Technical 🆘Manual transmission problems (LOUD NOISE)

[rmjbn1]

I'm already looking for a new transmission. The problem is that there are several versions for sale, similar ones I believe, with different part numbers. All produced by Fiat: Bravo, Delta, Giuletta, Mito.
But the codes on eper are different. Do you know if they are all interchangeable (plug and play) or if something changes in the gears?

The same gearbox used on different models will physically fit and work.
Ratios will change from different models.
Usually the biggest difference is in the final drive ratio.
If you go for a taller top gear, you'll lose on acceleration.
This site gives the gear ratios, and includes a few different models:

DIFFERENTIAL - Fiat - NUOVA BRAVO - eLearn - 4CarData

However, I already knew I had a worn gearbox: the gears were having a bit of trouble shifting. Furthermore, a couple of times recently, fifth gear seemed to get stuck inside (always during a downshift).

Before you decide on a new gearbox, this can also be due to:
Hydraulics (is it better with engine off, or the same?)
Worn cables (disconnect cables from gearbox and see if you can move the selectors by hand)
Damage in the selector mechanism on top of the gearbox

 

[DragonHeart6]

Yes I'm sure the mileage is correct. The obd mileage can be faked but I opened this car completely and the state of the various parts corresponds with this mileage. Also governmental revisione since 2018 corresponds and before 2017 it was 1 owner and he was 78 years old. Car was kept in garage and looks good outside besides some scratches. Mileage can always be faked but the car had factory timing belt, thermostat, suspension and the car had never been open before me , it was in roughly bad state but it can't have more than those km. The interior looks new and there are no wear indicators anywhere. (Yes I also checked obd). When I bought the car the seller was so patient with me that he let me check the car completely. I brought my diagnostic tool and a borroscope camera and checked everything around the engine , I even removed the timing belt cover and looked at everything. Looked inside the engine with the camera and so on. It wasn't in best shape but for the price I paid and with the repairs I did (around 2500) just in parts, I'm still under the value of this car on the market in Italy and those cars are in the same bad shape because nobody will fix their cars like I do unless they are doing it themselves otherwise it's impossible and economically not worth it.

Wow, I think you got a bargain, because the Bravo is a really well-made car, even compared to today's cars. Can I ask how much you paid for it?

 

[DragonHeart6]

The same gearbox used on different models will physically fit and work.
Ratios will change from different models.
Usually the biggest difference is in the final drive ratio.
If you go for a taller top gear, you'll lose on acceleration.
This site gives the gear ratios, and includes a few different models:

DIFFERENTIAL - Fiat - NUOVA BRAVO - eLearn - 4CarData

Before you decide on a new gearbox, this can also be due to:
Hydraulics (is it better with engine off, or the same?)
Worn cables (disconnect cables from gearbox and see if you can move the selectors by hand)
Damage in the selector mechanism on top of the gearbox

Thanks so much, I was looking for this graph. Do you know how to read it? Do higher values mean longer gears?

 

[bugsymike]

Generally higher axle ratios mean lower gearing.
For example a 5:1 axle would be used for towing but a 3:1 would have more of a problem if all other things were equal.
A lower axle ratio 3:1 can give a higer top speed at lower engine revs so a quieter drive with a less strained/screaming engine.
These are extreme examples just to give an idea.
A really extreme example was an old vintage recovery lorry I used to own that was capable of towing a 13 tonne lorry, however it's top speed was 25mph and unladen it was possible to pull away in 4th gear.

 

[DragonHeart6]

Generally higher axle ratios mean lower gearing.
For example a 5:1 axle would be used for towing but a 3:1 would have more of a problem if all other things were equal.
A lower axle ratio 3:1 can give a higer top speed at lower engine revs so a quieter drive with a less strained/screaming engine.
These are extreme examples just to give an idea.
A really extreme example was an old vintage recovery lorry I used to own that was capable of towing a 13 tonne lorry, however it's top speed was 25mph and unladen it was possible to pull away in 4th gear.

So in this case the sixth gear of the Bravo 1.4 16v T-Jet 150 is longer than the Bravo 1.4 1.6v?
That is, at 3000 rpm will it go faster? Another question: does the 1.4 16v correspond to the 1.4 1.6v T-Jet 120 engine?
Sorry if I don't understand well

 

[bugsymike]

So in this case the sixth gear of the Bravo 1.4 16v T-Jet 150 is longer than the Bravo 1.4 1.6v?
That is, at 3000 rpm will it go faster? Another question: does the 1.4 16v correspond to the 1.4 1.6v T-Jet 120 engine?
Sorry if I don't understand well

I would use the final drive ratio as the guide normally being old school as in the days of "top gear" being direct drive or 1:1 in a gearbox, so the only consideration was the final drive ratio, but I see what you mean about the variety of ratios.
Another small point is rolling circumferance of the driving wheels, so a low profile tyre that had a smaller "rolling circumferance" would have a lower top speed when compared with a standard profile assuming same diameter wheel and drive shaft speed.
So the speed at 3000rpm will also be affected by that "rolling circumferance" of tyre size used.
It would also help if Fiat used "overall gear ratio" instead of "rear axle ratio" and Final drive ratio".

 

[rmjbn1]

Thanks so much, I was looking for this graph. Do you know how to read it? Do higher values mean longer gears?

Yes, it's a bit confusing. As Mike says above, there are some strange terms used in that chart.
The 'Rear axle ratio' they list means the differential (which is not in the rear, but in the front, attached to the gearbox).
This is what I would traditionally call final drive - but on that chart they list 'final drive ratio' as the gear ratio once it's been through the differential.

Sorry, I'm not familiar with Bravos. I only became aware of this issue when someone on here replaced a 1.2 Panda gearbox (3.4:1 final drive) with a 1.2 Punto gearbox (4.1:1) and found the engine was revving like mad on the motorway!

Same gearbox, but very different internals.

So in simple terms, the lower the value given for gear ratio, the lower the engine revs for a given road speed, all other things being equal.
Eg. a 3.4 final drive will go faster at 3000rpm than 4.1

 

[rmjbn1]

First thing is to establish which gearbox your car has, and which other models would be compatible.
That site lists the T-Jet as having the M32 box? 1.4 as C514 and diesel as 530.
Note this table for the gearbox ratios does not include the differential

If this is correct, then you need to check which cars have that gearbox with a similar top gear ratio, and final drive (differential) ratio.
You can go a bit lower if you're looking to reduce revs on the motorway, but I wouldn't change it too much.