GT6 Mk1 Overdrive - intermittent failure

[will roberts]

I have a strange problem with my overdrive.  When I start a drive it engages OK in 3rd and in 4th, but after about 10 or 15 minutes driving, it becomes intermittent, and then fails to engage, initially in 4th but then in 3rd as well.  I have adjusted the proximity of the inhibitor switch mounted on top of the gearbox to ensure a better contact with the gear change lever extension bar, but to no avail.  It seems as though the fault occurs when the engine/gearbox/overdrive heats up.  If I leave it cool down, it operates OK again.

Does anyone have any ideas?

Will Roberts

[Pete Lewis]

this is normally the inhibitor switch but youve adjusted that on the same slant whats the switch like they can go very green inside ,  you can with care uncrimp them and clean up the contacts

 

check the gearbox oil level is important

 

does the solenoid click when stationary  can you hear it ???

 

as a Mk1 it should be a D type solenoid on rh siide

 

 

take off the plate off the drivers side , operate the OD the sol should pull the lever , in the lever is a hole , use a 3/16" drill to check the hole aligns with a hole in the case behind the lever.

 

the solenoid does have two coils one pull in the second holds it in and breaks a switch in the end of the solenoid to cut the pull in coil. 

  there could be heating troubles here

 

the sol could be corroded inside making it sluggish ,  have to take it off and clean the plunger....bottom screw is a sod to remove

 

there is no reason why 4th or 3rd make any difference , the only common point with this is  back to the inhibitor switch

 

do teh easy first

 

Pete

[Colin Lindsay]

Does it happen when driving, or also at rest? Mine does that too, but it's a chafing wire that earths as the car drives along. It doesn't happen at rest or in the garage, which is why it took ages to diagnose. I'll replace the wire once I get time.

[will roberts]

Thanks guys.  Some food for thought there.  

I fitted a reconditioned Type D O/D unit and inhibitor switch a couple of years ago (v low mileage since) and I'm confident it won't be corroded etc.

With the engine cold, and the ignition on, when I select O/D and 3rd/4th gear, I hear the click, which I believe tells me the circuit is closing and the solenoid is operating, right?  This tells me the electrics are OK.  So is the oil level critical?  Could this be affected by engine/gearbox temperature?

Will

[Guest]

Hello Will.

 

The combined g/box & o/drive use the same oil and it is SUPER critical that the correct level is maintained.

 

If the oil level drops it reduces the available pressure for the o/drive to work on which it relies to operate correctly (somebody will inform you of the science, I'm sure).

 

When the oil in the g/box & o/drive gets hot it expands and thins at the same time; therefore if your level is low this just exasperates the situation as the oil pressure drops accordingly. O/drive units are efficient workers but do not tolerate poor oil levels AND / OR incorrect grade oil.

 

You should be using a Hypoid EP90 oil to ensure the correct viscosity throughout the temperature / pressure range.

 

When did you last change the oil in the g/box which as mentioned also supplies the o/drive ?? Could it be possible that the filter gauze has become clogged and this may also be adding to your woes ?? 

 

Under no circumstances should you add any additives to the oil as this will prevent the o/drive working efficiently or in the majority of cases completely. 

 

From what you have said above, it appears that your problem is more than likely to be oil based IMHO.

 

Good luck.

 

Richard.

[Pete Lewis]

Theres a few with troubles this week, Nd theres a trend to work in 4th not 3rd, theres no OD reason for this , and apart from inhibitor switch setting Colins reminder about the wire chafe is again rellative to

gear lever position , if you re wire this get some silicon sleeved wire iys flexible , heat resistant and donst chafe through as easy as std flex.

 

places like maplins sell it not seen it in halfords

 

if you have a coulmn switch this does not apply

 

and on Richards reminder about oil the base spec needs to be GL4 not GL5

Theres lots of debate about some modern GL5 being more brass bronze friendly but

if you dont know stick to the Triumph spec most places sell EP80/90 GL4 including club shop

 

Laycock overdrives are designed to run on engine oil, this is spec on most Rootes cars and others,but the Triumph Gearbox is not going to last , and must have an EP oil to survive.

the OD will work quite happily on EP as Triumph tested and specified.

[will roberts]

Thanks to everybody.  I'll get the tunnel off again (probably next week now!) and check the oil level and wiring loom.  I spoke to Chic Doig yesterday and he also mentioned oil levels and possible wiring problem.  More food for thought!

 

Will

[Clive]

You say you can hear the solenoid click when cold, but how about when hot? If that is when the problem happens, you need to do your checks then. It is "probably" oil level or electrical. Though don't rule out a faulty solenoid.... A multimeter or simple test lamp will be your friend.

[mishmosh]

I have a similar problem . Currently i am running engine without a stat. OD operation much better !  However I suspect solonoid is to blame. 

[Pete Lewis]

Dtype solenoids do get corrosion inside, if you remover the side plate and operate the unit by hand you may feel its sticking

 

getting the bottom bolt out of the Sol. Is not easy, combination of long fingers, long screwdriver , flexible drives and homemade ingenuity ,

lifting the tail of the gearbox makes it easier, but remember to undo the Tail mounting from the chassis plate.

 

I have never tried but if you mark the castle nut end stop position then remove it

will the sol plunger slide out past the lever and out through the hole in the

front ??

I think the operating lever will restrict this idea ,