Lotus Elan

Air in the brake system

PostPost by: elan+2s » Mon Sep 29, 2014 5:31 am

The restoration of the car was completed in 2013. Here, the entire brake system was overhauled. The brake booster and the master cylinder are new. The brake calipers were given new seals and pistons.

Now I have the problem that always accumulates in the air brake system.

The first time this happen before about 2 months. I drove a distance of about 200 km. Have parked with working brake the car. When I wanted to take the car again after a few days, I could brake pedal are pass to the ground plate.

After I bled the system then everything was fine again.

Yesterday happened again the same. I last drove the car a distance of about 50 km. Turned it off again with a working brake. When I wanted to use the car again yesterday, I could pedal depress again. I suspect that again is air in the system.

Has anyone of you ever had a similar problem? I've checked all cables and brake components of leakage. There is nothing to see. Everything is dry.

How can the air get into the brake system?
I need your help.

Regards
Egbert
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PostPost by: Elanconvert » Mon Sep 29, 2014 7:45 am

hello egbert
I am no expert, but it sounds to me like a leak of fluid....if it was air in the system you would have a spongy brake pedal......I would check all unions, pipes etc.......sometimes fluid will only leak while the system is under pressure [being used], so there will be no evidence once the car is at a standstill......fluid can also leak into body cavities, annd stay there

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PostPost by: robertverhey » Mon Sep 29, 2014 9:17 am

Any evidence of external fluid leakage at any of the brake pipe unions? Or leakage into the booster vacuum chamber or back up the master cylinder pushrod? When you bleed the brakes, is air evident in the same outlet (ie caliper) each time (irrespective of the order you bleed them in)? Just trying to narrow down the location of the fault....
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PostPost by: robertverhey » Mon Sep 29, 2014 9:17 am

(Duplicate)
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PostPost by: gus » Mon Sep 29, 2014 2:12 pm

first I would suspect the booster, as it is one of the few places fluid can 'disappear'

next the master. sometimes a small flaw can cause fluid to weep when static, but it will work well under pressure.

look for fluid in the carpet.

'usually' dead calipers stay dead
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PostPost by: Spyder fan » Mon Sep 29, 2014 5:56 pm

If no loss of fluid, suspect master cylinder faulty. Sometimes the seals are faulty allowing fluid to bypass, quite often new cylinders are not assembled correctly or there are foreign bodies, bits of seal inside that allow the fluid to get past the seal and make your pedal go to the floor.

If you can push your pedal all the way to the floor, but then next push its all back where it should be and continues to work properly without the pedal becoming spongy if you wait a few minutes then you have a fault in the master cylinder and not air in the system.
Kindest regards

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PostPost by: au-yt » Tue Sep 30, 2014 9:10 am

One key thing with bleeding brakes, don't push the pedal to the floor it uncovers the fill port and lets air in. I was advised to put a 2" thick piece of wood behind the pedal.
The booster needs to be tilted diaphragm down to let the air go to the back of the piston so it bleeds out. In fact the guys in the brake shop who told me this said they didn't need to bleed the whole system just the lines to the booster when they changed a booster.
Keep us informed of what you find.

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PostPost by: elan+2s » Tue Sep 30, 2014 9:15 am

hello,

I thank you for your answers.
Before I pursue the various theories, I'll bleed the system again. I have today ordered to a Eezi-bleed device in order to vent the system with pressure.
So far I've worked with a vacuum device that sucks the brake fluid at the bleeder screws. I'm in the method not quite sure whether air is drawn in at the threads of the bleeder screws over and thus the vacuum does not arrive where he is.

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PostPost by: rgh0 » Tue Sep 30, 2014 12:18 pm

au-yt wrote:One key thing with bleeding brakes, don't push the pedal to the floor it uncovers the fill port and lets air in. I was advised to put a 2" thick piece of wood behind the pedal.
The booster needs to be tilted diaphragm down to let the air go to the back of the piston so it bleeds out. In fact the guys in the brake shop who told me this said they didn't need to bleed the whole system just the lines to the booster when they changed a booster.
Keep us informed of what you find.

Graeme


Graeme I don't know what you mean by the "fill port" and "lets air in". If you mean the port to the fluid reservoir that is at the end of the cylinder for the single Girling master cylinder and sealed with a valve when the cylinder pedal is pushed. I don't know the details of the dual Girling master cylinders as I have never pulled one apart -- they may have a side port arrangement for the second cylinder but in either case it does not let air in just connects to the brake fluid reservoir

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PostPost by: au-yt » Wed Oct 01, 2014 10:43 pm

Hi Rohan
The wording I used was quote from the guys at the brake and clutch place.
The words about not pushing the pedal to the floor is also in the Lotus Workshop manual.

Cheers
Graeme
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PostPost by: robertverhey » Thu Oct 02, 2014 12:23 pm

Now I just had to follow this up because like Rohan I've been scratching my head about how air could get into the cylinder due to pushing the piston too far.

Sure enough, the factory manual does say this, but it specifically applies to tandem cylinders, not to the trusty old single circuit girling cylinder.

R
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PostPost by: au-yt » Thu Oct 02, 2014 10:03 pm

Point taken, more head scratching needed!
I must admit for a such a simple system lots of people myself included have had problems getting the brakes bled.
One idea I read and tried was to run a tube from the bleeder valve to the master cylinder and circulate the fluid. Little trick with this use plumbers tape on the bleeder thread, stops the air getting past the threads as you pump the pedal.
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PostPost by: PeterK » Fri Oct 03, 2014 6:20 am

Plumbers' tape (PTFE) on the threads of the bleeder valve is useful, especially when using any vacuum device. Not sure that I would recirculate my brake fluid back into the master cylinder though - it will be aerated, which kind of defeats things..
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PostPost by: alan » Fri Oct 03, 2014 6:37 am

au-yt wrote:Hi Rohan
The wording I used was quote from the guys at the brake and clutch place.
The words about not pushing the pedal to the floor is also in the Lotus Workshop manual.

Cheers
Graeme

i've always pushed the pedal to the floor maxi when bleeding brake and no problems :?
Alan.B
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PostPost by: oldchieft » Fri Oct 03, 2014 11:03 am

Covered in this post
lotus-talk-f50/changing-brake-fluid-t32028.html

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