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Discussion Starter #1
I'm about to begin restoring a 71 Spider Junior (type 105.91) that I have owned for about 12 years awaiting the spare time to restore it.

I just got it running again after 10 years in storage and a few questions are bugging me. First, what is the yellow dash light in the middle directly between the tach and speedo (see photo)? It is constantly illuminated and I cannot remember or figure out what function it serves.

Second, what should I look for as to interchangeability of differentials? Will any 105 series differential interchange? My intent is to get a taller ratio (4:11 ?) to replace the 4:56 that is in it now.

I greatly appreciate the info so freely shared on this board and look forward to becoming a contributing member. Although I have owned and done extensive work on Alfas before, it was all in the 60s and 70s with 750 and 101 series spiders.

I purchased this car in 1999 along with most of the new parts and spares to restore it. I plan to do a ground up restoration over the next couple years and am getting all the parts lined up and work space organized. The previous owner got in over his head but not before he made a few modifications that I plan to reverse, including cutting holes to mount speakers (in the panel between the interior and trunk). It needs a few new body panels in the usual places like rockers and floor pans. Other than a few mods to the body done by the PO, it appears to be stock except for some DCOE-28s that I was fortunate to find and use to replace the Dellortos. Currently it is a strong runner even though it has one bad exhaust valve.

Regards,
Jim
 

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And the other red light is the brake fluid level indicator. They are easy to mix up.

"cutting holes to mount speakers"

In most countries this offense is punishable by DEATH (if DEATH with all capital letters happens to be unavailable, several standard deaths might also suffice).
 

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Discussion Starter #4
Thank you both for the replies. Jim, it is indeed the parking brake indicator. I had not thought to check that function and the switch at the brake handle is very sensitive (as it should be) and if not fully down it shows an indication.

Inner Circle, Agree some sort of punishment is merited for cutting holes in body panels. Although not a purist, putting aftermarket speakers in a car such as this offends my sensibilities. I appreciate the heads up on the brake fluid level indicator. I will ensure that circuit works.
 

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Any diff with ATE brakes (about 99% of the 1051/115 diffs you're likely to find) will bolt in and work. Bosch Spiders use 4.10; earlier US cars for the most part use 4.56. There are 4.3 from other markets, but they're rare in the US.
If the Jr has a 1300 in it 4.10 is a lot of gear to pull without a lot of power. It it has something bigger it might be fine.
Andrew
 

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Discussion Starter #6
Andrew,
I appreciate your comments and info. I really haven't made up my mind whether to pursue a different ratio or not.

As for power, it has way more then enough now and I doubt a 4:10 ratio would make it underpowered, at least for the type of driving I do.

When I first got the car and took it on a 1000 mile trip I was immediately reminded of my college days driving my 101 1300 Spider cross country and how fatiguing it is to maintain freeway speeds with the engine continually near 5K rpm. After restoration, the car will be a frequent driver and I'm out in the country so it will see a fair bit of highway driving.

Thanks again,
Jim
 

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I can't help thinking you're asking a lot for the engine to pull the 4.55 diff. Its around 11% faster in every gear but means your engine will feel around 20% less powerful.

Or put another way your engine needs to be 20% more powerful to pull that gear and maintain the current in gear performance.

At 70MPH its probably pulling around a true 4000 RPM (don't always believe the tacho) which I think is fine for that engine.

I've gone the other way, running a 2000 engine with a 4.1 diff for a fast road / trackday car. Its very perky and I cruise at 80MPH. I don't find it too noisy for the occasional trip.
 

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My Giulietta Spider Veloce has a 4.10 diff, but it doesn't have fifth gear.
If your Jr has a 4.56 rear end, .79 fifth, and stock size tires, it should be turning just under 20 mph/1000 rpm.
Andrew
 

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Discussion Starter #10
Interesting discussion and I appreciate the input. It has motivated me to do the work to accurately confirm my ratios and tach / spedo accuracy. I certainly want to avoid any expense and effort that proves unsatisfactory in the end.

I know my Jr has a 4:56 rear end but am unsure of the 5th gear ratio. It is stock so I can likely find the specifications. And it has stock wheels and tires. When driving on rural roads or open highway, though, I find myself with way more than enough power and "looking" for an additional gear to keep my revs reasonable. It could be that I have an aversion to sustained high revs but it may be influenced by my memory of my Giulietta Spider which did not rev nearly as high as the Jr. Could be a result of the much taller tires on 15" wheels on the Giulietta as well as what "seems" was a taller 5th gear ratio.

I've got some more homework to do.....
Jim
 

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If your Jr is a 1300, then the factory fifth gear ratio is 0.86.
Instead of changing the rear ratio, another option would be to install a non-1300 gearbox which would have an 0.79 fifth gear. This would lower the revs on the highway while in 5th but would leave the fun gears the same.
 
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