It seems some are better than others. However, yes, they are known for being notchy especially when cold. Mine appears to be a fairly bad one but you do get used to it after a year or so :thumbup: You can try different oils/different levels and some claim a difference.....
the F40 is a knotchy gearbox especially from 1st to 2nd, rest of the gears are normally fine tho, most cars that have that gear box sufffer from the same issues( Vectra Vxr, Astra mk6 vxr and the astra/ insignia 2.0 cdti diesels) plus a few alfa's
Using the correct gear oil will help, most regular gear oils are gl5 spec which can be too slippery for the syncros to work properly which will make the gear change nottchy.
the f40 and m32 boxes in the 159 are speced with gl4 and I expect the f40 in the 156 will be the same. Switching to the correct oil in my 159 made a big improvement.
Changing to GL4 oil worked for me too , in a 156 20 valve. It's not perfect, but much improved. It took a while to improve though; perhaps it takes a while for the friction reducing agents in GL5 oils to be rubbed off the synchroes(?)
Edit: Just thought I'd add: when I drained the original oil, at around 70,000 miles it looked new. Old gearbox oil always used to come out yellow in my experience, from synchro wear. I suppose no wear is good in a way, but it does seem to confirm that the synchroes aren't being given a chance to work properly with the GL5 oil.
My 20v F40 box was improved noticeably by changing to Fuchs Sintofluid 75W-80 synthetic, reducing the amount of oil to 2 litres and adding ZX-1 oil treatment. There are many threads on Vauxhall forums about the box and reducing the amount of oil seems to be a popular fix.
The problem always seemed to be the 1st - 2nd change.
Ha ha. Shame it takes nearly 200,000 miles to "run in" the gearbox. Oils/level etc made no difference to mine but I too think it is gradually getting better though I am only at 148,000. Or perhaps is it that we are just getting better at compensating for it :biglaugh:
Mine has been fine. I knew someone with a new 155 who had to have the gearbox replaced. Luck and oil grade seem to be important, and also not to overfill with oil.
I use Smith&Allen GL4 in mine and it shifts very well, even in freezing temps. Gear oil goes merky from condensation over time and should be changed every 2 years or so, if you want the box to last. They do free up with the miles. The box is strong with chunky syncros, so just change the lower gears at 3000rpm for super slick movement.
I find the gear stick mechanism wears and the linkage inside the box gets a bit of play. Apart from that they are a fairly quiet gearbox. I have one thats done 190000 miles and it's still very quiet. The diff bearings get play, but thats to be expected, a quaif would sort that out.
I'm going to try out that Tungsten Disulphide powder in my CV joints (not in the box!) soon, when I do the clutch
I have GL4 Fuchs Sintofluid 75W80 in it. Box has 240000 km on it and is buttery smooth when warm and pretty smooth when cold. I have a 159 2.0 JTDM with an F40 box with Castrol GL4 75W90 in it, and that one is pretty bad. it has 200000 on it. Going to change the oil in that to the Fuchs as well.
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