LOUD clunk when engagging overdrive

[spittymk3]

Well as the title says I now get a loud clunk as soon as I engage the overdrive...it hasn't done it before but now im rather reluctant to use it as im frightened of damage!! It does engage straight after the clunk so could it be the solenoid? Please help as I love using it!!

[Hogie]

How do you engage OD - keep the revs on or lift throttle before hand.  

You should maintain the revs or slightly increase as you engage. Likewise when  dis-engaging.

Have you checked the UJ's in the propshaft and drive shafts if you have them. These do not always make a  noise in normal gears (much softer change).

Do you dip the clutch when  engaging - many people do but should not be needed.

Engine/GB  mounts badly worn or spongy could do it.

Exhaust pipe touching the GB

Roger

[spittymk3]

thanks for your reply roger, I do keep the throttle on when I engage od, when I switch it out I must say its mainly throttle off to accelerate out of a corner. it all seems to be solid rubber wise, the only thing I have noticed it the exhaust is very slack, failed its mot due to this plus other bits but that could be it I guess? Got nothing else to go on really as its my first od car!

[thescrapman]

It should engage under load, but will come in with a "thump" if the OD is in good condition. Will be more "slurred" if everything is a bit worn out.

If it is a J-type it may have had teh pressure increased.

If it is an A-type it might have a good pump and accumulator.

Cheers

Colin

[spittymk3]

ah the scrapman! well on the way to the mot station it was such a smooth engagement, but on the way back when it was nice and warm it engaged with a good thump, I thought it was going to break and id be leaving a trail of cogs! when I finally get underneath it again and ill see what type of od it is!

[Hogie]

What oil do you have in the OD/gearbox.

If it is a thick oil (SAE90 etc) then at cold/cool temps it will be slow to act so the OD will be sluggish. When warmed up it will work quickly
If you use a thin oil (SAE40 etc) then at any temp it will operate quickly.

On my 4A I use Penrite 40 gearbox oil.
The TRiumph manual says 90EP - this is stupid.  
In the 50's the OD manufacturer stated DO NOT use 90EP

If it is coming in with a fair wallop then ease off the revs slightly when engaging (definaitely keep the revs on when disengaging though)

Roger (tin helmet on)

[spittymk3]

well a small update on the od...took it back to the mot station,playing with the od there and back and not a whisper of noise, it engaged softly and smoothly, I couldn't get it to do the thud once. Its rather annoying though as now I wont know what it was if it never returns...or atleast until im half way up the country and it falls out! Many thanks for your replies though gents, ill be changing the oil with what you say is best!