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DB18 gearbox adjustment

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

DB18 gearbox adjustment

Post by thomas@prags.co.uk »

David Beales rebuilt my DB18 gearbox in 2019 - we agreed that 2nd gear needed a bit of adjustment and he sent me instructions. Not being brave with mechanical things I didnt open it up to do the job and 2nd gear is now becoming annoying. (takes a while to engage) I am reluctant to take it to the only classic car specialist in my neck of the woods - expensive and I'm not overly confident that they know much about anything pre 1960s. Advice? Courage?

Simon Hyslop

Re: DB18 gearbox adjustment

Post by Simon Hyslop »

As a first step, have you tried putting the selector in 2nd and then pumping the change pedal up and down about 10/20 times? You probably have but it's worth asking.

If that doesn't make any difference then the answer lies in taking the top cover off the gearbox and making an adjustment to the locking nut for that gear. I have done it some time ago and I know I didn't have any special tools which are suggested for the job. However, whether I made something to hold the springs while adjusting the nuts or used something else, that part I don't rightly recall this minute. I hope that maybe encourages you to take up the floorboard and tackle it and with a bit of luck, a fellow owner who has done this particular job in more recent times will write with their knowledge.

qantasqf1
Posts: 299
Joined: Mon Mar 07, 2016 10:13 pm

Re: DB18 gearbox adjustment

Post by qantasqf1 »

Thomas, if 2nd gear is slow to engage then it sounds like the self adjustment mechanism isn’t working or has been incorrectly set, neither of which is a big deal. To sharpen up the action you need to increase the toggle action which is achieved by turning the pull rod adjusting nut anticlockwise. This increases the clearance between the band and the annulus and the resulting extra travel provides the increased toggle action.
This is how I fixed the same problem on a DB18:
1)Select and engage top gear.
2)Unhook the 2nd gear pull rod’s adjusting nut spring
3)Check the adjusting nut is free to turn on the pull rod (oil contaminants can render them sticky), but only turn the nut enough to ensure it isn’t seized, and then return it to its original position.
4)Slacken the brake band stop bolt locknut and screw the square head bolt clockwise in as far as it can go, then tighten the locknut.
5)Unscrew the pull rod nut half a turn and refit the spring.
6)Select and engage 2nd. Pull rod/strut travel will now be greater than its preadjustment travel. There should also be a gap between the stop bolt and the strut.
Fit the cover and road test. If 2nd gear is still lazy then toggle action needs to be further increased by repeating the previous steps; if it’s too fierce turn the pull rod nut clockwise 1/4 turn. When 2nd gear action is OK unscrew the stop bolt until it touches the strut.
I’m going to stick my neck out here.
Once the brake bands have bedded in automatic band adjustment is rarely called into action so sticking adjusters can result, especially if regular gearbox oil changes aren’t carried out although I know none of us would never, ever skip this task. Oh, dear me no. Given this I can’t see why the stop bolts shouldn’t be discarded altogether so when toggle action becomes sufficiently fierce then manual adjustment is fine as long as the pull rod nuts are only turned clockwise 1/8 turn at a time.
Does anyone else have any thoughts on this?
Maverick is the name....well, it’s actually Steve.

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