Front brakes uneven brake force

[arman]

Hi everybody

My 1974 450 SEL went to the workshop to have a problem with the front brakes fixed.

The right hand front brake wouldn't brake that much anymore while the left one was relatively easy to block. That felt a little nervous because if you stepped on the brake somewhat firmer the car would not hold straight forward but instead go first a little to the left and then back again.
My instructions were that they would disassemble both front brakes and clean and grease them and put them back together, bleed them and top off the fluid level.

Well they phoned from the workshop that they had found the problem. The right front brake was damaged, stuck, corroded and was leaking. I'm aware of the fact that if you don't drive that much that also can be a problem for all moving parts in such an old car.

They suggested to replace the old caliper with a rebuild caliper, which I thought was a good idea.

But when I got my car back the braking was somewhat better but this swaying wasn't gone. I presumed the brake force was still uneven which was confirmed when I brought my car to a test centre: the right hand brake had almost 30% less power which was just within the margins for approval.

Now then I started to think why didn't it work out with the rebuild brake caliper? Why had the former caliper gone bad in the first place? Is there something else that should be checked? I recall a thread about brakes and someone was explaining about the brake lines -which can be damaged on the inside- causing brake fluid flow problems? Could it be the brake line or something else?

To replace the brakeline should of course be a rather inexpensive operation.

I wanted a second opinion from you guys before I go back with the car.

Thanks in advance!

[wbrian63]

Usually, it's the flexible lines that develop corrosion internally and cause braking problems. The steel lines seem to last forever. Of course, if the brake system was neglected and lots of moisture got in, there's always a chance. However, usually, they'll just rust out and leak before they get blocked bad enough to cause uneven braking.

When the flex lines get blocked, it usually results in a brake that won't apply, or won't release.

Restriction in the lines usually manifests itself by the symptoms you describe - pulling to one side when brakes quickly applied, and the pull eases after a bit. The cause is the restriction in the line preventing sufficient flow, but eventually allowing enough flow for the pressure to equalize.

It's easy to check for collapsed hoses and corroded lines - but the lines need to be disconnected at both ends. A little compressed air should reveal if there's a blockage.

[TJ 450]

Ideally, both front calipers should be rebuilt at the same time, so as to ensure that there is no alteration of balance. The condition of the rear brakes should also be taken into consideration.

The flexible brake hoses are definitely a candidate for this sort of problem as well. They are marked with a date of manufacture and should be replaced every 10-15 years or so. The original hoses are usually still present, even on 30+ year old cars!

Last, but not least, how are the front suspension components and wheel alignment. If there are problems here, then they may have an adverse effect on braking performance as well.

Tim

[pez]

These are all accurate, correct points in my opinion. I would start by replacing all flex brake hoses, flushing the brake fluid a few times to ensure all moisture is out [under vacuum], and having all 4 calipers rebuilt.  Only then can you eliminate enough variable to question other issues.  Also, look at your tire wear - pull could be coming from bad suspension issues, but this would not affect braking force. it's also possible that there is an issue in the master cylinder....o-rings could be worn of rolled over on the main piston, but unlikely to be this unless you have ruled everything else out.  Also, check to be sure that you have not crimped any hard metal brake lines - I have seen this happen when people go off road with their cars, or when they encounter wildlife and drive over them unexpectedly.

[craigb]

I often make this remark on forums. Those flexible lines are really cheap and I guess once you have a braking problem in relation to one, you never forget it, not to mention the adverse affects you might have from a problem. Lucky for me it happened on a mini when I was 16 and I have never forgot. 

I didn't realise they were date stamped and will check that in future, but in the past as a matter of course, if I get a new car I replace them and I know I have guaranteed performance after that. I think on Autohaus they are less than $10 each. Add in $15 each for caliper kits and if you really want to lash out another $70 for a new master and for under $200 you can replace your entire hydraulic system and know exactly where you stand. Of course if you buy a car with receipts for work that is different. And a leaking hydraulic system, with warning light to tell you the reservoir is low, is not the end of the world, but one of those lines suddenly blocking and putting all braking force to one side is like a turning brake on a tractor and as with my mini could have easily put me into a tree. The internal rubber had gone soft and and looked like the rubber pushed forward to block it.

But spread the word everybody, flex lines are probably cheaper than the cost of having someone bleed your braking system, so if your having a problem just make a habit of replacing them, rather than pay them to rebleed the whole system again. Also I agree with the comment about rebuilding all the calipers. If you have a problem with one, chances are the external dust rubber was gone allowing the moisture in and every chance the others are gone too.

Dissapointing your workshop didn't offer this advice.

[arman]

Guys, thanks for your thoughts and comments.

I will ask the workshop to replace that flexible brake line.

I'm also disappointed that they didn't suggest this theirselves. But I know they don't have a possibility to check brake force in their shop but they could at least test the brakes of the car when they finished their job by driving it around the block! I mean I left the car to them in the first place to get the brake force issue solved!

I probably read your thread somewhere earlier craigb thanks for that. This is the cheapest way to solve and even avoid uneven brake force when you replace the flexible lines every 10 year or so.
I still don't get it that an experienced work shop like this one, being in business with MB cars since 1968, can't figure this one out theirselves.

I will get back on this matter when the brake line is replaced.

Regards Arman

[pez]

I am not so sure I would totally trust that shop.  All work should have a thorough test drive,  and uneven braking force should be a big red flag to any tech.

Also, do be sure that you are thoroughly bleeding the brakes at least every year...in your part of the world, I would do so in the spring.

[AAB]

ARMAN,

When I gave my 74, 450SEL a brakes birthday 10 years ago, 3 of the 4 the rear caliper  pistons were seized !!

I gave them another birthday a couple of months ago, & all was well.

This time around I replaced all of the piston rubbers, all flexible hoses & master cylinder.

I intend to flush out the brake fluid every 2-3 years from now on.

Regards from Melbourne, Australia,

Alex

[arman]

Well I finally went back with my 450SEL to the workshop and yes there was a faulty flexible brake line on the front RH brake. And yes the symptoms are that the car will pull to one side at first which feels very 'nervous'. Then after a second or so the brake force will be more equal again and the car stops pulling to one side as wbrian63 is describing. This behaviour is now totally gone with two brand new flexible lines installed on the front brakes.

BUT still the front brake force is uneven, about 25 percent. So the LH front brake still locks first when firm braking is done (while the right hand one just has been replaced with a rebuild caliper??).  In fact the RH brake doesn't seem to get locked at all.

That's maybe why one should rebuild brake pairs at the same time as TJ 450 suggests. Strangely this workshop recommends to replace the best braking caliper on the LH front with a rebuild one as well. Now this I don't get and I refuse to replace the best braking caliper with a rebuild one or am I wrong? I rather tell them to find another rebuild RH caliper and see if that's one is better?? If that's the case than I could return the first rebuild caliper and get my money back for that one. What do you guys think?

In the mean time (between the earlier and this last workshop visit) the LH rear brake also got more problematic not wanting to come off the disk really after braking resulting in a low 'humming' while driving slowly. I even noticed a somewhat higher temperature on the outside of the hub cap on the rear LH wheel when I had driven the car for a while on the highway. Well this was also caused by a faulty flexible brakeline. This problem was solved at once just by replacing it for a new one.

Now the cars braking performance is a lot better and the feeling of 'full controle' while braking and not be pulled to one side is absolutely fantastic.

My question is now: is it true that if you change your flexible brake lines every once in a while, will you be able avoid a more expensive caliper failure? I mean once the brake line does block or restrict the brake fluid flow, will that lead to caliper failure due to lack of sufficient movement of the parts?

Regards,
Arman