Technical Spongy Brakes?

[Middlewich]

Hi,

Could do with some advice on my brakes, they are all new, pipes, pistons etc, just finished bleeding them, no leaks but I still get full travel in the brake pedal.
It’s brand new fluid, and as I said no leaks, so I am a bit at a loss so any advice would be welcomed?

 

[thepuddlejumper]

Hi I had a similar problem a few years back, and bled the system about 6 times before purchasing an easybleed. It worked, still not sure why my initial attempts didn’t work.

Ralph

 

[berkeleyman]

Hi, have you "adjusted" the brakes by driving backwards and applying the brakes?

 

[F123C]

I'm not sure if your problem is spongy brakes (i.e. air still in the system) or a long travel on the brake pedal before the brakes are fully applied?

If spongy - bleed them again. I'm not sure how much experience you have with bleeding brakes so I'll just mention the following :-Make sure you close the bleed nipples before letting the brake pedal up and open it as you press it down. Don't re-use new brake fluid that has been already bled from the system unless it has been left to stand for a few days. Don't shake the can of fluid or use one that's just been transported (i.e. possibly shaken). As 'puddlejumper' says above you might have to use a pressure bleeder (or a vacuum bleeder ) but traditional manual bleeding should work fine if done carefully. At the end of bleeding, pedal should be solid, don't worry too much about excess pedal travel at this time.

If a long travel on the brake pedal is the problem - this indicates an adjustment problem, if all the air has been bled out. Lots of other members have had trouble with the brake shoes not automatically adjusting as they should. Some have had problems with replacement shoe return springs being too strong and pulling the shoes back through the adjusters. An old trick was to try driving forward and then backwards and repeatedly jabbing the brake pedal while doing so. (obviously this needs to be done carefully, preferably not on the public road, so maybe use a car park?). You don't have to drive fast. (5-10mph is enough). Then adjust the handbrake if necessary.

If you still have a 'long pedal', try clamping off each brake hose (gently) to locate the brake(s) causing the excess pedal travel. Clamping each hose in turn can also be used to check if there is still air remaining in one or more brakes.


AL.

 

[John Pritchett]

I've just bought a 1969 500l and the brakes are horrendous. I've noticed that the brake master cylinder is leaking down by the brake pedal so this will be changed next week. I'm watching this thread with interest.

 

[the hobbler]

John;
If it only the master-cylinder that you are having to replace, then with a bit of luck you should get a decent pedal back by just bleeding the brakes---FURTHEST from the master-cylinder 1st, and work your way round so that the last wheel to bleed is the slave cylinder NEAREST the master-cylinder (if you have a r/h/d car:---n/s/r--o/s/r--n/s/f--o/s/f). Don't forget to keep a good eye on your reservoir---it's a bugger when you find that you have emptied the reservoir and have to go through the whole procedure again! When changing the master-cylinder, take the pipe from the reservoir to the master-cylinder off at the reservoir, and attach it securely to the new master-cylinder before you fit the new master-cylinder--trying to secure the pipe 'in-situ' is very awkward.
With regard to having difficulty in getting a decent pedal, even when everything is new--this is not a new problem. I have found it normally is 1 of, or a combination of, 3 things. (1)--The new shoe-return springs are too strong. Try stretching them slightly, or refit the original springs. (2) the latest friction discs in the 'auto-adjusters' on the shoes don't seem as 'grippy' these days and, (3) some of the 'pattern' brake shoes seem to have slightly thinner linings on them---MBG have had a batch of 500 shoes (but sadly, not for the 126) lined by FERODO, and these have slightly thicker linings on them. For people with '126'brakes on their 500s, I have used METELLI brake shoes (from Axel Gerstl) very successfully.:bang:

 

[F123C]

Another thought.....

OP didn't say if he fitted a new master cylinder.

If he is using the original master cylinder, it's possible that the seals have failed.
Master cylinder piston(s), in normal use, only travel part of the way down their bore(s). If corrosion occurs (not unusual in older cylinders, especially if the brake fluid hasn't been renewed approx. every 2 years), it occurs in the unswept i.e. unused portion of the cylinder.

If brakes are bled using the traditional manual method, the piston(s) now travel the full length of the cylinder bores and the seals become damaged by being pushed over this corroded area.

The result can be brakes that can never be bled fully and/or a brake pedal which creeps downwards under sustained pressure. Try holding the pedal down hard, if it gradually sinks to the floor, the seal(s) have failed.

The only cure is to either renew the master cylinder, or if a replacement is unavailable, to recondition the cylinder by sleeving the bore (some brake specialists offer this service) and fitting new seals.

If the corrosion is not too bad, you might just get away with polishing the bore and fitting new seals.

There is a tool available for honing/polishing the bore, it looks like a smaller
version of an engine cylinder bore honing tool - i.e. a tool driven by an electric drill with 2 or 3 spring loaded arms each carrying honing stones.

(Some achieve similar results using some fine abrasive paper wrapped over a length of wooden dowel or similar).

AL.

 

[John Pritchett]

Some great advice there. I'm hoping it's just the master cylinder in my case, everything else looks fairly new and dry.

 

[Middlewich]

Thanks for your wisdom.

Used the easybleed, I borrowed from a friend, great peice of kit and highly recommended. Now my approach is the back and forward, as this is easy and doesn’t require strip down, if this fails then springs, if this still hasn’t resolved the issues the shoes.

Unfortunately in the midst of this, my brand new alternator from Motobambino has seized solid. No idea why or what has caused it, taken off and no electrical smell so I can only guess mechanical. Hopefully they will replace as defective? :bang::bang:

 

[F123C]

Could you say if you replaced the master cylinder? (I'm not sure from your 1st post).

There's not much that could jam an alternator other than a foreign object getting in between the rotor and stator (possibly a brush? screw came loose? any possibility that something could have gotten in through a ventilation slot before it was fitted?) If it was mine, I'd strip of the rear 1/2 casing to check rather than go through the hassle of returning it to under guarantee.(but that's just me, I love taking things apart ...)

AL.

 

[F123C]

Applying the handbrake removes the rear brake shoes, springs and possibly slipping adjusters from the equation as regards excess brake pedal travel. This allows you to concentrate on the front brakes first by clamping off the brake hoses to see if one or both front brakes are causing the excess pedal travel.

If you're not familiar with clamping standard rubber-type brake hoses, I'll just say that as the hole inside the hose is less than 3mm, there is no need to clamp the hose tightly, in fact doing so risks damaging the internal woven braid which provides the main strength to the hose.

Proper brake hose clamps are available on-line or from Motor Factors. Alternatively you could lightly clamp the hose using a small visegrips or similar. Please place suitable packing between the jaws and the hose to prevent damage.

Afaik, braided Stainless Steel hoses (Aeroquip, Goodridge etc.) should not be clamped (If anyone knows me to be wrong about this, please chime in - I wouldn't want to be spreading incorrect information)

AL.

 

[John Pritchett]

Well I fitted the new master cylinder and the brakes are much better than before. I am not convinced all the air is out of the system though, as however much I bled them, there were still a few tiny bubbles. I had to use traditional method as the vacuum pump I bought wouldn't fit the nipple satisfactorily and my easy bleed won't fit the reservoir. The brake pedal goes about half way before brakes apply, but they can lock the wheels now. Unfortunately, I haven't had much chance to take it out and give it a proper run and evaluate it properly.

 

[the hobbler]

A common fault when bleeding brakes is to open the bleed nipple too far--you only need to JUST open the bleed nipple to carry out the bleed. If you open the nipple too far, you can actually pull air IN to the operation, which makes it look as if you haven't removed all the air out of the system. Don't forget to start with the wheel-cylinder FARTHEST from the master-cylinder and finish with the wheel-cylinder NEAREST the master-cylinder. Have you got the original brake-shoe return springs on, or are they new ones? As has been found out by a number of people, the new 'pattern' brake shoe return springs are slightly shorter than the original--this produces too much brake-shoe "pull-back" as the friction of the automatic adjusters is overcome. The answer is too either slightly stretch the new springs, or revert to the original springs. It has also been found that the lining on some of the 'pattern' brake shoes is thinner than the original. Both these situations will produce a pedal that, whilst eventually effective, produces a 'long pedal' before the brakes work. Middle Barton have had a batch of '500' shoes made with correct specification 'Ferodo' linings on them.

 

[John Pritchett]

I haven't touched anything else, all looked well, just a leaking master cylinder. I've just bought the car, so don't know what the brakes should feel like. I'm hoping to get to a few shows etc and meet up with other owners to compare. I want to get the underside cleaned up and protected before I take it out properly.

 

[giardini]

There's a lot of talk about buying and borrowing an "easybleed", I just wanted to point out how easy it is to make one: the (whatchamacallit) air pistol can be found second-hand, dead cheap on most flea markets, and the picture is self-explanatory about the rest, I hope I've cracked how to attach it to the post ! Yesssss !

 

[John Pritchett]

I've got one of those, how is the tube attached? Are there any internal mods?

 

[giardini]

The tube just needs to be connected to the top of the tank, and the rigid "feed" tube that descends into the tank shortened, so as not to "suck up" the brake fluid that collects at the bottom.
The only drawback is that the tank is not transparent, so make sure to empty it
before it starts spewing brake fluid out the front !

 

[John Pritchett]

Thanks, another little project onn the list.

 

[Middlewich]

I have taken the new springs off as per Tom’s instructions, you can see the new springs are at least 6mm (1/4”) shorter than the old ones. Not sure if the mod has fully worked yet till tomorrow when I get it on the road. I wondered why putting the brakes on was so hard now. The new springs are the bottom two.

 

[Middlewich]

All sorted, thanks for your help everyone.:slayer: