'98 Octavia 1.6 glx,74kw,swaped original gearbox with '03 1.8t gearbox,now my speedometer is reading 20km/h lower than before(10km/h lower than actual gps speed,with original box reading was 10km/h more than gps).vag-com cluster coding didn't change anything.is anyone here familiar with eeprom editing?seems that's the only option left...i got my cluster eeprom out with vag eeprom programer,cluster is 1u1 919 034 j 

2 hours ago, O1GLXCRO said:

now my speedometer is reading 20km/h lower than before(10km/h lower than actual gps speed,with original box reading was 10km/h more than gps).

What size tyres do you have? I may have an idea...

195/65-15 winter tires,no difference on 205/55-16 summer ones as they both have similar diameter

2 hours ago, O1GLXCRO said:

195/65-15 winter tires,no difference on 205/55-16 summer ones as they both have similar diameter

It's not the rolling radius then. OK, I know your old gearbox was a 5 speed; is the new one 5 or 6 speed? There are differences in the internals other than just 2 extra gear wheels.

original gearbox was rod-operated 5 speed 02K gearbox,now it's cable-operated 5 speed 02J gearbox.

difference is that 02K is reading speed from gearbox output shaft and 02J is reading speed from differential.

9 hours ago, O1GLXCRO said:

02K is reading speed from gearbox output shaft and 02J is reading speed from differential

Well, I would consider the gearbox output shaft to be the differential input.

On 24/01/2022 at 10:37, KenONeill said:

Well, I would consider the gearbox output shaft to be the differential input.

yes,but output shaft is rotating 3-4 times faster than diferential...

2 hours ago, O1GLXCRO said:

yes,but output shaft is rotating 3-4 times faster than diferential...

Are you sure? I thought the diff would normally have more teeth and therefore for one revolution of the diff there would be >1 revolution of the output shaft. I haven't seen the inside of one of these gearboxes though.

 

Sounds like fixing it is not straightforward. Another approach might be to try and convert the signal to the ECU - maybe there is some off the shelf product out there that can do that.

According to https://workshop-manuals.com/audi/a3_mk1/power_transmission/5-speed_manual_gearbox_02j/technical_data/gearbox_identification/code_letters_allocation_transmission_ratios_capacities/

An 02J EHA box has a 3.647 final drive - a ratio of 62:17 (62 teeth and 17 teeth). The overall ratio in top gear (5th) is 3.056 which is calculated by the final drive (3.647) multiplied by the gear ratio of 5th (0.838). Pretty sure the diff is the 62 toothed part of that equation.

 

You say the speedo is reading 20km/h lower than before, but at what GPS speed is that?

 

Do you know the exact ratios in the box you removed and the box you fitted?

Edited 25 January, 20224 yr by petrolbloke

original gearbox was DUU which has 4,25:1 final drive ratio and 0.85:1 5th gear ratio...

speedo is now reading 10km/h lower than actual gps speed up to 100km/h and 15km/h lower above 100km/h.with old box it was reading 10km/h more than actual gps speed up to 100km/h but i'm not sure about reading above 100km/h,was it 10 or 15 km/h more...

6 hours ago, petrolbloke said:

Are you sure? I thought the diff would normally have more teeth and therefore for one revolution of the diff there would be >1 revolution of the output shaft. I haven't seen the inside of one of these gearboxes though.

 

Sounds like fixing it is not straightforward. Another approach might be to try and convert the signal to the ECU - maybe there is some off the shelf product out there that can do that.

I'm speaking about shaft that is going to the diff(input shaft-connected to the engine,output shaft connected to the diff),not the driveshaft...in the parts catalog it's listed as output shaft.