Very interesting discovery while doing a brake job

[Henrik]

Today I encountered a very interesting problem:

Lately my brakes have started to feel a little spongy so I decided it was time to bleed them. The first three “corners” went well without incident but when it was time to bleed the last one, the right rear, I was surprised to find that there was no brake fluid coming out of the caliper’s bleed screw. I was using a power bleeder with the system pressurized @ 20 psi so it was really weird that there was absolutely no fluid coming out. I concluded that there must be a blockage somewhere in the RR circuit so I started cracking open the connections, starting at the caliper working my way upstream. After a while I found that the connection upstream of the flexible rear brake hose (100460) was fine (brake fluid spewing out) but the connection on the downstream side of the hose was BONE DRY. Once I got the hose out I tried shoving a coat hanger through it and is was completely blocked! Not sure if the hose has collapsed internally or if there is an obstruction - autopsy to follow - but that thing is 100%, totally blocked.

It’s amazing to think that during my 7 years of ownership I have probably never had brakes on the right rear ….

I would be curious to hear if anyone else has encountered something similar.

17798

[DMCMW Dave]

I would be curious to hear if anyone else has encountered something similar.

17798

All the time, most especially on cars that have been stored a long time. We consider replacing (original) hoses to be part of a brake hydraulic rebuild job.

[Henrik]

Oh wow - I had no idea. Thanks!

[vwdmc16]

A few weeks back some of us in the NCDMC club rebuild our member David P's brakes which had worked very poorly since he bought the car. We had trouble bleeding the rebuilt LR caliper, turns out the metal transfer tube on the caliper was clogged so essentially even with the cleaned pistons, new seals and pads, Daid only had 7/8th of his braking potential, we assumed it was the flex line too but we installed new stainless flex hoses too. With the tube all cleaned up they work great!

[Henrik]

All the time, most especially on cars that have been stored a long time. We consider replacing (original) hoses to be part of a brake hydraulic rebuild job.

Do you recommend I go ahead and replace all four hoses?

[ramblinmike]

Do you recommend I go ahead and replace all four hoses?

They're all the same age. This isn't a DMC-specific issue. Pretty much accepted practice for all older cars.

[Ron]

... when it was time to bleed the last one, the right rear,...
A side note-
You should bleed your brakes from the longest line to the shortest line: RR, LR, RF, LF

[Citizen]

A side note-
You should bleed your brakes from the longest line to the shortest line: RR, LR, RF, LF

I ask not to cast doubt, but to learn. Why is this?

...

[Ron]

It gets the air out faster, but more important, it reduces the chance of air getting into the shorter line, at junctions, as it passes...ie the air upstream and right at the junction would already be bled out. Also, on some cars, if you bleed the fronts first, you will not get a full stroke when you go to the backs (the fronts do most of the work and push more fluid...depends on the setup/stages). And, it helps prevent proportioning valves (if equipped) from hanging. Just a SOP in most manuals...

[eagle-co94]

I've heard it both ways, bleed furthest and work your way closer to the reservoir or start closest and work in the opposite direction. I personally start at the RR with my cars, LR on the Mini as it's RHD.

[DMCMW Dave]

Do you recommend I go ahead and replace all four hoses?

I would.

[David T]

I have also seen where a hose fails and acts like a check valve locking a caliper to a rotor. The bleeding of the farthest point is a myth carried over from the early single braking system. In today's cars there are now TWO hydraulic systems. In the Delorean, one for the front and one for the back. Bleeding the rears has NO effect on the fronts and vice-versa. I prefer to start at the LF. Then I finish the front system by going to the RF. I proceed to the LR and finish with the RR. Then I go around and do it all again. In between each wheel I top off the master cylinder so I do not draw in any air and have to start all over again. You can do the rears first if you prefer but you do either both fronts and then both rears or the other way around so you do one system at a time.
David Teitelbaum

[Henrik]

Great info, everyone. Thanks.

Here is another thing I am wondering about: As I replace the brake hoses in all four corners I am obviously going to lose a lot of brake fluid being that I am working on the low points of the system. So, in the process, if the master cylinder ends up empty is there a separate process for bleeding it or will the power bleeder be able to purge the air out of it too?

[eagle-co94]

Not sure about that one, but whenever I do brake work I keep topping off the reservoir so I don't have to worry about getting air into the system. You'll notice you need to top off by the amount of fluid you're losing.

[Ron]

I have also seen where a hose fails and acts like a check valve locking a caliper to a rotor. The bleeding of the farthest point is a myth carried over from the early single braking system. In today's cars there are now TWO hydraulic systems. In the Delorean, one for the front and one for the back. Bleeding the rears has NO effect on the fronts and vice-versa. I prefer to start at the LF. Then I finish the front system by going to the RF. I proceed to the LR and finish with the RR. Then I go around and do it all again. In between each wheel I top off the master cylinder so I do not draw in any air and have to start all over again. You can do the rears first if you prefer but you do either both fronts and then both rears or the other way around so you do one system at a time.
David TeitelbaumNo, David...Think about what you just said, "carried over from the early single brake systems" and " today's cars there are now TWO hydraulic systems" -- So, for each of the two systems, it would still hold true! And, as I said, you do the rears first, for the reasons I said. Look up what can cause a proportioning valve to hang on some systems or why some people have trouble bleeding the rears and you will see. Bottom line is whether single, right hand, left hand , one stage, miuti-stage, you should bleed from longest to shortest (not necessarily back to front right to left, which is correct for a D), that way you cover all cases.

[STILL waiting on you to answer the question on the rectifier BTW. Sheesh!]


Great info, everyone. Thanks.

Here is another thing I am wondering about: As I replace the brake hoses in all four corners I am obviously going to lose a lot of brake fluid being that I am working on the low points of the system. So, in the process, if the master cylinder ends up empty is there a separate process for bleeding it or will the power bleeder be able to purge the air out of it too?
Buy a cheap pack of nipples to put over the lines as you go along, assuming you want to save new fluid in the lines (not worth the trouble to me, not to mention it is good to flush it all out).
David will probably tell you the master cylinder must always be bench bled, despite many others saying you dont (and are tired of even responding to it anymore) -- The power bleeder should take care of it -- Just remember, if you ever let the reservoir go dry, you MUST start the bleeding process all over.

[LEVY]

I have also seen where a hose fails and acts like a check valve locking a caliper to a rotor. The bleeding of the farthest point is a myth carried over...........
David Teitelbaum

The first part of your post is true and little hard to diagnose if you are not familiar with the brake system.

And for tye second part, no, is not a myth, you are terrible wrong on that, unless you have four separate systems, one for each wheel and activated by four individual pedals, on per whhel, then you need to follow Ron's instructions if you wanted to do it the right way.

LEVY

[Henrik]

Buy a cheap pack of nipples to put over the lines....

Great idea! Who sells them, what are they called etc?

[Ron]

Great idea! Who sells them, what are they called etc?Vacuum Line Caps. They come individual or in an assortment at most auto parts stores. I like those similar to those below because they are tapered and easy to get off. ( Those shaped like a baby bottle nipple are good for the CO hole too ;-)

17809

[David T]

On the Delorean there is no proportioning valve. The piping coming off of the master cylinder goes directly to tees, one for the front and one for the rear. The front system is independent from the rear except for the common reservoir. Bleeding one system has no effect on the other. It is that way on purpose. If you had a leak and were to lose one system the other will operate until you lost enough brake fluid to light the warning light. If you were to continue you could eventually lose enough brake fluid to lose the other working system. You should not have to bench bleed the master cylinder, it seems to only be necessary when first installing one, not if it should run dry. The plastic caps are a good idea to keep things from getting messy but even if you don't use them, you still have to remove all of the old fluid so it doesn't matter if you lose it. As for bleeding, it is a ritual and each person will have their own personal preferences on how to do it. On some cars it is very important to do it exactly as prescribed according to the manual. On a Delorean is is not so important as long as you bleed it enough to get all of the old fluid out and all of the air. As you can see, there are many ways to bleed and they all seem to work on a Delorean so it isn't so important the order. The Delorean has a VERY simple piping set-up.
David Teitelbaum

[LEVY]

On the Delorean there is no proportioning valve. The piping coming off of the master cylinder goes directly to tees, one for the front and one for the rear. The front system is independent from the rear except for the common reservoir. Bleeding one system has no effect on the other. It is that way on purpose. If you had a leak and were to lose one system the other will operate until you lost enough brake fluid to light the warning light. If you were to continue you could eventually lose enough brake fluid to lose the other working system. You should not have to bench bleed the master cylinder, it seems to only be necessary when first installing one, not if it should run dry. The plastic caps are a good idea to keep things from getting messy but even if you don't use them, you still have to remove all of the old fluid so it doesn't matter if you lose it. As for bleeding, it is a ritual and each person will have their own personal preferences on how to do it. On some cars it is very important to do it exactly as prescribed according to the manual. On a Delorean is is not so important as long as you bleed it enough to get all of the old fluid out and all of the air. As you can see, there are many ways to bleed and they all seem to work on a Delorean so it isn't so important the order. The Delorean has a VERY simple piping set-up.
David Teitelbaum

David, you are 100% wrong! You might not be right but you are always wrong.

When you have one pump with two separate systems, specially with no proportioning valve, air in one system may cause the other no to work at its full capacity, that is why you need to start from the fartest wheel. Manufacturers may help to soften this problem by adding some extra line on the closest wheel but still, an smart person should never start at the closest wheel

LEVY

[David T]

I guess we will just have to agree that we disagree on this. Try it both ways and see if it makes any difference. I have and I do it my way for simplicity. I have bled brake systems many different ways and they can all work except when it comes to ABS systems, they are VERY fussy about how they get done. The only way I WILL NOT use is using a vacuum bleeder. I will only bleed under positive pressure because the bleeder nipples will leak when using vacuum on them. I do not like pressure bleeders because most reservoirs are not made to handle pressure and they can explode. My favorite method is to use a "One Man" bleeder and use the brake pedal to pressurize the system. I can do it myself or if I have an assistant handy it just goes faster. Using a pressure bleeder is also inconvenient to refill the reservoir. You have to continually undo the connections to fill with fluid. The master cylinder is actually 2 separate pumping chambers with 2 pistons both actuated by the same rod. If one fails the other will still work. This was started back in the early '60's so a single failure would not cause a complete loss of all of the hydraulic service brakes. Very easy to identify, there is only 1 tube connected to the smaller master cylinder with tees for each wheel. It is true, once you lose one of the systems the braking will not be as good, especially if you lose the front which does a higher percentage of the braking anyway. That is why, if that brake waring light ever comes on, you had better stop the car as soon as you can! If the Delorean had a proportioning valve it would block off the leaking system. It doesn't. IMHO a major safety failure since most other cars of the era DID have them.
David Teitelbaum

[LEVY]

....If the Delorean had a proportioning valve it would block off the leaking system. It doesn't. IMHO a major safety failure since most other cars of the era DID have them.
David Teitelbaum

No proportioning valve would block a brake system in case of a leak, proportioning valve is there to limit the pressure to the front wheels in a pre-determined proportion, hence it's name "proportiining valve".

Vehicles equiped with rear mounted engine don't really need a proportioning valve, so it's not a safety failure at all!

LEVY

[David T]

Actually the valve commonly called a proportioning valve in most cars is really more than just a proportioning valve. There is a shuttle in it so when one system loses pressure the shuttle moves over to block it off and there is a switch inside that will light a warning light so you know there is a problem. Lotus Engineering did a fantastic job designing a car where they didn't need to fudge the brake system with a proportioning valve but it would have been nice for that safety feature of the shuttle. That way you wouldn't continue to lose brake fluid out a leak and compromise the still operating other system. The way they designed the system was to size the brakes so well that they didn't have to use a valve to do it.
David Teitelbaum

[LEVY]

Actually the valve commonly called a proportioning valve in most cars is really more than just a proportioning valve. There is a shuttle in it so when one system loses pressure the shuttle moves over to block it off and there is a switch inside that will light a warning light so you know there is a problem. Lotus Engineering did a fantastic job designing a car where they didn't need to fudge the brake system with a proportioning valve but it would have been nice for that safety feature of the shuttle. That way you wouldn't continue to lose brake fluid out a leak and compromise the still operating other system. The way they designed the system was to size the brakes so well that they didn't have to use a valve to do it.
David Teitelbaum

If your statements were true, you would never be able to bleed your system, think about it!

What happened to your quote: " I may not always be right, but I am never wrong" ?

LEVY

[DavidProehl]

A few weeks back some of us in the NCDMC club rebuild our member David P's brakes which had worked very poorly since he bought the car. We had trouble bleeding the rebuilt LR caliper, turns out the metal transfer tube on the caliper was clogged so essentially even with the cleaned pistons, new seals and pads, Daid only had 7/8th of his braking potential, we assumed it was the flex line too but we installed new stainless flex hoses too. With the tube all cleaned up they work great!

Just saw this thread and was going to share this story. Yeah, this happens! I can't believe I drove the car on the brakes I had. Looking back and comparing it to how it works now it was downright dangerous before. As everyone has said, replace your hoses while you are doing your brakes.

[David T]

Not too long ago I helped a local owner with his brakes. The car pulled to one side and didn't stop well. Once we took everything apart we found all of the pistons were stuck except ONE on the front!!!!! The hoses were also bad. Now he is very impressed with how straight and quickly it stops! As for bleeding procedures and proportioning valves, all I can say is we just don't agree about it and we are both entitled to our opinions. BTW, you should test the emergency brake once in a while just to make sure it works and the light comes on just in case you ever need it! Especially if you recently did any work on the service brakes.
David Teitelbaum

[MartyP]

Just saw this thread and was going to share this story. Yeah, this happens! I can't believe I drove the car on the brakes I had. Looking back and comparing it to how it works now it was downright dangerous before. As everyone has said, replace your hoses while you are doing your brakes.

Same thing for me, I drove a whole summer with only front brakes, as both rear hoses where plugged. So I changed all 4 hoses withy new stainless ones.

I noticed this when I changed the master cylinder that was leaking, and then tried to bleed the system and it wouldn't work, I even thought that the new master cylinder cylinder was faulty !!! But it was the rear rubber hoses.

[Henrik]

Same thing for me, I drove a whole summer with only front brakes, as both rear hoses where plugged. So I changed all 4 hoses....

So it appears that driving unknowingly without brakes on fewer than four wheels might be pretty common among D owners and that bleeding your brakes is a good tell-tale if that is the case. It's easy and quick so all owners really should make that a part of the annual check.

Anyway, four brake hoses from DMCH have been ordered.

[DCUK Martin]

All the time, most especially on cars that have been stored a long time. We consider replacing (original) hoses to be part of a brake hydraulic rebuild job.

Where's the "what he said" smiley these days?

New m/c, refurb callipers and new hoses is the single most common job I do.

FWIW I'm with David up to a point, on the DeLorean, it does not matter which corner you bleed first, but from bone dry, it is important to do the rears first because of the way the two chambers in the m/c work.

Taking the front and rear as two systems, if you'd like to explain to me how air can go from the longest to the shortest any more easily than from the shortest to the longest, you might convince me otherwise.