Gearbox

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Dollywobbler
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Gearbox

Post by Dollywobbler » Thu Dec 15, 2005 6:57 pm

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

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Post by Stewart (oily!) » Fri Dec 16, 2005 4:36 pm

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.
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Jaba
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Post by Jaba » Fri Dec 16, 2005 10:23 pm

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 !
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ken newbold
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Post by ken newbold » Fri Dec 16, 2005 10:25 pm

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.
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Dollywobbler
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Post by Dollywobbler » Fri Dec 16, 2005 10:49 pm

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

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Mike E (uk)
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Gearbox

Post by Mike E (uk) » Fri Dec 16, 2005 11:45 pm

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)

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Jaba
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Post by Jaba » Sat Dec 17, 2005 6:11 pm

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
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Mike E (uk)
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8V gearbox in a 16V?

Post by Mike E (uk) » Sat Dec 17, 2005 6:45 pm

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

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Post by AlanS » Sat Dec 17, 2005 7:21 pm

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.


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Post by ed4ferrets » Sat Dec 17, 2005 9:13 pm

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:
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ken newbold
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Post by ken newbold » Sat Dec 17, 2005 9:17 pm

Strangely enough I suspect the bell housing could be the same, but it's the gear ratios that are different.
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Vanny
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Post by Vanny » Sat Dec 17, 2005 10:24 pm

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'

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Post by jeremy » Sat Dec 17, 2005 10:55 pm

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 » Sat Dec 17, 2005 11:32 pm

Yes! Looks impressive tho!