Dexter brake unit

[Nude up]

As I returned from bermagui recently it was evident my dexter brake unit was not working. A few basic checks power and signal from the car all good. Power to the electric motor driven pump good but not turn.
Having time on my hands and the replacement cost of around $1200 nothing to lose I pulled it apart. No rocket science inside.

There is the upper chamber which is the reservoir and the lower chamber held a circuit board elec motor connected to a pump and the proportional valve.
I removed the elec motor from the pump and found the pump seized. With no manual to work with I disassembled the pump. It's a Parker 3 piston cartridge pump and one of the piston had popped out of the housing and jammed the pump

With the aid of some wet and dry to remove a few burrs I have managed to reassemble the pump which now rotates freely.

So tomorrow I will reassemble the whole unit and try it out. I have also emailed Parker to try and get a replacement cartridge if it fails.

[barra mick]

Nice work nude up

Saved some money rhere

[Nude up]

I will be happier when it’s all up and running. Parker in the uk have emailed me back and trying to match the pump cartridge.

[Nude up]

After a few emails to the uk last night it appears that Parker do make the hydraulic pump but the one I want is licensed protected by dexter.dexter do not sell spares for their units.
I cleaned the pump parts lapped them so the pump now spins freely I reassembled the unit temporarily refitted it connected the breakaway battery pulled the pin out and the pump run and the brakes came on. Great success! Just need to replace the brake pads I noticed they were worn then I can bleed the brakes. Saved my self a few dollars in the process.

[Nude up]

Disaster I refitted the dexter unit pull the breakaway switch and the pump runs. I relined my brakes and bled them but when I connected the car up I found that the pump wouldn’t run, pull the breakaway switch pump runs. After many wiring checks cars output all good brake actuator checked as per the manual it passes the test, 12 volts being supplied to the pump but when I connect it to the pump the voltage drops to 3.47 and it’s pulling 11.5 amps.
I pulled the unit apart again the circuit board looks good it’s completely sealed no way of checking it.

So it looks like I will have to buy a new actuator. I am a bit disappointed in the dexter unit no spares no repair.

Any body used a felk actuator Aussie made all parts available just no reviews.

[denis barden]

Low voltage and a Hi current seems to me that the motor for the pump is working but may be a bearing not turning or corroded somewhere.
When working at Katherine airport many years ago an old Aircraft Mechanic told me-If you not sure of a problem -Replace the hardest working component-What moves wears
Cheers Denis

[Nude up]

Low voltage and a Hi current seems to me that the motor for the pump is working but may be a bearing not turning or corroded somewhere.
When working at Katherine airport many years ago an old Aircraft Mechanic told me-If you not sure of a problem -Replace the hardest working component-What moves wears
Cheers Denis

The low voltage high current draw is with the pump not running. The pump runs when the breakaway switch is pulled 12 volts from a different part of the circuit board but from the source the car. It’s frustrating the pump has 2 connections to the pcb positive and negative.
The pcb has 4 wires to it earth power from the car the signal wire from the towpro and power from the break away battery. The pcb has diodes resistors and relays on it but are all sealed to the card so you can not check them.

Ps I am getting to be an old aircraft mechanic

[denis barden]

Okie Dokie
Get your self a Jewlers eye piece and If you can chech the CCT board for any Copper/Gold tracks that have burnt out and check for any dry soldered joints
Check and remake all earth points -run a new earth to your trailer-Even if they look good
It was working so a guess would be its corrosion thats stuffed it
Lookn out of the box-If your car elect windows dont work its not the elect motors its probable the cables inside the door jam that wears inside -That is the cheap copper cable they use breaks inside the plastic outer covering creating an open circuit
Good Luck

[Nude up]

After reading what I wrote got me thinking all night. I substituted an external 12 source to power the pump put the trailer plug in push my towpro button brakes worked. Put the car 12 volt source back 12v at the pump but as soon as you connect the pump to it it drops to 3.4 volts. So I ran a 12v wire direct from my battery pump works after a bit more checking I have an automatic 25 amp circuit breaker under the bonnet which goes battery c/b trailer plug. Bypassed this brakes work. Quick trip to Drysdale essential of course new breaker $14 my brakes now work.
This has done my head in and am now really happy to have found the problem.

[Davoo]

Hi
Hope all is going well! New to this but the info you guys give is great! After a few tests I believe my piston is playing up also.
I’m halfway pulling my dexter actuator apart and have come to a standstill at this point. Would you be able to pass on any tips to get this part off?

Also wondering were you able to source any new gaskets before putting back together?

Any help would be appreciated or else it’s a $1200-1300 replacement by the look of it.

Cheers!!