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Rear drum brake binding after front disc conversion


xychix

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Here's the easy way.

Put the cylinders on the back plates. 

On the bench, assemble the bottom spring in the shoes. 

Angle the slots in the cylinders slightly so you can place the tops of the shoes in them without locating the bottoms.

Place the bottom of one shoe in the bracket.

Put the top spring in one shoe, lever it over and onto the hole on the other. 

Using a lever (large, long screwdriver or similar will do), lever the bottom of the remaining shoe against the spring and you'll be able to locate it in the bottom carrying bracket. You can place the end of the lever against the hub and push against a flat portion of the curved part of the shoe that the friction material is bonded to. 

Job done, no bruised knuckles or swearing required :)

Edited by lo-fi
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1 hour ago, lo-fi said:

Here you go:

Apologies for the poor lighting and production quality. Hopefully you get the idea :)

Looks like a breeze indeed. Although I've pulled mine apart in order to get this topspring BEHIND the shoes hoping it would not pull the knob of the adjustment wheel.
Still have 2 to 3 strokes of the pedal left before I get proper pressure :(    even after dialing all 4 knobs to full shoes against the drum...

Will make a bigger bleed bottle and press a few liters trough...

Did pull the hub of, just as fast in the end. didn't manage to het the lower sprint in the top 2 holes, put it back in the 1 lower (where it sat). Although that could potentially cause brakes not retracting enough but never lack of pressure as far as I can guess...


... Just flushed ~1 liter (0.5 per side) trough with no difference. Time for a beer as it's 39C here... 

Edited by xychix
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bit fed up as I don't know what a good next step would be.

Clamping the hose gives a pedal (will retest this tomorrow)

Adjusting the pads against the drums, brake, adjust again. repeat a few times still gives me 2 pumps at least.
So the problem IS in the rear axle. (note that with the zeus discs at front and the defender 90 master it's closer to a defender as to a 109...)

One part tells me to do the following to the rear axle
- replace all bearings
- replace all seals
- replace slave cylinders
- replace pads
- maybe even replace drums.... but as I have 4 drums around from which 3 are looking quit OK that feels wasting money...
- replace all brake springs

this should essentially give me a new rear axle brake setup.....

(uploading a few pictures of the rear left in a minute) 

 

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Think about it methodically before firing the parts cannon at it.... 

It boils down to the rear taking more fluid (one way or another) than the master cylinder is designed for. 

I think (correct me if I'm wrong), "the master you've got now is designed for a disk front, drum rear?

Are you 100% certain the drums are in spec? It's quite possible to get the adjusters feeling like they're tight, but there being a long way to go until it's actually putting much braking effort in with the pedal, particularly if the drums are worn. 

If you've "pumped up" the brakes with a second movement of the pedal, if you let off, then immediately reapply the brakes, what happens? Do you get a firm pedal straight away, or do you have to pump again? 

If you bleed until you're confident there's no air in the rear, do you find air in the system if you bleed again after a drive? 

 

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56 minutes ago, lo-fi said:

Think about it methodically before firing the parts cannon at it.... 

It boils down to the rear taking more fluid (one way or another) than the master cylinder is designed for. 

 I think (correct me if I'm wrong), "the master you've got now is designed for a disk front, drum rear?

 Are you 100% certain the drums are in spec? It's quite possible to get the adjusters feeling like they're tight, but there being a long way to go until it's actually putting much braking effort in with the pedal, particularly if the drums are worn. 

 If you've "pumped up" the brakes with a second movement of the pedal, if you let off, then immediately reapply the brakes, what happens? Do you get a firm pedal straight away, or do you have to pump again? 

 If you bleed until you're confident there's no air in the rear, do you find air in the system if you bleed again after a drive? 

  

if I give it more than 2 seconds I'll have to do another double pump.
I've done the bleeding on my own this time with a hose in a half filles brake bottle and another half bottle to top up the reservoir.
Coulnd't find anyone willing to slam the brakes 92 times with 39Celcius outside (and likely hotter inside).
Also means I closed the nipple ~5 seconds after I let go of the pedal.

@arjan, flexhose is replaced.

Haha if I'm left with the only option do do a rear disc conversion as well I'll also have to slam a thick engine in.

Edited by xychix
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1 minute ago, xychix said:

yes, a zeus kit as in 1 order, new.

Try clamping the rear flexi hose gently and protect the rubber to prevent damage. This will isolate the fronts from the rears and you can see if pedal travel has improved or not, pointing you towards the problem.

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12 hours ago, Bigj66 said:

Try clamping the rear flexi hose gently and protect the rubber to prevent damage. This will isolate the fronts from the rears and you can see if pedal travel has improved or not, pointing you towards the problem.

Yeah did that already. With the rear axle shutdown there is perfect braking.

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10 hours ago, jordan_meakin said:

With this much trouble, I'd be reverting to original spec. - at least it'd be usable!!

Reason to go for the Zeus kit is because front also required a major overhaul.

And it's likely "just this one thing" thats needs sorting out to give good brakes.

Another option would be to place the pressure reducing dial in de rear pipe. That will likely cause the front brakes to be actuated earlier...
It's hard to believe that a wheel cylinder for a series (sIII  partno. 243296 / 243297, bore 31.8mm/1.25 inch) takes that much more fluid compared to a defender rear slave (partno. RTC3168 / RTC3169 bore 22,2 mm).

hmmm given the difference in bore there might be a substantial difference in fluiddisplacement...
Other option to try (as I've now swapped pipes, hoses and master all in one go) is to put back the series master cylinder which should have a bigger displacement.
let them feed the rear first (as it's no the current situation) and then pressurize the front (on which now substantial less fluid is needed). Biggest disadvantage on trying this is that i'd need to cut and reflare the pipes to do so... and potentially again to flip back to the def 90 master...


Crappy process to go trough but I should understand a fair deal on brake systems by the time it works.....

Good thing is they all use the same:
576973 (drums 11")
548169 (upper return spring)
RTC3418G (shoes axle set for rear)

I've gotten a defender 90 master NRC9529  (others in this field are the 110/130 NRC8690 and the 109 NRC6096)

From readings elsewhere I understand that the 90 might have a 60/40 bias to the front while the NRC8690 would have a 50/50. which would mean more fluid to the rear...? 

Edited by xychix
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Your springs should on the inside of the shoe pulling the side of the shoe onto the support points , and the nail is a big no - are you sure they are 109 rear cylinders ? They should be 1.250" . It looks to be leaking a little too - damp on spring and the dust cover .

 The adjuster snail should hit the stud on the shoe approximately on the centre line through the centre of the snail and the centre of the hub , there is a leading shoe and a trailing shoe as Red90 mentioned a few posts back .

The maximum oversize for 11" drums is 11.06" , worth checking considering your situation . 

 

cheers

Steve b

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2 hours ago, xychix said:

The promised picture of the 'nails' in my rear brake setup....

maybe a bush trick to make a 10" slave work in a 11" drum..... ? god knows...

109.thumb.jpg.52f83574d85fd38afda92117d393cdbc.jpg

I’d be taking those nails out sharpish if you’ve not already done so, that’s a bodge at best. The slave cylinder will need to match the drum diameter to allow the piston to move the shoe out far enough to make contact with the drum. If the shoes are correctly adjusted against the drum and the cylinder bled to remove air then the fluid displacement from the master cylinder should be enough to move the piston the required distance without the need for a second application of the pedal. Can you check visually with the drum removed and someone pressing the pedal gently? 

Without reading back through the entire thread, maybe you’ve already rectified and checked these things so apologies if you have. I’m not sure but I’m sure I’ve heard that the 10”SWB cylinders are smaller than the 11” LWB cylinders so if so, is there a chance the parts have been mixed? At least you know the problem is on the rears for sure 👍

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2 hours ago, Bigj66 said:

 

 Without reading back through the entire thread, maybe you’ve already rectified and checked these things so apologies if you have. I’m not sure but I’m sure I’ve heard that the 10”SWB cylinders are smaller than the 11” LWB cylinders so if so, is there a chance the parts have been mixed? At least you know the problem is on the rears for sure 👍

I'm not sure about any part on this vehicle besides stuff I've put on myself.

I've removed the nail as it seemed odd to me as well.
I've already got the spring to the inside of the shoes.
The lower spring is still in the wrong holes as it was impossible. Far to tight to fit on (not a bit tight but clearly impossible)

drums all read "max 11.06 inches", are you considering measuring this to determine if the drums are worn over that diameter?

Edited by xychix
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44 minutes ago, xychix said:

drums all read "max 11.06 inches", are you considering measuring this to determine if the drums are worn over that diameter?

Yes. I suspect you'll find them way out of spec. 

The springs must be in the correct holes. You won't stretch the bottom spring over with the shoes in place, you'll have to use the method either me or Gazza suggested. 

 

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1 hour ago, lo-fi said:

Yes. I suspect you'll find them way out of spec. 

The springs must be in the correct holes. You won't stretch the bottom spring over with the shoes in place, you'll have to use the method either me or Gazza suggested. 

 

yep, I took the hub off... spring counts 19 windings, will check with a new part to see if it's the correct spring fitted (no idea if there are multiple options).

Is there a method of measuring the drum diameter in a reliable way? or wil 'just a tapemeasure' be good enough? 
Finding the longest crossing with a tapemeasure I get to 27,8cm which converts to 10.94 inch.

Edited by xychix
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My point was that if say for instance you have the cylinder off a SWB drum but the drum off a LWB will the travel on a single pedal stroke of the SWB piston be enough to engage the shoe with the drum? I’m almost certain the cylinder and drum diameter are matched as is the master cylinder so maybe check to see if what you have is all compatible with each other irrespective of the front discs.

Others with more knowledge than me will have better information but it was just to carry out a sanity check of what you have fitted to eliminate a mismatch from the issue you are having.

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16 minutes ago, Bigj66 said:

My point was that if say for instance you have the cylinder off a SWB drum but the drum off a LWB will the travel on a single pedal stroke of the SWB piston be enough to engage the shoe with the drum? I’m almost certain the cylinder and drum diameter are matched as is the master cylinder so maybe check to see if what you have is all compatible with each other irrespective of the front discs.

 Others with more knowledge than me will have better information but it was just to carry out a sanity check of what you have fitted to eliminate a mismatch from the issue you are having.

I've just held on the drum 'half' with a bright lamp next to it and have an assistant slowly press the brake. On half a stroke the shoes seem both evenly seated against the drum and I can't turn the drum by hand anymore.

Will get the other rear wheel of again as well and do same sanity checks there. Also will remove the nails there and reset all springs in proper holes and on the proper side by removing the hubs.

Somehow it might come back to air trapped somewhere in the system.

question: is a brake pipe small enough to push bubble out while bleeding or can bubbles stay in corners on the pipes? (eg. is the fluid thick enough not to pass by an air bubble in the piping itself) (p.s. Using DOT 4) 

And thanks all for the support! That really helps a lot to force me to look at things again and again.

Edited by xychix
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I was so focussed on my clearly faulty / messed-up rear setup that I missed the point that when there is loads of air in the rear lines the master still should push trough and actuate the front brakes.
 
Did an extensive amount of bleeding and if I now brake with the proper intention to stop I feel the inner part of the master hitting the next and getting on the front brakes. So at least it stops, it stops that good that I can draw black lines on the tarmac.
If I do a few short pumps I can even get all 4 wheels blocking on gravel road. (especially driving backwards the difference with rear brakes after 2 short pumps and a proper pump is clear against only 1 proper stroke can be felt clearly. I assume that there’s not enough fluid for rear brakes as the master is a bore 25mm while the rear servo’s on a 109 normally are 33,2 mm bore).

This basically was the result of a chat with Drew from Landypoint.fr whom made me rethink the working of a proper seperated circuit system without faulty valves or other carp in between.

If 110 rear cylinders are same bore as 90 rear cylinders AND they fit a 109 backing plate that should pretty much match the master and allow for proper movement hence braking.
that would basically give me a defender 90 braking characteristic (yes I understand that wouldn
't be ideal for a 109 SIII station even though it will be empty in the back most of the time)

I've by now also understood that 110 slave cilinders won't match a 109 backing plate.
Edited by xychix
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Good lord.  Do you have the shoes assembled correctly yet?  Let's see a picture.

As mentioned earlier, install all the springs to the shoes with one upper end disconnected.  Put the assembly over the hub.   Connect the upper spring.  Now use a pry bar to get one shoe in place. Then switch to the other starting at the bottom.  A proper pry bar is all that is needed.  Make sure you understand the leading and trailing shoes per the pin location as detailed in my writeup.

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