overdrive conversion

[Fizzy]

right i just want to check im not missing any parts, as i intend to get this all done in a day and dont want to wait to order something ive forgotten.

ive got :

OD gearbox (d type i assume?)
OD propshaft
a mount ?

im ordering

switch cowling
stalk switch

i have been given the mount, but looking at the canley D type pages, i cant find one that looks like it. im not sure where its supposed to bolt to so i cant visualise how it works. it looks like the mount i have is a 1 piece component that replaces the 2 piece one in the canleys diagram ? also i keep seeing 'OD mounting plates' - what are these? as for the speedo angle drive, i know the conversion can be done without one as long as your cable is in good nick, so it is one part im going to try and avoid using. if i end up needing one, no big deal. but if i dont need one, its 40 quid in my pocket.

so with GB, prop, cowling, switch and the mount i have, do i have everything i need (disregarding the angle drive)

[mikeyb]

the one piece mount does indeed replace the two piece one

the mounting plate bolts between the two chassis rails at the rear of the gearbox and the rear mount sits on and is bolted to it.  It will be different to the non o/d one, however you may be able to re-drill/reposition to suit. I have a slight recollection though that it is ribbed and makes the mount sit too high.  A suitable replacement is easily fabricated from a piece of 3mm sheet steel.

For a D-type you will need a relay to operate the solonoid, and of course all the relevant cabling.

[Docman]

I read somewhere that putting in an OD trans also meant changing the rear end, so that's why I didn't get the one I found on ebay a while back.

Is this incorrect?

[mikeyb]

rear end of what - sorry I don't understand?  ....

[heraldcoupe]

Overdrive mounting plate is flat, the non-overdrive plate has a bulge which raises the mounting by about half an inch. If you have basic workshop tools, you can make an overdrive mountimg plate from sheet steel, by matching the footprint of the non-overdrive type, and putting a 90 degree bend along the back edge to provide some rigidity.

The current overdrive metal/rubber mounts aren't great quality. If you can find a good secondhand one I would recommend using it in preference. The repros work but aren't going to be long lasting.

You will need a wiring harness to connect the overdrive electrics. A relay will also be needed for the D-type, though the J-type ran without. Given the price of overdrive switches, I would be inclined to fit a relay even with the J-type as an extra line of defence.

I'm not convinced you can fit the speedo cable without an angle drive, unless you intend hacking a hole in the transmission tunnel and bringing it out that way. Whatever you do, don't buy a  new angle drive without inspecting it first. Quality has been notoriously poor, I do my best to seek out secondhand originals. Quality may have improved by now, but tread carefully.

There's no need to change the final drive ratio. This was the state of play with the GT6, different ratios between overdrive and non-overdrive cars. Never the case with Spitfires though.

Cheers,
Bill.

[Davemate]

When I did mine the gearbox mounting plate's front holes lined up with the back holes on the chassis.

[CHRIS211083]

Hi Fizzy, overdrive mounting plate £16 from chic or a flat piece of metal with 6 holes in it. Its also best buying the wiring and solenoid kit for the OD from a suppler as the wires are all the correct colour and type.

Here is a link to a picture of the plate/mount and OD
http://www.rimmerbros.co.uk/Item--i-GRID005560

Chris.

[Fizzy]

thanks for the help. i was round a friends earlier and i was able to check the mounting plate area to see how it works. ill get the relay, wiring and switch all from the same place hopefully. the cutout that the tunnel needs, is this to accomodate the OD unit, or is it just so you can still get at the prop bolts ?

[Fizzy]

thanks for the help. i was round a friends earlier and i was able to check the mounting plate area to see how it works. ill get the relay, wiring and switch all from the same place hopefully. the cutout that the tunnel needs, is this to accomodate the OD unit, or is it just so you can still get at the prop bolts ?

[CHRIS211083]

My tunnel has no cut out but i have the metal band type prop.

Chris.

[bob dunn]

the speedo take of is further away so there is a longer cable .

[Richard B]

It's to allow the gearbox to drop down after fitting to the engine, and to get to the propshaft bolts. There is no access from underneath.

[JensH]

Got this from some US-side, can't remember URL sorry. Was for a 1500, so J-type OD box?

[Docman]

MikeyB wrote:

rear end of what - sorry I don't understand?  ....

In the states, the rear axle differential is usually referred to as "the rear end" or "banjo".
I was told that the gearing in that would also need to be changed if an overdrive transmission was installed.  I had difficulty understanding why since the majority of the transmission gear ratios stay the same, so I passed.  Also, I don't expect that I'll be doing much long distance travel, so the standard gearing should suit my usage just fine.
The idea of having the top specification was really my only motivation to make the change.
Now if my 4 speed should expire...................

[neilnaz]

Docman I think the story about Overdrives and Spitfires goes as follows:

GT6 came with 3.89 differential with overdrive and 3.27 differentail without overdrive so final drive similar
Spitfire (1500) came with 3.63 differential with or without overdrive so the final drive was very different. Any Spitfire driver will probably tell you the benefit of overdrive. Some GT6 drivers may tell you of the benefit of overdrive if they have used a 3.63 differential (the strongest differential) which gives a good final drive and pick-up and allows the use of overdrive to be of benefit.

[Richard B]

You don't need to change the final drive on a Spitfire if fitting overdrive.

However a GT6 with a 3.27 & an overdrive is incredibly long legged (suits a 2.5  8) )

[Pete Lewis]

you need holes in the d type plate to enable access to the drain plugs form unserneath for servicing .

the solenoid takes a intial current of 10 amps then once engaged drops to 0,5amp, switched by a contact in the end of the solenoid .
Pete

[Fizzy]

is there anything difficult about making the wiring for the overdrive myself ? my current budget is approximately zero, so anything within the realms of being feasible to do myself would be very handy. looking at the canleys diagram, i cant see anywhere i could go very wrong, theres only one loose end (2 spade connectors) on the diagram, which im assuming is to a live feed ?

[heraldcoupe]

yamaha_fizzy wrote:

is there anything difficult about making the wiring for the overdrive myself ? my current budget is approximately zero, so anything within the realms of being feasible to do myself would be very handy.

Making the loom is straightforward, building it in-situ means you can optimise cable lengths to keep it neat.

Before jumping in though, do a little online window shopping to see if you can get the correct colour coded wires in the right grades, it's not always so straightforward. The right connectors and crimp tools are also important, fine if you already have them, but a substantial outlay if you don't have them to hand. Don't be tempted just to solder them, vibration kills solder joints in vehicle looms.

Cheers,
Bill.

[Fizzy]

parts on the way 8)

in total i'll have

od box
od prop
od mount
od mount plate
od switch/cowling
angle drive
half od loom (relay connecting half)
hopefully making the other half (gearbox end) only one confusion :

in this canley diagram, part 36 is what i intend to make, however im not sure what happens as 4 wires go into near the reverse switch end. how do you make this ?

http://www.canleyclassics.com/?xhtml=xhtml/diagram/spitfireiiioverdrive.html&xhtmlcatalogue=xhtml/catalogue/spitfireiii.html&category=gearbox&xsl=diagram.xsl

speaking or the reverse switch, ive just been to have a look and my switch is on top of the gearbox under the selector arm, yet in that diagram it says its on the side of the OD unit somehow ? whats going on here ? is it a problem ?

just to make sure im not missing anything my plan is :

remove current gearbox and prop
cut tunnel further back
replace mounting plate, fit mount
change box/od oil
fit box and prop
wire it up
see what happens

couple of other things i want to be sure of

how much to cut the tunnel back by ? will a hacksaw do the job ? is a cover for the new gaping hole essential ?

is the mounting plate a straight swap out ?

im not sure what a solenoid is, but i hear a lot about it being a failure point. can it be checked out of the box ?

inhibitor switch ? not entirely sure what this is, or where it goes, or what it does. from what i can tell it also forms the reverse light switch ?

apologies for all the questions, i want to get this done in a day/weekend so dont want to be waiting for parts or being stuck

[Richard B]

Don't panic,

you have a pm

[thescrapman]

yamaha_fizzy wrote:

speaking or the reverse switch, ive just been to have a look and my switch is on top of the gearbox under the selector arm, yet in that diagram it says its on the side of the OD unit somehow ? whats going on here ? is it a problem ?

That is because it is the inhibitor switch, not the reversing light switch

Your gearbox should have a bracket bolted on at the front of the top housing for mounting the switch, and also the should be an actuator sticking off teh front of the remote to actuate the switch.

Items 46 and 11 respectively.

Cheers

Colin

[Fizzy]

ahhhhh. i didnt get the bellhousing, i had it removed to reduce weight as i had the gearbox posted to me. i didnt actually check, but i assumed i could use my current bellhousing ?

have i cocked up here ? :o :o :o :o

is the inhibitor switch the same part as the reverse switch, as i now have 2 'reverse' switches?

[Richard B]

Is your existing gearbox a 3-rail and is your new gearbox a 3-rail. If so they are interchangeable.

Is either of them a single rail then I think you have some extra work.

[Fizzy]

yes both 3 rail, where is the bracket supposed to bolt to?  can get a bracket online, but am yet to find the pivot thing