Gearing question

[carlo]

Don't know if any of you mechanically minded chaps can help me with this one.Have just bought a second 405 2.0 automatic, they're both identical year, spec, engine size etc. Wheels are identical too. I thought the latest one was noisier than my first one but have just noticed that it is definately lower geared.At 3000 revs in third it's doing 50mph, and at 3000 revs in top it's doing 70mph. My other one was doing about 75mph in top and 55mph in third, both at 3000 revs again.Is this gearing an exact science, is there often a fluctuation in cars which should have identical gearing? Or could the rev counter be faulty? Can you change the gearing on a car??! It's slightly peeved me, seeing as the car has plenty of torque and is always a good 'lugger'.

[Mr_Bo11ox]

The speedometer is the most likely to vary from one car to the next. Can you check em with a GPS or something?

[Ratdat]

As Mr.B says, it's most likely to be speedo error. Gearing is exact so if the gearbox and final drive ratios are the same then overall it should be identical. The only factor than can affect it is wheel and tyre size. Small variances can also be seen by under inflated tyres.

[carlo]

Being a bit of a thickie, I presume in that case I'm probably actually going faster than the speedo says?

[r.welfare]

I'd go with speedo fluctuation too. Both my 405s are slightly different to each other, despite being the same engine, gearbox, final drive, wheels and tyre sizes. The saloon is doing 72 (per Tom Tom) when reading 3000rpm/76mph indicated, the estate indicates 80 at the same rpm/actual speed!

[Richard]

Is there a chance that it could be the torque converter slipping? It's unusual for a speedo to be pessimistic, if one of them is wrong it'll be the one that says you're going faster.

[carlo]

It would be nice to know what the actual top gear ratio is, according to Peugeot. Unfortunately they have deemed it not important enough to include this information in the handbook. Appreciate the replies.