Overdrive clutch type

Post by **Old and Slow** » Thu Jun 20, 2019 7:55 pm

AFAIK overdrives are built with "sun and planet gears" and are switched in by a solenoid operating a brake band. If there's no brake band the drive passes straight through. however if there's some debris in the O/D then this might put your trip to France at risk. I wonder if flushing out with a couple of oil changes might be a quick solution, not to get the O/D working, but to minimise the likelihood of something else going wrong.
Greater experts than me might have a view on this.

Post by **Oldconn** » Thu Jun 20, 2019 8:24 pm

My understanding is that the overdrive has a double cone clutch. One face at a time is engaged, while the other face is free to spin. If either face is worn out, you can experience slip , whether in direct drive or in O/D. Mine is beginning to slip slightly in direct, but not in O/D. So if you lose one side of the lining entirely, I would imagine you would lose drive completely. Could you piece of debris be a segment of a cone-shaped band of clutch friction material?

Post by **gtcse8** » Thu Jun 20, 2019 8:34 pm

Sorry Phil but you can`t "Flush" an OD unit, not in the way you can Flush an engine by replacing the oil after running the car.

The OD picks up the oil from the GB and then pressurises it through an eccentric pump driven by the gearbox outpout shaft, the oil does not get splashed around, as it does in the engine by the crankshaft.
The oil then drains back through the casting of the OD back into the GB.
Mark

Post by **jag12** » Thu Jun 20, 2019 9:12 pm

The overdrive uses the gearbox oil not engine oil

Post by **gtcse8** » Fri Jun 21, 2019 7:48 am

EDIT

I had engine on my mind with reference to "Flushing after running.
The point I was trying get over was that the engine oil has a far harder life than the GB oil.
The engine oil is sent to the top of the heads and then flows back into the sump, hitting the camshaft and crankshaft and being violently thrown against the inside of the block, thereby washing any contaminates into the sump.

The GB oil has a far easier route, and is only "Stirred up by the gears in the GB section.
The bit that is collected by the eccentric pump is then pushed through the hydraulic clutch at the rear of the box, then it simply drains back into the bottom of the box.

Post by **Rev Light** » Fri Jun 21, 2019 9:43 am

Just to note - I did actually send a picture to the specialist mentioned in a previous post, but have not yet had a response.

halfpenny · Post by **halfpenny** » Fri Jun 21, 2019 12:29 pm

Give him a call; he's very reasonable, but you will have to contact him

Post by **Old and Slow** » Fri Jun 21, 2019 4:47 pm

Thanks to all above for clarifying my initial (inexpert) comment. I don't think I'd risk the trip to France then.

Post by **Rev Light** » Sat Jun 22, 2019 10:24 am

I am the eternal optimist. I will be cruising on the lesser roads at lower speeds.

Mark is going to supply me as used overdrive, which will keep thing simple when it is time to change. More ducks to line up.

Steve.

Post by **David Tew** » Sat Jun 22, 2019 3:24 pm

When you change the OD make sure you fit (or make) the correct gasket with an oil-return hole at the bottom. I've seen them assembled with a plain gasket which causes oil to collect in the OD rather than doing it's job in the gearbox.

Post by **Dennis Nicholas** » Sat Jul 06, 2019 10:29 am

Rev Light
Have a look at http://www.buckeyetriumphs.org/technica ... 1/JOD1.HTM
All will be revealed.
Bear in mind that Scimitar GTE Overdrive introduced from Chassis No. 932478 incorporated gearbox and overdrive units of a new design.
Also google J type Laycock overdrive units. Popular motoring did a good strip/overhaul article (Nov 1977).
Also Moss Europe have a good exploded diagram for J spares for Triumph Spitfire.

That will keep you busy for a while

Dennis

Post by **Dennis Nicholas** » Sat Jul 06, 2019 11:05 am

Looks like buckeyetriumphs have changed their webpage set up. Try https://static1.squarespace.com/static/ ... Part+I.pdf

There are subsequent parts 11 and 111. Just search on their site "J type overdrive".