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+--- Thread: 4 speed gearbox ratios (/showthread.php?tid=1890)
RE: 4 speed gearbox ratios - Zetomagneto - 16-10-2018
(16-10-2018, 09:42 PM)Tony Press Wrote:Someone will suggest a five speed box in ha minute.Higher axle ratio needed.(16-10-2018, 06:16 PM)Chris KC Wrote: If top gear feels too low, the final drive ratio needs to change, no amount of tinkering with the gearbox will change that. Once top gear is where you want it, review the suitability of the intermediate gears.
For 'performance' driving a CR box is likely to feel better on the road, at the expense of some capacity for 'crawl' and mountain ascent perhaps.
As I said- with a one to one top the only way to change the gearbox is fit an overdrive !!
RE: 4 speed gearbox ratios - Colin Reed - 17-10-2018
I think members have misunderstood what Tony Press said , If you change the Diff Ratio or tyre Size all gears are changed, If you just Want a higher top gear the only way is an overdrive top gear.
Cheers All
Colin
NZ
RE: 4 speed gearbox ratios - Chris KC - 17-10-2018
(17-10-2018, 02:27 AM)Colin Reed Wrote: I think members have misunderstood what Tony Press said , If you change the Diff Ratio or tyre Size all gears are changed, If you just Want a higher top gear the only way is an overdrive top gear.
Cheers All
Colin
NZ
Quite so Colin. Not sure it helps Rich with his question though.
RE: 4 speed gearbox ratios - Hedd_Jones - 17-10-2018
Theres a bloke down the road from here with a supercharged A series in his 1928 Singer Junior.
He has an aditional 2 speed step up box (1:1 and overdrive) mounted between the gearbox output and axle input (crawl under the car and its mounted using the shelving angle with all the holes in it).
He did tell me what it was off. It was a piece of very old machinery. It was meant ti be a step down, he just turned it arse about face.
Must be like having an eaton 2 speed axle on a lorry.
RE: 4 speed gearbox ratios - Zetomagneto - 17-10-2018
(17-10-2018, 07:34 AM)Chris KC Wrote:He wants all the gears to be higher, it pulls away in 2nd, hardley uses 1st, and feels like it needs another gear when in 4th,so obviously needs a higher final drive.You could fit an overdrive, it has been done on a number of vintage cars, but not enough space on a seven without serious hacking.(17-10-2018, 02:27 AM)Colin Reed Wrote: I think members have misunderstood what Tony Press said , If you change the Diff Ratio or tyre Size all gears are changed, If you just Want a higher top gear the only way is an overdrive top gear.
Cheers All
Colin
NZ
Quite so Colin. Not sure it helps Rich with his question though.
Mgb units have been fitted to Austin 12/4s , you can’t get a higher final drive for those.
RE: 4 speed gearbox ratios - Bob Culver - 18-10-2018
Hi Wooster.
Agreed Sevens do sound to be buzzing around but the gearing is not untypical for many cars to the 1960s. 15 mph or lesss per 1000 rpm was common even on cars to 1.2 litre and more.
Presumably your car has a saloon diff ratio. Surprising to many, but the sports models were geared lower still. Max power revs were then more available.
The low 1st gear ensured the saloons were seldom stranded on hill starts despite low power, whereas many other cars and light trucks could not cope fully loaded.
RE: 4 speed gearbox ratios - Hedd_Jones - 18-10-2018
Yes Bob. My RL (3 speed - 4.9 axle) will not go up the iron gate pass near Ruthin 3 up. The RP will (4 speed -5.25 axle).
RE: 4 speed gearbox ratios - Charles Levien - 18-10-2018
(15-10-2018, 09:21 PM)wooster Wrote: Hi All
I rarely use 1st while driving my Ulster rep. It pulls away in 2nd with no problems. And fourth always seems a bit short (I mean it feels like there ought to be a 5th). Is it possible to have the gearbox modified, to alter the ratios to make 1st usable and 4th higher?
Cheers
Rich
It sounds like you want to go faster in top? I would say most fun is to be had with a lively car that is not over geared — this will prove useful in traffic and better suited to hill climbing or sprints if you want to give that a go.
I would look at fitting a close ratio gearbox and tuning your engine to run reliably at around 4000 revs. That should get you along at around sixty (mph) which is a useful speed if you have a decent journey to do.
Charles
RE: 4 speed gearbox ratios - wooster - 18-10-2018
Thanks all, lots to think about there. Don't want to change the wheels but might look at dif.
Cheers
Rich
RE: 4 speed gearbox ratios - Chris KC - 19-10-2018
Just keep in mind Rich that trying larger wheels (if you are on small ones) can be an easy way to assess the impact of a final drive ratio change, without rebuilding your axle.