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special sport front brakes

davidian
Posts: 23
Joined: Sun Feb 17, 2019 11:32 am
Location: la vinuela spain

special sport front brakes

Post by davidian » Mon Jun 17, 2019 2:53 pm

Hi Readers
My special sports has always suffered an imbalance to the front brakes which I have been unable to cure .I have renewed the seals in the cylinders , the master cylinder , renewed the hoses and bled the system more times than I care to remember but to no avail. David Beales mini manual makes little reference to the front brakes, only to say turn the adjuster until the drums lock , then back off until the drums turn .this I did many times, I searched for Girling online but could find nothing that resembled my brakes, I even wrote a piece in the club magazine and received two replies both suggesting I had the ex panders done up too tight, so I loosened the fixings but it made little difference . As the linings looked fairly new I put it down to bedding in and drove the car hoping it would cure itself but now a few years later the problem is still there , Any suggestions .
David

Stan Thomas
Posts: 507
Joined: Sat Feb 13, 2016 2:14 pm
Location: Penkridge. Staffs.

Re: special sport front brakes

Post by Stan Thomas » Mon Jun 17, 2019 6:05 pm

Hi David,

Firstly, given you have attended to the relevant components, it is not your hydaulics - as the very purpose of using such a system is to provide total balance of braking force applied to the wheels. That said, I trust you have also checked out the mechanism and operation of the rear brakes, as not knowing the "feel" of the imbalance, I cannot rule out such a possibility of that being your problem.

Still further, the actual adjustment of the brake shoes will not cause an imbalance when braking. That said, do you have the correct brake lining material which must of course be the same on all four shoes. Is there a chamfer on the edges of all the linings - and if my memory serves me correctly - are there brake shoe steady posts which I think are fitted on your car - and are they correctly adjusted so the shoes are square to the drums?

If you clear those hurdles, your problem therefore lies within probably two areas dependant upon the severity of the imbalance. Could be a faulty brake on one wheel, or something more remote like suspension wear or mis-alignment. Can you say therefore whether or not the imbalance is a "grabbing" action, or a gradual one dependant upon road speed - and just how bad is it? So try this:

Press down on each corner of the front of the car to assertain the damping is firm and equal.

Drive the car in the top of the camber of a quiet road and see if there is a tendency to wander left or right when you let go the steering wheel. Do it again with the handbrake partially applied. Then do a third test if it is completely safe and reasonable to do so by performing an "emergency" stop.

Let us know the results so we can assist further!!

davidian
Posts: 23
Joined: Sun Feb 17, 2019 11:32 am
Location: la vinuela spain

Re: special sport front brakes

Post by davidian » Mon Jun 17, 2019 7:06 pm

Hi Stan. Thank you for your reply. The fault initially came to light on the rolling road brake tester at the I T V station( Spanish MOT ) about seven years ago, and despite my best efforts failed four times , in desperation I took it to the village garage who put it on their rolling road and found that if the pedal was gently pressed to hot up the brakes they improved so I was advised to drive round and round the ITV station car park with the brakes on until it was my turn , the car did pass, the imbalance deemed to be within allowable limits . It is inclined to be more noticeable at low speed with the front of the car dipping toward the good side, and on the road I keep my distance from other traffic as the brakes dont exactly fill me with confidence . The linings all look the same, no contamination, they are square to the drums, the drums are not scored, its a mystery .
Regards David .

Barrie
Posts: 98
Joined: Mon Feb 29, 2016 11:50 pm
Location: Sydenham Hill SE London

Re: special sport front brakes

Post by Barrie » Mon Jun 17, 2019 10:27 pm

I had the same thing on an SS.
After a lot of heartache (much of which you've already been through!) I found that one of the internal surfaces of the drums, although not scored or marked, was less worn on the outer edge and therefore engaging only on the outer edge of its brake linings. All was well when I had the drum skimmed.
I hope this is the answer to your problem.

Stan Thomas
Posts: 507
Joined: Sat Feb 13, 2016 2:14 pm
Location: Penkridge. Staffs.

Re: special sport front brakes

Post by Stan Thomas » Tue Jun 18, 2019 7:49 am

Hi David,

Right - now we are getting somewhere! It sounds very much to me that you may well have a mix of lining material on the shoes - hence the change in braking effect as the linings are heated by aggrivated application.

Barrie may well be right about the drums, but if they are "skimmed" on a lathe quite a deep cut must be taken to get under the glass-hard glaze that occurs on the surface of cast iron under working conditions. Ideally therefore, they should be ground.

Then there is another problem arises because now the drums have a larger working diameter, so the surface contact of the linings will have altered, requiring much longer bedding in. So again, ideally thicker linings should be fitted and ground to the exact diameter of the drums.

However, what I suggest is to thoroughly inspect the drums for squareness and ovality. Remove the brake shoes and replace the drums and check with a D.T.I. guage. Then de-glaze them with emery paper (a lathe would be helpful, but watch your fingers!).

Then for what it is worth, have the shoes re-lined, after seeking advice from a brake lining specialist regarding specific material. Have the linings bonded, not riveted. Ideally, If you can run to it, have slightly oversize linings fitted and ground to suit your drum diameter.

Sounds long-winded I know, but think of the consequuences if you suddenly had to do an emergency stop with the brakes you have at the moment!!

Regards,

Stan.

davidian
Posts: 23
Joined: Sun Feb 17, 2019 11:32 am
Location: la vinuela spain

Re: special sport front brakes

Post by davidian » Tue Jun 18, 2019 10:06 am

Hi Stan
What you said about mixed linings makes sense. The last time the car was used I joined the local M G group for a jaunt around the mountain roads (not an ideal environment for a SS ) but had to give up half way because the car was beginning to over heat and the brakes were fading, when I felt the drums the nearside brake was too hot to touch but the off side was just warm so the near side was doing all the work. What I will do next is to put some engineers blue on the drum ,spin the wheel and look at the result.
Regards David.

davidian
Posts: 23
Joined: Sun Feb 17, 2019 11:32 am
Location: la vinuela spain

Re: special sport front brakes

Post by davidian » Sun Jun 23, 2019 7:49 pm

Hi all.
Not been able to access the site for a couple of days and my recent posts haven't appeared so to bring you up to date I may have found the problem.I have some motor repair books which are probably late nineteen thirties and I read the chapter on Girling brakes which was of no help but I found a chapter on Bendix brakes which had an appendix entitled " The new Bendix two leading shoe brake" and upon turning the page there was a picture and diagram of a brake exactly like the one fitted to my car and Consorts .So I removed the drums to compare and the only difference was the means of adjusting the bell crank eccentrics. In an earlier post I mentioned the test I did with engineers blue which appeared only on the leading shoe, so it looks like the trailing shoe is not making contact with the drum when you wind in the adjuster.Will dismantle the brake tomorrow to see if there is anything broken/ missing compared to the Bendix.
Regards David.

Barrie
Posts: 98
Joined: Mon Feb 29, 2016 11:50 pm
Location: Sydenham Hill SE London

Re: special sport front brakes

Post by Barrie » Sun Jun 23, 2019 10:17 pm

Wonderful detective work!
I hope it's successful.

clevitt
Posts: 74
Joined: Wed May 18, 2016 1:02 pm
Location: West Hertfordshire

Re: special sport front brakes

Post by clevitt » Mon Jun 24, 2019 6:33 pm

David,
My copy of the David Beales booklet includes two pages about the Girling Two Leading Shoe Brake, and mentions that two versions of the bellcrank and strut arrangement are used. When I recommissioned the front brakes of my Special Sports, I adjusted the bellcranks to take out the play and then, in order to confirm, observed the shoes through the hole in outer face of the brake drum whilst an assistant operated the foot brake. With the hole at about one o'clock, I could see the top of the shoe moving forward and at about five o'clock I could see lesser movement of the bottom part of the shoe moving forward. I was therefore reassured that the bell cranks were working correctly , but never thought to do the same wih the trailing shoe. Could your problem be due to the trailing shoe not moving on the bad side because the trailing edge piston is stuck in the cylinder?
Chris

davidian
Posts: 23
Joined: Sun Feb 17, 2019 11:32 am
Location: la vinuela spain

Re: special sport front brakes

Post by davidian » Mon Jun 24, 2019 7:56 pm

Hello
I have put several posts on the forum today but they are not appearing. am I doing something wrong?
David

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