Lower ratio 5th gear

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snakeknuckles
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Joined: Wed Jan 16, 2013 7:47 am
Your car is a: Fiat 1982
Location: Maryland

Lower ratio 5th gear

Postby snakeknuckles » Sat Mar 04, 2017 10:25 pm

I just took my first highway ride in my fully restored '82 turbo. I would like to know the options for getting a lower ratio in 5th. Is the only option a new trans or can I get a different gear set for my trans? It is pretty wound out at highway speed...

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So Cal Mark
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Re: Lower ratio 5th gear

Postby So Cal Mark » Sun Mar 05, 2017 1:41 am

get an automatic rear gear, those were 3.55 instead of the 3.9 that you have now
Mark Allison
allisonsautomotive.com Fiat and Alfa Romeo parts and service. Performance parts our specialty!
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snakeknuckles
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Location: Maryland

Re: Lower ratio 5th gear

Postby snakeknuckles » Sun Mar 05, 2017 6:39 am

Perfect. Tx. I am going to say that that rear will be a good match for the turbo... I wonder can I just change the gear set in my diff?

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baltobernie
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Re: Lower ratio 5th gear

Postby baltobernie » Sun Mar 05, 2017 11:11 am

IMO, the 3.55 rear ratio is a mixed bag for a 5-speed Spider. While it does provide a more-relaxed highway cruise, it lengthens the transmission ratios for gears 1 thru 4 as well. There's also no speedo gear for this ratio in the manual transmission, so your speedo and odo will be off. I kinda like the OE transmission gearing with the 3.9 rear (and 23" tires). First gear is a stump-puller, useful for creeping at a traffic light or starting from an uphill start. Typical "rolling" stops are easily performed with a minimum of clutch slippage in 2nd gear. That is a little more difficult with the 3.55. I have a friend with a built 2L and 3.55 rear, and there is a noticeable difference.

(Again, my opinion), the optimum solution is to replace only the 5th gear with a 0.82 one. 3,000 RPM is now 65 MPH vs. 58.

Of course, it's a lot less-expensive to replace a rear axle than to buy a new or modified tranny. To answer your question, yes, you can replace just the axle gears. But you need a box of shims and a good bit of knowledge to do this right. Most guys simply replace the entire axle, an easy job. But good luck finding a 3.55 axle. There weren't many automatics from the factory to begin with.

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So Cal Mark
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Re: Lower ratio 5th gear

Postby So Cal Mark » Sun Mar 05, 2017 11:22 am

personally I prefer the 4.3, I want the acceleration and I like cruising at 4k, he already has the 3.9 and I agree the 3.55 is only ideal for freeway cruising
Mark Allison
allisonsautomotive.com Fiat and Alfa Romeo parts and service. Performance parts our specialty!
Headers, ignitions, wheels, cams, flywheels
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djape1977
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Location: Belgrade, Serbia, eastern Europe

Re: Lower ratio 5th gear

Postby djape1977 » Sun Mar 05, 2017 7:02 pm

or just buy one of my taller 5th gear ratio gearboxes
0.82 ratio. you don't loose any acceleration except in 5th gear
what you have now is 0.92 or 0.88
0.82 will drop rpm in fifth by 750-900

snakeknuckles
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Location: Maryland

Re: Lower ratio 5th gear

Postby snakeknuckles » Sun Mar 05, 2017 8:23 pm

Well it is a tough call. I rebuilt my 5 SPD and i like the way it is working although I would consider pulling it out if there were an available gear set for 5th. Is there? Or do I have to change trans? On the other hand I have been playing around starting off in second and i don't think I'd miss my current 1st gear ratio... the turbo makes good torque right off the line in 2nd. If i can buy a 11/39 ring and pinion I might just try the install. I know they are tricky to set up. I did one once a while back on a '57 chevy.

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RRoller123
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Re: Lower ratio 5th gear

Postby RRoller123 » Mon Mar 06, 2017 6:27 am

I have always thought these cars should be three speed sticks, Don't need 1st or 5th, they are both too low. :wink:
'80 FI Spider 2000 (rolling hobby, being "restored" now)
'74 X1/9 (many years ago)
'79 X1/9 (fewer years ago)
2011 Chevy Malibu (daily driver)
2010 Chevy Silverado 2500HD Ext Cab 4WD/SB
2015 Keystone Montana High Country 343RL

snakeknuckles
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Re: Lower ratio 5th gear

Postby snakeknuckles » Mon Mar 06, 2017 5:53 pm

So now I'm a little more confused: What I now understand is that the 3.56 ring and pinion will not fit in the 3.90 carrier so that the only way to get 3.56 is to find an automatic rear? Can anyone confirm? Does anyone have automatic rear for sale?

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baltobernie
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Re: Lower ratio 5th gear

Postby baltobernie » Mon Mar 06, 2017 9:08 pm

snakeknuckles wrote: What I now understand is that the 3.56 ring and pinion will not fit in the 3.90 carrier so that the only way to get 3.56 is to find an automatic rear?
That may be true; I've seen ring gears replaced, and assumed that ratio changes are possible. I might have replied incorrectly. Sorry.

djape1977
Posts: 981
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Your car is a: 1970 fiat 124bc
Location: Belgrade, Serbia, eastern Europe

Re: Lower ratio 5th gear

Postby djape1977 » Tue Mar 07, 2017 12:16 pm

regarding taller fifth gear -
two of my rebuilt gearboxes with taller 5th gear have ended up in US already, one on east coast, one in west coast.
selling just the gear sets is not an option at this moment, as i have a limited stock of them and it's a big question if i can get more. i am looking into having them made though. if i would sell them at a price of 250-300$ per set, would that be interesting to you guys here?

regarding diff ratio -
there's three types of rear axles used on 124
main gears are not interchangeable between different types

snakeknuckles
Posts: 44
Joined: Wed Jan 16, 2013 7:47 am
Your car is a: Fiat 1982
Location: Maryland

Re: Lower ratio 5th gear

Postby snakeknuckles » Wed Mar 08, 2017 12:32 pm

I'd be in on a kit for ~$250 to change ratios on 5th... BTW, I googled 3.56 fiat spider rear this morning and... heavens to murgatroid! I found one for sale at Bayless. <$1000. delivered- its on the way. Can't wait to use a little more of that 140 mph speedo - which will have to be recalibrated...

djape1977
Posts: 981
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Your car is a: 1970 fiat 124bc
Location: Belgrade, Serbia, eastern Europe

Re: Lower ratio 5th gear

Postby djape1977 » Wed Mar 08, 2017 4:35 pm

changing diff ratio requires changing speedo drive unit as well, in order to maintain accurate speedo reading.
changing gears inside the gearbox doesn't.

from my experience, any taller diff ratio then 3.9 will result in poor acceleration, unless you have a highly tuned engine, 150+hp

carl
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Your car is a: 1971 128

Re: Lower ratio 5th gear

Postby carl » Thu Mar 09, 2017 8:54 am

I have no dog in this fight, drive a 128 with four speed at 75 mph and you will think any spider gearing is wonderful. I have a good friend with the auto spider rear axle in his 2L spider and it works just fine. Really strange to drive at first because every gear feels one gear higher, found myself cruising on the interstate for miles in 4th because the revs seemed right and then realized I had another gear.

As noted, the speedo will be off but don't try to fit an auto speedo drive on your five speed, it will punch a nice hole in the rear case.

djape1977
Posts: 981
Joined: Sat Apr 21, 2012 6:08 pm
Your car is a: 1970 fiat 124bc
Location: Belgrade, Serbia, eastern Europe

Re: Lower ratio 5th gear

Postby djape1977 » Thu Mar 09, 2017 4:30 pm

carl, you do know that there's a 5 speed and a 5 speed with taller gearing that's straigh bolt on to your 128?

your car should be 4sp with 13/53 main pair, giving 4.07/1 final drive ratio and a direct drive 5th gear.

128 was also made with 5speed gearbox, where 5th is overdrive gear, 0.9 ratio, and final drive was the same, 4.07

later, Zastava motor company in Yugoslavia made those gearboxes and derivatives.
5sp 4.07 ratio
5sp 3.76 ratio (17/64)

if you can find a Yugo gearbox somewhere in US, it would be later one, 5speed with 3.76 ratio. don't forget to get the sway bar as well, it has additional curve to it to bypass somewhat larger gearbox housing.

if you can't get it in US, i have sent one such gearbox already to NY, with sway bar, it was 550$ delivered


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