Jem45
Posted a lot
Posts: 1,021
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May 28, 2021 21:02:34 GMT
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Hi all,
My old Volvo wagon has a soft brake pedal. Suspect this is air in the system after recent rear brake work but just want to check something...
The pedal is rock hard with the engine off but then goes soft when on - do I remember reading somewhere that this is more indicative of master cyl problems?
Any simple checks I can do to isolate the problem?
Sorry if this is 'brakes 101' - I'm no expert.
Cheers, Nick
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Carbs 'n chrome
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60six
Posted a lot
(╯°□°）╯︵ ┻━┻
Posts: 1,658
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May 28, 2021 21:14:28 GMT
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check the brake servo - this uses air from intake to assist braking - sounds like your servo may have a leak - far easier than fixing a master ylinder
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Some 9000's, a 900, an RX8 & a beetle
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May 28, 2021 21:20:15 GMT
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It just means that the servo is working and highlighting that something is not quite right - probably just a little air as you suggest. If there was alot of air you'd be able to feel it even without the servo.
Nick
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1967 Triumph Vitesse convertible (old friend)
1996 Audi A6 2.5 TDI Avant (still durability testing)
1972 GT6 Mk3 (Restored after loong rest & getting the hang of being a car again)
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Jem45
Posted a lot
Posts: 1,021
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May 29, 2021 19:58:13 GMT
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Cheers both. Hope you're right Nick. Now if I can just get those bleeding bleed screws loose!
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Carbs 'n chrome
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May 29, 2021 20:45:00 GMT
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Good luck with that......
Nick
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1967 Triumph Vitesse convertible (old friend)
1996 Audi A6 2.5 TDI Avant (still durability testing)
1972 GT6 Mk3 (Restored after loong rest & getting the hang of being a car again)
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e30ben
Part of things
Posts: 66
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May 30, 2021 20:45:29 GMT
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Cheers both. Hope you're right Nick. Now if I can just get those bleeding bleed screws loose! Penetration oil on them first leave a few days. A kettle of hot water may help on top when you go to loosen them off, using a 6 sided short socket should see you right |
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Jem45
Posted a lot
Posts: 1,021
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May 30, 2021 21:27:52 GMT
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Tried all that Ben - no go mate. They are cheese. Think the best bet is to remove the rear calipers (front 2 are fine) and see if a local machine shop can help. I bloody hate old cars sometimes...
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Carbs 'n chrome
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Any update on this brake issue Jem45? I am having the same problem. Brake pedal is firm when engine is off and after the engine is started the pedal travel is excessive with a spongy feel. I've tried 2 different attempts to solve this 1- Toyota servo with a jaguar XJ12 series 3 master cylinder 2- Lexus servo with its matching master cylinder. Car has the ABS system removed with 'normal' servo in its place   |
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Jem45
Posted a lot
Posts: 1,021
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Sort of.... I'm pretty sure that an effective system bleed would resolve it but the issues described above have made this challenging and plenty of P80 platform Volvo owners have trouble with this. Plenty don't as well so who knows?
The rear calipers have 2 bleed screws each and conventional wisdom seemed to be that you could get away with using just the lower one for bleeding purposes, because of the inherent influence of gravity! My lower ones were not usable - they had turned to cheese as stated - but I got the calipers off, inverted them and bled from the upper screw - i.e upside down.
This has improved the situation I think. The brakes still feel a bit 'remote' but operationally, work OK as far as I can judge.
I can't find any replacement rear calipers secondhand for mine (they're "v70_XC specific" and no phase 1 XCs ever seem to be broken for parts) and are mega bucks new to import from Europe so am just going with it. I don't suppose this is all that helpful for you... dunno if you're dealing with a Volvo either, but if you've gone as far as replacing the servo etc.. then I guess that bleeding the system isn't a concern for you. Good luck with it mate.
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Carbs 'n chrome
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Another thing that can cause a long pedal is a flexihose (Or several of them) past their best and ballooning slightly under pressure.
Of course, changing them means bleeding everything….. Would generally expect bleed nipples to be on the top of calipers etc as the air will push up to the highest point.
Good luck….
Nick
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1967 Triumph Vitesse convertible (old friend)
1996 Audi A6 2.5 TDI Avant (still durability testing)
1972 GT6 Mk3 (Restored after loong rest & getting the hang of being a car again)
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Another thing that can cause a long pedal is a flexihose (Or several of them) past their best and ballooning slightly under pressure. Of course, changing them means bleeding everything….. Would generally expect bleed nipples to be on the top of calipers etc as the air will push up to the highest point. Good luck…. Nick Following on from vitesseefi'a suggestions, have you tried clamping individual hoses and seeing what happens to pedal travel then? Might help isolate which wheel is at fault, if any? |
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^^^^ Yep, exactly this - meant to suggest myself.
Has got me out of the poo more than once before
Nick
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1967 Triumph Vitesse convertible (old friend)
1996 Audi A6 2.5 TDI Avant (still durability testing)
1972 GT6 Mk3 (Restored after loong rest & getting the hang of being a car again)
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jimi
Club Retro Rides Member
Posts: 1,815 
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I know that the 140 series had a very specific bleeding sequence, I changed the master cylinder seals on the friends 144 estate many years ago and could not get a a hard pedal, tried everything and got nowhere. Ended up speaking to the workshop foreman at the local Volvo dealers who new instantly what the problem was, he wrote down the bleeding sequence and said follow that exactly. I did and got a rock hard pedal. Can't remember the sequence (was over 30 years ago) and it may not be relevant to your car, but it might be worth asking the question at your local dealers  |
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Black is not a colour ! .... Its the absence of colour
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Jem45
Posted a lot
Posts: 1,021
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I know that the 140 series had a very specific bleeding sequence, I changed the master cylinder seals on the friends 144 estate many years ago and could not get a a hard pedal, tried everything and got nowhere. Ended up speaking to the workshop foreman at the local Volvo dealers who new instantly what the problem was, he wrote down the bleeding sequence and said follow that exactly. I did and got a rock hard pedal. Can't remember the sequence (was over 30 years ago) and it may not be relevant to your car, but it might be worth asking the question at your local dealers This is true for the P80 platform Volvo's too - i.e 850s and ph1 V70s. The sequence is nearside rear, offside rear, nearside front, offside front. Dunno what model freespeech has though. |
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Carbs 'n chrome
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jimi
Club Retro Rides Member
Posts: 1,815
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This is true for the P80 platform Volvo's too - i.e 850s and ph1 V70s. The sequence is nearside rear, offside rear, nearside front, offside front. Dunno what model freespeech has though. That's pretty much a standard bleeding sequence, starting at the furthest from the master cylinder and working towards it. 👍 The 144 I worked on was somewhat more complicated, dual circuit with the front calipers having 4 pistons and 2 bleed nipples, each pair on one caliper was fed from a different circuit and each rear fed from a different circuit. This meant that if one circuit failed you still had brakes on 3 wheels, Quite a smart idea, however the bleeding sequence involved a lot of jumping round the car to different nipples Edit. Curiosity got the better of me, a bit of Googling turned up this Can't say it was definitely the sequence I was given, but it certainly looks similar |
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Last Edit: Dec 4, 2021 23:39:38 GMT by jimi
Black is not a colour ! .... Its the absence of colour
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Another thing that can cause a long pedal is a flexihose (Or several of them) past their best and ballooning slightly under pressure. Is this not an mot failure or at the very least an advisory? I've had wof failures for it here in New Zealand. |
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Rich
Club Retro Rides Member
Posts: 6,237
Club RR Member Number: 160
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Soft brake pedal questionRich
@foxmcintyre
Club Retro Rides Member 160
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Another thing that can cause a long pedal is a flexihose (Or several of them) past their best and ballooning slightly under pressure. Is this not an mot failure or at the very least an advisory? I've had wof failures for it here in New Zealand. Yes, if a tester can spot it. A lot of MOT test bays run unassisted these days so it’s hard to spot issues like that on your own sadly. |
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Is this not an mot failure or at the very least an advisory? I've had wof failures for it here in New Zealand. Yes, if a tester can spot it. A lot of MOT test bays run unassisted these days so it’s hard to spot issues like that on your own sadly. Depending on what year the Volvo is, it might be MOT exempt anyway |
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Another thing that can cause a long pedal is a flexihose (Or several of them) past their best and ballooning slightly under pressure. Is this not an mot failure or at the very least an advisory? I've had wof failures for it here in New Zealand. As Rich says. Though quite often there’s nothing to see externally, even if there was someone to look. It doesn’t take much expansion to give extra pedal travel. My first experience of this, as a near total novice was my Herald 1200 failing it’s MoT in 1987 because the tester felt the pedal travel was excessive (it was). Then, when simple adjustment failed to improve it, I spent many hours and money I didn’t have renewing almost the entire braking system, including converting from drum to disc brakes at the front. The only things I hadn’t changed were the front flexis…. One of them was knackered, but the only way it was found was by going around the car with a hose clamp. The hose in question was swelling along its whole length as the amount of pedal travel was directly proportional to clamp position. New hoses and the brakes were immediately excellent. A lesson! I have heard of cars being fussy about bleeding order but never actually encountered one. Think it’s more of an issue if the system has been completely drained or if something at the front end has been changed - like master cylinder. Nick |
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1967 Triumph Vitesse convertible (old friend)
1996 Audi A6 2.5 TDI Avant (still durability testing)
1972 GT6 Mk3 (Restored after loong rest & getting the hang of being a car again)
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I can understand your explanation of the long travel caused by a damaged/failed flexi pipe.....but
...why is there no excessive travel when the engine is off ?
The brake pedal has a firm to rock solid feel when pressed.
The condition only happens after the engine is started.
ie........ long pedal travel and a spongy feel
I know the pedal goes down a little after the engine is running when the brakes are applied but there should still be a firm to rock solid feel.
My car is a Lexus.........the only modification was the removal of the ABS system which was replaced with a 'normal' servo and master cylinder
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