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Happy new year to all TR register members, many of you have given extremely helpful advice to me during my rebuild. 'May the forum be with you'

 

Here is another question for your exalted wisdom.

 

I am considering replacing my gearbox with an overdrive box. I have discovered that there are two types, an A type and a J type. Can anyone tell me what the difference is and which is the better. I expect there are advantages to both.

 

I have a 1960 TR3A.

 

Cheers.

 

Chalky :blink:

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A types are typically a little more expensive than J types. As standard, A types work on 2,3 & 4 but J types only work on 3 & 4 as standard. It is however relatively simple to make a J type work on 2.

J types, as far as TRs are concerned were only ever fitted to the TR6 after something like 1971, I think.

 

Down to nitty gritty.

 

There are two types of A type, 3 and 4 syncro. The 4 syncro box is better and this was fitted to the handful of TR3b cars exported to the US and later cars (TR4 onwards). Both come in overdrive or non-overdrive variations.

 

The TR A type gearbox will fit straight into your chassis with no major difficulties. Saloon boxes will require a little more work to make them fit and a J type gearbox will require the greatest amount of work to make it fit and work properly. The advantage of the J type being availability and cost to purchase.

 

If you want to keep things simple and useable and do not particularly mind a minor move from originality, I would advise finding a TR A type overdrive gearbox. If originality is paramount, a 3 syncro A type TR box is the only option.

 

Regards

 

David Ferry

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Guest Geoff Carter

J Type o'drive units were fitted to TR6's around 1974 when the de-tuned 125 bhp cars were introduced. I know, as I bought one to fit to my 1971 TR6. A types have a single rubber block rear mounting that fits to the chasis with 4 bolts. J types are easily identified as the have two rubber mounts at 45 degrees to the o/d unit on both sides.

 

Boxes are easily removed. Seats out, tunnel out and out through the passenger door. It's a one man drop if you're prepared to sweat. I've done it solo at least three times. Going backs is still solo but slightly more difficult.

 

Geoff Carter TS1923 RYD 761

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Thanks for the information chaps but I still don't know why one might be better than the other except for the ease of fitting and availability.

 

could you enlighten me a bit further, is one more robust over the other, for instance,

 

Thanks.

 

Chalky :blink:

 

Thanks for the information chaps but I still don't know why one might be better than the other except for the ease of fitting and availability.

 

could you enlighten me a bit further, is one more robust over the other, for instance,

 

Thanks.

 

Chalky :blink:

Edited by chalky
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J-type gearboxes are much cheaper because they were fitted in the Triumph saloons. They give less problems, they have no solenoid lever (no adjustment needed). The J type solenoids work without a relais.

The J types engage with a short delay (one second or two), and you have to adapt the rear mount, conversion kits are available trough Moss.

If originality is not an issue, I would go for a J type, but it depends of course on what you find or are offered.

The J type boxes are mostly newer, less wear, a lot of Triumph saloon cars were discarded with low mileage and much less abuse than a TR sidescreen.

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Thanks for all the information guys. One last question as a matter of interest, why is one called A type and one J type ? anyone know.

 

 

Chalky B)

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Thanks for all the information guys. One last question as a matter of interest, why is one called A type and one J type ? anyone know.

Chalky B)

 

Hi Chalky, can't help with your query, but here's some more info. for you.

 

 

Looking at Roger Williams’ books “How to Restore” and “Improve” the TR5, 250 and 6, it would appear that the J-type O/D unit is somewhat improved and more robust than the A-type, and therefore more capable of handling TR6 2nd gear torque, which was actually lower than the pre ’73 cars. Quote from “Improve” p.52: “….. then fit a post 1972 (J-type), gearbox and if required, the related overdrive unit. This actually achieves two improvements: the ratios are slightly ‘taller’, as already mentioned, and the gearboxes and their overdrive units are much more rugged and reliable.”, “Restore” p.106 “It is worth making the point that the ‘J’ type gearbox and overdrive is a much better unit than was its predecessor.”.

 

From Graham Robson’s book Triumph Cars, the internal gearbox (A-type) ratios were changed in mid 1971 from GBs CD51163/CC89817 to the slightly higher (taller) ratios used in the J-type box. There’s a comment in Roger William’s “Restore” book p.103, “The ‘J’ type overdrive is protected as it will slip before anything breaks, but the ‘A’ type will break and require a professional rebuild.” He goes on to state that the later A-type boxes did not have 2nd gear O/D enabled, and this was only re-introduced with the early CR/CF cars with A-type boxes (J-types were fitted from CR567). This may tally with GR’s statement. RW also refers to an “improved/modified unidirectional gear” fitted to the late A-type O/Ds. Does anyone know for sure when the improved parts were fitted to A-types?

 

A plate should be found on the O/D unit, which starts 22, 25 or 28 which indicates the percentage ratio of the unit, eg on my 6 unit , a J-type 25/115838 - the prefix indicates the O/D percentage increase in output shaft speed, 22 = 22% or 0.82 (Input shaft revs divided by Output shaft revs), 25 = 25% or 0.797and 28 = 28% - which some O/D units are geared for, fitted to some 2.5 saloons. The second part of 6 digits indicates the type of vehicle the O/D was built for AFIK.

Edited by jonlar
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Hi Chalky

 

Just to give you my line on this - the a and the j type overdrive boxes have all sorts of differences and merits - some of which have been outlined in the previous post so i wont repeat them.

 

What you will find is that it is much more involved to fit a j type in an 'a type' car, simply because the j type is longer, the solenoid points the wrong way, the wiring is different. Fitting a 'lesser' a type box is fine, but always ask yourself the question why ! I say this based on experience, not conjecture. Bear also in mind that the a type overdrive unit is the one which can be uprated most, so if you go for a non TR box I would say use an a type.

 

The reality is that the TR a type overdrive box is actually very good in the main (although the weak point in the driveline I have found) and my advice would be to find a TR3a or early TR4 box (this is a better box) and do the job properly. The difference in price is about £300 for a core unit and having the wrong box in your car WILL affect its value when it comes to the bit. You WILL also have problems, even if it is only the exhaust rattling on the bigger / longer j type etc. which are minor but will draive you mad.

 

The only exception to the above in my opinion would be the stag a type box which has the same overdrive unit, but a better bottom end to the gearbox. These can be easily converted to fit the TR (either by changing the tail casing and sol housing on the overdrive and the input shaft on the gearbox when you are rebuilding) or by running a steel adaptor (available from ORS in Sheffield for about £20). I use a converted stag a type gearbox and overdrive on my rally TR4 and it is the best one ive had in a long line.

 

Bear in mind also that saloon a type boxes cost circa £150, stag circa £350 and TR upwards of £450.

 

I had my stag box rebuilt for £300 and the overdrive unit uprated and reconditioned to 'race/rally' spec for £450. A rebuild on a TR a type box is probably the same sort of money. Ive not done a saloon box but presume the same as the main costs are labour or common jobs.

 

It appears to me then that all you save money on is a part of the difference in 'core prices', which is largely swallowed up by the conversion bits you need. I say if you can get a TR box take it, in circumstances where you can then perhaps look at alternative or non standard stuff.

 

Hope this helps you.

 

Regards

 

Tony

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