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Overdrive Glitch - Help needed


Spitty2Dream4

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Hello all knowledgable ones.

decided to take the spit up to 70 mph for the first time tonight... All went wondefully and smoothly after about a mile at 70 mph IN overdrive, BUT, when I slowed her down she would not come OUT of overdrive. At one point in third gear it seemed like the clutch was slipping and the car could rev a little (not much) while still in gear. The problem then rectified itself.. all this was within a quarter of a mile after slowing from 70 to 40 and then urban driving. All seems ok now while driving around our leafy suburbs.

Is this something to do with too much or too little gearbox oil getting to the overdrive unit?

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Hi S2D4

This could be an indication of low gearbox oil.  
It could also be an indication that the overdrive needs overhauling.
The behaviour you describe in 3rd gear (presumably with the overdrive engaged) is classic overdrive slipping: the cone clutch is slipping inside the overdrive, and the one-way clutch is becoming engaged - this is why the revs rise a little.  You should not use the overdrive if it is slipping like this because it will quickly burn the friction material on the cone clutch leading to an £expensive overhaul or refurbished exchange unit. (ask me how I know :-( )

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979 wrote:
thanks bod.... so what should i do now?


sorry.  Overdrive remedies are beyond my skills.  After knackering my old one (in my defence, it was dying when I got the car), I got a refurbished unit from these people: http://www.overdrive-repairs.co.uk

If you do want to attempt your own overhaul, there is a pretty good resource here which re-publishes some old Laycock documents: http://www.buckeyetriumphs.org/technical/jod/JOD1/JOD1.htm

Others on this forum may be able to suggest techniques for cleaning filters, oil ways, etc. and it is certainly worth trying, but if the friction material has been damaged, an exchange unit will be the ultimate solution.

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filler plug is on the right-hand side of the gearbox casing.  You have to remove the gearbox tunnel to get to it.  Several people have made little hatches in their gearbox tunnels to let them get access to the filler/level plug without the aggro of removing the tunnel.

The oil is topped up until it starts to trickle out of the filler hole.

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I'll check what overdrive it is.

BTW the slipping in third gear only occured for a second or so when I was trying to switch out of overdrive.
From trying to come out of overdrive to the point where the fault rectified itself was only about 200 meters.
It has never done it before, but there again I haven't taken her up to 70mph before. I'll try checking the oil first.. hope that checking the oil level isn't going to be too tricky.

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bodders1 wrote:
  You have to remove the gearbox tunnel to get to it.  


This is not totally true. I have topped up my gearbox oil a few times without taking the tunnel out. You can get to the plug, but you can't use the standard spout on a gear oil bottle.

I used an old fashoined pump type oil can, depending on level it can mean a lot of pumping, but I prefer that to all the hassle with carpets and trim and the rest to get the tunnel out.

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that's a handy tip...
how far behind the bell housing is the plug? Did you have to jack the car up or have it on ramps?

Any thoughts on the overdrive only slipping when trying to come out of overdrive? would this be oil pressure or could it still be terminal?

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bodders1 wrote:


Spitty2Dream4's signature says he has a 78 Spitfire, so that will be a J-Type overdrive


Not neccesarily, If previous owners mixed and matched it could be one or either. I revamped ,new engine etc but still kept the old D type .They are easy to work on ,clean filters and adjustment to the solenoid lever is so easy its untrue
J type being an upgrade, like bringing out new models of cars, made to be adjusted with more test equipment or taking into service agent
D type adjusments; a spanner a twist drill and Bobs your aunty

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Over drive slipping when coming out of overdrive suggests that it hasn't managed to move the driven plate fully back, which could well be, I think, due to low oil pressure. Which in turn could be due to low oil level....

Or is the overdrive plate spring return?????? Not sure, and don't have the book to hand. If it is then it could be as simple as a partially sticking solenoid.

If you have managed to drive without slipping in both non overdrive and overdrive, I would not condem your overdrive unit just yet.

Regarding jacking the car up to get to the fill plug from underneath, you'll probably need to lift it a bit to get in, just remember that the car really should be level....

Having said all that, you might be as well off draining what's in there and filling with new oil, so you know that there's no water or anything else nasty in there. Then I'd definately take the tunnel out. Also you can compare the amount you take out to what goes in to see if it was low.

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Since I was going to get access to the filler plug, I was concidering replacing the gearbox oil anyway. Might as well.
Oh well, I suppose that's another big job to add to my "To Do" list.
Hopefully a dose of nice fresh oil will solve any sticking problems.
But what about the possiblilty of a sticky solenoid, Is there an easy fix?

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Before you go grovelling underneath lift the carpet by the clutch pedal to see if any one has already converted the tunnel.

If you do decide to go underneath unless you are extremely thin with multi jointed arms you will need to jack it up or drive up some ramps.

Three words you need to rememeber when you crawl under a car SAFETY, SAFETY, SAFETY.

If you use ramps you need to jack up the rear to level things and then use axle stands never just use a jack.

One additional tip to go with the pump oil can, I found a length of flexible fuel pipe that was a jam fit on my oil can that I could push in the gear box and pump the oil through either that or get a can with a flexi spout.

Welcome to the pleasures of Spitfire maintenance.

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bhuffer wrote:

One additional tip to go with the pump oil can, I found a length of flexible fuel pipe that was a jam fit on my oil can that I could push in the gear box and pump the oil through either that or get a can with a flexi spout.


On the oil pump thing - I persevered with 5 mins at a time pumping oil into my gear box until I got one of these which pumps oil in 0.5L per shot.  Recommended

http://cgi.ebay.co.uk/HILKA-PRO-CRAFT-OIL-SUCTION-GUN-12-HOSE-1PT-CAPACITY_W0QQitemZ140328992169QQcmdZViewItemQQptZLH_DefaultDomain_3?hash=item20ac427da9&_trksid=p3286.c0.m14&_trkparms=65%3A12|66%3A2|39%3A1|72%3A1688|240%3A1318|301%3A0|293%3A1|294%3A50

Back to the OP's problem - I've had my fair share of overdrive fun over last few years and a J-type sticking on is more likely due to too high oil pressure - maybe a sticky relief valve or a bit of crud in there.  I'd start with a complete oil change (including removing the sump of the OD) and see how it drives after that.  

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Assuming it's a J type, while you have the sump off, undo the largest of the plugs (the ones with 2 small recess holes in them). This reveals the pressure filter, which will just drop out with its aluminium sealing ring, and which really needs cleaning out in parrafin or petrol. It's like a small oil filter the size of a cotton reel. If you don't have a pin wrench to remove the plug, you can use some pointy pliers and an adjustable spanner to get the plug out. It's not very tight. If you have a Haynes manual (I suggets you get one if you havn't already) then it's all in there.

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