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Old 16-06-15
youcanlaugh youcanlaugh is offline
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Lightbulb How to repair a Faulty ABS / HBB Motor Pump on a Pajero / Montero / Shogun

The following is my account of what happened when my HBB/ABS unit failed on me and how I ended up repairing it. I detail how I diagnosed the problem and how I rectified it cheaply. I saved myself several thousand dollars doing this so I thought I'd share it in the hope that it may help somebody else who finds themselves in the same position. I don't warrant any of the procedures here and you carry them out at your own risk (sad that I feel I have to say this but I feel I should just to cover my own backside).

I'm not a registered mechanic, just someone who couldn't afford/refused to pay the AUD$3200 that Mitsubishi Australia were charging for a new ABS/HBB unit. I also didn't want to fit a second hand unit as the pump may have been in the same state as mine and, who knows, a pump failure could have been the reason why the vehicle was at the wreckers yard! :-)

UPDATE: I've since found out that you can purchase the lower motor assembly from Mitsubishi. Part number MN102843 (shown as 54242 in their diagrams, I will make a new post in this thread). Price in WA on 2/7/15 was AUD917.40

So, I was recently driving when suddenly all the brake warning lights lit up on my instrument panel and a loud electronic buzzer starting going off.

I pulled over and checked the obvious (brake fluid levels, fuses, connections) but nothing would stop this problem. I was only a few Km from my work unit so I started driving back slowly using the semi-auto gears to help brake the engine but after about 2Km I suffered what felt like complete brake failure. Thankfully there was nobody in front of me at the time. As the road had 2 lanes in my direction and most of the traffic was headed in the other direction, I drove the last Km back to the work unit using engine braking and the handbrake.

Even with my full weight pushing against the brake pedal, I was barely able to hold the car still when I put it in drive.

I had a look on Google and found similar stories and references to the ABS and the HBB (Hydraulic Brake Booster).

For all the procedures below, disconnect the battery.

I read that there were 2 relays (ABS Pump Motor Relays) that may cause this problem so I located them. They are in a little black box located near the Master Cylinder at the back of the engine bay on the drivers side. (My experience was in a right hand drive so there may be slight differences on the left hand drive). The box is black and has 2 brake signs in white with A and B printed above them.



Both of my relays were pink and had 4 pins each but I know some Mk3's have 1 pink 4 pin relay and 1 black 5 pin relay.

Looking at the wiring diagrams, I think they both serve the same purpose and both are used as SPST (Single Pole Single Throw) relays meaning that they use 4 wires each. One is a set of low ampage (in this case, connected to the ABS ECU-Engine Control Unit) and a high power side, providing a higher ampage to the electronic pump motor. By applying 12 volts across the low ampage side, the other side makes the connection and allows the higher power to flow.

If you're not familiar with relays, take a look now. They are used for things like headlights, horns etc where higher ampage is required.

The image below shows the 4 pin relay.




I have labeled the pins. 1 & 2 (The smaller pins) are the low ampage side. A & B (The larger pins) are the higher ampage side. So, if you apply 12v across pins 1 & 2, then A & B become connected allowing power to flow. Remove the 12v from pins 1 & 2 and A & B disconnect from each other.

To check them requires a simple multi-meter.

Switch your multi-meter to it's most sensitive resistance setting. It should read 1 when the multimeter leads are not touching each other. Touching the 2 multimeter leads together should give you a 0 reading, meaning a direct connection.

So, first off, remove the relay and connect one multimeter lead to pin A and the other multimeter lead to pin B. The multimeter reading should not change and should still read 1 (as there should not be a connection).

Next, connect one multimeter lead to pin 1 and the other multimeter lead to pin 2. There should be a reading slightly above 0. If it goes straight to 0, there is a problem as that means there is a short connection, which is what mine were reading. It pretty much means that the relay is fried and is just connecting pin 1 directly to pin 2.

The last test is slightly more complex. Connect the multimeter leads to A & B then connect pin 2 to the negative side of the car battery and pin 1 to the positive. You should hear a click and the multimeter should read 0 (or there abouts). When you remove the leads from the battery the multimeter should go back to 1 (showing that pins A & B have disconnected again). If this is the case, your relays are good and can be replaced.

Anyway, I checked my relays and found one of them to be faulty.


I managed to get one from a wreckers yard so I slotted that one in. I reconnected the battery and started the engine but I still had the buzzer and warning lights going off. I started checking connections and fuses and then noticed that the buzzer/lights had stopped. I wasn't happy as I hadn't really done anything specific to stop it but I decided that I would drive it home (at a time when there was very light traffic the next day) where I could have a better look. The next day, I started her up again (no warnings) so drove her home. I even stopped at the auto parts store and picked up a new set of front & rear pads and 2 litres of DOT4 brake fluid as I knew my pads were starting to wear thin and I was due a brake fluid change.

Got her into the garage and changed the front pads. No problems.

The next day, I started the first rear set of pads and noticed that I couldn't bleed the brakes so decided I needed to start the engine to get the booster working. The buzzer/warning lights were back. I tried to think what had happened and then realised that I hadn't heard the strange pump sound that I often heard when I first turn the ignition to On.

I read up a little and found that that Mk3 Pajero/Montero/Shogun uses an electric motor to pump fluid into an accumulator (a nitrogen filled canister). The idea is 2 fold. An electric booster takes up far less space than a conventional vaccum booster, plus it stores enough pressure to give you several boosted brake pedal pushes, even after the ignition is switched off.

Light bulb moment. The pump may have stopped pumping when I had the initial problem. That would have explained how I then made it about 2Km before I lost all brake boosting.

I located the pump. It is right under the HBB/ABS unit as shown below



I gave the motor a little tap with a hammer and it started turning followed about 30 seconds later by the buzzer stopping again. I'd located the problem!

So, how to repair the motor. You can't purchase the motor seperately. Oh no, that would be way too easy and cheap.

Mitsubishi only sell it as part of the entire HBB/ABS unit.

The first thing I did was email a couple of motor rewind companies to see whether anyone would even consider looking at it for me. One of the companies replied giving me the name of a guy about an hours drive away who actually specialises in automotive motor repairs (I didn't even know that was a full time job).

I phoned him and he was very helpful. He told me that he had repaired a 12v motor from a Prado the year before for AUD$280, although that motor needed everything replacing so mine may be cheaper.

I spent half a day trying to get the motor off the unit with the unit still in situ. Don't bother! It was a waste of time and I really should have just removed the entire unit from the get go. I also later found that there is a small circular disc between the motor and the pump that would have been pretty much impossible to put back in situ.

The next morning I started what I thought would be the huge chore of removing the entire HBB unit. It was surprisingly easy.

Here goes...

Before you do anything, disconnect the battery.

Next, put something under the unit so that any brake fluid doesn't drip onto the bodywork as it is highly corrosive and will eat through the paint in no time.

I suggest you also remove the air filter and casing to give yourself some more room. (I took a bit of time to think of this so you will still the air filter casing in position in some of the photos). It's just a case of removing the connection to the Throttle valve (after removing the 2 breather tubes) and then removing the the filter box itself (held by 3 bolts). I won't detail how to do it here as, if you can't get the air inlet off by yourself, then I really suggest you don't start playing with the brakes! ;-)




Pump the footbrake 40 times to remove all the pressure from the accumulator. If you don't do this, you may end up covered in brake fluid when you disconnect the brake lines.

Last but not least, have a cuppa tea to help start the job... (Hey, I'm English)

So first job is to disconnect the electric connectors from the HBB unit. There are 4 of them.




Now drain as much of the brake fluid out of the master cylinder reservoir as you can. I used my wife's turkey baster (hopefully she won't be reading this).

Next disconnect the 4 brake lines from the HBB.



I put paper in the holes in the master cylinder, and covered the exposed brake pipes with celophane wrapping (Gladwrap) and put a plastic sandwich bag over them, just to try and stop any dirt getting into them.



Next we need to disconnect the brake pedal from the HBB. For this you need to lie in the footwell and look at the foot pedal. The pedal is connected to the HBB by a snap pin (lock pin) and and clevis pin.

So remove the snap pin (below)



followed by the clevis pin







Now, while still under the dashboard, undo the 4 nuts that hold the HBB unit. You may want to support the HBB in the engine bay to stop it moving/falling and to help this process.



It's a tight queeze on one of the nuts. I used a little 1/4" ratchet with a small extension.

With the 4 nuts removed, you can move back to the engine bay and pull the HBB unit away from the bulkhead, being really careful not to damage the rubber boot or the brake lines.





There is a gasket and spacer on the bolts between the HBB and the bulkhead. Mine came off with the HBB and remained on the bolts. Just keep an eye on it to make sure it stays there.

With the HBB unit out of the car, place it on a clean protective surface. I used a heavy plastic bag to help catch any brake fluid.

Turn the HBB unit upside down and disconnect the motor cable from the HBB and then remove the 2 bolts holding the motor to the HBB unit



Watch out for the 5mm spacer/washer that fits between the motor and the pump. You'll be needing that/





That's the motor out...

You can open it up by removing the 2 bolts.

Here's what mine looked like



The casing was chock full of carbon dust. It's a surprise it could spin at all.



The motor was knackered. It needed a complete rewire, the bushes were worn down and needed replacing, the commutator had several sections missing (meaning that not all the wire would be magnetised) and the top bottom bearing was wobbly.

The guy I found fixed all of this for AUD$280. Very Happy!

Now to get it back on.

First reattach the motor to the pump (remembering to put the 5mm spacer/washer back in



At this stage, I tipped the HBB upside down to remove as much of the brake fluid from the reservoir as I could (just to help speed up the bleeding process later on).

Get the HBB back into position with the rubber boot going through the hole in the bulkhead (taking care not to damage the rubber boot or the brake lines).

Have a quick check from the footwell that the end of the HBB is sitting around the brake pedal correctly so we can fit the clevis pin again later.



Once it is in place, put something under the HBB unit to keep it in position to help ensure the 4 bolt stay firmly pressed through the bulkhead. This will make the next stepo a lot easier.

Get back into the footwell and replace the 4 nuts that hold the HBB in place. According to the workshop manual I found, the nuts are meant to be done up to a torque of 14+/-3Nm (124+/-26 "/lb). Good luck to you getting a torque wrench under there. I gave up and just did them up to what felt right.



Push the Clevis pin back through the brake pedal and secure it with the snap pin







Now, back in the engine bay, reattach the brake lines. Be very careful as it is easy to strip the screwthread in the master cylinder housing (as I almost found on one of my lines when it started going in at an angle). You'll feel when the screw is far enough in.






Reattach the 4 electrical connections (remembering to reattach the harness at the back of the unit.



Refill the reservoir with clean DOT3 or DOT4 brake fluid (I used DOT4). The DOT4 I used was a lot darker in colour than the stuff already in the reservoir which was handy as it was really easy to see when it was coming out at the nipple when I was bleeding the system.

Time to bleed the brakes.

The manual says to do it in this order:
Front brake lines (filling)
Accumulator (HBB)
rear brake lines (filling)
power supply (HBB)
ABS (HBB)
rear brake lines (bleeding)
front brake lines (bleeding)


Remember to constantly check the brake fluid level in the reservoir as you go.

I bled the front right, followed by the front left. (I continued bleeding it until the new brake fluid started coming out)

I then reconnected the battery turned the ignition to 'On' and was greeted with the sweet sound of the ABS pump motor going for about 30 seconds while it filled the accumulator. Once it had stopped, I slowly pumped the brake pedal a few times to fully fill the accumulator. (You need to continue slowly pumping the pedal if you notice air bubbles appearing in the master cylinder. I didn't have any bubbles)

I then did the 'power supply' step by doing the following:
1) Turned ignition off. Pressed brake pedal repeatedly until it went heavy (all power assistance gone=accumulator empty). About 40 presses
2) Turn ignition 'On' and quickly press the brake pedal about 20 times. Wait for the pump motor to stop (if it is going)
3) Turn ignition Off. Pressed brake pedal repeatedly until it went heavy (all power assistance gone=accumulator empty). About 40 presses
4) Turn ignition 'On'. Confirm that the motor starts and the manual reckons that the motor should stop in 25 seconds.

Mine took 35.
If it takes more than 25 seconds repeat steps 1-3.

I then rebled the front brakes (with ignition off)

I then bled the back brakes (with the ignition on)

All seemed fine, so I topped off the reservoir.


HOWEVER... I then started the engine and I found I had the anti-skid warning light was illuminated, as was the red brake watning light. I decided to go for a slow drive.

After a while, the anti-skid light went out, but the red brake warning light remained. I decided to continue to drive as I wanted to check the ABS.

As the ABS bleeding process requires the MUT-ii computer (and I didn't happen to have on lying around) I took the car out to a sandy bit of ground and drove around, braking hard to activate the ABS. All was good.

I came home and decided to recheck the ABS motor relays to see if that was my red brake warning light problem. Sure enough, although I had replaced one, the other one was also shot. I am guessing that they both shorted out when the pump stopped working.

PROBLEM FINDING A REPLACEMENT RELAY

At the time of writing, Mitsubishi wanted AUD$108.50 for a single relay plus they were going to have to order it in as they were out of stock. Let's face it, a relay should really be a $20 item.

To make matters worse, none of the wreckers yards I tried had one.

I started looking around the internet and discovered something very interesting. Basically, I found a photo of a Toyota Landcruiser (60, 75 & 80 series) headlight relay and it had the exact same fitting at the bottom except that it had a little plastic 'tower' coming out of the base which would stop it fitting into the Mitsubishi relay mount. I managed to find the spec was 12v/30A. Although I couldn't find what they Mitsubishi spec was, I reckoned it must be around the 30A level. I phoned a few wreckers yards but, once again, none of those relays around. I then phoned a Toyota dealer who had them in stock for AUD$54.

To cut a long story short, I went down and purchased it. Opened it up and it looks exactly the same inside. I cut off

the plastic 'tower'. It pushed it into place and it works like a dream.

I have made another post about the relay here: Replace Mitsubishi Pajero ABS Pump Motor Relay with Toyota Landcruiser 60,75,80 series Headlight relay


I hope this post helps someone out and saves them some money.

The costs involved at the time of doing this (June 2015 in Western Australia)

My total bill was:
Refurbish ABS Pump Motor: $280
1 x ABS Pump Motor Relay (from wreckers): $22
1 x ABS Pump Motor Relay (modified New Toyota relay) $54
Total: $356

Plus 2 Litres of DOT4 brake fluid and my time.


Mitsubishi new unit price would have been:
New ABS/HBB Unit $3200
2 x ABS Pump Motor Relays: $217
Total: $3417

I could have purchased a 2nd hand ABS unit from a wreckers yard for $990 but I wasn't happy with the idea of purchasing a unit that may have been just as bad as mine or, worse still, faulty and the reason that other car was at wreckers yard


So, a saving of $3061. Result!


If you notice any issues with this post, let me know and I'll update it as I searched all over but couldn't find a post showing how to do this repair so it really was a DIY job, but a very satisfying project.

The guy who refurbished the Pump Motor for me in Western Australia was Mark from T.k.f. Auto Rewind & Wholesale 0411 147 078. Really helpful guy.

Last edited by youcanlaugh; 07-08-15 at 03:28 PM.
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Old 16-06-15
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Don't think I will ever need to do this BUT what a great write up and tremendous step by step explanation of the process. Well done on taking the time and effort. I am sure someone will refer back to this one day and save them selves some dollars just as you have done.

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Old 16-06-15
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You Can .......................... yes good write up.
For those interested or have the need there are a few of these assemblies on Ebay at the moment for about $350 which is damn cheap.
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Old 16-06-15
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This is the ultimate sticky (gee that sounds dodgy) an absolute masterclass in a "how to" thread. Well done youcanlaugh having just gone through this exact problem in the past week, it will be super useful to others.
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Old 16-06-15
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My Paj is possibly heading this way. Not sure if it's the accumulator or motor and the workshop guys are just guessing as far as I can tell (at my expense).
This could potentially end up saving me a lot thanks.
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Old 16-06-15
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Fantastic write up mate. Job well done. Glad someone has finally found a place that will do this. With any luck it'll save someone else a couple grand in the future. Great work
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Old 16-06-15
RUGGA RUGGA is offline
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You SIR, are a dead set legend !!!

If someone askes you any time soon " What have you been up to? " you lookem straight in the eye and just say " nothing much OH THATS RIGHT, I JUST SAVED THE WORLD (for Gen 3 owners with the shitty HBB problem that could/should cost a kidney to fix). Many thanks from me and the many that will follow, undoubtedly. The number of brake units are only going to grow with age But there is now a (cheaper) light at the end of the tunnel......

Thanks
Mick

Last edited by RUGGA; 09-12-16 at 04:56 PM.
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Old 16-06-15
RUGGA RUGGA is offline
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Mate, I won't steal your thunder, why don't you link your relay thread here ( and vice versa ) also for future help so are easier to find. (Just a link, not merged)... Sorta, 2 birds with one stone....... Maybe add some tags too.. Ok, that's it from me.
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Old 16-06-15
youcanlaugh youcanlaugh is offline
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Thanks for the Thanks guys. Appreciate it.

Quote:
Originally Posted by RUGGA View Post
Mate, I won't steal your thunder, why don't you link your relay thread here ( and vice versa ) also for future help so are easier to find. (Just a link, not merged)... Sorta, 2 birds with one stone....... Maybe add some tags too.. Ok, that's it from me.
Rugga, must be a case of great minds. As I was writing it I just couldn't decide whether to write up about the relays in this post or to do it separately. I decided that, as I had done it, I would include it in here, but it was niggling me. What do you reckon? Just remove the part about the Toyota parts swap, or put the relay testing part in its own thread? I may re-read the whole thing in a day or two and try to decide then, but happy to hear your thoughts.
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Old 16-06-15
madspeed madspeed is offline
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excellent writeup. you could put the contact info for the motor rebuilder. My local rebuilder ( Canada ) quoted over $500 for the rebuild.
5 hours labor - $300
copper wire - 130
insulation 60
Bearings 50

total $540
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