same 1st and  top gear effective ratio’s.  The big difference is the 5 speed closes up the gaps between gears and doesn’t leave a huge hole between the top gears. 

Today consisted of removing the rear axle from the car and replacing the differential with the Quaffe 4.11:1 limited slip unit.Removal of the axle was straight forward.To remove the differential, both axles needed to be removed.  I removed the brake drums, brake shoes, slave cylinder and adjusting unit.  Removal of the slave cylinder and adjusting unit may have be unnecessary but one of my axles was a bit stubborn and I needed room for a puller.  After removing the axles, I loosened all the nuts holding the differential in place and removed it.  A little bit of tapping with a soft mallet was necessary to get the unit started.  After it started, it almost fell out.

Inspection of the inside of the axle housing showed small amounts of metal fillings on the internal magnet.  My mechanic friend who was lending a hand said this was normal and nothing to worry about.  Since the axle had less than 2000 miles on it I chose not to change either the axle bearings or axles seals.  If there were more miles on the axle I would have taken the opportunity to change both.

A through cleaning of the interior and exterior of the housing  and I was ready to put the new diff in. (See the picture of the new vs. old when I get the film developed).  Before applying the gasket I wanted to test fit the new diff.  A slight problem.  It didn’t fit.  After looking carefully, the new ring gear carrier was hitting the diff housing.  Was I supposed to notch the housing?  This didn’t seem right.  After a bit of lift, set down, think, scratch, lift, set down, think, stare, think, wiggle, stare, I figured it out.  Carefully aligning  the carrier bolt holes with the diff housing would allow the diff to fit.  The big trick was getting one side of the gear in and slowly rotating the input shaft until the diff fell into place.

As they say in the shop manuals, reassembly is the reverse of disassembly.  The only hitch with the reassembly is I broke one of the spring clips holding the brake slave cylinder in place.  Looks like I’ll be ordering one on Monday.   

Part numbers are from the Caterham Parts CD.  If you haven’t gotten the parts CD, drop everything you are doing a buy it.  The parts listing is complete but the real reason is for some of the racing movies that come with it!

The engine is still at the Jay’s but I’ve ordereda new transmission from SPComponents. I ordered theQuaffe close ratio 5 speed and a 4:11 to 1 rear gearset. In addition to the transmission I also orderedseveral clutch parts from British Auto Specialist.When I receive all the parts, I’ll post a complete parts list and a description of the conversion.