brake servo problems

For Speed 20, Speed 25, 3.5 Litre and Crested Eagle cars
DaveT
Posts: 96
Joined: Tue May 22, 2012 12:53 pm
Name: David Turnage
Location: Colchester, UK

brake servo problems

Postby DaveT » Mon Feb 16, 2015 1:04 pm

Hi,

I have just rebuilt the air valve and servo on my Speed 25 and having set it all up, the difference is significant (as expected). However, I am a little concerned about the time it takes for the servo (and brake pedal) to recover to the original position - is this a common problem? Does the new seal in the servo have to bed in? Am I using the wrong lubricant within the servo? Or perhaps the air valve push rod adjustment needs a bit more attention?

All suggestions welcomed.

thanks

Dave
Dave T
Colchester, UK
sp25 DHC
Jensen 541

DaveT
Posts: 96
Joined: Tue May 22, 2012 12:53 pm
Name: David Turnage
Location: Colchester, UK

Re: brake servo problems

Postby DaveT » Mon Mar 02, 2015 12:37 pm

Looks like I have fixed this myself (with some advice from Roger Gooding). It would appear that castor oil is the lubricant to use (available through Amazon - I couldn't find any in the local chemists). Also slight lengthening of the servo output rod results in the internal servo spring always trying to push the cylinder a bit further open even when it cannot be pushed any further, and this seems to improve the recovery time of the servo system. Hope this post helps someone else in the future.

cheers

Dave
Dave T
Colchester, UK
sp25 DHC
Jensen 541

johnlayzell
Posts: 149
Joined: Mon May 21, 2012 2:44 pm
Name: John Layzell

Re: brake servo problems

Postby johnlayzell » Mon Mar 09, 2015 7:04 pm

Thanks, Dave!

After a servo rebuild a few years ago, I barely noticed any appreciable difference. Can't recall what oil I used (probably engine oil), but certainly not castor oil.

Also assume you adjusted the length of the servo rod by turning out a few turns.

On my "to achieve" list!
1925 SC12/50
1937 SP25 VDP Saloon
1970 Peking to Paris Rally VW Beetle

johnlayzell
Posts: 149
Joined: Mon May 21, 2012 2:44 pm
Name: John Layzell

Re: brake servo problems

Postby johnlayzell » Mon Oct 05, 2015 8:00 pm

Dave,

Is the 'servo output rod' the longer one from the larger aft servo motor or the shorter one from the forward smaller cylinder control valve? Both connecting rods are adjustable.

Thanks!
1925 SC12/50
1937 SP25 VDP Saloon
1970 Peking to Paris Rally VW Beetle

DaveT
Posts: 96
Joined: Tue May 22, 2012 12:53 pm
Name: David Turnage
Location: Colchester, UK

Re: brake servo problems

Postby DaveT » Tue Oct 06, 2015 12:15 pm

it is the longer one, but I recommend that you read my other thread on this subject for the final answers

viewtopic.php?f=16&t=516

best regards

Dave
Dave T
Colchester, UK
sp25 DHC
Jensen 541

johnlayzell
Posts: 149
Joined: Mon May 21, 2012 2:44 pm
Name: John Layzell

Re: brake servo problems

Postby johnlayzell » Tue Oct 06, 2015 12:37 pm

Thanks Dave!

Really appreciate your prompt reply, which unfortunately I find is not always the case from all on this Bulletin Board!

I check it every day! I've have also checked your other post

I have just adjusted all the brakes settings according to the manual, and am surprised that the brake pedal almost goes all the way to the floor before I feel any pressure. Not reassuring! Car is still up on jack stands and without engine running.

According to the 'Technicalities' - Clayton Dewandre Brake Servo article to which Wayne Brooks refers, under Adjustments, 'The rod protruding from the motor which is coupled to the pedal shaft should be pulled out as far as possible when the brakes are in their fully "Off" position'. This sounds the opposite of lengthening the rod - or am I totally misunderstanding?

Cheers!
1925 SC12/50
1937 SP25 VDP Saloon
1970 Peking to Paris Rally VW Beetle

DaveT
Posts: 96
Joined: Tue May 22, 2012 12:53 pm
Name: David Turnage
Location: Colchester, UK

Re: brake servo problems

Postby DaveT » Wed Oct 07, 2015 12:52 pm

Hi,

without the diagram, or the car, in front of me, all I can remember is that the instructions from the bulletin article seemed counter intuitive - but worked!

I will try to revisit this when I have something to refer to in front of me.

cheers Dave
Dave T
Colchester, UK
sp25 DHC
Jensen 541


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