Jump to content

11" front brake bleeding improvements...


ejparrott

Recommended Posts

Am I right in thinking its generally considered a good move to modify the plumbing on 11" brakes to aid bleeding, by taking the fed from the flexi pipe to the bottom cylinder rather than the top, and then running a second copper pipe back to the top cylinder, with the nipple in that? As Kettle obviously needs some attention to her brakes, I thought it might be a good time to make mods!

Link to comment
Share on other sites

Apparently so,

Les Hanson recommends that approach. He has pictures somewhere on this site.

I've not done it on the 109, but will be doing it on the Station Wagon.

Mind you the brakes on the 109 are more than adequate as is - Some plonker pulled out in front of me when I had a full trailer load - he then stopped to turn right. I hit the brakes and I locked up all 8 wheels, not bad for 6 year old BritPart brakes!

G.

Link to comment
Share on other sites

It's not likely to do any harm as long as you make sure the extra lines are tucked neatly close to the swivel housing to protect them from impact damage and pinching by steering rods, but I can't see it being of any help at all. The problem with bleeding the front brakes is not the pipework itself - you will merely be adding to the total length by modifying it. The problem lies in the design of the slave cylinders; their pipe and bleed ports are half way up the sides of the cylinders rather than at the top, so any air above the ports tends to stay put. Making sure the pistons are fully retracted minimises the size of the air pocket. The only way of guaranteeing all air is removed is to either use a vacuum bleeder or remove the hubs and brake backplates from the swivels and bleed the brakes with the slave cylinders orientated so the pipe ports are at the top/

Link to comment
Share on other sites

The only way of guaranteeing all air is removed is to ..... remove the hubs and brake backplates from the swivels and bleed the brakes with the slave cylinders orientated so the pipe ports are at the top

Interesting idea...never thought of that!!

Link to comment
Share on other sites

It's a right pain to do it, though. It does make a small difference to the feel of the pedal, but isn't really necessary - you should be able to lock the brakes up having bled the fronts normally with the pistons fully retracted and clamped.

Link to comment
Share on other sites

  • 10 months later...

Gave the brakes a good service yesterday ready for MoT. Front n/s needed a new wheel cylinder at the top, but of course the pipes were stuck so I've ended up replacing both (good job I went to get some more brake pipe first...just in case!). As I'd got that much to do anyway I decided to re route the plumbing to put the bleed nipple in the top. It certainly does make it easier to access the nipple! Bit hair raising bending the bottom pipe for the straight fitting, which has the steering arm on the bottom of the hub right in the way, but we did it. The system is full of air, but I can't get the o/s nipple to release, so I'm going to get her in for MoT first, then I'll replumb that side the same and give it another go. At the moment she's pulling up dead straight, and she does still stop pretty quick so I'm happy. Last thing I want to be doing is fiddling and then rushing for the MoT.

Link to comment
Share on other sites

I did it the modified way (see here - http://www.retroanaconda.com/landrover/2010/04/rebuilding-the-axles-part-2/) when I put my 88" back together and found it very effective.

Had no issues bleeding them out from dry, just made sure the cylinders were fully retracted and it went through first time.

Les Henson states that he used a 90 mastercylinder, what is the advantage of this? Is it a straight swap for the original ?

Link to comment
Share on other sites

The 90 master creates higher pressure in the front circuit as it's designed to operate disc brakes. The rear circuit should operate normally. It firs the SIII servo without modification, but the trade off for higher pressures is less volume displacement. This will mean that less fluid is forced down into the slave cylinders, so you would have to be very careful about the accuracy and frequency of your brake adjustment or the front brakes will not move fare enough to apply real braking effort.

Link to comment
Share on other sites

The 90 master creates higher pressure in the front circuit as it's designed to operate disc brakes. The rear circuit should operate normally. It firs the SIII servo without modification, but the trade off for higher pressures is less volume displacement. This will mean that less fluid is forced down into the slave cylinders, so you would have to be very careful about the accuracy and frequency of your brake adjustment or the front brakes will not move fare enough to apply real braking effort.

Thanks for that

Link to comment
Share on other sites

clamping them is always a problem, the backs of the cylinders aren't flat or square. I usually put a strap round the shoes to hold the cylinders in.

i find a g clamp without the wobble plate/pad on the end of the screw helpful for this, the head of the clamp neatly hooks on the back of the piston leaving the screw to go down the bore of it, regardless of shape you can get good purchase this way

or using a small G clamp where the pad of the screw part will fit in the bore

Link to comment
Share on other sites

Well...what a game.... Turns Out I'd only got one skimpy g clamp afterall.

In the end I've spent this morning re piping the offside to match the nearside, and had to change the bottom cylinder due to stuck nipple and fitting. I've redone the adjustment again, completly, and bled about a litre of fluid through it, and just for a change I'v bled nearest to furthest. I think I've got a good pedal now, but I said that last week. Just got to pop her on the road and try them for real ( ahh the joys of living in a cul de sac!)

Link to comment
Share on other sites

"The problem with bleeding the front brakes is not the pipework itself - you will merely be adding to the total length by modifying it. The problem lies in the design of the slave cylinders; their pipe and bleed ports are half way up the sides of the cylinders rather than at the top, so any air above the ports tends to stay put."

You have an overly simplistic undertanding of hydraulics as you are only considering a static condition. Google 'Entrainment'. When you pump the pedal you achieve turbulent flow in the cylinder which mixes the oil and air drawing the bubbles out the port. The position of the bleed port in the cylinder is pretty academic.

The problem is because there is only so much fluid that can move with each pedal stroke. With the OEM routing the air may move out the top cylinder into the line leading to the bottom cylinder but may not get all the way through so when the pedal is released it makes its way back up to the top cylinder. Swapping the bleed nipple to the upper cylinder means that any air that gets shifted into the line will naturally make its way further through the system towards the bleed nipple.

Link to comment
Share on other sites

  • 2 weeks later...

I've been mulling over brake bleeding for weeks and in the end found the "clamps trick" on the web.

I haven't tried it it but the old girl is sitting on jacks, noise upwards, and I pulled the front linings (haven't figured out how to remove the rears yet) and cleaned the cylinders inside so they now slide okay (well I hope).

I don't know if the master cylinder is okay, and I'm considering a pressure bleeder.

Before splashing out coins tho, I'll give the clamps a try.

Link to comment
Share on other sites

"The problem with bleeding the front brakes is not the pipework itself - you will merely be adding to the total length by modifying it. The problem lies in the design of the slave cylinders; their pipe and bleed ports are half way up the sides of the cylinders rather than at the top, so any air above the ports tends to stay put."

You have an overly simplistic undertanding of hydraulics as you are only considering a static condition. Google 'Entrainment'. When you pump the pedal you achieve turbulent flow in the cylinder which mixes the oil and air drawing the bubbles out the port. The position of the bleed port in the cylinder is pretty academic.

The problem is because there is only so much fluid that can move with each pedal stroke. With the OEM routing the air may move out the top cylinder into the line leading to the bottom cylinder but may not get all the way through so when the pedal is released it makes its way back up to the top cylinder. Swapping the bleed nipple to the upper cylinder means that any air that gets shifted into the line will naturally make its way further through the system towards the bleed nipple.

I use a pressure bleeder. And my understanding of hydraulics is good enough - the amount of people I have helped with clutch problems, where they have been unable to properly bleed the system because they haven't elevated the nose of the vehicle to make sure the port end of the clutch slave is higher than the piston end because of trapped air testifies to that. Turbulent flow will clear some of that air, but not all of it.

A big problem with 109 and late 88 brake bleeding is the PDWA valve on the chassis - that creates all sorts of havoc. Even with the disc system fitted to my 109, the bleeding still took a long time and over five bottles of fluid through the Ezibleed for each end. For those rebuilding an entire brake system, I'd recommend removing that valve (it doesn't seal off a leaking circuit, it merely activates a warning light) and using the reservoir cap from a Defender or Discovery with a float sensor, which will detect slow leaks as well as big leaks, unlike the PDWA, which only triggers on big leaks.

Link to comment
Share on other sites

The flow will take care of it. On Land Rovers I've bled 101 brakes plus a few NADA 109 drums which are both the famous twin leading shoe design for the last decade or so using nothing more than the rerouted lines and pedal with never any hassle. I have also filled and bled the hydraulic system of a few hundred new build excavators/diggers using this method and the cooling oil in the APU generator on your beloved Boeing 737 is done this way too. Lets just say its a well known method in industry and having the bleed at the top isn't really a problem as long as you get the flow.

The simple solution to the PWDA valve is to let gravity run fluid through the system make sure you have fluid on both sides of the piston before applying pressure. Removing it as you say also works but if it ain't broke I don't fix it. You also have to be a little careful as in some locations such a mod from OEM can fail your inspection and, of course, insurance companies love to know about such changes.

Link to comment
Share on other sites

  • 3 weeks later...

I've had a lot of Land Rovers over the years and the brake bleeding issue has cropped up many times. A while back, someone told me the secret to bleeding the brakes easily and effectively and it's so effective you'll all want to laugh the first time you do it.

What you do is BACK OFF ALL THE ADJUSTERS before you start bleeding (really, counter-intuitive though it may seem, it's the right thing to do). Then, when you pump the pedal, you push a lot of fluid into the system, against a lot of springs. When you then open the bleeder nipple, all the cylinders work together and produce a huge rush of fluid, enough to push out those recalcitrant bits of air stuck in the slave cylinder's nooks and crannies. It absolutely works and has saved me much swearing and general bad-temperdness. Try it, much easier than rerouting pipework! Plus, it's not a bad thing to give the cylinders a long-travel workout out, nor to readjust the brakes regularly anyway.

Don

  • Like 1
Link to comment
Share on other sites

Yeah, adjustment is whats giving me problems at the moment! I've got all the air out, I'm pretty confident of that now, but we still have intermitent pulling, which only just passed the MoT. That I'm convinced is purely adjustment, but getting all 4 right without a rolling road is proving difficult

Link to comment
Share on other sites

Pulling is normally a sign of contamination, either from a leaking hub seal or from leaky brake cylinders. Temperature affects the friction/lubrication created by the contamination, so the pull will be intermittent with brake temperature, not just pedal force. I found once that a leaky cylinder and its resulting dirty contamination of the drums and shoes caused that side to be more effective than the clean side under light braking and cold temperatures, only becoming the more logical weaker side once hot or braking hard. I suspect there are other variables in there too, like drum and shoe condition, shoe material, fluid/oil specification and so on. It's only likely to be an adjustment issue if the brakes always pull squarely on a second pump at all temperatures and pressures - while the hydraulic pressure should distribute evenly to move all shoes into equal contact regardless of maladjustment, in practice the fluid flow rate is just a little restricted to a slack shoe and so the pressure on that side will take a brief moment to equalise with the opposite wheel.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...

Important Information

We use cookies to ensure you get the best experience. By using our website you agree to our Cookie Policy