4x4 gear ratios

[Vanny]

Couple of thoughts to throw into the ring.

1) Speed sign accuracy
From the strategies i know of some are deadly accurate to within a few metres per hour, most over read by a mile or so (deliberately) and some have a logarithmic correction to them so if they are set to 30, 30 shows as 30, 32 shows as 33, 34 shows as 36 and so on. Basically, don't read too much into the display, unless you can corroborate the reading else where.

2) Sat nav accuracy
Sat nav road speeds vary. It depends on the number of locked satellites and how fast your sat nav can obtain and process data. Generally newer sat navs that can lock 16 satellites will give you a more accurate reading and will account for tyre inflation/wear that your speedo can not. The best way to get a reading is a nice big dyno with a cylinder of a known size. Not to say that these rule of thumb methods aren't suitable, just be wary there will be differences from car to car, trip to trip, warm day to cold day etc

3) PSA Ratios
If you look more at Peugeots specifically the 205 and GTi6 there is a huge amount of information about existing gear ratios for the BE1 and BE3 boxes. Be wary that for some reason ratios do change with model years, I've counted three different sets of ratios for the 1.4 BX based on the technical bulletins

http://www.205gti.com/techgearboxUK.htm
http://www.rallyparts.co.uk/cwp_change/

I shall be following this thread with interest, especially if you do get an improvement in fuel economy on longer runs, might tempt me into a 4x4

[barry badger]

Counted the teeth on my donor box fifth gear and they are 38/25,( so the right ones), but i can't get one of the gears off. The one that is splined onto the shaft won't come off with anything i possess. I ground down the legs of a smallish 3 legged puller so that they would fit under the gear but one of the legs broke before the gear moved! any suggestions what i can use/buy. The gap between the gear and the bearing is about 1.5 mm.

[barry badger]

I've now fitted the new gears and road tested it, all ok . I had to buy a 3 legged hydraulic puller to get one of the gears off my donor box but the gears on the gearbox in the car came off with no effort.
the new revs/speed are:-
50mph= 2400rpm..... old 50mph=2700rpm
60mph=2900rpm..... old 60mph=3300rpm
70mph=3300rpm..... old 70mph=3900rpm
80mph=3700rpm..... old 80mph=4400rpm
90mph=4250rpm ..... old 90mph=5000rpm

Even on this shortish road test the car was much more relaxing to drive i look forward to going on the next long run. Hopefully there will be a reasonable improvement in the fuel consumption.
I'll post fuel consumption figures after i've completed 500miles or more.

As regards speed sign accuracy there's one on the formby bypass which i pass regularly, if i pass it in the 4x4 my speedo reads about 1 or 2 mph faster than indicated by the sign, whereas if i pass it in the txd the discrepancy is 5 or 6mph.
I notice in the 4x4 often if i'm approaching a speed camera side by side with another car the other car will start braking whereas i don't, i think my speedo is more accurate than most.

[David]

That sounds much better. What gearbox did you nick the 5th gear out of? Also what engine does your 4x4 have in it? I might do this mod on mine when I finally get it put together & on the road.

[barry badger]

The gears were from a 1.7td gearbox.
If/when i get round to overhauling the gearbox i might put the original 5th gear back in and lower the differential ratio instead. I need to work out which ratio will work best.

[David]

I have found internally the gearboxes seem to be the same, the only differences is the cog that screws to the crown wheel & the bell housing/ diff casing. otherwise everything seems to be interchangeable.

[Jaba]

The gears were from a 1.7td gearbox.
If/when i get round to overhauling the gearbox i might put the original 5th gear back in and lower the differential ratio instead. I need to work out which ratio will work best.

Changing the diff ratio is a bit more tricky as you need to change the crownwheel from a gearbox with the same no. of teeth on the mainshaft as your own box. Most BX pinions have 16 teeth but GTi has 17 and 16v has 14.
You could swap out the whole mainshaft as well I suppose but you will change all the gears not just 5th.

Speed calculation for speed per 1000 revs using GTi gears is :

5th gear 37/32 (1.156)
times final drive ratio 61/17 (.2786)
times wheel circumference 1.8
times 60
= 34.7 kmh
= 21.5 mph

In this case for a GTi there is no higher final drive ratio available so the 5th gear change is the only option.

[citsncycles]

This sounds good - looks like I'm now in the market for a TD 5th gear (or similar) for my 4x4.