Jump to content

Missing Overdrive


Rijidij
 Share

Recommended Posts

We picked up our new (to us) GT6 Mk2 on Thursday. Purchased from a fellow club member.

I haven't posted until now because we have been having too much fun driving it, but about 1/2 hr into the long drive home up the A1 the overdrive disappeared.
She jumped out of OD in 4th. I reengaged and it was OK for a few minutes then the revs jumped again.
I tried a few more times but with no success.

I tried again after we stopped at Services for lunch. It worked for 5 minutes only, and that was the last time.

I haven't been too concerned. OD was an optional extra after all, so we've continued to enjoy the car.
But of course I would like get it working again as soon as possible.

I had to crawl underneath today to rotate one of the exhaust U-bolts - to gain a critical inch of clearance.
While I was there I took the opportunity to remove the gearbox filler plug and check the level. A few drops of (nice, clean) oil oozed out, so I guess the level is OK.

Please help me to find my missing overdrive.
I'm a complete newbie to classic Triumphs, so any suggestions or advice would be very welcome.

Link to comment
Share on other sites

The most common and simple failings are  the wiring from the gearstick switch which chafe and can short where they  run through the hollow  gearstick.

The next is the inhibitor switch mounted on the front of the remote , this is a simple  push switch operated by a cam on  the  front of the  remote  its adjustable with card shims, a simple  test is hold the  gear leaver to one side when in  3rd  4th it may just make the contact

If its a Dtype OD  the solenoid is on drivers side these can fail they have two coils inside and a switch in its end you cant fiddle with

They can corrode and the  coil wont hold in   can be hard to remove only two screws but lower has poor access

Do the  simples first.

Do a search theres lots of clues on here Gully did a good write up when we solved his problems 

Pete

Link to comment
Share on other sites

I have had problems on 2 cars (in 25 years!) With the solenoid earth wire fracturing. Not obvious until you swap it, but the insulation had hardened causing the wire to break down inside. Both times it was the original wire...

Also echo Pete's idea of inhibitor switch.

Plus check the filters, I can't remember how easy/hard that is to do on a GT6.

You could put a "test bulb" in the circuit, across the solenoid. So that it can be seen when driving. If the bulb goes out when the overdrive stops working, that would confirm electrics at fault.

Link to comment
Share on other sites

Had the same symptoms on my vitesse with OD dropping out . Following Petes suggestion once od had dropped out hold the gearstick in 3 or 4 and see if od returns. It did in my case and it was easy enough to realign the inhibitor switch which sits on top of the gearbox 

Paul 

this is the link 

 

Link to comment
Share on other sites

All good suggestions and probably covers where you should look to start with. I'll just add... electrical problems tend to show up as the overdrive "cutting" out, with a sharp transition as you would get by turning it off. Hydraulic problems tend more towards it slipping a bit first. However, back when my GT6 had a D-type it developed a very characteristically hydraulic symptom that turned out to be due to an electrical issue - missing insulation that made for rapidly intermittent shorts to ground - but you could hear that one, it sounded like a machine gun.

Link to comment
Share on other sites

Finally got a chance to take another look today.

Scrabbling around under the dash, I discovered a blown 30A blade fuse - not in a proper fuse block, just plugged into a couple of spade connectors.
I didn't have a 30A fuse to hand, so I borrowed a 25A from my Land Rover.
Before I plugged it in, I put a meter across the connection, put her in 4th and turned the ignition on. Flicked the OD switch and... Eureka! 12V (ish).

This was looking promising. I plugged in the fuse and took her for a drive. 

Sadly, still no overdrive. 

When I got back, the fuse was still intact. I could also hear the relay clicking on and off.

I'll test the voltage from the relay tomorrow - if I can get to it...
But it's looking like the solenoid might be fried. Does that sound about right?

Link to comment
Share on other sites

Yes you need  to check the relay has a feed  the  relay may be triggering ok  but not have any feed to switch the solenoid

Or a feed from relay to sol.   Then  hopefully the relay trigger line is interupted by the inhibitor switch not the power line relay to solenoid.

Have you  sussed what the 30amp blade fuse is doing ,  the OD  takes around 10amp to pull in , the switch is the  sol. Cuts  this coil 

Instantly down to 0.5amp holding coil   

Pete

Link to comment
Share on other sites

Been thinking about this as I was running along the canal du midi (damn hot even this early)

And putting facts together. 30amp blade fuse, takes 60amps to blow. This implies a dead short somewhere. And the od was working.

So something had caused the fuse to blow AND disabled the od. My guess is a connection come off (or wire broke) and initially shorted but now no longer. Or indeed solenoid burnt out causing big current draw, but now gone open circuit.

Whatever, I think the gearbox tunnel needs to come out. So take a brave pill and have a proper look. Usefully you can check other stuff while the tunnel is out...

 

Link to comment
Share on other sites

I just hope your back is in good order and you are feeling flexible enough!

I have a dislike for removing spitfire tunnels. And GT6 means a fixed roof, which can make matters worse. It was much easier (like so much) when I was in my 20's.

Link to comment
Share on other sites

clive,  running and thinking ............too much information   Ha 

enjoy the sun 

all tunnels are a pain some worse than others ,   just make sure you have some decent thick foam strips to adhere and take up any silly wonky gaps , the seals sold are pretty hopeless, with 50yr old wonkies,     and tunnel sealing on a GT6 is a must .to keep hot air ...OUT.

Pete

Link to comment
Share on other sites

I would first check that the relay is actually getting a voltage on the output side. You can hear it click but is it actually making contact. Ihad similar symptoms a year or so back, and a quick clean of the contacts in the relay sorted it. As the relay is located on the bulkhead near the battery (Or should be) this is easy to check, before taking the tunnel off

Link to comment
Share on other sites

You're right. The fuse is in the feed to the relay.
I was probably so excited to find the blown fuse which I was convinced would solve my problem that I didn't check whether it was coming in or out.

On my car the relay is bolted to the back of the driver's side parcel tray.

DSC_0082.thumb.JPG.905d4e5f884e4a22783b22bf5faab52b.JPG

I'm not sure if I was testing it correctly, but both the output wires appeared to be "live" (current between terminal and ground).   

Link to comment
Share on other sites

10 hours ago, Rijidij said:

You're right. The fuse is in the feed to the relay.
I was probably so excited to find the blown fuse which I was convinced would solve my problem that I didn't check whether it was coming in or out.

On my car the relay is bolted to the back of the driver's side parcel tray.

DSC_0082.thumb.JPG.905d4e5f884e4a22783b22bf5faab52b.JPG

I'm not sure if I was testing it correctly, but both the output wires appeared to be "live" (current between terminal and ground).   

There should only be 1 output? 

Switched live in with earth other side of the "coil" (though could be unswitched live with switched earth, like the horns on our cars) terminals 85+86 on your relay

The other 2 connections should be fused power feed and an output...30+87

Link to comment
Share on other sites

The switch is on the steering column.

Yeah, according to the receipts the gearbox and OD were fitted as part of the restoration in '15.

The relay has 5 pins. The middle one is unused. There's a 12V (fused ;) ) feed, earth (bottom of the photo).
And 2 other (both red - very helpful) wires that go through the bulkhead, then back down under and alongside the transmission.

I went underneath again, and I can't feel anywhere that's rubbed or frayed through and possibly causing a short.
But I won't know for sure until I get the tunnel cover off and have a proper look.

I might just replace the relay for now. That's cheap and easy.

Link to comment
Share on other sites

I'd be seriously tempted to rip out all the overdrive wiring and replace it with correct colours and proper fittings, putting the relay somewhere more accessible. But then I'm confident that my electrical skills are superior to the numpty previous owners.

Link to comment
Share on other sites

Well, I didn't get to take the tunnel cover off this weekend. The weather was too nice and we decided to drive her instead.

I did replace the relay and it was an opportunity to decipher the PO's wiring.
The new relay was working - just the same as the old relay... But then I noticed the fuse was hot. Really hot!

"Ah-ha" I thought (more like a, "You idiot. Why didn't you think of this earlier?" thought).
I put an ohmmeter from the relay output pin to ground and, you guessed it, zero resistance. None. Nada. Zip.

Definitely a short circuit. Or a cooked solenoid.

On the bright side - at least I now know why the overdrive stopped working.

Link to comment
Share on other sites

The solenoid armature cann get corroded and it sticks ,    it only travels a short movement if it does not contact the switch inside

It will demand a heavy  10+amps and not switch  down to 0.5amp and the hydraulic valve wont be opened

Should you need to Get  the sol off is a challenge on its lower of its  2   screws   search Gully's post and courier article on an simple method.

Pete

Link to comment
Share on other sites

  • 1 month later...

Well, I've finally bit the bullet, put on my big boy pants and took the tunnel cover off today.

It wasn't as bad as I expected. I took the cover plate off and was greeted with a weird burnt, tarry sort of smell.
I tried the switch and the armature did move, but only a few mm.

I kind of expected this so I had a replacement solenoid on hand... but how in blazes do I get the lower bolt out?

I've searched for Gully's post but can't find much. Does anybody have a link?

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...