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John Morrison

j type overdrive in an A type Chassis

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Hi All,

looking at fitting a J Type overdrive box, into a TR 250, obviously A type Chassis.

I've had  a look at various articles, and I know that there are conversion kits for the

rear crossmember at around £150.00, just wondered if anyone has done this, and has

a proven successful solution?

A photo or two would be great too!

John.

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I did it to my 4A but no pictures I’m afraid. It’s been fine for 6 years so far. 

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Hello John,

I am about to fit my third - to my latest TR3A.  One went in a TR3A and one in a CP TR6 - both easy as pie,

I used the Moss conversion rear bracket which is now strong and works well.  Get the J type drive flange re-drilled to fit your TR4A propshaft, and fit a clutch friction plate from the J-type donor (Triumph 2000 in my case but 2.5 PI before) as the splines are different.

The only other thing you'll need is the speedo cable fitting from the gearbox end of the J-type donor car.  

You might know that the J-type box comes in different overdrive ratios - 23, 25 or 28% - which is marked on the Box ID plate.  The higher the better.

It is a very straightforward swap and need hold no fears - Good luck.

Regards,

Willie

 

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If the J type is from a saloon, then the speedo drive ratio will be wrong (3.5:1 - TR is 2.5:1)  so speedo will read 18% slow.

There are a number of ways around this.

Bob.

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Hello Bob and John,

Thanks for the reminder Bob - I sent my speedo to JDO Instruments to be cleaned and recalibrated - it was then spot on.

I forgot about that - silly me!

Regards,

Willie

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Thanks Guys,

I'll keep you posted on success or not?

John.

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John 

I put a stag box with a 28% J type in my TR4, but it had been converted to TR spec by Pete Cox so I only had to worry about fitting it - I also had a Moss conversion kit - it wasn't difficult to fit but had to adjust the mounting holes a little and a bit of a fiddle fitting the rear mounting which comes with a shroud to protect it from oil - I also found that I had to relieve certain parts of the bracket to give better clearance to the solenoid and J type sump as I felt there was insufficient clearance.

All the other advice is spot on, but I think you will need a new speedo cable - can't remember if it's longer of shorter but one of those two!

Also be aware that there are slight variations in the cross member mounting for the different models, but they can be modded to fit - its only the mounting hole spacings that need adjusting.

I have got a non Moss mounting kit which uses a GT6 rear mounting, and to be honest, doesn't look very strong - I have a feeling these ones were some of the original kits which have evolved over the years to be stronger/better.

Finally, if you do redrill the output flange to match the TR propshaft spacing, it's got to be spot on accurate, otherwise you will get unwanted vibrations 

cheers

Rich

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Thanks Rich.

I wander if instead of re-drilling the output flange it is possible to

swop the TR one?

Anyone know?

John.

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John - I'm sure that should work fine - just make sure the seal area is not damaged otherwise you will be having a self renewing anti rust process happening! Obviously it if was fine on the old box, it should be OK now

Cheers

Rich

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1 hour ago, John Morrison said:

Thanks Rich.

I wander if instead of re-drilling the output flange it is possible to

swop the TR one?

Anyone know?

John.

The TR flange will fit onto an "A" type saloon OD, don't know if the "J" type is different.

Bob.

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Happy to b ecorected Tony,

thouth all Tr up to 5's or 6's were the round type.

John.

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Hi to all.

I am new on this forum and also new to being a tr4a owner. I have wanted one of these for many years now and only now has the dream come true. The car I own is a 1967 TR4A which was imported from the US. I intend to convert it to RHD, as I bought the car to drive and enjoy here in the UK. The other conversion I want to do is fit an O/D Gearbox in the car. I have read a lot on the forum re. J type boxes, and have purchased one that I believe came out of a TR6 (not a 100% sure of the donor car). I will either purchase or fabricate an adaptor plate for mounting the box and scrounge together all the electrical components needed.

The one question I have is regarding the prop shaft, can I modify my original or will a shaft out of another type of Triumph fit. If I can modify, does anyone know of a specialist who can do this, as I feel the shaft will need rebalancing.

Looking forward to years of tinkering and fun with my new addition to the fold. I have been into classic bikes before this and this is my first venture into Classic cars.

Cheers. Phil

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Phil - you don't need to change the propshaft - depending on whether your box really was a TR6 one, in which case fine, or obne from another vehicle in the triumph range, such as a triumph 2000, you may have to change the rear gearbox flange as the bolt spacings are different to TRs - there are other things you will need to be aware of as well if it isn't an original TR box .

Have you got the  gearbox serial number - it will be stamped into the bellhousing near where the clutch cross shaft goes through the box? 

Cheers  

Rich

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Phil, Rich

My saloon gearbox has a different spline arrangement from that on a TR gearbox so the flange will not swap from one to the other.

I got around it by having a machine shop put 4 extra drillings into the saloon flange to suit the TR propshaft, this was 20 years ago and no issues so far

George

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Hi Rich and George.

Thanks so much for such a prompt reply.

I have attached a pic of the spec. plate which is on the side of the gearbox, is this of any help.

There is another number on the box which I suspect is a casting number

Any help or advice on this conversion will be more than gratefully received.

Cheers..

 

serial number od box.jpg

od box.jpg

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Hi phil,

and welcome to our TR Register Forum.

You have bought a great car, and sure you will enjoy years of pleasure. Now, you will have realised that there is a wealth of

knowledge here, and all your questions will be answered. But you will also have a local group, (Where abouts are you?)

there is much knowledge, plus maybe an extra pair of hands or two, should need it.

Ask away, and enjoy!

John.

 

 

 

 

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Messages crossed !

That photo shows the overdrive plate, you have a 25% ratio overdrive.

The gearbox number s stamped into the boss where the clutch cross shaft enters the gearbox, will likely be

Two Letters and 4 or 5 numbers (From memory)

John

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Hi John.

I live in Blackwater near Truro in Cornwall.

I am currently in Ghana, West Africa where I work. I will be retiring back to the UK later this year, so I can enjoy my car and bikes, plus my old Fergy TE20. A lot to keep me busy when I get back.

I will get my brother in law to get a picture of the numbers you have mentioned and pass it on to you.

Thanks for such a nice welcome and hope to meet up with you guys sometime soon.

 

 

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I hope you realise that the gearbox mainshaft is different if OD fitted (a lot shorter)

Bob

Edited by Lebro

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Hi Bob.

Thanks for the advice. I purchased a complete gearbox with O/D fitted, so hopefullyy should not have issues with this.

Cheers. Phil

 

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Update time folks.

Gearbox is fitted and both gearbox and overdrive work well.

Quite a satisfying out come really. One final question, we jury wired the overdrive, to test,

we are using the saloon type gearknob switch, which I have to say does fall very readily to hand.

Looking at final, proper wiring now, and picking up supply from the keyed fuse at the fusebox, just wondered if

an inline fuse would be a good idea, and if so what amp fuse to use? I was surprised how 'Light' the gearknob switch and wiring is.

John.

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