GTAm Differential quandary - Alfa Romeo Bulletin Board & Forums
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post #1 of 27 (permalink) Old 06-06-2019, 02:35 PM Thread Starter
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GTAm Differential quandary

On 1532307, there is the typical 'Slittone' set up and the rear axle as it came from A.D.

Fortunately the front suspension and brakes were there also, but not much else, as the poor car had been turned into

a 'racecar/taxi/trashcan'. If you have been following the story of this car, you already know.

Bottom line, inside the differential, it is the 'small unit', as not a proper 2 liter car/body even though
it was powered by a proper 2.0 Am, in the day.

My question: is this 'small LSD unit' (thick splined axles) able to carry the addl. torque that Gtam motors made then? They were readily available, and not a cause of great concern. Same went with the motors.

Have decided to keep all GTAm motor and parts in a box, install a hot (read: disposable, or not as $$$, just to putz on the track) as here, no chance of competing with a car of value. I really ignore if 'real Am's are being raced as some do in Europe, or in the USA
risking OEM parts?

So, a TS or 2.0 motor as fearing that grenading the 'real Am motor' is not a good idea, but have concerns on the diff, as also a 'precious' part. The car will not see racing again, until the next custodian might. That, will be my kids' problem.

Any advice on this LSD or alternative set up to go and drive?

Thank you all !

Regards, Alberto
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post #2 of 27 (permalink) Old 06-06-2019, 05:41 PM
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Hi Alberto

It is so long ago I investigated this that may memory may well be wrong....

However, I was under the impression that AD used the cam and pawl differential system....my understanding there are some, unknown to me, advantages with a serious disadvantage of quite violent engagement....

Also the spline count differs to standard GTA stuff.

I have a spare NOS one I bought out of Greece many years ago, if you are interested...

Others, more knowledgeable please chime in...also, I seem to recall an earlier thread!

Richard
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post #3 of 27 (permalink) Old 06-07-2019, 07:56 AM
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I have a GTA unit which is smaller than the AD GTAm unit in my GTA rear axle. It has held up just fine for years on the track behind my GTA engine in different (mild to radical) states of tune. It's disadvantage is it runs partially locked, (set-up-pre install) at all times, and makes turning the car (on-off trailer, or low speed driving) difficult. At speed, on the track, it's just fine and is trouble free.
The GTAm pawl type, is locked or unlocked, and more non-race friendly. I have similar, GTO locker type differential, in my 275 GTB. The "violence" of the lock-unlock cycle is overstated. It just requires a learning-curve, which includes a few interesting spins at speed. Once you know what to expect, it's just fine. I've had the 275 about 40 years, and both street or track combined, only swapped ends 3 or 4 times early on as I learned. It is NOT user friendly on a damp track with dry and wet spots, noticed or unnoticed.
A big advantage of the locker type is heat build up. A clutch type LS gets hotter. This is less an issue today with synthetic lubes, conventional mineral based lubes needed frequent changes on the clutch type.
I believe either type can absorb the power of a GTAm engine, it's a matter of ease of low speed, or off track use and heat. All the above is only my opinion from my own experiences over many years.
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post #4 of 27 (permalink) Old 06-07-2019, 08:50 AM Thread Starter
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I am lost now. Will have to take internal photos and post them. Apples and Apples.

Thank you though, for the replies, getting somewhere now.

Regards, Alberto
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post #5 of 27 (permalink) Old 06-07-2019, 04:33 PM
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As Franco said: 'its like a shoe without a heel '

you said: 'The car will not see racing again.'

so just use what you have: 'small LSD unit' (thick splined axles)'
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post #6 of 27 (permalink) Old 06-07-2019, 04:52 PM Thread Starter
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Quote:
Originally Posted by alfa-sport View Post
As Franco said: 'its like a shoe without a heel '

you said: 'The car will not see racing again.'

so just use what you have: 'small LSD unit' (thick splined axles)'
It will not see racing at 10/10ths, but once on a racetrack, 9.5/10ths?

Anyhow not competing against anyone, just go out and have fun.

Will post photos.

Regards, Alberto

Last edited by aguirola; 06-07-2019 at 04:57 PM.
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post #7 of 27 (permalink) Old 06-08-2019, 03:37 PM
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Hi Alberto,
Your desire to have ‘race ready’ unit even if it is not destined to the track is legitim. Consider this: On GT Am Autodelta team cars, auto-lock was ratchet type, with high closure ratio (47% and more on demand), 15 splines and its ref. number was 10533.17.043.E02 (the same was used also on 33 cars so capable to support and manage any power that GT Am engine could produce), and to be mounted on GT Am, the ring and pinion 10551.17.021.99 was requested. This slip diff. was suitable only for the track and not street use, it is not easy to find, and its price is high. In my opinion, you should search ‘standard’ ZF unit used with 2000 engines (it supports perfectly GT Am power as well-is the ‘small one’ as you call the one present on your car the same thing?). Its ref number is 10544.17.043.01 (10516.17.043.01 will do also) and it is 25 splines and ‘mild’ closure (25%) so suitable for street use. If you need further info, send me e-mail.
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post #8 of 27 (permalink) Old 06-08-2019, 03:49 PM Thread Starter
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Quote:
Originally Posted by ARGTAReg View Post
Hi Alberto,
Your desire to have ‘race ready’ unit even if it is not destined to the track is legitim. Consider this: On GT Am Autodelta team cars, auto-lock was ratchet type, with high closure ratio (47% and more on demand), 15 splines and its ref. number was 10533.17.043.E02 (the same was used also on 33 cars so capable to support and manage any power that GT Am engine could produce), and to be mounted on GT Am, the ring and pinion 10551.17.021.99 was requested. This slip diff. was suitable only for the track and not street use, it is not easy to find, and its price is high. In my opinion, you should search ‘standard’ ZF unit used with 2000 engines (it supports perfectly GT Am power as well-is the ‘small one’ as you call the one present on your car the same thing?). Its ref number is 10544.17.043.01 (10516.17.043.01 will do also) and it is 25 splines and ‘mild’ closure (25%) so suitable for street use. If you need further info, send me e-mail.
Just sent a reply.

Regards, Alberto
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post #9 of 27 (permalink) Old 06-10-2019, 06:12 AM
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Quote:
Originally Posted by aguirola View Post
On 1532307,
Bottom line, inside the differential, it is the 'small unit', as not a proper 2 liter car/body even though
it was powered by a proper 2.0 Am, in the day.



Regards, Alberto
wasnt the early gtam built on a 1750 body and block?
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post #10 of 27 (permalink) Old 06-10-2019, 06:49 AM
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LSDs

For clarity, I`m referring to the clutch disk type of LSDs that came as factory installed units.

Both the "small" (that fit 101 &105 diffs) and the "large" version as used in the 2 liter 115 series as well as the different housing LSD in the 119 transaxles, all use the same inner floater plates, clutch disks, and ramp plates/axle/gear assemblies.

The difference in these are the internal drive sprockets/axle receivers, and of course the outer housings that fit the smaller ring gears (or larger) and different size bearings to fit the various "housings".

"Small units" can be built using 2 or 4 clutch disk which results in the same level of "lock-up" as the larger housing units.

In the late '60s I bought an LSD unit for my '67 Duetto. It originally came with 4 clutch disk, but they were assembled with 2 on each side,paired together "side by side" to result in lower lock up (effectively a 2 disk set-up). The clutch disk just needed re-positioning for more lock up.

I`ve built several LSDs for the smaller 101/105 using the large units from transaxle versions, as cores to machine to fit. These required either using 2 liter axles or welding up and re-splining to 2 liter spline size and design, as well as shortening the axles, (due to LSD internal parts).

FYI: For the clutch disk LSds the heavier 15 spline axles were really un-necessary as LSD units like these never are fully locked and are not delivering "locked stresses & twisting" as a welded unit or ratchet type units would.

Richard Jemison
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post #11 of 27 (permalink) Old 06-10-2019, 08:57 AM Thread Starter
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Here are the photos. The ratio is a 4.77
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post #12 of 27 (permalink) Old 06-10-2019, 09:00 AM Thread Starter
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post #13 of 27 (permalink) Old 06-10-2019, 09:03 AM Thread Starter
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Quote:
Originally Posted by davbert View Post
wasnt the early gtam built on a 1750 body and block?
I assume the AD cars were all 1750 bodies (105..), but eventually, the engine grew to to 2 liters.

Regards, Alberto

Last edited by aguirola; 06-10-2019 at 10:09 AM.
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post #14 of 27 (permalink) Old 06-10-2019, 11:43 AM
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Quote:
Originally Posted by aguirola View Post
Quote:
Originally Posted by davbert View Post
wasnt the early gtam built on a 1750 body and block?
I assume the AD cars were all 1750 bodies (105..), but eventually, the engine grew to to 2 liters.

Regards, Alberto
Confusing because the engine size of a GTAm using the 1779cc block is 1985cc. Monoliner has larger bore.

I assume the engine size of 2000GTAm's was also 1985cc using the 1962cc block but do not know ...
Pete

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post #15 of 27 (permalink) Old 06-10-2019, 12:09 PM
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im not an gtam expert but the arese museo car and good number of gtam were built on 1750s i reckon. you can tell by them by floor mounted pedals. sometimes the smaller taillamps but this isnt fool proof to ID them as i recall.

here are a few:


https://www.autoblog.gr/wp-content/g...t-am-for-sale/

https://www.bonhams.com/auctions/22723/lot/325/

https://www.artcurial.com/fr/lot-197...6#popin-active
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