TR2/3/3A TR3A - Gravity Bleeding???

lbcs_r_fun · May 5, 2011

We have now finished replacing the brake and clutch hydraulic systems on our TR3A project. We replaced just about everything, including lines, unions, master cylinders, fluid reservoir, wheel cylinders and the calipers were re-built. We even did a leak-down test with dry shop air.

Last night we filled the reservoir (new) with Dot 5 and started bleeding (conventional two person method). Before we started bleeding we waited a couple of hours to allow for some of the air bubbles to escape from the reservoir. Starting with the furthest wheel cylinder, we bled the rear brakes and got lots of air out of the system. We continued with the front calipers and did the driver side first, OK. When we got to the passenger side caliper, we hit a snag. No matter how many times we went through the bleeding process (three reservoir refills) we continued to see air bubbles. It seemed as though we were introducing air back into the system. No clue how this could happen unless the M/C seal was leaking! Throughout the process we had a third helper monitoring the fluid level in the reservoir. It never got below one third full.

So, we are sitting here scratching our heads! So, before we invest in a fancy pressure bleeder, "Speed Bleeders" or other fancy gadgets, what about "gravity bleeding". The posts I have read on the various motor-head websites indicate that this is a very effective method, particularly when the conventional two-person method fails. Has anyone tried gravity bleeding their TR?

Thanks in advance!

T

tdskip · May 5, 2011

Everything is tight and no leaks anywhere? Bleeding with DOT5 is a bit more tricky than conventional (still worth the effort but reasonable people differ here) but you shouldn't need a different approach.

What bleed nipples are you using?

Are the nipples new and have thread sealant on then?

Are you using smooth brake application strokes and being gentle when pouring the DOT5 in?

Are you sure the air bubbles are coming from the lines and not sneaking in from the hose you put on the bled nipples?

Gravity bleeding can work OK on clutch lines - in fact just did this on the Bugeye and it worked great - but doubt it will help too much on the brakes.

TomMull · May 5, 2011

T,
I've done gravity bleeding successfully on the clutch (no helper available), I just loosened the bleeder screw and let it drip with no hose to pot of fluid even. I know logic would allow air to come in as fluid ran out but it didn't. I've never tried it on the brakes but I tend to think it would be more difficult because of long horizontal runs. If you haven't already, I try conventional two person bleeding with a hose into the pot of fluid and, of course, check for leaks.
I also assume you've read the post on master cylinders above.
It seems unlikely that the MC would cause air infiltration to one side only, but who knows.
If everything is working properly, it's my experience that vacuum or pressure bleeding is not necessary, although the equipment has become quite cheap.
Tom

Don Elliott · May 5, 2011

Once you have the car on the road, try the brakes. You may have to pump them. This will tell you more. I'm sure you have lots of other details that you know you can complete and let this one be one of the many prototype de-bugging items you must leave on your list till you can find the proper solution.

TRDejaVu · May 5, 2011

tdskip said:
... Are the nipples new and have thread sealant on then?

Slight thread hijack.

Up until now I have always fitted bleed nipples clean. Wouldn't a sealant harden and cause a problem with future removal?

If not, I have to bleed the Jag brakes this weekend; what sealant should I use for a brake bleed nipple?

DNK · May 5, 2011

Speed Bleeders have something on them

TomMull · May 5, 2011

I don't think thread sealant on bleed nipples is of any benefit. The seal should be at the tapered base, not the threads. Further, most thread sealant is for one time use, repeated bleeding after setting up will negate any benefit. My 2p. Tom

lbcs_r_fun · May 5, 2011

lbcs_r_fun said:
We have now finished replacing the brake and clutch hydraulic systems on our TR3A project. We replaced just about everything, including lines, unions, master cylinders, fluid reservoir, wheel cylinders and the calipers were re-built. We even did a leak-down test with dry shop air.

Last night we filled the reservoir (new) with Dot 5 and started bleeding (conventional two person method). Before we started bleeding we waited a couple of hours to allow for some of the air bubbles to escape from the reservoir. Starting with the furthest wheel cylinder, we bled the rear brakes and got lots of air out of the system. We continued with the front calipers and did the driver side first, OK. When we got to the passenger side caliper, we hit a snag. No matter how many times we went through the bleeding process (three reservoir refills) we continued to see air bubbles. It seemed as though we were introducing air back into the system. No clue how this could happen unless the M/C seal was leaking! Throughout the process we had a third helper monitoring the fluid level in the reservoir. It never got below one third full.

So, we are sitting here scratching our heads! So, before we invest in a fancy pressure bleeder, "Speed Bleeders" or other fancy gadgets, what about "gravity bleeding". The posts I have read on the various motor-head websites indicate that this is a very effective method, particularly when the conventional two-person method fails. Has anyone tried gravity bleeding their TR?

Thanks in advance!

T

Gee, after reading all of the comments, a light bulb went off!
Regarding gravity bleeding, at least, would the restrictor valve in the TR3A hydraulic circuit make gravity bleeding impossible?

Any thoughts?

To answer a few questions:
What bleed nipples are you using?
Those that came with the new wheel cylinders and rebuilt calipers.

Are the nipples new and have thread sealant on then?
Yes. Everything is brand new.

Are you using smooth brake application strokes and being gentle when pouring the DOT5 in?
Yes. In fact almost to a point of being funny!

Are you sure the air bubbles are coming from the lines and not sneaking in from the hose you put on the bled nipples?
I personally was the one operating the brake pedal and did not see what was happening at the bleed nipple, but my partner is very experienced at this. 

Next chance at trying this will be tomorrow. We have access to a pressure bleeder and will try that. We're keeping our fingers crossed! :eeek:

TR3driver · May 5, 2011

lbcs_r_fun said:
Regarding gravity bleeding, at least, would the restrictor valve in the TR3A hydraulic circuit make gravity bleeding impossible?

Probably. But I disabled mine, as I don't like having the brakes drag all the time. And so when I tried gravity bleeding my TR3 for the first time last year, it worked great. Much easier than roping the wife into helping

TR3driver · May 5, 2011

TRDejaVu said:
If not, I have to bleed the Jag brakes this weekend; what sealant should I use for a brake bleed nipple?

No sealant IMO. As noted, the threads do not seal, the seal is at the tip of the bleeder.

But a small amount of anti-seize would be a good idea, IMO.

sp53 · May 5, 2011

Do a little more gravity bleeding and then drive it. Some say that the dot 5 gives a spongy pedal so be aware of that. I have dot 5 in a tr3 and I do think it might be a little spongier, but i think the clutch works better.
Steve

JohnnyMead · May 6, 2011

TomMull said:
T,
I've done gravity bleeding successfully on the clutch (no helper available), I just loosened the bleeder screw and let it drip with no hose to pot of fluid even. I know logic would allow air to come in as fluid ran out but it didn't.

Tom,
How long do you let the fluid drip?
This sounds like a good application for clutches in that the system is short and vertical.
John

Geo Hahn · May 6, 2011

TomMull said:
I don't think thread sealant on bleed nipples is of any benefit. The seal should be at the tapered base, not the threads...

I think the idea of sealant on the threads is to prevent air from sneaking past them whilst the bleeding process is going on. If air can slip back in on the up stroke, then the down stroke will continue to present air bubbles ad infinitum.

I avoid this by closing the bleeder for each up stroke rather than relying on the threads and hose to be air-tight.

lbcs_r_fun · May 6, 2011

We want to thank everyone for their suggestions. Late today we finally got the last bit of air out of the driver side caliper/line. We did this with a makeshift pressure bleeder and 5 psi shop air. Never was able to use gravity bleeding due to the restrictor. Nice solid pedal (for Dot 5)! :banana:

T

svtmikey · May 7, 2011

Just wanted to make a few comments, since I just wrote my ASE (A5) braking systems exam last Thursday....of course I don't know if I passed yet, but I did study a bit for it and this stuff is fresh in my mind....tommorrow it will be gone!!!
There should be no difference between Dot3, 4, 5, or 5.1 as far as pedal feel goes. They are all fluids, and you can't compress fluids....that's why we use them to transfer force in hydraulic systems like brakes and and car lifts etc.
If you have a spongy pedal...it will be becuase of air in the system.
Dot 5 is not really any different to bleed than DOT 3 or 4 either. The only thing you need to watch out for is that 5 tends to aerate a bit more, so if you are power bleeding you need to watch the pressure a bit. If you are pedal bleeding 5 they recommend you push the pedal, close the bleeder and wait 15 secs to allow the microscopic air bubbles to form into larger bubbles that are easier to bleeded out(never done this myself). I usually use a suction bleeder anyway just becase it is easier, speed bleeders are great as well.
Also becuase it does aerate, DOT 5 should never be used in anti lock systems...not a problem with our cars, but I have heard a lot of people wanting to put 5 in their modern cars because it won't hurt the paint and is not hydroscopic (absorbs water).....definitely a no, no though.

Mikey

TR3driver · May 7, 2011

svtmikey said:
They are all fluids, and you can't compress fluids

Not true. Everything is compressible to some extent, even steel. And DOT 5 is slightly more compressible than DOT 3/4/5.1, particularly at high temperatures.

Don Elliott · May 8, 2011

In 2001, I drove my 1958 TR3A 2400 miles from Montreal to VTR in Breckenridge Colorado. For at least two years before that my brakes were rock solid with no sponginess. I had been using purple silicone brake fluid in the system for over 10 years by that time. I drove over Estes Pass (Altitude 12,095 feet) and stayed above 10,000 ft altitudue for over a week. Day after day my brakes got spongier and spongier till about the 5th or 6th day, I had to start pumping the brake pedal one full push or more before I could get any stopping power.

At that altitude, the included air in the silicone brake fluid which had had no issues at sea level, must have come out of solution and with the help of a TR friend from Ohio, we bled the brake lines. All kinds of bubbles came out. When there were no more bubbles, we considered the problem resolved. For the rest of my stay at VTR and since then, 10 years later, I have never had to bleed the brakes again

svtmikey · May 8, 2011

Wow..this is like a homework assignment.

If you just want to be right, then OK....you are correct.

In fact everything is compressible with enough force, but we are talking about brake systems in the real world.

It's funny, I had the exact same arguement with my instructor and still got the question on the exam wrong.

In the "real world" however, when talking about brakes, you are simply not going to get those pressures and temperatures.

First, Automotive Technology: Principles, Diagnosis, and Service by J.D. Halderman states: "Hydraulic systems use liquids to transmit motion. For all practical purposes, a liquid cannot be compressed.".

Also, although Pascal’s Law states that “when force is applied to a liquid confined in a container or an enclosure, the pressure is transmitted equal and undiminished in every direction", you are not going to feel a 3.6% compression of the fluid in you brake pedal since the multiplication of force is going from the Master cylinder to the brake cylinder, not the other way.

Added to this is the fact that brake fluid temperatures should never reach 600F, and again the chart is misleading.

Remember, the DOT and SAE have established brake fluid standards and the "Dry boiling point" of DOT 3 is 401F (wet is 285F), with DOT 5 being 500F (dry) and 356F (wet), well below the 600F in the chart.

As well, the text book states: "During a standard brake system test, a vehicle is braked at this rate 15 times. Temperatures at the front brake pads can reach 1300°F (700°C) or higher, sometimes reaching as high as 1800°F (980°C). Brake fluid and rubber components may reach 300°F (150°C) or higher.", so your brake fluid would never have reached the temps in your chart anyway....in the real world that is.

So yes you are correct in theory and on paper, but in the real world we still got marked wrong on the exam, and you still hit the tree!

Don, you are absolutly correct, (above book also states) "DOT 5 brake fluid has been known to create a braking problem during high-altitude (over 5,000 ft [1,500 m]) and high-temperature driving. The high altitude tends to vaporize (off-gassing) some parts of the liquid, creating bubbles in the brake system, similar to having air in the brake system."

Mikey

TR3driver · May 8, 2011

Suit yourself, Mikey. But sometimes the text books are simply wrong. Agreed, the pressures and temperatures given are extreme limits, but both do happen in "real world" driving. In fact, that chart was taken from a report on "real world" testing of production cars descending from mountain passes, and they did have failures due to both boiling and lack of travel (due to compressibility).

I haven't been to any Alpine passes yet, but there are some pretty high ones around here, and I do enjoy driving my TR hard on mountain roads. If you look close at Don's photo above, it reads "Elevation 11542 ft", and I've been there several times.

But even using your book's value of 300F, and 800 psi (which is a reasonable pressure for a panic stop with cool brakes), the chart gives a compression of 1%, which seems worth considering to me.

Check out Nelson's article, where he first predicted the extra pedal travel due to DOT 5 compressibility, and then measured it on his own car.
https://www.buckeyetriumphs.org/technical/Brakes/Fluid/Fluid.htm

Oh, one other point, the SAE only specifies minimum boiling point under specific test conditions. That doesn't mean the fluid will always boil at exactly that temperature. Thus, for example, there are many racing fluids around that are rated DOT 4, but don't actually boil until well past 500F (when dry). The "wet" test points are also rather optimistic; G.R. Browning reported finding cars in service with water contents as high as 6.7% water in the brake fluid (and corresponding boiling point of 260F).

svtmikey · May 10, 2011

Boy to did ever highjack this thread with our "theoretical tomatoe throwing"

My apologies to lbcs r fun!!!

None of this is helping him with his problem.

I am a bit embarassed to ask this, since it should have been the first thing I asked.....did you bench bleed the master cylinder BEFORE you installed it.

If you did not, you will have an extremely hard time getting all the air out no matter how you try to bleed the system.
I would bet that is your problem, not the baloney we have been talking about.

Sorry,

Mikey

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TR2/3/3A TR3A - Gravity Bleeding???

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