Jump to content

Installing an overdrive gearbox


Roger K
 Share

Recommended Posts

I have a nasty feeling I'm discovering the hard way that it's not possible to fit an overdrive gearbox to a non-overdrive GT6 MkIII from inside the car.  It's sitting in there, at an angle in the footwell, and is clearly significantly longer than the non-o/d unit.  Was there a difference in the bodyshells for overdrive or non-o/d?  Maybe a shorter tunnel, with a cover plate?  Or have I got to move, or remove the engine?

Roger

Link to comment
Share on other sites

the only difference is a short length of the prop tunnel needs  cutting and made removeable to gain access to the prop coupling bolts( say 6" )

there is no body change on any of the cars 

there is a very different rear mounting chassis  plate and metalastic   mount .

inside the car is the only way unless youre some sort of magician there is absolutely no underside access.

make sure the engine is supported to give you a quite accurate parallel alignment of the back plate and the clutch hsg.

you dont need to remove the engine 

most manage this without serious problems apart from the weight  

Pete

 

Link to comment
Share on other sites

Thanks Pete, I have the mounting plate and mount.  I can see there's no underside access, but if I moved the engine forward 5-6" that would do it.  A lot more work, though.   

I've found mention of a panel, YKC1486, which was used on the 1500 Spitfire.  Does anyone know for sure if this would have been fitted to a MkIII GT6?  I don't remember one from my old o/d MkIII, but that was a long time ago now.  I didn't really want to cut this bodyshell, but I may have no choice...

I have found photos of YKC1486 - I can make one, but is it right for GT6?

 

Link to comment
Share on other sites

There are actually two different covers depending on GT6 or Spitfire - I only found that out recently. The Spitfire version (the most common S/H these days) is an entire section of tunnel from top to floor; the Gt6 version is only really a flap that goes over the top. If you need measurements I have some in the garage I can measure, Roger, so you'll know where to cut the existing tunnel back to. Spitfire left below, GT6 right.

RvkxIEs.jpg.0d378f4c0434a5150865722538670c33.jpg  wLpUIbr.jpg.9b11ce1cb002ab7993f083e70bbde912.jpg

Link to comment
Share on other sites

Thanks Colin, that looks great - I'd be very grateful if you could post some dimensions of the correct plate.  If you have dims for the cut out, that would also be really helpful - but I'm guessing that might be more tricky.

If the panel's off the car, any chance of a paper template of the entire piece, with holes etc. marked?  Sorry, I don't ask for much, I know...

I'll start an ebay search for 611938 - and get my tin snips out just in case.

Super-speedy response from all, thanks very much.

Roger

Link to comment
Share on other sites

9 minutes ago, Roger K said:

Thanks Colin, that looks great - I'd be very grateful if you could post some dimensions of the correct plate.  If you have dims for the cut out, that would also be really helpful - but I'm guessing that might be more tricky.

If the panel's off the car, any chance of a paper template of the entire piece, with holes etc. marked?  Sorry, I don't ask for much, I know...

I'll start an ebay search for 611938 - and get my tin snips out just in case.

Super-speedy response from all, thanks very much.

Roger

Done... well it will be later this evening. The cutout will be (obviously!) slightly smaller than the plate but on my only O/D car it's hidden under the carpet and the centre trim. I'll update asap.

One of the GT6 plates in the USA:

https://www.ebay.co.uk/itm/193767607411?hash=item2d1d730c73:g:1~kAAOSweAlfvy~d

I'd prefer the Spitfire version as they make the end of the prop easier to get at.

 

Link to comment
Share on other sites

11 minutes ago, Colin Lindsay said:

Done... well it will be later this evening. The cutout will be (obviously!) slightly smaller than the plate but on my only O/D car it's hidden under the carpet and the centre trim. I'll update asap.

One of the GT6 plates in the USA:

https://www.ebay.co.uk/itm/193767607411?hash=item2d1d730c73:g:1~kAAOSweAlfvy~d

I'd prefer the Spitfire version as they make the end of the prop easier to get at.

 

Thanks very much Colin, really helpful.  I know what you mean about the Spitfire version, but I'm trying hard to keep the car as correct as I reasonably can.  I've attached a photo of what I think I need, although the white marking is the probable size of the plate, not the hole.  It's difficult to know where to measure from - the handbrake mount might be best, as I don't know if the overdrive and non-o/d cars have the same profile to the cut hole in the metal tunnel, if you see what I mean.  The mounting holes for the padded knee trim might give some clues as well.  If I know how far back the panel should come, and how wide it is if straightened out, I can probably work out the rest.  

Thanks for the ebay link - making that doesn't represent much of a challenge so I'll save on postage!

 

IMG_0595 2.jpg

Link to comment
Share on other sites

Wow, that's radical.  

Thanks Nick.

For the more usual D-type box, apart from the cut out at the top of the tunnel, did the factory cut any metal away for the speedo right-angle drive?  Not sure it's strictly necessary.

Link to comment
Share on other sites

Measurements for the standard O/D gearbox (or have I read it wrong and you're fitting an MX5 box? In which case disregard.)

The Spitfire tunnel cover plate is 5" high, 5" deep and 5.5 inches across the inside, but a total width of 7.5 inches to the outer edge of each horizontal side flange. The flange on each outer side lower edge measures approx 1 inch - hard to be exact with the curvature but I reckon it's exactly an inch after comparing both. 

From the side profile the plate is vertical at the rear but slopes at the front from 5" at the base to 4" at the top. There is a beaded flange towards the front, 1 3/8" in from the sloped front edge at the very top and parallel to the rear edge. The rear edge overlaps the rest of the tunnel by approximately 1" when fitted by three self-tappers, one on top and one each side. 

D3F44221-8355-4C67-9772-364345405C2E_1_105_c.jpg.7c2768ddde6031e90933dd601ef7c45a.jpg 17440E29-1361-4EB4-9B4B-9C3E4CB367B0_1_105_c.jpg.456a7320926deb896bc73861ef92a7b0.jpg 498CAE16-7EE1-4D84-8D7E-DC2DB8BAD314_1_105_c.jpg.cdd76fcfa89e1fa27aca6f07113d7321.jpg

 

Link to comment
Share on other sites

no added clearance for the angle drive but DO fit a 7/16" washer between the angle drive and the speedo output

stops any pre load on the drive or it can fail early

my old Vit6 built wit OD and the tunnel was as Nick shows bit of a hatchet job with a crude tin cover 

on a local car we cut one side and top bent the tunnel up and away , folded back when finished 

Pete

Link to comment
Share on other sites

No, I'm not fitting an MX5 'box!  Just the standard 'D' type overdrive 'box in place of a straight 4-speed.  Quite by chance, Nick's car looks to be Carmine as well as mine which confuses matters.

Thanks all, I've cut the tunnel to give minimal clearance whilst I come to a decision about which cover plate to use.  The gearbox is back in, new clutch engaged nice and easily and tomorrow I'll get all the bellhousing bolts back in properly.  One more question - the parts book seems to show that b/h bolts go through from the back facing forwards, nuts on the engine side.  Rather oddly, the spring washer is shown under the head of the bolt, on the aluminium bellhousing side, and just a full nut on the engine side.  Is that right?  Seems an odd way of doing it to me, I'd expect the spring washer under the nut on the engine bay side.

Colin, those dimensions are brilliant, thanks very much.  I may well go that route - but would you mind measuring the other cover, 611938, so that I can do a comparison?   Sorry to ask for more...

Link to comment
Share on other sites

a cover can be of any shape  , mine was assumed /looked original and reminded me of the light shade in a inspection lamp

parts list tech illustrations are very basic and you are correct spring washer under the nut 

which way round is what ever suits you 

more modern would outlaw spring washers as useless   a good flat washer is better at holding tight .

Pete

 

Link to comment
Share on other sites

On someone else’s recommendation I used the later spitfire type tunnel cover on my mk2 Gt6.  You’ll appreciate the extra clearance when trying to get the overdrive box in and it can’t be seen.  Interestingly, my car was converted to overdrive and had not had its tunnel cut or a cover plate.  I assume either the body was put onto the chassis with the overdrive gearbox in place or perhaps the gearbox and engine were installed together.  You could tighten the prop shaft bolts at the gearbox end from underneath without the cover plate but it was a faff.  I had to remove the overdrive for repair so cut back the tunnel and bought a cover plate at the same time.

Bob

Link to comment
Share on other sites

On 23/05/2021 at 17:55, Pete Lewis said:

no added clearance for the angle drive but DO fit a 7/16" washer between the angle drive and the speedo output

stops any pre load on the drive or it can fail early

my old Vit6 built wit OD and the tunnel was as Nick shows bit of a hatchet job with a crude tin cover 

on a local car we cut one side and top bent the tunnel up and away , folded back when finished 

Pete

Pete, do you mean 3/8"?  Just tried a 7/16" and it's too big.  What type of washer - steel, copper or fibre?  I think there is a sealing surface inside the right angle drive, and a simple stamped-out 3/8" steel washer might allow a leak.

Link to comment
Share on other sites

the speedo drive has its own oil seal ,               any suitable washer is fine 

odd its normally a 7/16 but in essence its to ensure the angle primery spindle is not pre loaded 

if you look at rimmer site they dont offer warranty unless its been  fitted  the main clue is in a BL technical note advising to fit 

eg  https://rimmerbros.com/Item--i-120694

Link to comment
Share on other sites

Just tried to fit the speedo angle drive, no luck...

Two things: does the required washer go between the angle drive and the gearbox, or the angle drive and the speedo cable?  I presumed it was the gearbox side, but the cable I have won't go fully into the angle drive.  Is that where the washer should be?

Secondly, how should the angle drive be orientated?  Should it be nose down, so the cable passes beneath the solenoid?  If I try to fit so the cable goes over the solenoid, the top screw on the angle drive is pressed up hard against the floorpan, see photo.

IMG_0615.jpg

Link to comment
Share on other sites

the washer def goes between the drive and the gearbox  this just ensures the primer drive is not pre loaded its this that causes angle to fail early 

if the rear support plate and mount are all as should be then you will have to add some relief to clear the floor so a bit of trimming looks needed

as for route over or under , dont remember but under seems the best option

Pete

Link to comment
Share on other sites

Thanks Pete - I'll fit a copper washer inside the retaining cap to the gearbox.  Does it matter what thickness?  If the cable goes under the solenoid, I don't need to trim the floor, but it's an absolute sod to attach the cable to the angle drive with the solenoid in the way.

Any ideas why the cable won't go all the way into the angle drive, even on the bench?  It's a good 1/8" off the outer seating on the angle drive body, and I don't want to force it.  Cutting the end off the cable inner isn't ideal, as the square forming to the end of the cable inner is set and sawing through it will fray the end strands out making life difficult.

Link to comment
Share on other sites

youre right not to force it , odd it should be a nice easy fit , so the inner cable seems too long ???

there is an old trick  the outer case is a spiral wound affair  if you get some grips on the outer sheath and rotate this will extend or shorten the outer 

to suit the length of the inner depends which way you turn it(i wont say screw it)

(this used to happen on the truck assy track if a cable got caught dangling and the track grabbed it the cab transfer hoist just drags the cable  makes it too long 

so solution was a guy with some moles give the outer a good twisting 

so give that a try and report back you cant wreck anything 

Pete

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

×
×
  • Create New...