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TR4A IRS AXLE NUMBERS


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Hello All,

I've failed to find anything on the forum about TR4A IRS axle numbers. Plenty about chassis/commision, body and engine numbers, a very little about ZS numbers, but nothing about the number stamped on the underside of the axle.

 

My car, first registered 24/08/1966 is chassis/commision number CTC 65403 O, Engine number CT 65527 E, Body number 65761CT, has a ZS number of 66069 (or possibly 86069, hard to read) and an axle number of CTC 60763.

 

I gather that none of these numbers are supposed to match, but does anyone have any idea about how IRS axle numbers fit into the scheme of things please?

 

Does it seem likely that my axle is the original?

 

All help and comments very welcome.

Cheers

Tony

Edited by tonycharente
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  • 4 weeks later...

Hello again,

I think I may have come up with an answer to my own question...

 

I've just received my car's BMIHT Factory Record certificate which confirms my car's Chassis N°, Engine N° and Body N°, but does not cover the Axle N°.

 

I've also found that the first TR4A was CTC50001, making my car "CTC 65403 O" the 15403'rd car built, by it's build date (which I now also know to be 03/02/1966).

 

My Axle N° is CTC60763, making it (I presume) the 10763'rd IRS axle built.

 

Now here comes my theory. Most TR4A's were still being shipped to the USA, where many TR4A's were supplied with live axles. So could it be that out of the 15403 cars built through to mine, 4640 (15403 less 10763) of them were live axle? Does that seem the right kind of proportion? If so that would comfort me in thinking my axle is (also) original.

 

All thoughts and comments very welcome.

Cheers

Tony

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Tony

 

I have access to 3 TR4A's, all UK RHD vehices and can advise the following:

 

1st Car built 5/8/65 - Chassis number - CTC 580-- Diff No CTC 55621 - 99% certain this is original

 

2nd Car built 6/8/65 - Chassis number - CTC 580-- Diff No CTC 54938 - pretty certain this is original

 

3rd Car built 11/5/66 - Chassis number - CTC 692-- Diff No RR4417 - told this is a factory reconditioned unit

 

For interest, the first 2 cars above were built a day apart and the chassis numbers are 51 different. I have access to the Heritage certs for all these vehicles but as you have noted, they don't include the diff number.

 

However, somethings seems a bit odd in as much that your car was built 3 months later than the 3rd car above, but has a chassis number 4000 odd lower ????

 

On the basis of the above info, I don't think yours is the original diff but also I suggest you double check your dates

 

Also look at the post 5 down from yours, headed "diff id"

 

Cheers

 

Rich

 

 

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Hello Rich,

and thank you for your info.

 

The "diff id" post doesn't provide the build date or chassis n° of AlanG's TR4A diff i(marked CTC 66298), so I can't extrapolate anything from that. I will ask him if he could help us with this info.

 

My car is also UK RHD.

 

Difficult to conclude too much comparing with the three cars you mention, other than Triumph don't seem to have had FIFO stock control with their axles if CTC 54938 is indeed original.

 

 

However making up a table of your first 2 cars and mine gives:-

 

1st Car built 5/Aug/65 - Chassis number - CTC 580-- Diff No CTC 55621 : roughly 8030th TR4A built : 5621th IRS axle : Therefore Live Axles ??? = 2409 = 30%

 

2nd Car built 6/Aug/65 - Chassis number - CTC 580-- Diff No CTC 54938 : roughly 8070th TR4A built : 4938th IRS axle : Therefore Live Axles ??? = 3132 = 38%

 

My Car built 3/Feb/1966 - Chassis number - CTC 65403 Diff No CTC 60763 : 15403'rd TR4A built : 10763'rd IRS axle : Therefore Live Axles ??? = 4640 = 30%

 

Interestingly the 1st car and my car both point towards 30% of Live Axle cars - would that have been about right I wonder (and the 2nd car had an out of sequence diff fitted if it is, as you believe its original diff?

 

Perhaps others would care to provide their numbers (no need to provide exact chassis n° ...) and I'll add them to the above table? (I rendered the dates "transatlantic").

 

Cheers

Tony

Edited by tonycharente
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Any apparent correlation between diff numbers and commission numbers is more likely coincidental than meaningful . . . . .

 

Commission, engine and gearbox numbers all followed a mysterious path, probably based mainly on what fell to hand at the time . . . . axles and diffs seemed to have been chosen almost at random.

 

I'd be very wary of reading too much into the numbers !

 

Cheers,

 

Alec

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Any apparent correlation between diff numbers and commission numbers is more likely coincidental than meaningful . . . . .

 

Commission, engine and gearbox numbers all followed a mysterious path, probably based mainly on what fell to hand at the time . . . . axles and diffs seemed to have been chosen almost at random.

 

I'd be very wary of reading too much into the numbers !

 

Cheers,

 

Alec

Hello Alec !

 

I thought I was the less than optimistic one !!!

 

According to one site:

 

In response to dealer requests, approximately 25% of TR4A were produced with a solid rear axle (also called a live axle), similar to the earlier TR4.

 

One would reasonably expect the percentage to be higher than 25% early on in TR4A production, so my figures seem quite reasonable to me... ...but then I would say that wouldn't I :) :) :) ?

 

Cheers

Tony

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Just to add a slight complication to the numbers, all solid axle TR4a`s continued to use the same chassis numbers as the TR4 i.e CTxxxxx from CT50001 Some were also dealer converted in the US back to IRS as well.

Stuart.

Edited by stuart
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Just to plug my 66 TR4A in (from my Heritage letter - not a certificate - from the archive and library in Studley, Warwicks dated 1987 and costing $5.00! - yes, USD!)

 

Chassis CTC/63536-LO (Left-hand drive and Overdrive)

Engine Number: CT/63562-E (anyone know what the "E" means? apart from "Engine"?)

Body Number: 64250/CT

 

Specification: LHD, North American Export

 

Built: 15 December 1965

Despatched: 10 January 1966

Destination (Dealer) Standard Motor Triumph Co. Ltd, Baltimore USA

 

Details of Equipment: Wire Wheels, Overdrive, Independent Rear Suspension, Heater and 165 Michelin X Radial tires

Colour: Triumph Racing Green

Trim: Black (leather)

Hood (top) Black

 

Key Numbers: 917, 890

Edited by ron88
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Just to plug my 66 TR4A in (from my Heritage letter - not a certificate - from the archive and library in Studley, Warwicks dated 1987 and costing $5.00! - yes, USD!)

 

Chassis CTC/63536-LO (Left-hand drive and Overdrive)

Engine Number: CT/63562-E (anyone know what the "E" means? apart from "Engine"?)

Body Number: 64250/CT

 

Specification: LHD, North American Export

 

Built: 15 December 1965

Despatched: 10 January 1966

Destination (Dealer) Standard Motor Triumph Co. Ltd, Baltimore USA

 

Details of Equipment: Wire Wheels, Overdrive, Independent Rear Suspension, Heater and 165 Michelin X Radial tires

Colour: Triumph Racing Green

Trim: Black (leather)

Hood (top) Black

 

Key Numbers: 917, 890

Thanks Ron, but I also need the axle number, please, in order to make full use of your numbers.

 

It's not on the Heritage certificate - it's stamped on the lowest surface of the axle, so readily readable from underneath but you do have to "get out and get under".

Cheers

Tony

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Hello Stuart

"...all solid axle TR4a`s continued to use the same chassis numbers as the TR4 i.e CTxxxxx from CT50001"... is not a complication - it's exactly what my "Therefore Live Axles ???" calculation is all about. Assuming the solid axle cars were still within the same numeric series (50001 and up) that is...

 

 

Here's a carry forward of my table, with two more cars added:-

 

 

Car built 5/Aug/65 - Chassis number - CTC 580XX Diff No CTC 55621 : roughly 8030th TR4A built : 5621th IRS axle : Therefore Live Axles ??? = 2409 = 30,0%

Car built 6/Aug/65 - Chassis number - CTC 580XX Diff No CTC 54938 : roughly 8070th TR4A built : 4938th IRS axle : Therefore Live Axles ??? = 3132 = 38,8%

Car built 15/Dec/65 - Chassis number - CTC/63536 Awaiting Diff N° info... : 13536th TR4A built : Awaiting Diff N° info... :

Car built 3/Feb/66 - Chassis number - CTC 65403 Diff No CTC 60763 : 15403'rd TR4A built : 10763'rd IRS axle : Therefore Live Axles ??? = 4640 = 30,1%

 

Car built 19/Sep/66 - Chassis number - CTC 73477 Diff No CTC 66298 : 23477th TR4A built : 16298th IRS axle : Therefore Live Axles ??? = 7179 = 30,5%

 

New comments :-

Awaiting the Diff number from Ron, please.

 

Alan, your details fit in perfectly with my theory !

 

Rich, "Car built 6/8/65 - Chassis number - CTC 580-- Diff No CTC 54938 - pretty certain this is original" : If this car's diff is indeed original it's beginning to look like it must have been found at the back of the stores. However I'm as yet a long way off having a statistically significant sample - Alec may yet prove to be right!

 

More chassis and diff numbers needed please... ...no need to provide the full chassis number if you prefer not to.

 

Cheers

Tony

Edited by tonycharente
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Tony, I'll try and check over the next few days but the diff has been rebuilt twice so I don't know whether or not the numbers still match, however I have the U.S. higher gear ratio so perhaps the casing was kept.

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Pretty sure this is the number, but note that it's "BTC" which denotes the 4.1 to 1 ratio. So BTC 50083

 

attachicon.gifIMG_4404.jpg

Thank you very much for this additional info, Ron - even if it it does rather ruin my theory! I had never heard of "BTC" prefix diffs before, but a quick search on Google came up with

 

Unlike the solid axle diffs, the IRS diffs are stamped w serial no's on the

bottom, CTC xxxxx for standard (3.7) gearing -- and BTC xxxxx for the 4.11s

 

It does rather screw up my calculations, though, since your "50083" serial number on a December 1965 built car makes it look as if these "BTC" diffs might have had their own series number sequence? Or else perhaps they built a batch of 4.11 diff axles towards the start of the IRS production, so that yours is the 83rd axle built and it just waited around in the stores all year waiting for someone to order an overdrive IRS who wanted the 4.11 ratio (a rare order I believe) ? I wonder how many BTC diffs were produce?

 

Or perhaps I should now give up and admit Alec was right ???

 

My table updated:-

 

Car built 5/Aug/65 - Chassis number - CTC 580XX Diff No CTC 55621 : roughly 8030th TR4A built : 5621th IRS axle : Therefore Live Axles ??? = 2409 = 30,0%

Car built 6/Aug/65 - Chassis number - CTC 580XX Diff No CTC 54938 : roughly 8070th TR4A built : 4938th IRS axle : Therefore Live Axles ??? = 3132 = 38,8%

Car built 15/Dec/65 - Chassis number - CTC/63536 Diff No BTC 50083 : 13536th TR4A built : 83rd IRS axle : Out of sequence : 4.11 Diff ratio "BTC" axle

Car built 3/Feb/66 - Chassis number - CTC 65403 Diff No CTC 60763 : 15403'rd TR4A built : 10763'rd IRS axle : Therefore Live Axles ??? = 4640 = 30,1%

Car built 19/Sep/66 - Chassis number - CTC 73477 Diff No CTC 66298 : 23477th TR4A built : 16298th IRS axle : Therefore Live Axles ??? = 7179 = 30,5%

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From an early edition of the TR-Register Magazine:

 

For the TR4 there were two rear axles; 3.7-1 which had a serial number starting with BT1 and 4.1 whose serial numbers started with CT1 (here there is some confusion as they could have been reversed in parts manuals, but duly noted that the two different axle ratios were available on both the 4 and 4A)

 

4A serial numbers started with 50001 or BTC 50001 (so mine was the 83rd 4.1/1 ordered for the 4A)

 

Somewhere I was told that the 4.1/1 ratio only made sense with overdrive; Having had a 3.7 fitted on mine for a week I thought it "lugged" in low gears and promptly had my original 4.1 refitted. Happy ever since.

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Many thanks for the extra info Ron.

 

I was very interested to receive your comments on 4.1 versus 3.7, as I am in the process of going the other way...

 

My car originally had the 3.7 ratio, despite having overdrive, as I think most did. I'm having to have the axle rebuilt anyway (two pinion teeth broken off) and have chosen to have a 3.45 ratio diff fitted as I very much prefer long legs. I live in the French countryside, rarely drive in town, often drive a long way, don't feel the need to do sprint starts. I haven't got it back yet, so don't know how it will feel, but my idea is that should overdrive top prove too long at low revs I can always use direct top. I am hoping that overdrive top will not prove to be too long at higher revs... ...you've worried me that you've felt it necessary to revert to 4.1 from 3.7 though!

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It's not a question of being right or wrong.

 

Standard Triumph did not do 'matching numbers' . . . . . a handful of cars across the Standard and Triumph model ranges have been noted as sporting the same number as commission and engine, for example, but that's about as far as it goes. Coincidence, no more and no less.

 

Commission, engine, gearbox and axle numbers each followed their own sequences, with occasional major anomalies - if, for example, reconditioned units were fitted to a new car. From time to time blocks of numbers might be missed for some good reason, or specification changes might result in an adjustment of numbering, or any one of several other good production line reasons.

 

There's nothing new about trying to derive logic from S-T numbers, the subject was pretty well wrapped up and put to bed back in the '70s, when original unmolested TRs were commonplace. No amount of wishful thinking will establish a reliable correlation another 40 years on !

 

Cheers,

 

Alec

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Its very rare to find 4.1 axles on 4a`s for a start and solid axle cars did have the diff number on them too.

Stuart.

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Tony, I can only say that I have driven both and much prefer mine (4.1) around town. On the motorway, with overdrive, the engine is quite smooth. Have gotten the car up to 100 with no problems or exceedingly high revs. So, it's a matter of "feel" and personal taste, I think, for the diff you prefer..

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Exactly right, Ron, it is a matter of feel and personal taste. But also a question of use and location. I'm blessed with empty country runs around where I live so most of the time I'm in overdrive top wherever I go. Also in April I plan to do a four day touring classic car rally with the Triumph, and the STARTING POINT is 270 miles from home. I'm really looking forward to seeing what it's like with a 3.45 diff!

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  • 4 weeks later...

Hello all,

Just to report on driving my TR4A with overdrive now with a 3.45 diff fitted...

 

I started by comparing the speedo readings at various speeds with the GPS speed, and they are now pretty well spot on - which means the original set up was exaggerating by 7% !!! (3.70 / 3.4545) This is on 165/80 x15 tyres. I believe original radials would have been 165X80, which in turn I believe technically corresponds to 165/82X15, so this would only have explained a tiny part of the exaggeration I'm observing.

 

Then assuming (???) the rev-counter is true, the car is now doing 3000 rpm at a genuine 70 mph, (overdrive top), which is great. This makes the car totally at ease on dual carriage ways. And as regards acceleration, it may be a little slower in the first couple of gears, beyond that it's just a question of using the (seven...) gears. And absolutely no problem pulling overdrive top even from 40 mph.

 

...for me it's a wonderful improvement !

 

Cheers

Tony

Edited by tonycharente
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