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bren_1.3

106 Rallye Gearbox/clutch Problem

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bren_1.3

the 106 is returning some bad fuel economy..something like 20mpg.

 

i think its a combination of things but heres whats lead to me think about fuel economy...

 

i'd recently noticed the clutch slipping, which i took to be just wear and tear, so after pulling the box off to replace the clutch i noticed that the release bearing had been digging into the pressure plate quite substancially. not to worry though as everything was being replaced. so new clutch/pressure plate and release bearing went on. a week later sat at traffic lights i lost all gears and a whine eminated from the release bearing everytime the pedal was depressed or left in neutral. the clutch biting point was almost on the floor aswell.

 

ive narrowed the problem down to the clutch arm on the box, which appears to have a lot of play in it, it looks like the nylon bearing has worn. and ive backed the clutch off on the cable as far as it will go to allow slection of gears with a bit of a fight.

 

so hopefully, ill get the box off tomorrow to set about repairing the problems...so thats the story so far.

 

now i do a lot of duel carriageway/ motorway miles to and from work. roughly 30 miles a day. and with the such short gearing of the rallye gearbox im sat at roughly 4000rpm doing 70mph. which isnt helping fuel economy surely.i have a 1.1 gearbox from a 205 that has no play in the clutch arm and is in decent nick. question is, does this 1.1 gearbox have longer ratios for motorway cruising than the rallye box? im sure it does but would like some conformation if possible.

 

thanks.

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welshpug

there is a nylon bush there as you know, if the locating tab breaks it turns in the hole as the shaft is offset in the bush, it then sits too far away from the pressure plate.

 

not sure about the 1.1 box, i've never seen the ratios or been in a 1.1 that has had a rev counter!

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bren_1.3
there is a nylon bush there as you know, if the locating tab breaks it turns in the hole as the shaft is offset in the bush, it then sits too far away from the pressure plate.

 

sound like a bit of a common problem then?!

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welshpug

not sure about common but I have heard of it before! cheap enough though, but the box does have to come off to replace the lower one, not so with the upper one luckily, but the clutch arm pins do often seize in solid.

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sutol

I wouldn't put a higher diff with a low powered engine if you want economy. The only way to improve your fuel consumption is to make sure that the motor is well serviced and keep your foot off the accelerator.

 

A high speed diff will keep the revs down but a small engine will be working harder at lower revs that at higher revs on a light throttle.

Try sticking to the speed limits for a week and see how much fuel you save :D

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bren_1.3
I wouldn't put a higher diff with a low powered engine if you want economy. The only way to improve your fuel consumption is to make sure that the motor is well serviced and keep your foot off the accelerator.

 

A high speed diff will keep the revs down but a small engine will be working harder at lower revs that at higher revs on a light throttle.

Try sticking to the speed limits for a week and see how much fuel you save.

 

i didnt think the diff has much to do with overall gearing though? a diff is just to let one wheel turn faster than another...if a longer 5th gear is available to achieve 70mph at 2500rpm than at 70mph at 4000rpm then surely the engine isnt working as hard at that given speed, and is under less stress. the only thing that will suffer from longer gear ratios is the acceleration of the vehicle?

 

as a sort of comparison, it would be like changing a 205 xs box for a 205 UK rallye box which has the longer ratios.

 

just as a quick edit - im saying that at 70mph ON THE SPEED LIMIT of motorway/duel carriageways the car is revving harder than id like, and seeing as the car spends most of its time as in daily.. at that speed/rpm then surely using a longer 5th gear to drop rpm would be beneficial to economy. i think youve missed the point somewhat?

Edited by brens_1.9_wide_arch

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sutol
i didnt think the diff has much to do with overall gearing though? a diff is just to let one wheel turn faster than another...if a longer 5th gear is available to achieve 70mph at 2500rpm than at 70mph at 4000rpm then surely the engine isnt working as hard at that given speed, and is under less stress. the only thing that will suffer from longer gear ratios is the acceleration of the vehicle?

 

i think youve missed the point somewhat?

compare it with riding a mountain bike which is geared for 100 mph when your legs are pedaling as fast as you can. It would not be possible to maintain say 20mph in top gear because you wouldn't have the power to keep the things turning.

By the same token you would be able to maintain 20mph quite easily when pedaling faster in a lower gear and use less energy.

A small engine uses more fuel when it is working harder in a high gear.

When 5th gears became fashonable in the late seventies, some small cars could not pull the higher gear and were considerably faster in 4th than in 5th.

The diff ratio gears up the gearbox and spaces out the gears, change the diff to a lower one in your car and the gears become closer together and 'shorter' , max speed in each gear comes sooner than before at similar revs.

Put in a higher diff and the gears become longer with a higher road speed in each gear.

 

Happy Birthday by the way :D

Edited by sutol

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Rob Thomson

Hmmm... generally speaking petrol engines are more efficient at low speeds with a wider throttle opening, than high speeds with a low throttle opening. It's all about volumetric efficiency; the higher the compression (i.e. the fulller the cylinder, the wider the throttle opening) the more efficient the engine. That's why small engines are more efficient than larger engines; a small engine working hard is more volumetrically efficient that a large engine that's not as stretched.

 

In most cars you'd want higher ratios to keep the revs down and save fuel. The 1294 Rallye engine's a nightmare though, because it's completely off-cam below 5k, and that means it won't be so efficient at low revs. I reckon high ratios would save you fuel, but probably not all that much to make it worthwhile.

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pugrallye

The final drive ratio in rallye box is quite high if I recall, something like 4.5 to 1, which is one of the highest availiable. There are tables on net display the different variations on gearing across the MA range. But fitting a 1.1 box will definately have an effect on your engine speed at 70 mph you will suffer with acceleration a bit though as those engines arent known for their torque lol

 

The plastic clutch arm bushes used to be notorious for snapping, lol

 

As for VE, I always understood from what I remeber of theory that VE dropped off with increase in RPM?? You have higher efficency at low rpm, hence most torque is produced low down in rev range (or tuned as such) might be wrong though as old age is kicking in lol

Edited by pugrallye

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bren_1.3
The plastic clutch arm bushes used to be notorious for snapping, lol

 

the plastic bush had indeed broken! it took out the release bearing and broke an arm off the selector fork in the end. luckily no damage to the pressure plate! :)

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