Speedometer recalibration fix

[Turbofiat124]

Back in the late 90s, I installed a 140 mph speedometer from a 1970 Spider in my 1980 Spider. The main reason was the original tachometer started to go nuts so I used an earlier style tach. So later on, to match it I used an earlier style speedometer.

As you know the earlier style speedos uses a screw on end and the later style uses a clip on end. But you can't just use a cable from an earlier model. I found the earlier style cable to be too short to reach the transmission. Or at least if you order one for a 1970 model. I don't know why unless it exits the firewall in a different location. Perhaps if I ordered a cable from a 1977 model it would have been the correct length. Anybody know for sure?

The popular conversion is to source a 140 mph speedometer from a 1978 model but these are kind of rare being a one year only deal.

My "fix" was to lay both speedometer cables side by side, remove the cable from the sleeve and cut the sleeves in the same location about 6" from the speedometer end. Then swapped ends and crimped a piece of 5/16" tubing over both of the sleeves and wrapped them with electrical tape. That created a longer cable with a screw on connector. This has been working fine for about 15 years.

Back in the summer my speedometer starting going nuts. It got to where it was reading higher than normal, might not work at all then this is what it was reading at around 60 mph.



Then one day it stopped working altogether. So I'm not sure if it's the speedometer or the cable. At any rate I'm going back to another 85 mph speedometer because I don't have another 140 mph speedometer.

But here is the thing. Even before I swapped out speedos or final drives, the speedometer has never been correct. I could be doing 60 mph and the speedometer would peg out at 85 mph with the old speedometer.

This was before I installed a 4.1:1 final drive after the pinion gear in the original 3.8:1 final drive broke.

The only thing I can think of that would throw the speedometer off that much was I switched to 14" 60 series tires on Panasports after I bought this car. I think the Spiders originally came with 13" 80 series tires. So by dropping down about one inch diameter tires would that have messed the speedometer up that much? Well assuming a "series" equals one inch.

As you may know, the gear drive is what determines how fast the speedometer turns. You can swap out an 85 mph speedometer for a 140 mph speedometer and will not affect the calibration. So I have read. Also unless you cut an access hole out in the driveshaft tunnel, the gear drive cannot be removed unless you drop the transmission. I'm not in the mood to do that.

As of right now I have:

14" 60 series tires
4.1:1 final drive
unknown gear drive in the transmission.

I've got a spare 85 mph speedometer from a 1981 model I plan on installing and a new cable unless my cable is about to break causing it to act weird.

All I need to know is if I want to correct this issue and get my speedometer to read correctly, what is the fix? I've heard there is a gear reduction thing that fits between the cable and speedometer or cable and transmission that will fix the problem.

Just wondering if anyone has done this and how to do it, where to get it...

[djape1977]

all fiat speedometers are 1/1000, so your problem doesn't come from there

what you need is a speedo drive unit with correct number of teeth for diff you have.
you can remove speedo drive unit without removing the gearbox completely. just drop the crossmember that supports the gearbox

[Turbofiat124]

I wondered if the initial inaccuracy was due to original 85 mph speedometer going bad. Is that possible?

As far as I recall, when the speedometer would "peg out "at 85 mph at 60 mph, everything on the car was original except for the wheels/tires.

Now that I have seen the current 140 mph speedometer read higher than it should. Well it has always read high. I mean higher than normal as in the photo I took before it finally stopped working.

Over the years I have mismatched parts from used parts laying around. I have no idea what gear drive I actually have right now. I do not have the transmission that matched the 4.1:1 axle I installed.

I have a 131 axle with a 3.5:1 final drive I would really like to install. The guts are not interchangeable because it's not the "pumpkin" design.

I think the turbo would benefit more from having a higher final drive.

The width of both axles seems the same. But the trailing arm mounts are different. Also the 131 has drum brakes but I have heard of people installing 124 Spider disc brakes on 131s so it must be possible.

[djape1977]

if you're running a 3.9 diff and a speedo drive from a car that had 4.3 ratio, diference is enough to account for that big speedo inaccuracy

also, if you're using tyre size larger then what was initially on the car that speedo drive came off, that increases speedo error

going 3.5 will be way too long
what HP is your turbo car making? 3.5 will be suitable to 150+hp, and then you'll end up with a car that doesn't have that good acceleration, but will pull strong from 60 to 120+mph driving topless 40yr old car at those speeds is not something you want, trust me on that one

my favourite combo is 4.1 ratio and longer fifth speed, 0.82, and with turbo it would be 3.9 tops

131 rear axle is not really an upgrade over 124 rear end. over in europe , we call 131 diff "chocolate diff", because it seems that insides were made out of brown stuff.
if you want an upgrade, go for 132/argenta rear end. it's pretty much indestructible, people run it on 400+bhp race cars

any fiat rear axle with drums can be converted to discs. it's just a matter of swapping over anchor plates

[Turbofiat124]

if you're running a 3.9 diff and a speedo drive from a car that had 4.3 ratio, diference is enough to account for that big speedo inaccuracy

also, if you're using tyre size larger then what was initially on the car that speedo drive came off, that increases speedo error

going 3.5 will be way too long
what HP is your turbo car making? 3.5 will be suitable to 150+hp, and then you'll end up with a car that doesn't have that good acceleration, but will pull strong from 60 to 120+mph driving topless 40yr old car at those speeds is not something you want, trust me on that one

my favourite combo is 4.1 ratio and longer fifth speed, 0.82, and with turbo it would be 3.9 tops

131 rear axle is not really an upgrade over 124 rear end. over in europe , we call 131 diff "chocolate diff", because it seems that insides were made out of brown stuff.
if you want an upgrade, go for 132/argenta rear end. it's pretty much indestructible, people run it on 400+bhp race cars

any fiat rear axle with drums can be converted to discs. it's just a matter of swapping over anchor plates

I'm running a 4.1:1 final drive and possibly a 3.9:1 gear drive (not real sure). There is supposed to be a colored dot on the gear drive which identifies which ratio it is. I'll check it out to see if the mark is still there.

I think the original tire size was 13" 80 series, can't remember the width. I'm currently running 14" 60 series 185s.

So I have a lower final drive and slightly smaller diameter tires.

I dynoed my Spider at 123hp/139 ft lbs of torque at the rear wheels about 15 years ago. So given the drivetrain loose I estimated around 154 BHP. The problem with the 4.1:1 final drive is the engine makes no boost in 1st gear, around 3 to 4 lbs in 2nd gear. 3rd gear I can hit full boost (7 lbs). I can actually pull out in 2nd gear on flat land and barely slip the clutch.

I once drove a Subaru WRX. I thought it was gear way to high to be honest as most factory turbocharged cars.

In constrast with my 1500cc turbo Yugo, after fitting a 2.25" exhaust system I can hit full boost/full throttle in 2nd gear and spin the tires. I think the Yugos sent to the United States with the 1100cc engines and 4 speeds had a 3.8:1 or a 3.7:1 final drive.

[DieselSpider]

I am running the 4.30:1 with a Diesel Engine/Transmission package designed for a 3.38:1 diff. With the turbo it gets to the red zone way too soon.

[djape1977]

i've had my lada with 2 litre fiat twincam in it dynoed at 125hp at the wheels, and that was with no turbo. engine assembled out of fiat parts bin. just stock parts from different fiat models. 4.1 diff ratio, 205/60/13 tyres.

[Turbofiat124]

i've had my lada with 2 litre fiat twincam in it dynoed at 125hp at the wheels, and that was with no turbo. engine assembled out of fiat parts bin. just stock parts from different fiat models. 4.1 diff ratio, 205/60/13 tyres.

The US spec cars were de-tuned to meet strict emission standards back in the 70s and 80s by using lower compression pistons (8:1), altered cam profiles, cat converters. So our fuel injected 2 liter engines only made around 100 BHP. The carbed 2 liters in 1979 and 1980 made around 82 BHP because of smog pumps and other devices.

I know a guy who used to own a Euro spec Lancia Beta HPE with "same" 2 liter engine and L-jet fuel injection system as my Spider. I think his was rated at the same BHP has my turbocharged Spider because it was not detuned like my engine.

On the same token, our 1100cc Yugos made the same HP as the pushrod 900cc models sold in Europe! The Yugo 55 which stood for "55 hp" I think had the 900cc pushrod engine and made the same power as the 1100cc engines we got. We never got the 900 pushrod engines. Later we got the 1300 fuel injected models with a whopping 65 BHP!

Like most European cars that were sent to the United States, we never got a choice of what engine size we wanted. They always sent us the largest engine in production. I guess to focus on building one engine that would meet emission requirements, to make up for a loss in HP due to emission control devices and the fact gasoline prices were much lower than in Europe, so fuel consumption was not an issue.