Rijidij Posted June 29, 2019 Report Share Posted June 29, 2019 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 More sharing options...
Mathew Posted June 30, 2019 Report Share Posted June 30, 2019 Try some fresh ep90 gl4 spec oil. Look at the drained oil, are there any black flex's in it? Make sure electrical connections are good, is the relay holding? Just to get you started. Link to comment Share on other sites More sharing options...
Pete Lewis Posted June 30, 2019 Report Share Posted June 30, 2019 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 More sharing options...
Clive Posted June 30, 2019 Report Share Posted June 30, 2019 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 More sharing options...
Paul H Posted June 30, 2019 Report Share Posted June 30, 2019 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 More sharing options...
NonMember Posted June 30, 2019 Report Share Posted June 30, 2019 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 More sharing options...
Rijidij Posted June 30, 2019 Author Report Share Posted June 30, 2019 Thanks for all the suggestions. No time to do anything today, but I'll certainly follow up on theses. From NonMember's description it does sound more like an electrical problem. Link to comment Share on other sites More sharing options...
Rijidij Posted July 2, 2019 Author Report Share Posted July 2, 2019 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 More sharing options...
Clive Posted July 3, 2019 Report Share Posted July 3, 2019 Not necessarily. Can you hear the overdrive solenoid clicking, and is your 12v across the solenoid? Or measured somewhere else? Link to comment Share on other sites More sharing options...
Pete Lewis Posted July 3, 2019 Report Share Posted July 3, 2019 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 More sharing options...
Clive Posted July 3, 2019 Report Share Posted July 3, 2019 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 More sharing options...
Rijidij Posted July 3, 2019 Author Report Share Posted July 3, 2019 I think you're right Clive. But it will have to wait until the weekend - my garage is much too small. I hope the weather is kind. Link to comment Share on other sites More sharing options...
Clive Posted July 3, 2019 Report Share Posted July 3, 2019 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 More sharing options...
Pete Lewis Posted July 3, 2019 Report Share Posted July 3, 2019 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 More sharing options...
DanMi Posted July 3, 2019 Report Share Posted July 3, 2019 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 More sharing options...
Clive Posted July 3, 2019 Report Share Posted July 3, 2019 Had another thought... The blown fuse was stopping the relay working. But the fuse would"normally" be in the feed to the relay from the battery, not in the switching circuit. Think investigations are required... Link to comment Share on other sites More sharing options...
Rijidij Posted July 3, 2019 Author Report Share Posted July 3, 2019 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. 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 More sharing options...
Pete Lewis Posted July 4, 2019 Report Share Posted July 4, 2019 This is not the general location its very likely to be a retro fit overdrive and wiring could be anywhere the previous owners have installed it Does it have the switch in the gear knob or a stalk on the column ?? Pete Link to comment Share on other sites More sharing options...
Clive Posted July 4, 2019 Report Share Posted July 4, 2019 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. 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 More sharing options...
Rijidij Posted July 4, 2019 Author Report Share Posted July 4, 2019 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 More sharing options...
NonMember Posted July 4, 2019 Report Share Posted July 4, 2019 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 More sharing options...
Pete Lewis Posted July 4, 2019 Report Share Posted July 4, 2019 Well with a column switch it reduces the problems of the gear lever mounted short circuits version Pete Link to comment Share on other sites More sharing options...
Rijidij Posted July 7, 2019 Author Report Share Posted July 7, 2019 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 More sharing options...
Pete Lewis Posted July 8, 2019 Report Share Posted July 8, 2019 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 More sharing options...
Rijidij Posted August 11, 2019 Author Report Share Posted August 11, 2019 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 More sharing options...
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