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preselector gearbox kickback!

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thomas@prags.co.uk
Posts: 47
Joined: Tue Sep 11, 2018 11:37 am
Location: Inverness

preselector gearbox kickback!

Post by thomas@prags.co.uk »

I've had my DB18 Barker 4str convertible since 1973 - when I joined DLOC. It has been in fairly regular use ever since!
I need some advice please! I used to get occasional 'kickback' from the selector pedal on the rare occasions I wanted 1st gear - usually cured by reselecting the gear and trying again. Not happened for years though. However.... I now cannot select 2nd gear without the 'kickback' - particularly tricky since i was trying to negotiate a bit of a hill at the time. Tried going through the gears several times but 2nd still violently unavailable! Whats going on? I am not mechanical and my usual advisers are 'off line'. I do hope its not a serious gearbox out job!?
Thomas Prag

Phillmore
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Joined: Sat Feb 13, 2016 1:25 pm
Location: Worcestershire Herefordshire border

Re: preselector gearbox kickback!

Post by Phillmore »

Is it very stiff to put back down again?
Andy

1954 Conquest Mk1, 1956 Conquest Mk2, 1957 Conquest Century Mk2, 1955 Austin A90 Westminster

terryfrombury
Posts: 154
Joined: Fri Feb 12, 2016 10:25 pm
Location: Cheshire, UK

Re: preselector gearbox kickback!

Post by terryfrombury »

The mechanism in the box is supposed continually to adjust the different bands. Sometimes one of the gears does not self-adjust as it should, becomes slack, and you then get a violent kick-back.

Stan Thomas
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Re: preselector gearbox kickback!

Post by Stan Thomas »

Before you do anything, pump the gearchange pedal a couple of dozen times in each gear and see if that helps!

"Terryfrombury" is right to a degree, but usually when a gear is not self adjusting, the gearchange pedal rises higher and higher requiring an ever-increasing pressure to depress.

This is because when this happens, the force exerted by the bus bar spring becomes much greater due to the angularuity of the leverage designed into the mechanism. However, it would be unusual to manifest itself as a sudden "kick-back" - more of steadily increasing rise in pedal height requiring greater foot pressure to depress it again.

For that reason, I'd say almost invariably it is your selector mechanism linkage is worn or out of adjustment.

As a simple test "de-adjust"your linkage by shortening or lengthening one of the linkage rods and see if it "moves" the problem to another gear.

To check for the symptoms "Teryfrombury" says, you will need to remove the lid on the gearbox and release the directional-wind spring from 2nd gear, undo the adjusting nut a turn, and re-assemble. Then pump the gearchange pedal and you should see the adjusting nut tighten itself up if all is O.K.

thomas@prags.co.uk
Posts: 47
Joined: Tue Sep 11, 2018 11:37 am
Location: Inverness

Re: preselector gearbox kickback!

Post by thomas@prags.co.uk »

Many thanks all - glad I finally got myself logged into the the forum!
All very helpful. Yes it is absolutely firm when I try second. I recall we did a linkage adjustment some time ago which cured the previous episode. I will check that out. It's been driving so well for the last couple of months - too early to tuck it away for the winter! I'll let you know how I get on.

grahamemmett
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Re: preselector gearbox kickback!

Post by grahamemmett »

Hi Thomas

If you go to to
www.db18.org
and then select Document Store Page
you will find the Wilson Gearbox manual which describes its operation. After reading this you’ll conclude that your gear change rods have been somehow moved and the absolute stop is because you are not able to move the bus bar.
On the same website, go to the Technical Articles Page where you’ll find a number of papers on the gearbox including how to set the adjustment correctly. These have been provided by Steve Moore from Australia and are excellent (and hilarious)
Graham Emmett ¦ DLOC Chairman ¦ chair@dloc.co.uk ¦ 07967 109160
Northwich, Cheshire
DB18 1949 LCV522 (Yes that one with the P100s)

thomas@prags.co.uk
Posts: 47
Joined: Tue Sep 11, 2018 11:37 am
Location: Inverness

Re: preselector gearbox kickback!

Post by thomas@prags.co.uk »

Graham
many thanks - never knew about the DB18 website! I will sign up when I have time . The car was supposed to get a check up with John Mackintosh (another local owner) who usually sorts my mechanicals - but we have failed to rendezvous so far. I have sent him the link to these articles etc.

thomas

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