No fluid to rear brakes after front to rear line change

No fluid to rear brakes after front to rear line change

Postby andyfanshawe [OP] » July 18th 2009, 11:44pm

Hi all.
Need some advice here.
1992 Astro 4 wheel anti lock.
Rusty front to rear 1/4" line, not leaking yet, brakes good, so decided to change. Made some up and reinstalled exactly as original.

Image
Image
Image

As you can see I reused the original factory connector under the firewall and joined to the ABS modulator using the original unions that were in excellent shape.

Time to bleed and finish off-just as i have done many times before. Phoenix injector down the master cylinder couldn't get any fluid to the under floor connector never mind to the rear brakes. Removed every connector one at a time in turn from the master cylinder down to the proportioning valve and to the ABS pump. Fluid coming out of every join. Fluid also coming out of the ABS where it goes out to the rear line. All okay there. Blocked lines then? No, both lines out and blew through with compressed air. Connected back up and no fluid flow.

Connected mityvac up at the connector under the firewall and started sucking. Vacuum at 23" Hg and holding. At the same time used the phoenix injector from the master cylinder, but still no flow. Now i know these are difficult to bleed sometimes, but this hard?

Any advice here?
I read a previous posting where someone left the lines open overnight and through the next day, and fluid appeared. Hmmm I wonder if its worth a try.

By the way, no idiot lights on, no ABS codes and everything working very well before the lines were removed and copied.

Thanks for any input.
Andy.
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Re: No fluid to rear brakes after front to rear line change

Postby astro355 » July 18th 2009, 11:55pm

I always gravity bleed the lines when I replace them. Make sure you have only one of the rear wheel cylinders open, not both. It makes it a lot harder if both wheel cylinders are open. Also, make sure the cover on the master cylinder is off and then make sure that the master cylinder does not run dry by adding fluid every 5 minutes or so.
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Re: No fluid to rear brakes after front to rear line change

Postby andyfanshawe [OP] » July 19th 2009, 12:43am

astro355 wrote:I always gravity bleed the lines when I replace them. Make sure you have only one of the rear wheel cylinders open, not both. It makes it a lot harder if both wheel cylinders are open. Also, make sure the cover on the master cylinder is off and then make sure that the master cylinder does not run dry by adding fluid every 5 minutes or so.


Thanks astro355.
I gravity bleed when I have plenty of time. For the other 99 times out of 100 (!!) I use a combo of methods. I was very surprised to say the least today when I couldn't get anything out. My thoughts at the moment are...If I can't suck it through or blow it through, how the hell can it gravity bleed???!!! But I need to put the fuel tank back and secure all the wiring etc, and change the fuel filter, so I'll let it go and see what happens.

Thanks for the response. Try again tomorrow.
Andy.
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Re: No fluid to rear brakes after front to rear line change

Postby astro355 » July 19th 2009, 12:47am

In dealing with ABS setups, they can cause problems when using a type of bleeding that involves pressure. I have seen a couple times when damaged occurred to ABS units when pressure was applied thru them.

Out of curiousity, what are those lines made of?
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Re: No fluid to rear brakes after front to rear line change

Postby 'cudapaul » July 19th 2009, 6:42am

In the pictures they look like soft copper. Big no-no! They need to be steel.

Might work in a pinch to get me home, but I ain't going to be driving it anywhere else!
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Re: No fluid to rear brakes after front to rear line change

Postby andyfanshawe [OP] » July 19th 2009, 9:07am

astro355 wrote:In dealing with ABS setups, they can cause problems when using a type of bleeding that involves pressure. I have seen a couple times when damaged occurred to ABS units when pressure was applied thru them.

Out of curiousity, what are those lines made of?


They are a copper/nickel alloy. These have been used in the UK for decades now. Every shop uses them. I've used them for the last 20 years at least. The front brake lines on my van are the same. No problems encountered at all. The original name way back in the day was kunifer 10, and probably still is. Revolutionised aftermarket lines.
Really surprised the shops in the states don't use them. Proven technology. No doubts about safety issues.

This is an interesting forum discussion
http://www.cobraclub.com/forum/general- ... nifer.html

I have certainly seen late model (not early) ABS pumps that have been damaged by pressure exerted the wrong way (ie pistons being pushed back in calipers) and causing damage because the fluid is under pressure going backwards. NEVER have I seen this the other way round. Obviously pressure is supplied through them anyway under normal braking. The standard practice in the UK now when pushing back pistons to replace pads is to clamp off the flexy line and crack open the bleed valve. This prevents any back flow of fluid.
The second biggest problem is the inversion of seals in the master cylinders when pushing fluid backwards. Many vauxhall cars (GM) encountered this.


Andy.
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Re: No fluid to rear brakes after front to rear line change

Postby astro355 » July 19th 2009, 10:01am

Where both rear wheel cylinders opened at the same time?

And there are some places in the states that use that line. Stainless has always been more popular for some reason.
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Re: No fluid to rear brakes after front to rear line change

Postby 'cudapaul » July 19th 2009, 3:55pm

You are correct, the Kunifer brake line is used by several large European OEM's, and aftermarket repair facililties.

One thing that I did run across is that splicing brake lines can be done but not with compression fittings. There are double flared fittings that are used to join two brake lines to prevent them from seperating under high hydraulic pressure, which looks like what you have in the picture.

My guess with the lack of brake fluid to the rear is something related to the ABS module. In the 92 I believe that it is located on the engine side of the firewall below the steering shaft. I have a service manual on the 91 which is most likely similar and I see if it offers any insights.
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Re: No fluid to rear brakes after front to rear line change

Postby astro355 » July 19th 2009, 8:21pm

When I replaced that brake line on my 89, it took a while for the fluid to get to the rear wheel cylinders. I opened the passenger side wheel cylinder only, ordered a pizza, topped off the reservoir and waited.
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Re: No fluid to rear brakes after front to rear line change

Postby andyfanshawe [OP] » July 20th 2009, 7:10pm

Thank you gentlemen who replied and offered advice.

Following advice given, I opened up the right rear bleed valve, topped up the master ctlinder and waited (no pizza this time though!)...............................................................

Image

1, 2, 3 hours and nothing, but the level had dropped in the reservoir.

So, I attached my mityvac vacuum pump, pumped the handle a few times and got it to 26" Hg! Never got the pump to do that before.

Image
That is one heck of a mighty pull I can tell ya! 30 minutes or so later and we have fluid flowing. A couple of careful slow presses of the pedal with the vacuum still there, and we have good flow. Repeat on the other side and we have fluid there as well. And air free!

So, my advice to all is to do what astro355 says and wait....patiently.....

Now I did fluid dynamics as part of my maths degree at university, but this is an interesting project. As cudapaul says (by the way thanks for the offer of looking in the shop manual) the restriction is in the ABS module. But why did the pressure bleeder not have much effect? Or even the vacuum pump at the same time? Well my lecturer wouldn't like this, but, the best way I can describe this is to compare it to thousands of people in a big room trying to get through a small door in a stampede and all pushing hard. Nobody gets through. But if they all go down to walking pace and not push, they will get through a lot quicker and easier :D Not very scientific I know but a good analogy I think!!

Anyway, the job is done and the van is back on the streets :rockon:

Image

Image

You guys are a pleasure to know. Thank you a lot for helping me out. i dont have to ask very often (been doing this too long), but we all need to at times, and it is fantastic to know the help is there if I need it! Even if I am thousands of miles away across the atlantic.

Now all i need to do is :layrubber:

Thanks.
Andy.
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Re: No fluid to rear brakes after front to rear line change

Postby astro355 » July 20th 2009, 9:33pm

I took fluid dynamics way back when I took my brake classes. This was a discussion in the brake class. I can't remember the reason behind it but it has something to do with atmospheric pressure and the valves in an ABS unit.

Good to hear that you got the fluid to flow.
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