Jump to content
boogie

J-type overdrive

Recommended Posts

Hi all,

This might seem a strange set of questions but I'm trying to understand how to operate overdrive as I've never driven with this before, and I'm hoping to have my car back soon- it really has been the slowest and most stalled of rebuilds ever known!! I know o/d can be used in 3rd and 4th on mine.

1. When should I operate o/d for the first time on a journey - do I have to be at a certain speed and in 4th at first selection?

2. Do I need to deselect o/d before shifting down from 4th to 3rd?

3. Do I need to deselect o/d before shitfting up from 3rd to 4th?

4. When I turn the engine off is o/d cancelled if I haven't already done it? ie will it still be in o/d when I next turn the car on?

5. Is there an easy way to know if o/d is selected whilst driving (other than the revs being lower)?

Thanks,

Steve

Share this post


Link to post
Share on other sites

I had exactly the same questions when fitting a J OD box to my car earlier this year Steve. From experience the answers are:

1/ Any time when you want to lower the engine revs in either gear.  Actually, depending on the reduction ratio you have,  you may find OD third to be almost the same as direct top so it's more the convenience of flicking a switch 3rd-3OD rather than changing gear. I have found the most use is as a taller 'fifth gear' giving more comfortable cruising at speed which is really why I did it.  You can actually use OD at any speed provided it doesn't take the engine revs too low but I don't think there's much point in doing it below 2000 revs.

2/ if you do not have a 'logic box', if you leave the OD switched on it will drop out as you change gear and then re-engage itself automatically.  This is the action of the interlock switches so it's changing from 4OD to 3OD. if you switch the OD off first you are effectively going 4OD-4th-3rd.

3/ No. As above it's like going from '4th' direct to 5th . If you switch it off in third it will go 3OD-3rd-4th so effectively changing down before changing up again to about the same gear.

4/ Yes, if you leave the switch on, the OD will be enabled as soon as you turn on the ignition but should only actually operate if you are in an appropriate gear. You would notice a big gap as the box goes from 2nd up to 3OD instead of to 3rd. A logic box stops that as it does kick out the OD and requires you to switch it on in each gear. 

5/ No unless you fit a warning light. 

Ideally you need to dip the clutch briefly as you engage and disengage OD to prevent a 'thump' in the transmission which probably isn't good for the longevity of the OD clutch.  

Share this post


Link to post
Share on other sites

Thanks Rob. I'm just hoping it works when the car comes back, but at least I know now how to use it and what to expect when using it

Share this post


Link to post
Share on other sites

Hi Steve

You shouldn't need to dip the clutch  when engaging or disengaging the O/D especially the J- type overdrive which should engage/disengage smoothly.  A lot of people just keep their foot to the floor.  Great fun.  However, if you have a tired rear end you might want to  dip the clutch! 

Roger

Share this post


Link to post
Share on other sites

Change up under power and blip the throttle when changing down. No need to dip the clutch.

Share this post


Link to post
Share on other sites
1 hour ago, Rogcastle said:

However, if you have a tired rear end

Hopefully you mean the car, not me!!!

Share this post


Link to post
Share on other sites

You lot obviously have no sense of mechanical sympathy :o:D.   You should at least feather the throttle when engaging OD; certainly not do it with the power held on. That may be fun but it can damage things. 

Share this post


Link to post
Share on other sites
5 minutes ago, RobH said:

You lot obviously have no sense of mechanical sympathy :o:D.   You should at least feather the throttle when engaging OD; certainly not do it with the power held on. That may be fun but it can damage things. 

What can you damage? 

Share this post


Link to post
Share on other sites

The overdrive clutch mainly plus its not good to, give shock loads to the the final drive, the UJs.......

Share this post


Link to post
Share on other sites

To be honest, given the spacing of the ratios I would suggest you use overdrive in 4th much as you would 5th in a modern.

use overdrive in 3rd in traffic to save the bother of changing gear.

Some talk of overdrive turning the TR box into 6 speed (CR with J type) or a 7 speed (CP with A type) but unless you have a close ratio box the spacing don’t really work.

Share this post


Link to post
Share on other sites

As Andy says, overdrive is mainly useful as a fith ‘overdrive’ gear.

but... i find it a lot of fun to blast around country lanes in 3rd/3rd od

this one gear plus electric overdrive engagement / disengagement covers a wide speed range and much fun can be had !

steve 

Share this post


Link to post
Share on other sites

I waited 45 years to buy my TR6 after being smitten in the seventies.  The Tr6 is sports car  and should be driven as intended,  that way you get the rewards and as a bonus  a smile on your face,  just change your UJ's more often if need be.

 

Roger

Share this post


Link to post
Share on other sites

Keep throttle on going both ways always. Going in it matches load to engine power and coming out it matches revs to road speed. Been doing that for nearly fifty years and never had any problem or wear connected to using it that way.

Stuart.

Share this post


Link to post
Share on other sites

It's certainly worth engaging o/d with your foot on the throttle. Whilst the J type is less fierce in engagement compared with the A type it can still go in with quite a jolt and is kinder on the transmission if you do.

Share this post


Link to post
Share on other sites

Imho opinion, the only point is to not engage the overdrive at low rpm/speed. 

 

Share this post


Link to post
Share on other sites

Steve, the only things I think I would add are, you can engage overdrive at any speed, you won't do any harm but the revs may be too low to be sensible - you'll soon get the hang of it! However, dis-engaging at high revs gives the possibility of over-revving the engine, so just be aware of the rise in rpm, much like changing down the gears.

Other than that, I was ALWAYS going down below 3rd and forgetting to disengage overdrive. When I changed back up to 3rd again I would get the half to one second delay before the revs fell as the OD cuts in and the engine was no longer "on song". An overdrive logic circuit (home-made with two relays) hasn't improved my memory but I'm now a much happier driver.

Yes, OD+4th for cruising and 3rd/OD+3rd for town or particularly twisty lanes, but also for when you're looking for that overtaking opportunity. When it comes just floor the throttle and slip out of OD - which is instant, by the way - and off you go.

Cheers, Richard

Share this post


Link to post
Share on other sites

Changing gear with od engaged can lead to clunky gear changes. Best to disengage the od when not using it and changing gears.

Keep a bit of power on changing up. Changing down a bit of power but if you can't keep power on dip the clutch to avoid shocks to the drive train.

The idea you ignore strain and knocks on a drive train on a 50 year old car is, in my view, not wise. You will have enough maintenance without making more of it by careless driving.

Share this post


Link to post
Share on other sites

Although in theory it shouldn't matter with the switches on the gearbox, but just in case...

Gareth

Share this post


Link to post
Share on other sites

I'm a little concerned about not knowing if it's on after I've switched the engine off then reversing when I first come to it again.

So, in respect of the logic device what's the recommended one to buy and who from? Our is it possible to fit a light to show when it's on or off? If so is there a wiring diagram for this?

Share this post


Link to post
Share on other sites

If changing down from OD4 to OD3, I tend to change gear more slowly, giving everthing a wee bit of time to disengage & re-engage, no big clunks

Share this post


Link to post
Share on other sites

Boogie,

Rather than remember a list of instructions for each situatuion, think about it this way:

The O/d is completely seperate from the gear box, they just happen to be bolted to each other. (and share the same oil bath!)

Triumph/ Laycock did not want the O/d to be engaged in lower gears, or in reverse, so provided a switch activated by the gearbox itself that is only active in 3rd and 4th.    So the O/d automatically disengages when you go down the box.     It will not work in the lower gears, or reverse (well, it could if you got busy and added a jumper wire to the activating circuit to bypass the switch, but you won't do that, will you?).

So, worry not.     If you do leave the O/d lever in 'engage' position, and you change up from 2nd to third, O/d will engage as you do so, and you will find yourself in O/d 3rd, which is about 4th without the O/d - a bigger upchange than you expected.    That's what the logic box is intended to avoid, not to protect you from accidental use in reverse, which is already arranged.

Just treat O/d as it was intended - an extra, higher gear, that you don't need  a clutch for!       You will find that on changing into O/d, a gentle lift of the throttle for the higher gear and lower revs will make for a jerkless transition.        As will a gentle press on the throttle when coming out of O/d. 

Enjoy your O/d!  

John

PS Duncan, when changing gear from 4th O/d to 3rd O/d, or the opposite direction, the O/d does not disengage and re-engage.    The O/d stays in operation.     J.

 

 

Edited by john.r.davies

Share this post


Link to post
Share on other sites
1 hour ago, boogie said:

I'm a little concerned about not knowing if it's on after I've switched the engine off then reversing when I first come to it again.

So, in respect of the logic device what's the recommended one to buy and who from? Our is it possible to fit a light to show when it's on or off? If so is there a wiring diagram for this?

Boogie

i have fitted the revington TR logic switch system to my TR3a with A type OD but i think you need to add a relay for the J type.

i have used my OD in anger and you can see it on my Videos  i have the momentary switch on the dash under my right hand.

you can knock off the OD with the switch or change gear.

its also not in OD when you come to start the car.

 

Share this post


Link to post
Share on other sites

Check the O/D interlocks work still  in the lower gears /reverse. Some boy racer wired mine to engage in all gears to help him climb hills faster in the 1970's/80's

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Restore formatting

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...

×
×
  • Create New...

Important Information

Please familiarise yourself with our Terms and Conditions. By using this site, you agree to the following: Terms of Use.