Brake Bleeding

[mark030358]

Gents,
Have rebuilt front/rear calipers and servo. Initially power bled the brakes but the pedal was soft. Then bled manually, longest lengths first as usual. However, after bleeding and checking for absolutley no bubbles in the bleed tube the pedal needs two pumps to go hard. The first pump the pedal travels about an 1", the second pump maybe 0.5" and is hard. As the car is not yet on the road, before I box up the carbs etc does this seem correct to you elan drivers?

cheers
MArk

[Foxie]

Mark,

It does not seem correct, but it has been my experience. Despite much time and effort, replacement of components including new servo, and various dia master cylinders, I have not completely eliminated this problem. I have traced the long travel to the front calipers; cramp the flexibles to these and the pedal is absolute solid. I had observed that the seals pulls back the pistons a significant amount. I have got some improvement here by fitting piston return springs, available from Demon Tweeks. 4lb springs give an improvement, 7 lb give more, but with evidence of insufficient retraction i.e. contact on the discs, so I went back to 4lbs. I think a larger dia m/c in combination with a greater ratio servo would be eliminate this problem, but seems to be a serious fault, compared to all my 1980- 1990 3 series BMWs . Check that the servo is oriented to facilitate bleeding, and that there are no high loops in the piping

Connecting a Gunson eezi-bleed, and then bleeding manually using the pedal IMHO gives a very effective bleed.

Sean Murray

[steveww]

I have always found that after replacing lots of stuff in the brake system that bleeding can take some time. I think that tiny air bubbles tend to stick to the surface of the new components. Additionally if you have fitted new pads as well these tend to be springy until they bed in.

I bleed the system through the best I can then go for a gentle drive to bed in the pads etc. Then bleed the system again and this usually results in a firm pedal.

Other things to check include the brake pedal links as this does ware and become slack giving longer pedal travel. For a really firm pedal get rid of the servo but you will need to increase the cylinder ratio or build up your legs

[tdafforn]

I second SteveWW,
My own experience with newly rebuilt brake systems is that time needs to be given to let the system settle.
One trick that can work really well is to hold the system presurised with the brake pedal held down over night.
The other method I have used successfully (so much so that I use it as my standard brake bleeding method) is to connect a piece of tube long enough to stretch from the bleed screw to the master cylinder reservoir. Then open the bleed screw and pump the pedal for about 5 mins. The brake fluid recirculates so does not need replenishing, and the flow through the pipes dislodges the small bubbles. If the tube is clear it is quite an education to see bubbles flowing down the tube even after 3-4mins of pumping.
Hope this helps
Cheers
tim

[M100]

If you have removed all vacuum from the servo and then pump the pedal then it ought to be rock solid.

Tapping the caliper bodies with a hide mallet will disturb entrained air and ease bleeding although to be honest I've only had to do this on my Elise and 90's Elan and not my Sprint.

I'm suprised you are having problems though as when I do a fluid flush on the sprint before the winter layup I actually run air through the eazi-bleed to remove all traces of the old fluid, then fill the reservoir and eazi-bleed bottle and then pressure bleed with the occasional pump on the pedal - usually takes 15 mins or so from start to finish.

Are you closing the bleed screw part way on the downward stroke of the pedal while there is still flow out of the valve? (this eliminates any bleed pipe to bleed nipple to caliper body sealing issues)

I seem to recall there are also some issues with the master cylinder pushrod and its position when the pedal is released. I assume you haven't touched this?

[Alasdair]

Are the front calipers replaced the right way up, LH- RH with bleed screws at the top? If not, air will stay in the system and cause the situation described.

[mark030358]

Gents,
Thanks for the advice will get back to you after following up on the recommendations.

cheers
Mark

[AnthonyBelcher]

Are the front calipers replaced the right way up, LH- RH with bleed screws at the top? If not, air will stay in the system and cause the situation described.

Hi Alasdair'

Thank you for these few words that you posted in 2005 which I found yesterday over 8 years later. They helped tremendously as I had done everything trying to bleed my Elan brakes. It's the law of sod where there are only two ways the calipers fit and of course I chose the wrong one. Now swapped over and bleed first time perfectly.

Thanks again

Regards
Anthony

[billwill]

Brake bleeding was discussed recently in:
lotus-suspension-f42/exchanging-the-brake-servo-t29208.html

But we did not cover upside down calipers...

[Pistacchio sprint 72]

I second SteveWW,
The other method I have used successfully (so much so that I use it as my standard brake bleeding method) is to connect a piece of tube long enough to stretch from the bleed screw to the master cylinder reservoir. Then open the bleed screw and pump the pedal for about 5 mins. The brake fluid recirculates so does not need replenishing, and the flow through the pipes dislodges the small bubbles. If the tube is clear it is quite an education to see bubbles flowing down the tube even after 3-4mins of pumping.
Hope this helps
Cheers
tim

Well, if you have get rid of first of the old brake liquide... otherwise you will just mix the old one and the new one.

[billwill]

Yes, as I said in the other topic; if you are uncertain of the age of your brake fluid, just replace it all.

Nowadays in the UK you have to deposit old brake fluid in suitable containers at your local civic recycle centre.

Brake fluid is only supposed to be good for about 2 years. It absorbs water vapour that seeps in when you release the brakes. That can build up, then if you apply the brakes long & hard and get the callipers really hot, the water can boil out of the brake fluid as gas (water vapour). The gas is compressible and acts like you have air in the brake system. Very bad to find out when you are riding the brake down a very long hill or mountain.

I always carry a small container of brake fluid in the boot on long trips, just in case it might need topping up.

[Pistacchio sprint 72]

If it needs topping up, it means you have a leak somewhere... isn't it?
it means you re n trouble if on a long trip

[billwill]

If it needs topping up, it means you have a leak somewhere... isn't it?
it means you re n trouble if on a long trip

Yes, it does... Topping up is a get-you-home procedure. Though a very very small amount of fluid is left on cylinder walls when the pistons retract and be lost, so over a very long time the fluid level can drop. That's why we have reservoirs.

[oldelanman]

If it needs topping up, it means you have a leak somewhere... isn't it?
it means you re n trouble if on a long trip

Yes, it does... Topping up is a get-you-home procedure. Though a very very small amount of fluid is left on cylinder walls when the pistons retract and be lost, so over a very long time the fluid level can drop. That's why we have reservoirs.

The reservoir of fluid is there to accommodate brake pad wear, not to allow for leakage - there shouldn't be any!

[billwill]

If it needs topping up, it means you have a leak somewhere... isn't it?
it means you re n trouble if on a long trip

Yes, it does... Topping up is a get-you-home procedure. Though a very very small amount of fluid is left on cylinder walls when the pistons retract and be lost, so over a very long time the fluid level can drop. That's why we have reservoirs.

The reservoir of fluid is there to accommodate brake pad wear, not to allow for leakage - there shouldn't be any!

Aye, you are probably more correct than me on this one.