Sinking Brake Pedal

geordie john

geordie john

Joined
Nov 25, 2023
Posts
54
Likes collected
30
Location
Scunthorpe, UK
Funster No
100,044
MH
Renault T821
Exp
2019
I have a Delphin T821 Tag with a sinking brake pedal with engine running. Mot is Due middle of Dec. Need urgent help as am running out of options. Started with handbrake being poor and discs pitted changed discs and pads rear adjusted handbrake all started from there. Peddle just sinks so i changed master cylinder bled them and bled them and pressure bled them still the same just cant get peddle to stay firm when engines running. There are no leaks as it maintains pressure with tester and i have visibly looked. Anything else i have missed. thanks in advance There's a drink in it for anyone who can tell me how to solve it thanks again.
 
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geordie john said:
all the way to the floor
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Does point to the servo. Have you tried clamping all the flexible hoses on each of the wheels to eliminate calliper travel. If it goes solid then release the clamps one wheel at a time. Obviously DONT drive it while doing this.
 
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geordie john said:
My theory probably still air in there. But getting it out is another matter without the tool.
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You can bleed the ABS by braking severely several times to make the wheels skid. This will purge the ABS unit. We used to do that with cars, but that might not be such a good route to take with a big motorhome.
 
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The Wino said:
On some vehicles it's a shared fluid supply. We had a Renault that was losl
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True. But that will have no effect on the brake pedal travel. The take off for the clutch is about a third up the fluid chamber. The worst that could happen to the brakes is a low fluid warning. 😊
 
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PaulandChrissy said:
Does point to the servo. Have you tried clamping all the flexible hoses on each of the wheels to eliminate calliper travel. If it goes solid then release the clamps one wheel at a time. Obviously DONT drive it while doing this.
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Good idea

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Sue and Rick said:
Good idea
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I believe the pads and discs have been changed (If I remember correctly). it’s not uncommon for the caliper travel to be quite long after pad/discs change, resulting in a massive travel on the brake pedal. Would be interesting to see the effect clamping the hoses. At least it will eliminate everything on the wheels.
 
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geordie john said:
was going to try that old school. couldn't find my set of mole grips. there in there somewhere. need my garage sorted cant find nothing lol
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Can't beat a tidy garage John 🤣 Place for everything 👌

Screenshot_20230925_191621_WhatsApp.jpg
 
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geordie john said:
nice one. my big garage loads of tools disco gear you name it and the kitchen sink lol. been told am a hoarder got everything
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Well you're the man to call if there's a problem then John as long as you got a week's notice to find the right tool lol 🤣

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If you tried to bleed the brakes before bleeding the new master cylinder you may have got air into the ABS module. Multiecuscan allows you to bleed the ABS by pulsing the internal solenoids. The procedure is described in the software.

Just seen your other post and you're a Renault base so Multiecuscan won't work - buqqer☹️
 
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PaulandChrissy said:
You can bleed the ABS by braking severely several times to make the wheels skid. This will purge the ABS unit. We used to do that with cars, but that might not be such a good route to take with a big motorhome.
Click to expand...

This is also recommended on Merc Sprinters apparently if you have issues with air 😊
 
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dunnah01 said:
If you tried to bleed the brakes before bleeding the new master cylinder you may have got air into the ABS module. Multiecuscan allows you to bleed the ABS by pulsing the internal solenoids. The procedure is described in the software.

Just seen your other post and you're a Renault base so Multiecuscan won't work - buqqer☹️
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just ordered an icarsoft from amazon at £170 said on the box it does Renault and ABS bleeding. If it dont work it goes back.
 
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geordie john said:
I have a Delphin T821 Tag with a sinking brake pedal with engine running. Mot is Due middle of Dec. Need urgent help as am running out of options. Started with handbrake being poor and discs pitted changed discs and pads rear adjusted handbrake all started from there. Peddle just sinks so i changed master cylinder bled them and bled them and pressure bled them still the same just cant get peddle to stay firm when engines running. There are no leaks as it maintains pressure with tester and i have visibly looked. Anything else i have missed. thanks in advance There's a drink in it for anyone who can tell me how to solve it thanks again.
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Brake diagnosis so far. Went back to old school diagnostics. Started with blanking outlets of master cylinder. Peddle crept to the floor engine running. Bare in mind that was a brand-new master cylinder fitted £140 bosch one. Exchanged it for another new one repeat test firm peddle. Next step connected rear master cylinder pipe bled O/S rear and N/S front as thats the circuit it runs on one pipe. Checked brakes firm peddle thought good am getting somewhere. So connected front pipe on master cylinder bled N/S rear and O/S front. Checked brakes engine running Brake peddle creeps to the floor again. Next i clamped the 3 flexi pipes on that circuit firm peddle again next i removed 1 clamp at a time on rear first firm peddle then i removed the last clamp on O/S front peddle sank to the floor as i was clamping the flexi pipe next port of call new O/S caliper. Got one on order will keep you posted on out come. Still need a new handbrake cable thou lol
 
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Well done like your persistence

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If I understand correctly the first new master cylinder must've been faulty because when the the second new m/c was fitted the pedal remained firm.
 
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