Converting a 4 speed gearbox to a 5 speed (1800)

[The Breaker]

Can it be done with ease; Upgrading the box?
Or is there a quick and simple answer to lowering rpm for long halls on the motorway?

Thanks

[balmy]

5 speed or 4 speed with overdrive can be done but neither are quick, cheap or particularly easy. Most require making the tunnel bigger ( higher )
A diff change can work - stick a 3.27 in for more relaxed motorway work if you can find one.

[locost_bryan]

Read this thread MORRIS MARINA/ITAL REAR AXLE/DIFFERENTIAL & OPTIONS for very detailed diff options, and this thread 1700 O Series Gearbox Options for gearbox options.

[The Breaker]

So I see its either a dip swap or a gear box swap then
So not an easy fix for a long hall on the motorway after all

[locost_bryan]

BL made the trans tunnel as small as possible to maximise the amount of interior space, so it limits what you can fit in there.

[The Breaker]

BL made the trans tunnel as small as possible to maximise the amount of interior space, so it limits what you can fit in there.

I dont know who or what BL is or what a trans tunnel is either

[PHUQ]

BL - British Leyland, the parent company of Morris at the time the Marina was designed and built.

Trans tunnel- Transmission Tunnel, fairly self explanatory, it's the bump between the seats to give clearance for the gearbox and propshaft. It's unusually small on a Marina as Bryan has said, good for interior space, bad for fitting bigger gearboxes.

[locost_bryan]

As Balmy said, the only easy option is to fit a taller 3.27 diff. You'll also need to fit the correct speedo drive gear in the gearbox, or else the speedo will read wrong. I think the differential option thread says which one you need. Rimmer Bros sell the 3.27 crownwheel and pinion for £384.00 (inc VAT) https://rimmerbros.com/Item--i-159803

[The Breaker]

So its going to be a lot of money and work. I think its best to walk away from this as soon as.....

[balmy]

The last 3.27 diff I picked up cost £70 I think.
Frequent some dolomite or early GT6 FB pages!

[The Breaker]

The last 3.27 diff I picked up cost £70 I think.
Frequent some dolomite or early GT6 FB pages!

Was that new or used?
Was it a complete diff shaft or an add on?
Did it up the ratio on top 4th gear and what about first? or was the diff a separate item and a separate gear its self?

[balmy]

Used. Claimed to have done only 27k miles and seems in good nick.
Complete diff. It ups the ratio in every gear. First is fine even when pulling away but then my car has a little more torque than a standard 1800.

[The Breaker]

But did it up the gear ratio where it felt like a whole gear? So first would feel like second and 4th would feel like 5th

[balmy]

But did it up the gear ratio where it felt like a whole gear? So first would feel like second and 4th would feel like 5th

No. Nothing like. It’s only a 11% difference but for me it makes enough difference for covering large distances ( 1000 miles done in 24 hours last year )

I’ve driven 5 speed converted Marinas.
Mine sites at exactly the same revs at 60mph as those in 5th as mine in 4th.

[The Breaker]

No. Nothing like. It’s only a 11%


Mine sites at exactly the same revs at 60mph as those in 5th as mine in 4th.

But still nowhere near as less reves as a 5 speed box then?