Gearbox

BX Tech talk
Post Reply
Dollywobbler
Over 2k
Posts: 3940
Joined: Sun Dec 04, 2005 2:25 pm
Location: Wales
Contact:

Gearbox

Post by Dollywobbler »

My friends on the 16v forum tell me that there is a mod to make the gearing taller for quieter cruising in my 16 valve BX.

But the synchromesh is knackered on third and fourth on my current gearbox so what's the point in modifying a duff box?

So my question is - can the 8v gearbox fit a 16v engine? My understanding is that the 8v has the taller gearing for less frenetic cruising.

Failing that, is there a simple fix/replacement option for the synchromesh on my current box? Apart from that, the box is fine with no whining or other problems.

Thanks

Ian
Stewart (oily!)
1K Away
Posts: 1604
Joined: Wed May 18, 2005 6:23 pm
Location: North Wales

Post by Stewart (oily!) »

The 8Valve box should fit without difficulty but what you need really is top gear from a turbodeisel to really quieten things down on the motorway.
Stewart
TZD 19 TD one of the few
Xantia Td estate, going soft
User avatar
Jaba
1K Away
Posts: 1893
Joined: Tue Jul 05, 2005 7:54 am
Location: Usually in the garage
My Cars: BX GTi, C3 Auto
x 80

Post by Jaba »

If you can resolve the clutch arm issue - by possibly just swapping the arms over from 16v to the 8v box then the easiest thing is to just swap the 5th gear from the 16v box into the 8v box. This will give you a much higher 5th gear for cruising at around 24mph per 1k revs. i.e at 70 mph you are spinning @ only 3000revs.

I dont have my tables to hand for the exact figures but I am sure that the 8v box has a much higher final drive ratio and conseqently a lower 5th gear......until the modders get at them !
The Joy of BX with just one Citroën BX to my name now. Will I sing Bye Bye to my GTI or will it be Till death us do part.
User avatar
ken newbold
Over 2k
Posts: 4408
Joined: Sun Aug 14, 2005 10:53 pm
x 5

Post by ken newbold »

You should be able to resolve the clutch arm problem by simply fitting a new clutch cable to match the gearbox. Thats what I did when fitting a TD gearbox in my Mk1.
They think it's all over, it is now!
Dollywobbler
Over 2k
Posts: 3940
Joined: Sun Dec 04, 2005 2:25 pm
Location: Wales
Contact:

Post by Dollywobbler »

just swap the 5th gear from the 16v box into the 8v box.
I think that's the mod proposed on the 16v forum but my box has knackered syncromesh so there's no point modding it! Unless it is fixable.

Thanks for all the input guys.

Ian
User avatar
Mike E (uk)
1K Away
Posts: 1115
Joined: Sun Aug 14, 2005 9:10 am
Location: High Wycombe, Bucks
x 1

Gearbox

Post by Mike E (uk) »

The BX16V first 4 gears are fine for road use.

Fit another 16V gearbox, then do the 5th gear mod. This can be done with gearbox still in the car.

original 5th: 20mph/1000rpm

5th gear mod:23mph/1000rpm

This is the optimum ratio IMO.

It drives nicely and still accelerates.
Any taller and you wont be able to engage it soon enough.
Any shorter and there is not enough benefit in changing it.

was 3500rpm at 70
now 3040rpm

was 4000rpm at 80
now 3500rpm

8)

Mike
User avatar
Jaba
1K Away
Posts: 1893
Joined: Tue Jul 05, 2005 7:54 am
Location: Usually in the garage
My Cars: BX GTi, C3 Auto
x 80

Post by Jaba »

Yangreen,

Your 16v box is knackered on 3rd and fourth only. So you can successfully move the 5th gearset into an 8v box - as indicated in your original post. Haynes describes this op. quite well surprisingly.

Suffice to say I have been doing this succesfully for several years b4 the 16v guys and am very happy with the results.

So get yourself a box from an 8v and get cracking :P
The Joy of BX with just one Citroën BX to my name now. Will I sing Bye Bye to my GTI or will it be Till death us do part.
User avatar
Mike E (uk)
1K Away
Posts: 1115
Joined: Sun Aug 14, 2005 9:10 am
Location: High Wycombe, Bucks
x 1

8V gearbox in a 16V?

Post by Mike E (uk) »

Arn't all the 8V gear ratios and final drive different from the 16V?

The 16V gearbox ratios are fine. (except 5th is a bit too lowly geared.)

Unless you are making a track car, why put an 8V box in a 16V?

I would replace the gearbox with an original one and worry about a 5th gear mod later.

Mike
AlanS
BXpert
Posts: 841
Joined: Mon May 16, 2005 9:53 pm
Location: Queensland, Australia

Post by AlanS »

FWIW, most problems with shifting gears in a BX I've found to be usually down to incorrect/incompatable oil in the transmission, the common one being 75/95 or a full synthetic.
I've had cases over here where I've written reams on what to do as a simple fix, had them argue that it made no difference and then in one case the guy sold the car and the new owner followed my guidelines and hey presto.........just like a brand new box; previous owner stuck by the garage's recommendations.
I use Castrol VMX80 with 125 mls of Nulon G70 additive. Run for a couple of thousand, drain it all out and replace with a fresh mix of identical stuff. The reason for the drain out is to get rid of all the crap in the box and when you see what comes out, you'll freak out, but all our manual gearboxes have had that treatment and in every case it made a spectacular difference.
If the box is noisy, the noise will be gone within a couple of miles and dodgy gearchanges can take anything from almost instantly to up to about 5000 klms, but in every case ir seems to do the trick. If you want to try a fix before going down the mod route, that's the cheapest option.


Alan S
By the time you're old enough to know it all, you can't remember why you were learning.
ed4ferrets
BXpert
Posts: 605
Joined: Sat Sep 24, 2005 4:10 pm
Location: Marshfield in the cotswolds ...
Contact:

Post by ed4ferrets »

A dumb question to ask perhaps but what is the difference between a 1.9 diesel gearbox and an 8v GTi gearbox (other than bellhousing)? :oops:
Marty said: "Take some small comfort from the fact that the driver of the other car, having failed the breath test will even now be in a little cell, with luck they will double him up with some mean bastard who will be tattooing a fandango on his arse"

'94 XM 2.1TD Break
'99 Xantia 1.9TD Break (almost there)
'63 Renault Caravelle
User avatar
ken newbold
Over 2k
Posts: 4408
Joined: Sun Aug 14, 2005 10:53 pm
x 5

Post by ken newbold »

Strangely enough I suspect the bell housing could be the same, but it's the gear ratios that are different.
They think it's all over, it is now!
User avatar
Vanny
Merseyside resident
Posts: 3581
Joined: Tue May 17, 2005 11:48 pm
Location: BXProject
My Cars: BX 16v Ph2 - Jazz
BX 16v Ph2 - XPO
x 79
Contact:

Post by Vanny »

ken newbold wrote: gear ratios that are different.

ie the number of teeth on each gear wheel, they need to be very different as the diesel will only rev to 4000rpm while the petrol will go to nearly double!


and yes it took me a while to realise this in my 'youth'
jeremy
Over 2k
Posts: 2112
Joined: Fri Jul 01, 2005 2:58 am
Location: Hampshire UK

Post by jeremy »

BX 19 GTi 0.86 1.07 1.36 1.85 3.25 R3.33 Final Drive 3.59
BX 19 TRi 0.76 0.97 1.28 1.85 3.25 R3.33 4.06
BX GTi 16V 0.757 0.969 1.28 1.85 2.93 R3.33 4.429
BX 19 RD 0.757 0.969 1.28 1.85 3.25 R3.33 3.94
Estate 4.0625
BX DTR Turbo 0.66 0.82 0.87 1.85 3.25 R3.33 3.94


I trust this totally confuses everything

jeremy
tim leech

Post by tim leech »

Yes! Looks impressive tho!
Post Reply