Refitting twin leading shoes brakes

[jordan_meakin]

So the springs on these are tighter than a nuns whasname. Any tips?

I have been told bleeding can be an issue with the dual cylinders. Any advice?

[Bowie69]

Large screwdrivers and small mole grips

[steve b]

 I locate the shoe to the piston with the spring hooked on both ends then lever the other end into the slot using a thin flat lever ( screwdriver ) directly on the back of the other cylinder . Make sure the bleed nipple is in the top cylinder .

cheers

 

Steve b

[Snagger]

I did it the same way as Steve says -  hook the spring in, engage the shoe into the piston, then use a big screw driver to lever the other end of the shoe into the back of the opposite slave cylinder.  It's a good way to hurt your fingers, so wearing some rigger gloves or similar may prevent some injuries if anything slips.

I don't see any benefit in changing the pipe system to put the bleed in the top cylinder - the bleeding problems are that the ports in the front cylinders are at the sides, not the tops of each cylinder, trapping air above the ports (regardless of which port has the bleed) and the PDWA shuttle valve, which caused me to continue suffering significant bleeding problems after I converted to disc brakes on both axles.  There is no disadvantage to moving the bleed nipple to the top, but no advantage either, so it seems a pointless expense of a little time and money.

When bleeding these brakes you can minimise the air gap by bleeding before fitting the shoes (since they're already off) and clamping the pistons fully retracted, which is further in than the shoes will press them back.  The best results I could achieve were very good but took time: I stripped the hubs off the axle ends to remove the brake backplates complete with their cylinders and laid the plates flat with their pipe sides up so that the air pockets were against the internal ports.  Once bled, reassembly gave a wonderfully firm pedal.  Periodic fluid replacement was simple enough, but rebleeding after any disturbance to the hydraulics needed a repeat of that procedure.  A vacuum bleeder that attaches to the nipple and sucks the air out and fluid through would be far easier and should be as effective, if you can find one, and would deal better with the PDWA valve.

[jordan_meakin]

Sounds like I'm going to have finger ache and head ache with these...

[jordan_meakin]

Replaced a cylinder as it was leaking... Failed it's MOT on a fog light bulb (yes, that's right - I was so angry that they didn't just do it!! And, I didn't have a spare handy). But, had some advisories so thought I would "quickly" do these before retest for a clean sheet. Wow, one thing lead to another and have replaced a large part of the transmission. In the meantime, leaky wheel cylinder. A month later, I just want it back on the road!!!

[rtbarton]

1 hour ago, Snagger said:

I did it the same way as Steve says -  hook the spring in, engage the shoe into the piston, then use a big screw driver to lever the other end of the shoe into the back of the opposite slave cylinder.  It's a good way to hurt your fingers, so wearing some rigger gloves or similar may prevent some injuries if anything slips.

I don't see any benefit in changing the pipe system to put the bleed in the top cylinder - the bleeding problems are that the ports in the front cylinders are at the sides, not the tops of each cylinder, trapping air above the ports (regardless of which port has the bleed) and the PDWA shuttle valve, which caused me to continue suffering significant bleeding problems after I converted to disc brakes on both axles.  There is no disadvantage to moving the bleed nipple to the top, but no advantage either, so it seems a pointless expense of a little time and money.

When bleeding these brakes you can minimise the air gap by bleeding before fitting the shoes (since they're already off) and clamping the pistons fully retracted, which is further in than the shoes will press them back.  The best results I could achieve were very good but took time: I stripped the hubs off the axle ends to remove the brake backplates complete with their cylinders and laid the plates flat with their pipe sides up so that the air pockets were against the internal ports.  Once bled, reassembly gave a wonderfully firm pedal.  Periodic fluid replacement was simple enough, but rebleeding after any disturbance to the hydraulics needed a repeat of that procedure.  A vacuum bleeder that attaches to the nipple and sucks the air out and fluid through would be far easier and should be as effective, if you can find one, and would deal better with the PDWA valve.

100%  

I modified the pipes on mine to place the bleed screw at the top and it was more trouble than it's worth, the pipe bends into the pipe nuts are very tight.

I didn't have to go as far as removing the backplates, but if you press the pedal quickly any air will be pushed through due to the narrow pipes and surface tension of the fluid.  Also fluid will squirt around inside the slave cylinders and pick up any air and expel it through the bleed screws.  If you press the pedal slowly air will have chance to bubble back up the pipe.

If you look at the cylinders on the backplate they are set so that the bleed screws aren't at the highest point, if they were fitted a few degrees further round there would be no problem.

The PWDA wasn't a problem, I just ignored it until all the air was out.  To centre the switch plunger release one bleed screw and press the pedal slowly until the warning light goes out.  If it doesn't go out, tighten the bleed screw and loosen one on the other side of the vehicle and repeat the procedure.  You would normally have to open a bleed screw on the opposite side of the vehicle to the side you last bled.

[rtbarton]

laid the plates flat with their pipe sides up so that the air pockets were against the internal ports

I'm not convinced, IIRC the internal drilling connect the top of the cylinder to the upper port, which obviously has to be at right angles to go through the backplate.  I cut a slave cylinder in half along its length to show this, but it got thrown away when I had a clearout.  I'll see if I can get my hands on one and repeat the exercise, this time I'll take photos.

If I'm right laying the backplate down won't help, although removing the bolts and rotating it so the ports are at the highest point will, but I got a hard pedal without going to all that trouble.

[AV8R]

A fluid reservoir pressurizer works very well. This system puts pressure by pumping fresh brake fluid in the reservoir. As soon as a bleed screw is opened, fluid starts flowing taking air bubbles with it. The reservoir is constantly replenished from a 5 litre tank so never runs dry. Takes about 0,5 L to bleed 4 wheels. And just 20 minutes to do it.

Yes, I've got 11"TLS brakes on my 88. The 255/85R16 tyres enlarge the diameter quite a bit so larger brakes are a must.

Edited August 7, 2017 by AV8R

[jordan_meakin]

43 minutes ago, AV8R said:

A fluid reservoir pressurizer works very well. This system puts pressure by pumping fresh brake fluid in the reservoir. As soon as a bleed screw is opened, fluid starts flowing taking air bubbles with it. The reservoir is constantly replenished from a 5 litre tank so never runs dry. Takes about 0,5 L to bleed 4 wheels. And just 20 minutes to do it.

Yes, I've got 11"TLS brakes on my 88. The 255/85R16 tyres enlarge the diameter quite a bit so larger brakes are a must.

Are they mega money?

[Bowie69]

An eezibleed will basically do the same, just a smaller reservoir.

Around £15 and worth every penny.

[jordan_meakin]

Oh, I bought one of those in preparation. A Gunson one do hopefully decent!

[Snagger]

I always used an Ezybleed, and they are well worth the money, BUT you must keep checking the level in its can because if you let it run dry even for a moment, you have to start all over again.  I found with high pressure it was better at clearing trapped air than pedal pumping, as well as more convenient and allowing work alone, but it's far from a silver bullet.  The trouble is that British Leyland cut every penny they could, and that means that the pipe routing is for shortest pipes, not for best bleeding.  If you ever repipe the vehicle, it's best to have the pipes from the master cylinder enter the bottom of the PDWA body and the lines to the axles exit the top, so the air will rise with the bleed flow rather than fight against it.

The front cylinders on the twin leading shoe system are symmetrical left and right, but the top and bottom cylinders on a side are identical, just orientated 180 degrees differently..  That is why their unions are at the 3 or 9 o'clock position instead of the 12 o'clock - more penny pinching to buy in cheaper bulk of only two versions of the cylinder rather than four.  BL assembly lines had the advantage of vacuum bleeders, so they didn't have to worry about the inconvenience their designs caused.

[rtbarton]

These are 2 methods I used to retract the slave cylinder pistons.  You can see how the cylinders are just off the horizontal.

 

Similar tabs were fitted to the bottom of the shoes.

 

 

[rtbarton]

I fitted the PDWA to the bulkhead.

The pipes from the master cylinder went into the top of the PDWA, as they were more or less vertical any air just rose up into the MC and out through the resevoir.

 

[AV8R]

21 hours ago, jordan_meakin said:

Are they mega money?

Quite, I'm lucky to do the work on my 88 in a profesional garage.

[jordan_meakin]

Well, popped the shoes back on just now. I think I have given myself a hernia but there you go. Brake bleadage tomorrow! MOT Friday so could be cutting it fine if I can't get pressure...

[Snagger]

13 hours ago, rtbarton said:

I fitted the PDWA to the bulkhead.

The pipes from the master cylinder went into the top of the PDWA, as they were more or less vertical any air just rose up into the MC and out through the resevoir.

 

How do you fit the mud shield to the foot well with the lower brake pipes protruding through the plane of the foot well lower slope?  Standing the mud shield off with spacers would create the clearance, but doesn't that let the mud up from the tyres?  And what about protection of the pipes from stones if they are exposed there?  I suppose a notch in the mud shield and a rubber sheet cover would work quite well, and allow access to the lower unions without removing the mud shield...

To be honest, they're a damned nuisance, costly and next to useless.  They only activate for a large pressure differential, and only if in good condition; most will have rusted and seized.  A level sensor in the reservoir cap will give a much more reliable and earlier indication of a leak than this does.  I plan to remove it, eventually, as I think it does more harm than good in my 109.

[rtbarton]

I knew someone would ask that!

I completely reworked the way the front wings were fitted.  

https://www.flickr.com/photos/rtbcomp/albums/72157632392137762

Unfortunately due to personal circumstances the project had to be abandoned, but basically I arranged for the wing to be removed quickly so the inner wing would be fitted inside the outer wing all the way down to the bottom, and not fastened to the bulkhead.  There would be a large gap between inner wing and bulkhead to stop the buildup of water and dirt that inevitably collects there.  This arrangement would also protect the footwells from dirt thrown up by the wheels.

I agree about the PDWA, but I had one and it was virtually new so I fitted it.  You can get a switch that detects excessive pedal travel to warn of worn linings, that should also indicate a leak.

[Snagger]

Quick release wings would be nice, and Series wings were very wasteful in under-bonnet space; it's amazing how much more space a Defender has for washer bottles, header tanks, air filters and such like above those curved inner wheel arches.  Sounds like you had a good plan.  I'm sure Fridge would find a way to actuate it, outdoing Project Binky's front end!

[rtbarton]

It didn't stop there, I modified the tub & roof fixings too. The tub could be removed with one spanner and without getting hands dirty or disturbing the wiring or front seats.  I reckon I could remove both front wings, tub & roof in less than 30 mins (with the help of a hoist).  It had a military fuel tank which helped matters.  IIRC the front washer bottle was inside and the rear one at the back, so no long pipes.

[jordan_meakin]

Success on the MOT! The eezibleed worked really well, quite amazed. I did it once, then took for a spin with a variety of braking styles, bleed it again and all seems good. I may do it again soon but certainly good pressure and loads easier than the traditional method.

[steve b]

Good to hear Jordan , Pressure bleeding helps lots .

 

cheers

 

Steve b

[jordan_meakin]

Thanks for all the advice chaps!

[simonb]

Having just changed the front wheel cylinders this wknd (and not the first time I've had to do this), this is the method I use. My bleed nipples are as Land Rover intended,  i.e at the bottom.

1. Put the drums on, don't adjust the shoes yet.

2. Clamp rear brake hose at axle connection.

3. Clamp "other" front hose.

4. Make sure reservoir is full.

5. Attach bleed hose and crack off nipple.

6. Press brake pedal (by hand) rapidly down, half way and release , 3 times. Do the 3 pushes within a couple of seconds.

7. Tighten up nipple.

8. Top up reservoir - it should still be at least 3/4 full.

9. Repeat 5-8 again.

10. Adjust shoes.

If required, move clamp to other front wheel hose and repeat. Finally remove all hose clamps. You should have a rock hard pedal with very little travel before the shoes bite.

Brakes are inherently high pressure, but the actual volume and flow of fluid moved is small. As rtbarton mentioned further up this post:

"if you press the pedal quickly any air will be pushed through due to the narrow pipes and surface tension of the fluid.  Also fluid will squirt around inside the slave cylinders and pick up any air and expel it through the bleed screws.  If you press the pedal slowly air will have chance to bubble back up the pipe."

I found exactly this, slow pedal pumping won't shift the air as the flow is too slow/small. Rapid and repeated movements of the master cylinder, gets enough fluid moving quickly enough to expel the air. Ezibleed and vacuum bleeders work on the same principle - higher fluid flow to move the air (either using air or vacuum to move the fluid faster).

Edited November 6, 2017 by simonb