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Auto Box Clonk


IanG
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Help please, loud clonk engaging drive or reverse on 1976 2.0 cav coupe automatic.

Not sure where to start, box or drivetrain?

Once engaged box performs faultlessly smooth changes and kickdown. 
 

Any tips and hints welcome!

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Posted (edited)

Start with the diff and prop shaft mate. If you gave lots of excessive okay, just one side jacking the rear axle up with handbrake off but box in locked P, you can rotate one wheel left/right to feel play and should gear clunking. It’s amplified at this point due to how the planetary gears in the diff work, but it will soon highlight where the clink is. Money is on the diff tbh.
Don’t forget to chock the car! And don’t go under without an axle stand! 

Edited by Jessopia74
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1 hour ago, Jessopia74 said:

Start with the diff and prop shaft mate. If you gave lots of excessive okay, just one side jacking the rear axle up with handbrake off but box in locked P, you can rotate one wheel left/right to feel play and should gear clunking. It’s amplified at this point due to how the planetary gears in the diff work, but it will soon highlight where the clink is. Money is on the diff tbh.
Don’t forget to chock the car! And don’t go under without an axle stand! 

Sound advice thanks, will check it out, is the diff the same on autos should I need a rebuild?

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itshighly unlikely you will need a rebuild but check for any slack as jess mentioned. noting that there will always be SOME just not excessive. can also be splines on the extension shaft or gearbox tail/ prop.

note also that even when new they always seem to have a bit of lift between the tailshaft and prop( up and down.)

any obvious wear should be obvious if bad.ehilst your checking under there make sure g box rear mount is ok.they can go soft or split.

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  • 3 weeks later...

Does it happen if you engage it on level ground with the brake on and gently release the brake?

If I set off too fast rather than a more controlled launch, there's often big clunk as the drive engages and the car lurches forward. Typically happens more when I shift from reverse to drive or vice versa. It's probably a lag as the torque converter fluid reverses.

 

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11 minutes ago, mepbowles said:

Does it happen if you engage it on level ground with the brake on and gently release the brake?

If I set off too fast rather than a more controlled launch, there's often big clunk as the drive engages and the car lurches forward. Typically happens more when I shift from reverse to drive or vice versa. It's probably a lag as the torque converter fluid reverses.

 

Hi, it does it with the foot brake on, that’s by habit will try it with brake off and see if it’s the same.

Once in drive it’s fine, very smooth, clonks when I go from neutral to drive or reverse.

Cars off the road waiting for my radiator to come back from repair, will let you know how I get on!

 

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  • 3 weeks later...

Well the car is back and on the road again, after a new steering rack and prop shaft uj, the clonk as it turns out was because osr wheel was loose. I had a local resto garage do a few jobs including new tyres, let’s just say it’s not the only fault  that has come to light since they had it.

Won’t be going there again…….

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7 hours ago, Trooker said:

That’s rough, so much for a resto garage?!

Yep, so far I have found;

 

Fuel lines not replaced

Radiator leak

Steering rack over adjusted

Fuel tank breather hoses perished

Carb choke part open

Carb gasket leak & over fuelling

One fog lamp not working

Both real wheels loose

 

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This is why ( if you can) try and do things yourself 

I whoud like to put my manta is a garage that way it will be done a lot quicker 

But l will keep going nice and slow and get there in a few years 

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2 hours ago, 1200bandit said:

This is why ( if you can) try and do things yourself 

I whoud like to put my manta is a garage that way it will be done a lot quicker 

But l will keep going nice and slow and get there in a few years 

The help and advice here has been outstanding, that really does help with motivation to DIY

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best to do most things yourself realy if you can do it and have the time.

i do all my own jobs and on the odd occasion over the years when ive trusted a trader ! things have always been found wrong afterwards.  tracking for one example .had a car set up once and went back 4 times. everytime they re checked it ,it was wrong. turned out to be all about how they actually fitted the equipment to the wheels. 

plus . you get  the enjoyment of driving a car (or anything realy) that you have actually built yourself so to speak.

ie. the car is still alive due to your own abilities.

and bearing in mind that most car enthusiasts are nuts anyway.we actually find pleasure in doing it all too !

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I got a cheep gas less welder (£70.00) could not get the hang of it .

Was going to get someone in to welded it but the more parts l removed the more welding it need’s 

Had a go at it and if l do say myself the welding done my me is very good

Its more satisfying and cheaper and l don’t think it could have been done better and if not happy with it is down to me

Got a lot going on at this time so have got to the manta for 5/6 weeks 
 

 

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yes a friend of mine tried a gassless one. he found it rubbish too.

normal mig with a co2/argon bottle works fine .most of the "hobby" welders are let down by the wire feed but once you get them working and get a tecnique they are fine for automotive use.

 

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