MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Competition Overdrive?

What is the difference between the competition overdrive and the regular D overdrive on our cars?
Ralph Ward

Hi Ralph:

I know there is close ratio gear sets available for the MGA/MGB 3 synchro gearbox. The "D" type o/d unit may have had a optional output ratio greater than the regular 20%. Suggest you contact John Esposito at Quantumechanics. John has extensive British overdrive knowledge.

Thanks: Rich Boris
67 B roadster
Rich Boris

imho, it's v8 type overdrive, uprated springs and clutch material liner
michel

Michel is correct.
Bill Spohn

The V8 OD has an uprated hydraulic system, 510-530psi engaged as opposed to the 400-420 of the 4-cylinder LH-type as well as uprated springs and a different free-wheel cage. The output flange is also different. The sliding member carrying the friction material is common, according to the Parts Catalogue any way.
Paul Hunt

So, does the higher pressure mean a more sudden, jolting engagement?
Ralph Ward

The V8 & MGC overdrive units are LH type - not the D type referred to in the original post.

Chris at Octarine Services

Ralph, the only competition overdrive I've driven is my own so I have nothing to compare against, but there is a noticeably more solid engagement than in other overdrives I've driven, including a standard LH in my BGT. It could be due to the high power output of my MGC where it's installed but if you engage the OD while on the throttle, it will put you into your seat.
Steve Simmons

No, the higher pressure holds the friction surfaces together tighter to prevent slipping under the higher torque of the V8. My V8 OD is smoother than my roadster - both LH-type, particularly on throttle-on engagement.
Paul Hunt

Paul Hunt, by freewheel cage do you mean the annulus?
Ralph Ward

The freewheel cage is part of the one-way or Sprague clutch and contains the rollers that 'jam' when the clutch is turned in its locking direction. It's maybe stronger on the V8 again because of the higher torque. It is the one-way clutch that transmits all the drive in non-OD forward gears. The friction material on one side of the clutch sliding member locks to the casing in OD forward gears, and more friction material on the inside of the sliding member locks to the outside of the annulus in direct drive. The annulus is on the output shaft and as well as having drive transmitted to it by the sliding member in direct drive also carries the planet wheels that give the uplift in revolutions in OD.
Paul Hunt

This thread was discussed between 31/01/2009 and 12/02/2009

MG MGB Technical index

This thread is from the archives. Join the live MG MGB Technical BBS now