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 - overdrive on second gear

Is it possible to get overdrive on secondgear. Have heard you can and what needs to be done.
Norman Matthews

You can bypass the lockout switch at the transmission and then you will have overdrive in all gears. If you do this the added torque on the overdrive in the lower gears will shorten its life. If you put it in reverse with the overdrive engaged you can distroy the OD very quickly.
John H

Why would you want to?
Ross Kelly

I put an overdrive in my car about ten years ago and it has workede fine. Recently, If left in O/D when shut down It will commence in 1st O/D and stay that way until I turn it off. Occasionally when in 2nd I can go to O/D a bit If I choose. The shift into O/D is much slower then in 3rd or 4th which I use a lot. I know this is dangerous if it goes in reverse. I do not believe 2nd O/D is going to hurt anything, do to torque. The 74 engine has only about 80HP at its best and there is no way its a torquey engine. I've even seen where a super charger will increase its Hp from what is really the 50's range. I just don't think the engine has enough torque to worry about. BOB
Bob Ekstrand

Some Triumph cars had OD on 2nd because they had a stronger OD than MGBs. V8s were modified to have OD on 4th only because the torque in 3rd was damaging them. There isn't OD on 2nd in MGBs for a reason, although you would have to use it pretty violently to cause the damage. Simply bypassing the lockout switch (or not bothering to install one) is extremely risky - you may remember to manually switch it off but others might not, and UK cars are driven by others on the MOT at least. You could say "switch it off beforehand" but there is nothing to say the mechanic won't accidentally turn it on. Some American cars had additional switches on the gearboxes and one of these operated in 2nd and 4th while the original OD switch operated in 3rd and 4th. If you wired these in parallel you would have OD in 2nd, 3rd and 4th but still have the safety of the lockout switch.
Paul Hunt 2

Many thanks for the advice all. Paul you have a very sound point.
Norman matthews

Hi Norman
A simple way to get overdrive in 2nd gear and 1st as well (but you'll probably never use 1od)
Bypass the od switch at the gearbox but put a relay in the od circuit and feed it from the reverse light switch.
By hooking it up this way you get od in all forward gears but when reverse is selected the od drops out
I ran a fairly highly moified 70MGB road car set up like this and it copped a fair bit of abuse over about four years of road and competition work and never had any trouble with it at all (lots of full throttle 2-2od changes) You'll find 2nd od a fairly handy gear especially if you do a bit of hillclimbing etc.
Hope this helps Gary
Gary

Still risky as it depends on the reverse light switch, its wiring, plus the additional relay and its wiring to lock the OD out in reverse.
Paul Hunt 2

Gary

Thank you for your information its the 2nd O/D i need when using the car up the Hills in this area of the UK. Again Paul would need to be sure to be sure!!!!!!!! Rgds Norman



Norman Matthews

Norman, I did this conversion to a later TR6 which only had OD on 3rd and top, it is a very worthwhile mod, I tapped the gearchange remote for an extra inhibitor switch as the boss is already cast. As Paul says whatever method you use it must be impossible to engage OD in reverse and I would also say it's inadvisable for it to work in 1st.
Ron
R. Algie

why would you want to do this in an MGB? With OD you have 6 ratios already...and if you DO hit reverse and back up even momentarily, you'll need a new OD unit.
P J KELLY

I find there is quite a gap between 2nd and 3rd. Not really noticeable on the flat, but in hilly country like parts of the Bristol area you have to rev the knackers off it in 2nd to stand any chance of being able to hold 3rd, so I can understand why Norman is interested. If you take the additional switch route, using the fore and aft movement of the selector rods to operate the switch, there is no more risk of having OD engaged in reverse than there is with the factory arrangement. You would need to use the same type of switch and not some flimsy micro-switch as the original is very robust and virtually unknown to fail in the closed position.
Paul Hunt 2

The biggest advantage I find is in heavy traffic, you can just snick in and out of overdrive rather than changing up and down between 2nd and 3rd [OK I'm lazy!]
Ron
R. Algie

This thread was discussed between 07/04/2008 and 13/04/2008

MG MGB Technical index

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