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Dart vibration at 5000 rpm in second gear

Ian Slade
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Re: Dart vibration at 5000 rpm in second gear

Post by Ian Slade »

You can get 34 to the gallon with the standard box, I regularly did in the '70's fuel crisis commuting from Sunbury-on- Thames to Fareham, dropped to 31 when the limit dropped from 60mph to 50mph, not all speed limits are economic :D
Owner since the 70's, Genghis is slightly to my left.

A.N.Other
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Re: Dart vibration at 5000 rpm in second gear

Post by A.N.Other »

It looks like the answer is to fit an overdrive rather than find the problem.
Colin,
I may be slow but I’m rough as well !

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John-B
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Re: Dart vibration at 5000 rpm in second gear

Post by John-B »

Big Col wrote: Mon Apr 16, 2018 8:56 pm It looks like the answer is to fit an overdrive rather than find the problem.
Does an overdrive work with second gear? If it does I doubt if I would use it in a similar situation where I was giving the car a fast run up a hill in 2nd.

I would like an overdrive for use with top gear, but I do hardly any motorway driving and I would wait until the car actually needed some repairs. The car goes beautifully in third and top. I only noticed the vibration in 2nd and will just refrain from pushing too hard in future.

Ian Hastings
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Re: Dart vibration at 5000 rpm in second gear

Post by Ian Hastings »

You say the problem was in second gear under load and at high revs and I am assuming that the vibration went away when other gears were selected.
You should bear in mind that the weak point of these gearboxes is the straight cut gears on 1st and 2nd which are on the layshaft.
Your problem points in that direction, in that you probably have tooth damage to one of the gears or there is bearing wear in the bearings supporting the layshaft although that would show up in 1st gear also.
I don't think that fitting an overdrive would make any difference to your vibration problems but doing so would give you the chance to rebuild and refurbish your gearbox at the same time.
Fitting an overdrive will make for more comfortable and relaxing motoring but it is not really intended for hard driving. It can be wired so that it will operate in 2nd gear as well at 3rd/4th by fitting a switch on the 1st/2nd gear selector rod, the raised casting is there on the gearbox cover for it, but it is advisable not to use too much power in 2nd gear with the overdrive engaged. Effectively it makes a gearbox with seven forward gears which can be fun to drive.

Vortex O'Plinth
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Re: Dart vibration at 5000 rpm in second gear

Post by Vortex O'Plinth »

Ian Hastings wrote: Mon Apr 16, 2018 10:42 pm .....You should bear in mind that the weak point of these gearboxes is the straight cut gears on 1st and 2nd which are on the layshaft.....
The ratios of the SP 'box are a nice match to the engine but it is certainly one of the weak points of the car in terms of durability, the basic design harking back to Standard models with considerably less power and torque. It's only first and reverse gears that are straight cut (hence the 'howl'); second, third and top are all helical cut (and generally quieter).

Overdrive is really only advantageous on top, where it makes for a more relaxed drive at motorway speeds. The most common overdrive ratio when applied to third gear makes it very nearly the same as normal fourth. There is no practical advantage in applying it to second gear, where it would struggle to cope with the available torque.
Nick

"Don't bother with the Air & Space Museum - there's nothing to see.......".

Ian Slade
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Re: Dart vibration at 5000 rpm in second gear

Post by Ian Slade »

The most suspect bearing causing the problem would be the one connecting the first motion shaft to the second motion shaft, failure of this bearing along with wear in the two main bearings is the reason for chipped teeth on first gear.
Owner since the 70's, Genghis is slightly to my left.

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John-B
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Re: Dart vibration at 5000 rpm in second gear

Post by John-B »

I won't be changing anything at the start of the show season, I'll just drive sensibly.

I'm reminded of a time I didn't drive sensibly. I said above that I had a clutch problem in 1969 and the local garage fixed it so that it would hardly disengage and I drove very early in the dark from Bristol to London and I wanted to get across London before the rush hour to Edmonton with a jammed clutch.

After being diverted around country lanes in the dark in fog I got onto the A4 and found myself behind a lorry chugging along at 20mph between Newbury and Reading. I got fed up and started to overtake as the road seemed devoid of traffic. It was still dark and the fog was dense but as I got alongside the lorry the fog got much thicker. I decided to go on and got past safely but slowed down when in front of the lorry, which came up close behind and tail-gated me into Reading until we stopped at red lights.

The next thing I knew was that my door was opened and a fist was shaking near my face. The lorry driver said several times "You frightened my little girl". I was shocked and couldn't move so I just said "I'm sorry" several times until he went away. I never knew whether he had a girl in the cab or quite what had frightened her.

What it taught me was that fog gets thicker when pushed aside by a lorry, and in those days fog was often really bad. If he'd had a knife I might have been in real trouble.

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