Technical Are there any differences between 60 and 75 gearboxes?

[chesh]

I've swapped my old 75 gearbox (1996) to a newer model (1999) but from a 60 or 55 model.

The car became slow as hell.
The gearbox is used but in great condition and doesn't have any noises or whines.
my old gearbox sounded like a bus, probably a diff problem.

I know the gear ratios are slightly different but that much?

 

[fingers99]

Not sure. The final drive could be different. Generally the Puntos with 14" wheels came with a lower final drive than those with 13s.

 

[dumbledore]

My 60S (1999) with 14' wheels uses 3600rpm in fifth to do 70mph. This may help in your investigation.

 

[chesh]

I get 75mph with 3600rpm on fifth gear.
But I feel it's taking too long to get to it. Accelerate is slower than before, top speed is not the problem.

 

[dumbledore]

If you get 75mpg with 3600rpm this will be the problem. Although is only 5mph difference to what I am getting this is enough to make the car feel slower. It appears that your final drive is not as before or you are using larger diameter tyres. Either will effectively reduce the final drive ratio which will cause all gears to have slower acceleration then normal.
My tyre size is 165/65/14, which is the standard size on my car.

 

[chesh]

I use the same tyre size as you are 165/65/14.
haven't touched the tires, just swapped to another used gear.
I'm pretty sure it was 60mph in 3000rpm on the old gear too.

could it be a different differential ratio?
the old gear was so whiny and had a bad diff. is a worn diff might feel fast as it's loosed or something?

 

[fingers99]

could it be a different differential ratio?

It's the most logical explanation.

the old gear was so whiny and had a bad diff. is a worn diff might feel fast as it's loosed or something?

Doubt it.

Possible solutions -- change the diff, change the rolling circumference of the wheels/tyres, increase torque (forced induction).

 

[Noddy]

I tried looking for information on the gearboxs a while ago and you cant find out much. However the gear ratios on the 55,60,75 & 85 are the same the sporting has a lower final drive and couldnt find anything out about the GT box.

As for the car feeling slow could you have missed something when changed the box? or could it be that now the car is quieter you mind is telling you its slower?

 

[dumbledore]

I use the same tyre size as you are 165/65/14.
haven't touched the tires, just swapped to another used gear.
I'm pretty sure it was 60mph in 3000rpm on the old gear too.

could it be a different differential ratio?
the old gear was so whiny and had a bad diff. is a worn diff might feel fast as it's loosed or something?

I doing about 59mph at 3000rpm, so subject to speedo variations it appears to me that the final drive of your box most likely is the same as mine. So the lower speed feel is most likely subjective. Surely a noisy gearbox cannot be more efficient then a quite one. This reminds me that my gearbox is quite noisy too, but seems to carry on. Do you remember by any chance if your old gearbox was causing engine vibration? or was it just noisy?

 

[chesh]

Do you remember by any chance if your old gearbox was causing engine vibration? or was it just noisy?

Yeah, it was so jumpy when I let go the gas pedal without clutch on 1-2 gears. I thought it's some engine or gear mount but I've changed them all and it was still jumpy.
Now driving is more comfortable and quiet but slow :chin:

 

[fingers99]

Compare published to actual standing 1/4 mile times at local dragstrip?

 

[chesh]

Compare published to actual standing 1/4 mile times at local dragstrip?

didn't understand that one

 

[fingers99]

If you can get close to the published standing quarter mile figures, then there is no issue. If you're miles off, chances are you've raised the overall gearing with the new gearbox.

 

[Noddy]

If you can get close to the published standing quarter mile figures, then there is no issue. If you're miles off, chances are you've raised the overall gearing with the new gearbox.

Find the 0-60mph time from the internet for you model. Get someone to sit beside you and time how long it takes to do 0-60. Compare the actual with the stated time.

 

[fingers99]

But 0-60 is harder to do (I mean, with some degree of accuracy).

And as the Swedes are nuts for drag racing, maybe the Fins?

Kimi would do a standing 1/4.