Brakes locking up

happy days

happy days

Active Member
Removed my master and slave cylinder in the 74 V8. Replaced seals and refitted. Pedal now feels hard, but does work well, the issue is, if engine is not running and you press brake pedal,then start engine the brakes are locked on, to free them I undo the brake pipe at the servo, lose a little fluid and all is well, any ideas . Cheers Mick
 
When mine did this it was the little white valve assembly on the servo. Think it was about 25 quid from wins.

Rich.
 
happy days said:
Removed my master and slave cylinder in the 74 V8.
Click to expand...

What do you mean by "slave cylinder" Mick? There is a brake master cylinder that supplies brake fluid to the 4 brake calipers but there is no brake slave cylinder. Do you mean the brake servo/booster? The clutch system has a master and slave....

Dave
 
on checking the W/S manual, it says remove air valve piston, from these pics have i lost mine on re assembly,
DSCF2342.jpg
DSCF2345.jpg
DSCF2344.jpg
cheers peeps
 
can anyone tell me if the large spring under the air valve as in picture three, posted by Mr Happy Days is meant to be there? I am having issues with the plunger not returning to rest and having checked mine and it only has the small byro type spring in the cap. I have heard of some sort of modification to the air valve and wonder if that is what it is. can anyone recommend a suitable spring if this is the case. I did look at a radiator cap spring but it looks a bit too beefy and I don`t want to use two feet to get it to stop.
any help welcome

Nick
 
NICK T wrote,...
can anyone tell me if the large spring under the air valve as in picture three, posted by Mr Happy Days is meant to be there? I am having issues with the plunger not returning to rest and having checked mine and it only has the small byro type spring in the cap. I have heard of some sort of modification to the air valve and wonder if that is what it is. can anyone recommend a suitable spring if this is the case. I did look at a radiator cap spring but it looks a bit too beefy and I don`t want to use two feet to get it to stop.
any help welcome
Click to expand...

Hi Nick,

The spring that you speak of was not originally fitted when the booster (servo) was manufactured, but it was later found that the brakes had a habit of sticking on slightly, especially with light applications of the pedal. To correct the problem a spring was introduced which was known as a "modification spring for the air control valve". The spring increases the pressure that is applied to the air control piston which in turn ensures that there exists the necessary separation between the air control valve seal and the air control diaphragm. This ensures that the air within the vacuum chamber can be evacuated and thus prevent the brakes from sticking on.

The spring is quite soft when compared to a radiator cap spring, indeed the latter would be excessive in the extreme.

Have you been to any brake repair businesses to see if they have a spare on on the shelf? A business that specialises in repairing boosters would be ideal if you can find one.

Ron.
 
Hello Nick,

Some more info on the modification spring. The overall length is 40mm, diameter 35mm, mass 2 grams.

Ron.
 
thanks for that Ron
the air valve kit that I purchased some time ago did not have the spring included, so I`m a bit stuffed.
the size you quote may not be to much of a problem but the 2 grams might be a problem.
I`l keep searching, I`m sure something will turn up

thanks again
Nick
 
Re: Brakes locking upa

Been there with this fault, I bought a servo off eBay with a view to overhauling it for a spare, it looked in better condition than the one fitted to my 2.2 tc , so I fitted it only to find this fault, after comparing the two servos I found that the Niro type spring in the air valve filter on the working original was about 3/8 inch shorter, put that spring in no more locking brakes, sorted
 
hi folks, still got this problem, fitted a modification spring but the only one I could find was rusty and quite thin in one spot, this has now perished completely so I need one of these modification springs again, this is definitely the cure but getting my hands on a good spring is proving a challenge, anyone got a spare.?
 
stephendavies said:
hi folks, still got this problem, fitted a modification spring but the only one I could find was rusty and quite thin in one spot, this has now perished completely so I need one of these modification springs again, this is definitely the cure but getting my hands on a good spring is proving a challenge, anyone got a spare.?
Click to expand...

If you still have the remains, you could go buy some piano wire the same diameter as the spring wire and make your own spring by winding the wire onto a form a little bit smaller than the desired final size and maintaining the helix angle. Not ideal, but it would get you running again.

Yours
Vern
 
You must log in or register to reply here.
Back
Top