Overdrive slipping

[dikkie]

My Jensen Healey has an 4-speed + overdrive gearbox from a Sunbeam Alpine in it. The overdrive has never worked, in a bid to get it going I've rewired the solenoid and confirmed it's engaging the overdrive (I can hear the clunk and see the actuator move). This Sunday I tried it out on the road, with disappointing results...

In 4th gear, 50mph, on the flat I flicked the switch, heard the clunk and waited for the revs to drop... they didn't. Worst than that, as I started coasting down the hill the engine revs dropped to idle and I lost drive. Uh Oh!

It was odd though; going down hill the engine revs would drop to idle but if I put my foot on down, the revs would pick up to 3k and the drive would re-engage and I could accelerate (like I was pedalling a bicycle). I promptly disengaged the overdrive and shortly after I regained full drive.



I don't have much experience of overdrive units but Google recons losing drive is usually due to incorrect gearbox oil (or lack of any oil!). Does this sound sensible? I'm thinking an oil change won't hurt either way!

The guys on the sunbeam forums recommend SAE30 non-detergent oil, does anyone have any recommendations on brand or where to buy locally (Bristol)?

[Camber Dave]

Hi Dikkie

I read you post recently and by coincidence found a flier for John E Evans.

He overhauled an overdrive for me many years ago.

His no is 02392 465256 Mobile 0777638 1520 No Web info available

His address was Hayling Island, Hants - I must of had it couriered.

It was a long time ago so not sure if he is still around.

Dave

[Iancider]

Dikkie,

I am not an expert but years ago I always had a go on older cars because the mechanisms were always quite simple and obvious.  I suspect that here you have a simple eletro-hydraulic actuator.  The solenoid uses hydraulic force to engage the epicyclic gear.  If the hydraulic pressure is not being sustained then the gear will just disengage.  It could be then, an airbubble in the hydraulics (bleed it), a seal gone so the pressure is lost slowly, the solenoid is too weak to provide enough motive force, or simply if the gear-oil is used for the hydraulic action the level might need topping-up.  It all sounds like a loss of hydraulic pressure because on coasting the drive gear would try to spin out of contact but on drive it would tend to re-engage.  Some overdrives were on the rear axel rather than on the rear of the gearbox.

There is some useful background on the different types on Wikipedia see- overdrive in Europe for common types: http://en.wikipedia.org/wiki/Overdrive_%28mechanics%29 plus on you tube. 
Good luck, Ian


and

There is a total of 5 in the series just look for Moss TV

[dikkie]

Thanks for the posts guys,

I'm learning a lot about the overdrive unit (well I bought the car to learn more so it's serving it purpose at least!).


Iancider - I think you're right about a loss of hydraulic pressure, as it was the simplest option I tried an oil change. I found this article particularly interesting, it explains about the effects of different oil choices in the overdrive:

http://www.quantumechanics.com/qm-htm/topic1.htm

Also interesting to understand why detergent oils should only be used in situations where the oil is filtered in some way (the detergent keeps the 'junk' suspended in the oil to be picked up by the filter, rather than settling on the bottom, but this is what you want in a gearbox where there is no filter)

I settled for the SAE30 nd oil, now when I try the overdrive I have the same problem but it doesn't go away when I disengage the overdrive (I guess that's progress ?!?).

My next idea is to check the solenoid actuator alignment, this may be out of whack, or a blockage in the operating valve stopping the correct seating of the ball. I'll let you know how I get on


If that fails I may have to send it off to the pros (thanks for the link Dave).

[dikkie]

For anyone who is reading this with a similar problem, I found this manual particularly useful:

http://www.ferrari250gte.com/i/resources_files/manuals_files/Laycock.pdf

[dikkie]

The oil change and adjustment of the solenoid didn't help so I bit the bullet and decided to get it off the car and service it myself, when I drained the oil this time it was filthy - loads of little black fibres in it! I couldn't work out why I hadn't seen them when I changed the oil the first time. Then I split the body in half and exposed the sliding clutch - the outer clutch surface has completely gone, just the rivets that should hold it in place is left (explains all the fibres in the oil).

I'm guessing the overdrive hasn't been used for so long parts of the clutch surface stuck to the braking ring, then when I engaged it the whole thing just tore itself apart.


(the old clutch is on the left, new on the right)

I've installed the new one and given everything a good clean and I'm pleased to report the overdrive now works - no more screaming down the dual carriageway for me

Thanks for everyone's helps - those videos were particularly helpful with getting it working

[Iancider]

Well done Dikkie,

That's what I like about older cars - they are generally quite simple and easy to service - if you can get the parts.  You should feel proud you conquered it.  I hope to see the car in action soon.

Regards
Ian

['The Gaffer']

Nice to see a good result