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MG MGB GT V8 Factory Originals Technical - LT77 Gear Ratios

Can anyone tell me the ratios for a late model SD1 LT77 gearbox. This has the larger Input shaft and uprated oil pump/ I belive the fith gear ratio is .78/1 as opposed to .82/1 of the earlier box, but am uncertain as the ratios of the intermediates. Can anyone supply this information.

Kevin Jackson
Kevin Jackson

Kevin,

The ratios should be -
5th 0.792
4th 1.000
3rd 1.396
2nd 2.087
1st 3.321

As far as I know the oil pump didn’t change throughout the life of the LT77 box, could you give me some details of what the upgrade is please?

Incidentally, don’t use ATF, fully synthetic SAE 75W-85 manual gear oil such as Castrol SMX-S has better lubrication, improves the change quality - especially when it's cold and it won’t leak so easily.

Geoff
Geoff King

Note what Chris Crane of RPI says about this gearbox:-

"It has become almost impossible to find a Rover SD1 (LT77) 5-speed transmission in good condition, in fact we have found it almost impossible to find them even in 'reconditionable condition'. Therefore, if we have an LT77 'used' for sale, it's spares or repair only, even if in seemingly very good order, such is our lack of confidence in these older transmissions for modern application/use."

http://www.rpiv8.com/transmission-3.htm#5spd

Maybe you should think of an R380 or better still a JT5 based on the Borg Warner T5 World Class platform.

http://www.5speeds.com/concept.html





Nigel Steward

Just seen there's a suitable T5 on e-bay:-

http://cgi.ebay.com/ebaymotors/MGB-V8-TR8-T5-Borg-Warner-Transmission-Conversion_W0QQcmdZViewItemQQcategoryZ33733QQitemZ8018787255QQrdZ1QQsspagenameZWDVW

Nigel Steward

Geof, thanks for confirming the intermediate ratios. They are in fact what I have in my gearing calculator, but was not sure if they were correct.
I had the gearbox rebuilt with new bearings and synchros and my gearbox man told me it was a late spec (D?) which has a larger input shaft and bearings, and a better oil pump, more than that I cannot tell you.
Nigel, The gearbox has been in the car for some time and was set up to run with ATF apparently you use different synchros if you use gear oil, I just went with what my gearbox guy said would be better.
The box is still a little baulky when cold but eases up once warm, so I will have to live with it. I must admit to favouring the T5 having driven a Sierra cosworth RWD with that box, and it had a much sweeter change, but when I did the conversion to V8 I was lucky to source an engine and box locally from a late SD1 with low mileage which was confirmed when we stripped the engine prior to rebuild and modification.
Engine spec is 3.5 with 9,75-1 compression stage 1 heads Real Steel Hurricane Cam, Edelbrock/Weber and performr manifold and RV8 exhaust system and produces more than enough power for road use,I might add that the braking system was fully rebuilt and upgraded with SD1 4 pot calipers and V8 discs.I am currently sorting out the suspension, to principly improve the drivability and hopefully find a bit more grip. The car is on 6x15 minilite replicas with 195/65 x 15 Pirelli 6000 tyres which were good value and seem quite grippy.

Kevin Jackson.


Kevin Jackson

This thread was discussed between 29/11/2005 and 30/11/2005

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