Overdrive Gearbox - A saga of many parts
Summer 2003 - I read in a book by Bill Price (The BMC/BL Competitions Department) that Special Tuning fitted a Triumph Dolomite Sprint overdrive to an 1800 cc Marina and rallied it.  I had heard in the MMOC that there were a couple of these conversions about, so I looked around on eBay for a donor Triumph Dolomite.

I couldn't find one, so I went to the next best thing, a Triumph Spitfire.  The Marina, Ital, Dolomite 1500 & 1850 and Spitfire 1500 all shared essentially the same gearbox so it sounded like a reasonable option to find a Spitfire with a J Type overdrive.

Off to eBay and I bid on one and was beaten, but thought that I would cheekily email the vendor and ask if he had another?  He did and I popped over to the Suffolk coast one Saturday to pick it up.


I had the gearbox rebuilt by Autogear Transmissions Ltd in Essex, Jim there was really helpful and when they supplied the incorrect inspection plate they sourced another one.  Good company.  The box was rebuilt with a Marina B Series input shaft and have bolted up the J Type OD to a Marina bellhousing on the front, goes straight on.  Rimmer Bros sourced an OD wiring loom from a Dolomite in preparation for getting it all together.


Spring 2005 - I dropped the gearbox over to Ben Claytons unit in Warwickshire, with a view to him and I fitting the gearbox during the summer.  Well things didn't work out, so in Autumn 2005 we decided that as the job wouldn't be a 'drive in, drop the old and fit the new gearbox and drive out' exercise, it would be best if Ben came to me and so the gearbox came back to Bedford.  I want to record this job for posterity, should any of you other Marinanauts out there want to have a go.  Ben and I are working from scant information on this conversion and there are no pictures about that help.


October 2005 - Obviously with a modification like this the installation wasn't going to be straight forward.  I decided at the outset to see how many standard BL parts I could use, to minimise fabrication work.  I had overcome mating the gearbox to engine by having a Marina 1800 input shaft installed in the gearbox.  The other issues to solve are; the gearbox to rubber bush bracket, the gearbox bush itself, the gearbox crossmember, the height of the gearbox, the width of the transmission tunnel, and the propshaft length.  What I have done below is list where we are to date, this isn't a finished story - yet. 


Gearbox to bush


Mark 1 - I thought that I would start with what the Spitfire has for a mount.  This bolts onto the back of the overdrive box and then the bottom of the bracket bolts to a crossmember.  This is too shallow for the Marina and has a very small bush.  It's advantage could have been that it mounts straight onto the top of a standard Mk1/2 Marina gearbox bush.  We offered it up, but it didn't work as it all ended up too far down the transmission tunnel.


Mark 2 - A perusal of the Triumph Dolomite parts manual yielded a different mount, this one is for a Dolomite Sprint overdrive.  The advantage of this one is that it moves the crossmember up to roughly where the Marina mount goes, sufficient for packing washers.  You can rob one from a scrap Dolly Sprint OD or buy them NOS from Rimmer Brothers (part no. 158875) 6.00 plus postage - bargain!

Gearbox crossmember & bush - Mark 1 - you can see that the Sprint mount finishes in a pin, which is mounted in the same crossmember bush as the late Marina/Ital (Triumph part no. 219227 / TXC 2642 / TKC 1044).  This lead me to source and offer up an Ital crossmember and bush.  The picture shows the unit I made up, painted and ready to go.  This looked very hopeful and lined up OK, but adding the extra depth of the bush, pushes the underside so low, it would foul over speedbumps - no go then.


Mark 2 - A bit of lateral thinking and desperation led us to the current solution.  Use the original Marina crossmember and bolt the Sprint gearbox mount through a suitable bush.  This is where we are at the moment, I have yet to measure up to find a suitable bush to fit - watch this space.


Gearbox height - if you have a quick look at the shot at the top of the page and compare it to the picture on the right, you'll see that the OD gearbox is about 2 1/2" taller.  There's the 1st and 2nd gear lockout switch close to the bellhousing, also the gear selector lever and mechanism has to sit on top of the overdrive, so that's pushed up too.  Also we still had to be careful of the Marina modders bet noir, the steering rack.  We can't go backwards at all as the bellhousing clashes with the rack.


We offered up the gearbox from underneath and measured up.  We were going to have to raise the line of the transmission tunnel by cutting and welding in extra metal.  


Ben wields a mean disk cutter and very soon the car and the garage were full of smoke and fumes.  The box is sitting up a little high in this shot, it'll probably drop and inch or so at the rear, but you can see how the gear lever comes up in exactly the right place..


Now we can play with the gearbox crossmember some more and get it exactly right.  The key thing is partly the angle of the engine and gearbox, but more a matter of not putting too big an angle on the front propshaft UJ.  When I get the dimensions of the gearbox bushes worked out, I'll post them here.


Width of transmission tunnel - The bellhousing and 4 speed gearbox are Marina type parts and present no problem.  However, just as the standard gearbox narrows off to the gearbox tail shaft, the transmission tunnel does the same, to fit between the seats.  By comparison as you can see above the OD box stays pretty much the same width all the way down and if jacked up too high it will jam between the crossmember mounting points on the underside of the body.  The point where it jams is a little too high for the propshaft, so with some lowering and a little judicious hammering, we can create some reasonable clearance.  Watch this space, or in fact that space.


Clearance - The two shots above show the clearance issues.  The red circle shows about a 20 thou clearance until I can drop the engine/box again and dress back the chassis mounting point.  The right hand shot shows the extra bushing at the sides, this is to allow space in the middle for a bush under the gearbox mount.  In this shot, I have changed the bolts into the gearbox itself, for longer ones with packing washers (3/8th UNC).  I have also slotted the hole in the crossmember, allowing me to move the gearbox mount forward and use less packing washers.  I think that given time I will design and fabricate a bespoke mount that overcomes all these things.


Bushes - None of the Marina , Dolomite or Spitfire bushes that I sourced were of any help, so whilst at the Autumn Restoration Show at Stoneleigh, I searched around the stands looking for likely candidates.  I haven't got a clue what any of them are, but once I have fixed the exact dimensions, I will identify some polyurethane replacements from SuperFlex and post the part numbers here.



Solenoid Position - You can see in the picture on the left that the OD solenoid seems pretty close to everything.  Well it's actually a little good news and a little bad news.  The mounting bracket is further back than the solenoid, so no probs.  However the front edge of the gearbox crossmember overlaps the solenoid and is very close.  To the extent that I could have used a shorter gearbox bush if it wasn't for the solenoid.  I am going to relieve the crossmember to make some space - I could leave it but I think that when the car is moving through the gears they may be in contact - one sure way of stopping the solenoid from working. Also it will clip the chassis mount for the crossmember so I will have to relieve the chassis mount, just like the other side.


Propshaft - I had hoped that (a) based on some notes from another overdriven Marina owner and (b) some wishful thinking; that I might get away with not shortening the propshaft, instead by moving the centre bearing back on its' mount and taking up the movement on the rear spline, that I could get it all to fit.  No such luck!  Having tweaked the engine mounts and fixed the position of the gearbox exactly, I have measured up and it looks like the prop will have to be shortened by 28 mm.......bother.  I spoke to Reco-Prop (UK) Ltd. in Luton and they have asked me to bring it and reckon that it will take about 10-14 days.  I'll post the results here. 


Speedo cable - What a Frankenstein monster this is - a Marina cable to match the instrument dial input and a Spitfire/Dolomite threaded gearbox output.  The side view shot above shows that the speedo output is on the opposite side of the gearbox to the Marina as well.  I have the right angle fitting for the output, to point it forwards and I rerouted the Marina cable to check for length.  It turns out that the new cable should be 17 cm shorter than the standard Marina.  I have contacted Speedograph Richfield Ltd and they confirm that they can make one up - really helpful on the telephone, although at the time of writing this, I have yet to receive the bespoke cable.  Cost 16.90 + vat - bargain.

Angle of engine - I wanted to get the angle of the engine and gearbox right, as unlike in an MGB where it is practically level, the Marina 1800 is canted backwards.  Luckily, the BL designers left me a clue as to the angle.  On the single carb model, they cast into the inlet/exhaust manifold an angle between the horizontal carb mount and the angled engine mount - some 3 - 4 degrees.  By adjusting the drop on the gearbox crossmember and laying a spirit level along the top of the cylinder head, I can measure the angle to the horizontal, in doing so it will help me position the gearbox tail at the right height.

And that's where we are at the moment Summer 2006, a 'kin great hole in the transmission tunnel, a partially mounted gearbox and the car off the road until it is done. 

Page 2 - On the road