2nd gear overdrive

[New Bloke]

Many many many moons ago, before Tim Berners-Lee had invented the TR Register forum, I read an article probably in TR Action about gearboxes. The thing that stuck in my mind was a statement to the effect that though Laycock provided an inhibitor switch system that only allowed overdrive in 2nd, 3rd and 4th, it would be a lot kinder to the internals if 2nd overdrive was used sparingly, if at all!!!

 

 

This stuck with me and even today I rarely use OD in 2nd. Am I being a pillock or is there a germ of truth in this article?

 

What is the general concensus?

[ianc]

With a 3.7 axle, using overdrive on 2nd means that you can exceed 60 (70, if you are prepared to go to 6,000 rpm) without any 'gear' change - and that makes overtaking and moving onto motorways much faster (and therefore safer).

Also, very useful when climbing steep hills.

With a modified engine, I use it quite a lot, and always have.

Ian Cornish

[peejay4A]

O/D on 2nd isn't generally recommended for the J type overdrive I have fitted to my 4A but I've enabled it anyway

[TR NIALL]

I also have it on a J type but seldom use it in anger,in and around Town Traffic I do use it.

[ianc]

J-Type overdrive - yet another of the 'improvements' made when moving from TR4 to TR4A!

Adds to the list:

- removal of drain plug on differential housing

- front lower wishbone mountings which come away from the chassis

- rear swinging arms which come away from the chassis

- differentials which break away from the chassis

- change of camber at the rear when moving from drive to over-run (and vice versa)

- less robust rear hub assembly

- handbrake which is unlikely to pass an MOT.

 

There are a few more, I feel sure!

 

However, the head and inlet manifold were undoubtedly the best standard offering for the 4-pot.

 

Ian Cornish

[New Bloke]

Ian,

I fear yor comment "- rear swinging arms which come away from the chassis" is misleading, they didn't actually come away from the chassis, the chassis tended to break in half there and it would appear they had come away. Happend to me in 1998 when just after the finish of the Le Mans 24hrs, I jumped in my 4A and set of round the track, just as I got to the still fullish grandstands on the start-finish straight, the back went all wobbley, a mighty "crack" sounded and a shed load of smoke was emitted from where the rear tyre now incanted about 15 degrees and rubbing on the inside body work.......Got great cheer from the crowd......

[New Bloke]

Pete, you say "O/D on 2nd isn't generally recommended for the J type overdrive", this is what I'm trying to get to the bottom of. Presumably it's not Laycox that say this but who are these experts and is this just something that was mentioned by someone and grew legs?

 

Tim

[peejay4A]

Good question Tim. The J type fitted to the TR6 was not enabled for 2nd gear and I suppose there must have been a reason for that.

 

Just referring back to Ian's comment about improvements from TR4 to 4A I'll ignore the dig at IRS which he has made yet again but I'm sure he knows that the J type was not fitted to the 4A. Oh and the handbrake passed the MoT and also did 13 times on the TR6.

[ctc77965o]

Hey Tim,

 

I don't think it hurts the OD itself, but it sure stresses the drivetrain & chassis on a TR4A. The correct 4A A-type OD has a 'cushioned engagement' feature which reduces the risk that you tear the diff out of the chassis as the OD engages. Even with that you get a powerful kick when selecting OD 2nd at max rpm.

[Tony Millward]

I have a J type OD with 2nd gear enabled on my 6. If I use it 'in anger', it slips (which feels like clutch slip). Used gently, it's a boon for traffic, I think it's great.

 

cheers

 

Tony

[peejay4A]

Hey Tim,

 

I don't think it hurts the OD itself, but it sure stresses the drivetrain & chassis on a TR4A. The correct 4A A-type OD has a 'cushioned engagement' feature which reduces the risk that you tear the diff out of the chassis as the OD engages. Even with that you get a powerful kick when selecting OD 2nd at max rpm.

 

It is enabled by the factory on the TR6 (and TR5?) with the A-type overdrive and which has a near identical chassis and drivetrain. So a conclusion that you might draw from this is that it's to do with the overdrive design and not the chassis it's in. I've not heard of a diff being torn out of a chassis due to drivetrain shock loads. I guess it might happen though it there's advanced corrosion in the diff mount area but that's not really different to the negative effects of chassis corrosion on a live axle car, say around the spring hangers.

 

Here's a quote from the Buckeye Triumphs site about the J-type. The content doesn't have any source attribution but there is some technical argument:

 

A second major difference is that the J type OD is much less robust. For example, the gear teeth are smaller and I assume will tolerate less force. The design of the hydraulics is also different in a way that subjects the gears to less force. Many claim that the net effect is that the J type is much less prone to failure. The only area that I find fault with the J type design is the pump plunger assembly discussed later. The less robust design and reduced torque capability limited the J type to overdrive only in 3rd and 4th gears. I don't find that a problem since I never use my A types in 2nd gear unless I'm testing operation in 2nd gear. And --- if it doesn't work in 2nd gear I run down and repair the wiring problem and then never use it in 2nd gear till the next test --- dumb!

Edited April 27, 2013 by peejay4A

[Motorsport Mickey]

Well risking peejays wrath I agree with ctc77965o the revised operating system in the J type overdrive helps reduce violent torque input in the independant suspension cars, and hence allows the diff mounts an easier life.

 

Yes, I do believe (having an idea of what car manufacturers do when their original offering is showing problems) it was either engineered or chosen by Triumph from a Laycock offering for that reason, if you have a well put together A type overdrive (mine is) the overdrive engages before my finger has left the o/drive stalk after pushing it down ! even in second gear at 5000 revs without removing the throttle ! The instantaneous shock loading does nothing for any fragile mounting which describes the independant diff mounts to a T.

 

I also agree with Ian and Tony, using 2nd gear overdrive even if input gently at less than warp drive enhances the driveability of the TR and eclipses even modern car flexibility when overtaking or needing seemingly instant gear changing.

 

Mick Richards

[peejay4A]

No wrath intended Mick. If it's there in 2nd I'll use it but I like to think I have a bit of mechanical sympathy. Which is probably why my diff hasn't fallen out yet.

[Guest ntc]

As Tony pointed out the J type do not like 2nd gear and will slip,and if uprated power and misused it will self destruct

[andyhall]

I was getting slip when in o/d 2nd on my 4a to the extent that I've disconnected it, not much fun trying to overtake getting halfway past then slip!!!!!, both the gearbox and overdrive we rebuilt a few years ago, engine is uprated so there is more strain on the overdrive clutch, I'll get round to it 1 day there must be a fix, but definitely a bonus when it was working.

 

Andy

[BlueTR3A-5EKT]

Been out in my TR today and was pleased to have the overdrive working in 2nd. when caught in traffic. That is A type on the back of a Stag box.

 

 

Slipping overdrive J types was a sensation I think Triumph attempted to get round on the works Dolomite Sprint. There was a special pump, springs and op pistons available for the J type from Leyland Special Tuning that we the 'trick'. Something to do with pump pressure being derived from road speed and the rotating output shaft speed as I recall.

 

It worked too as we fitted a J to my brothers TR 2, had it working in 2/3/4. He hill climbed and sprinted the thing for some years without mishap or slip.

 

He finally got bored with the solenoid and exhaust clouting the chassis and fitted an earlier box with A type. This gave a change in first gear ratio that meant the gear was quite low with the 4.1 axle ratio.......

Car now has a 3.7 fitted.

That changes the top end......

 

Thinking about it the A type should have been mated to the J gear set somehow. There was a main shaft that did that too from the Innsbruck or Stag. (Front tip diameter change )

 

Cheers

Peter W

[Superaquarama]

I should think Triumph was almost alone in having o/drive on 3 ratios, wasn't it ? Most other mfrs like MG, Jaguar, Volvo etc. only had o/drive available on top gear - presumably with good reason.

[New Bloke]

I'm not sure which type I have, it wasn't on the car when I bought it. Is there an easy way to tell without removing the tunnel?

 

 

I used it today and it was very smooth, didn't seem to jar anything

[New Bloke]

Incidentally, many many years ago, the OD stopped working, pre-internet I called directory enquiries for Laycock's number. I phoned them and spoke to a bloke in the technical department. After going through the electrical stuff and me telling him the solenoid was working he told me I could either:

Strip the OD unit down and rebuild with new parts ...or

Find a quiet bit of road, put the car in reverse, rev to about 2k and drop the clutch.

 

Needless to say I did the latter and (touch wood) not a bit of trouble since.

 

Tim

[Guest ntc]

And you started the thread and you don't know? to quote PF( Jesus wept) what a waste of time on here it has become

Edited April 27, 2013 by ntc

[New Bloke]

 

And you started the thread and you don't know? to quote PF( Jesus wept) what a waste of time on here it has become

 

 

 

Well, I know it's either a "J" type or an "A" type

[Davidw]

If you can get underneath it's easy. Look at the over drive unit on the back of the box and,if there's a ruddy great brass disk, it's an A. If there's a small, finned, rectangular sump, it's a J.

[MikeF]

I should think Triumph was almost alone in having o/drive on 3 ratios, wasn't it ? Most other mfrs like MG, Jaguar, Volvo etc. only had o/drive available on top gear - presumably with good reason.

Way back when..., a guy in our car club had an MG-B and naturally there was rivalry, not just on events. On the anything you can do basis, he fixed his overdrive to also work on second gear.... and it broke, more than once as I recall before he gave up.

2>o/d 2 >2 can be handy in traffic and is very satisfying in extending 2nd gear during spirited driving. When I opted for overdrive on exchanging my clapped out gearbox I was asked did I want A or J? The difference was summarised: A for originality, and for second gear - much over rated in opinion of the box man. Or J for better long time reliability [from simpler, less critical electrics as much as anything.]

 

Mike

 

Mike

[New Bloke]

Thanks David,

 

It's got a great big brass thing that seems to be moveable, is it?

 

Tim

[New Bloke]

And you started the thread and you don't know? to quote PF( Jesus wept) what a waste of time on here it has become

 

Edited by ntc, 27 April 2013 - 09:35 PM.

 

Sorry for wasting your valuable time, now I know it's an "A" type, does that make your time less wasted?