Brake compounds

Hi All,

New here. I live in London and I own a 1971 246 GT. I've had it for about ten years and it still takes my breath away. As with most newbies to a forum, I'll begin my first post with a request for some advice - please forgive my presumption.

I do most of the work to the car myself and the most recent project has been the brakes. Callipers have all been rebuilt and I have replaced the master cylinder. The system is nicely bled and I have a good pedal.

One thing which I have noticed is that the brakes are (and were prior to any work) very fierce. Only with very careful use of the pedal can I avoid locking the front wheels.

I find that by extending the pushrod between the servo booster and the master cylinder that I have dialed out some of the mechanical causes for this issue, but I was wondering if a slightly gentler front brake pad compound might be worth trying?

I was considering some kind of organic/ceramic pad. Does anyone have any suggestions regards pads or any other tips regarding this issue?

Thanks in advance.

Andrew

 

Welcome Andrew - Nice to have you aboard. Having owned three Dinos and driven many, I must observe that your lock-up experience is out of my norm. All of the cars that I have driven have enjoyed rather predictable braking pedal pressure and response.

A few questions may help me diagnosis the problem:

1) Do all four wheels lock up, or only the front or rear? If the rear are locking up then the proportional valve in the rear may be malfunctioning.

2) If the fronts are locking up then it is possible that the flexible lines are old (have they been replaced?) and acting as one-way valves owing to internal lining degeneration. The internal lining of the flex tubes can slough and cause a flapper or ball-valve-like mechanical one-way valve. The symptom is usually dragging of the brakes as the pressure fails to diminish with release of the pedal (in the offending corner) and the pistons fail to retract.

However, if the dragging caliper allows the pad to get warm but not hot, then the brake response may be improved to the point of excessive grabbing. This would be less likely if both front or both rears are experiencing the lockup.

3) Adjusting the push-rod between the booster and the master cylinder is tricky, and I commend you for attempting it. If it is incorrectly adjusted you will get dragging.

More information will be helpful. I suspect it is not a result of pad compound.

Jim S.

 

Hi Jim,

Some answers to your questions:

1. Only the fronts lock up. I didn't know there was an apportioning valve in the rear. I suspect that this might be a source of the problem. Any tips on adjusting it?

2. The flex hoses in the front are brand new braided lines, so there should be no problems with them.

3. The adjustment of the push-rod was foisted upon me (it wasn't something I'd rush out to do). I got brake bind after installing a new MC due to the piston not covering the return ports.

Thanks for getting back so quickly.

Regards,

Andrew

 

One last item I forgot to mention was the tires. If you have old, original-stock XWXs (unlikely) they will now have the same coefficient of static friction as an ice cube on a frozen lake. Old rubber grows hard, and slides easily.

Now, back to the proportioning valve. I am not familiar with the failure mode, but assume for a moment that it is kaput (a technical term). If you have little braking in the rear then all the braking will be on the front, and this might lead to your symptoms. On the other hand, if the failure mode is to equalize rear / front braking pressure, then I would have thought that the rear wheels would lock up first (after all, that is the purpose of the valve).

It is easy to service the valve, albeit care should be taken as there are no replacement parts available (that I am aware of). You will have to open the hydraulic system (leading to another round of bleeding). With the proper wrench disconnect the two hydraulic lines running to the valve, which is mounted on an upright just aft of the left (looking forward) rear wheel. It looks like a black or rusted cylinder.

Once out of the car you will need a vice and a large wrench to break lose the large cap-nut. It is often on quite tight, and hence the proper sized wrench will be helpful. Furthermore, impact with preload (an additional helper) on the wrench has always led to success in my experience. I would avoid heat as there are several rubber seals immediately below the cap.

Once you have the cap off, carefully remove and document the sequence of washers and springs. Photographs as you disassemble are always helpful, or draw a sketch.

You will likely find a nice collection of crud in the cylinder. Clean it all out and reassemble. Quite easy to do and you will sleep better at night knowing that it has been addressed.

Keep those cards and letters coming.

Jim S.

 

Thanks again, Jim,

I'll be servicing the proportioning valve later today. I also noticed that whoever installed the previous master cylinder seemed to have gotten the output lines the wrong way round (which I blindly followed, rather than reading up - duh), so I've gor the front brakes coming off the port closest to the booster and the rears coming off the '2nd' port.

I'll remedy this situaion and see if it makes any difference. More letters/postacrds (and maybe a pic or two) to come.

Thanks again,

Andrew

 

Hi All/Jim,

Brakes fixed. I suspect it was the incorrect plumbing on the MC which caused it. As it was, I went nuclear on the brakes and installed a hidden bias adjuster, which turned out not to be necessary, but nice to have anyway.

Also serviced and restored the rear pressure control valve (thanks for the tip, Jim) and replaced some nasty sections of steel brake pipe with modern make pipe.

Now if I could just get the eight-track to work...

Once again, thanks Jim.

Andrew

 

Hey Andrew -

Have I go a DEAL for you!!! How about another eight-track? I've got a Blaupunkt with maybe 5 or 6 tapes - including such hot items as "The Best of Mancini - Vol. 2," "Tom Jones - Help Yourself," "Hawaiian Heart Beat...The Vocal Romance of THE DON HO SHOW! - Live From Hawaii," and still in its original shrink wrapped 8 Track Stereo Tape Cartridge Continuous Play case "...Sounds Like... Herb Alpert and the Tijuana Brass - Casino Royale." And, if I look around, I might be able to find buried somewhere some Grand Funk Railroad, Cream, and Blue Cheer tapes. Perfect for your GT . . . .

Mark

P.S.
Glad you're on board! And, BTW, what is your Dino's serial #? Can you post some photos?

 

Lol. That's quite a collection. I've actually got an (roughly) working eight-track in the car, just no tapes. I might get lynched for this, but I did see a setupup where a guy had modified an eight-track to take an i-pod where the tape used to go. I thought that had potential, but then, who needs a music player in a Dino, when there is an orchestra located right behind you.

My car's chassis number is 02846 - first registered in the UK in 1973, but I believe that it is a 1971 model which was imported from New Zealand.

I'll take some pics once I've polished it up.

 

Hello Andrew,

is #02846 an original RHD car? Why do you think it was original delivered to New Zealand?
Very interesting.
Regards Matthias

 

Andrew - did you have difficulty servicing the proportioning valve? What did you find upon dis-assembly? Much crud?

Jim