Overdrive

Post by **polo2k** » Sun May 18, 2008 2:26 pm

Hi all, I was chatting with my brother last night and he came up with a thought for the transmission.
Apparently the MGB had an inline overdrive that simply sat on the gearbox output and then you shorten the propshaft to cope with it.
Apparently this was "the norm" on the TR6`s of the past

Has anyone had any experiance with this?

Post by **Alec** » Sun May 18, 2008 4:32 pm

Hello Ash,

the overdrive is attached to the gearbox not a stand alone unit.

I have a Marina engine in our Minor and have a Triumph gearbox with overdrive fitted (Triumphs and Marinas shared a common gearbox at one time. (Known as the single rail gearbox)
A very useful modification.

Alec

Post by **Willie** » Sun May 18, 2008 4:37 pm

I fitted an overdrive box to my MGB and it was inside the gearbox making it longer and needing a suitable prop as you say. To get up to 65 mph in third and flick it into overdrive was a very enjoyable experience!

Post by **paulhumphries** » Sun May 18, 2008 4:42 pm

You can convert certain overdrives to be a seperate unit.
There was an article on how to do such a few years ago in, I think, Practical Classis.
It involved adding an end plate and drive flange.
You needed a lathe to do the work as no kit of parts available (at the time)

I've got a Volvo P1800S gearbox with overdrive and did consider using the unit off that but far easier to simply fit a Type 9 5 speed.

Paul Humphries

Post by **Alec** » Sun May 18, 2008 5:17 pm

Hello Paul,

I don't believe it is practical (possible yes, anything is) to convert the common overdrives that are around. What is involved is making up a new end plate with an input shaft and bearing plus a suitable oil reservoir to operate the overdrive.

Yes a 5 speed is easier but an overdrive is a much more useful system. Particularly as Willie says for overtaking as the change up is virtually instant and can be done on full throttle.

Alec

Post by **AndrewSkinner** » Sun May 18, 2008 5:25 pm

If you add an overdrive wouldn't it get in the way of the cross member? or is it just short enough?

Post by **Alec** » Sun May 18, 2008 8:21 pm

Hello Andrew,

I had to move the cross member back to accommodate the overdrive.

Alec

Post by **alex_holden** » Sun May 18, 2008 8:41 pm

Did you have to make a new gearbox cover or modify the floor to make room for it? What other modifications were required - gearstick, speedo drive, propshaft, clutch?

Anyone know how much a good Triumph gearbox with overdrive costs? Do they have synchro on all four forward gears?

I have to say I find a 4 speed + overdrive a more attractive proposition than a lower ratio diff or a 5 speed box.

Post by **Alec** » Mon May 19, 2008 7:09 am

Hello Alex,

yes, all in all quite a few modifications. I originally used the Marina gearbox which needed cutting down around the bell housing for it to fit, conversion to hydraulic clutch, re-location of the rear crossmember, modified gearbox cover and a small gearbox in line for the speedometer cable to correct the cable speed.

I would add that I have a fairly comprehensive workshop but it was quite time consuming.

Alec

Post by **alex_holden** » Mon May 19, 2008 7:39 am

Possibly a winter project after I've got my saloon back on the road...

Which car(s) would a suitable Triumph gearbox have been fitted to?

Post by **alex_holden** » Mon May 19, 2008 9:01 am

Is this the right type of box?

Post by **Matt** » Mon May 19, 2008 9:26 am

Yup

Need a suitable bellhousing though...

Post by **alex_holden** » Mon May 19, 2008 9:41 am

Matt wrote:Yup Need a suitable bellhousing though...

One from a 1275 Marina gearbox? And presumably a Marina backplate to mate it to the Minor engine?

Post by **alex_holden** » Mon May 19, 2008 9:54 am

BTW according to this page they do have synchro on all four gears and spare parts are available for them.

Post by **superchargedfool** » Mon May 19, 2008 12:13 pm

my comment would be that due to spitfire owners paying good money for these boxes they are in demand and can command high ish prices.

Post by **Alec** » Mon May 19, 2008 12:38 pm

Hello Alex,

yes that is the gearbox. l mated it to a Marina bell housing. The later 'J' type overdrive does not need a relay, unlike the 'A' type I have.

Alec

Post by **bmcecosse** » Mon May 19, 2008 1:24 pm

In fact is the Marina gearbox not exactly the Triumph box anyway - with a bellhousing to suit the A series ?

Post by **Kevin** » Mon May 19, 2008 2:36 pm

they are in demand and can command high ish prices.

And so are the 5 speed kits.

Post by **alex_holden** » Mon May 19, 2008 2:51 pm

bmcecosse wrote:In fact is the Marina gearbox not exactly the Triumph box anyway - with a bellhousing to suit the A series ?

The Marina boxes aren't available with the overdrive though are they? I'm thinking you might be able to combine a Triumph overdrive box with a Marina bell housing, backplate, and a hydraulic clutch. I'm not certain which type of flywheel you would need.

Post by **Alec** » Mon May 19, 2008 5:04 pm

Hello Alex,

no the Marina was never fitted with overdrive.

As I said I used a Marina bellhousing with the Triumph box. I originally had a standard Marina gearbox originally but the gearbox tail piece fractured. I looked on E Bay and fortunately chanced on this overdrive gearbox. The first gear is actually a little high for the Minor (Even a 1275) and I intend to swop the Marina gears back into the Triumph gearbox.

Alec