Bleeding brakes
Discussion
Hi all. Recently replaced all callipers and pads on the Merc. First time I've tried, so go easy on me.
Fronts appear to have gone on fine. Bled them and had fluid coming through nicely. Backs, however, have proved more challenging. I can't seem to get anything more than a dribble of fluid from the back right bleeder. Rear left a bit better but still not what I would call clear fluid. Spent about an hour trying to bleed (using two-man manual pumping) but just can't get anything. Can't see any leaks anywhere (also replaced rear brake pipes).
I took the car for a very slow, and very short drive (on private land!) and the car seems to stop on a penny, so I'm guessing the fronts are still working even though the tears are not?
Any suggestions? Thanks.
'79 W123 230 Auto.
Fronts appear to have gone on fine. Bled them and had fluid coming through nicely. Backs, however, have proved more challenging. I can't seem to get anything more than a dribble of fluid from the back right bleeder. Rear left a bit better but still not what I would call clear fluid. Spent about an hour trying to bleed (using two-man manual pumping) but just can't get anything. Can't see any leaks anywhere (also replaced rear brake pipes).
I took the car for a very slow, and very short drive (on private land!) and the car seems to stop on a penny, so I'm guessing the fronts are still working even though the tears are not?
Any suggestions? Thanks.
'79 W123 230 Auto.
TooMany2cvs said:
No weight on the back suspension? Is there a load proportioning valve in there?
Mebbe put the axle stands under the axle, and try again? Or make sure it's level - some stuff, including VW T25s (similar era) has a tilt valve that increases the rear brakes if the tail's down.
Very interesting. I have no idea if there is load proportioning valve.Mebbe put the axle stands under the axle, and try again? Or make sure it's level - some stuff, including VW T25s (similar era) has a tilt valve that increases the rear brakes if the tail's down.
I will have to do some research. I did have the whole back end up in the air, and it was fairly high, so maybe it was enough to stop it bleeding. I have a mate with a ramp who I should be able to get it to, so I'll try it again when it's flat. Thanks.
//j17 said:
Try a little dribble of break fluid on each union in turn, then get someone to pump the brakes while you have a good look. If one's not sealing correctly and letting air in it should help identify it.
Ok, tried that. Nothing obvious I can see. I also replaced the master cylinder so pretty much all seals are new.PositronicRay said:
Blocked bleed nipple. Take it off and either blow it through or use some brake cleaner, refit and you're good to go.
(you can clamp the flexis to stop too much fluid leaking out when the nipples off)
Fairly sure they're not blocked. They are both new units, and when pumping the break with them open you can hear the air coming through. (you can clamp the flexis to stop too much fluid leaking out when the nipples off)
I have arranged to take it to a mate with a lift tomorrow, so I'll have another go with the car flat. He also has a proper bleeding pump, so may be able to force the air out.
Mr Teddy Bear said:
Not being flippant, but you are closing the nipple before matey lets the pedal up?
No problem. Yup, bleeder open, peddle down, close bleeder, peddle up and repeat. Fronts worked fine, but the rears just won't play ball. Also, when the callipers were off, brake fluid was dripping through the brake flex hoses so it must be getting that far.Mk3Spitfire said:
GadgeS3C said:
I'd try using a pressure bleeder such as a Gunsons Easibleed on it. I was really struggling to bleed the TVRs brakes awhile ago. Couldn't get them to bleed by manual methods, 5 mins with an Easibleed and sorted.
Thanks. eBay, £15. Ordered.Mk3Spitfire said:
PositronicRay said:
Blocked bleed nipple. Take it off and either blow it through or use some brake cleaner, refit and you're good to go.
(you can clamp the flexis to stop too much fluid leaking out when the nipples off)
Fairly sure they're not blocked. They are both new units, and when pumping the break with them open you can hear the air coming through. (you can clamp the flexis to stop too much fluid leaking out when the nipples off)
I have arranged to take it to a mate with a lift tomorrow, so I'll have another go with the car flat. He also has a proper bleeding pump, so may be able to force the air out.
Mk3Spitfire said:
Also, when the callipers were off, brake fluid was dripping through the brake flex hoses so it must be getting that far.
So that sort of knocks the load-valve theory on the head.Have you tried just gravity bleeding them? Just leave the nips open until fluid comes through.
TooMany2cvs said:
So that sort of knocks the load-valve theory on the head.
Have you tried just gravity bleeding them? Just leave the nips open until fluid comes through.
Ah ok. Yea, tried gravity bleeding them. Actually ended up leaving the things open over night but not a drip the next morning. Have you tried just gravity bleeding them? Just leave the nips open until fluid comes through.
Hopefully my mates lift and pump will sort it. On my way down now, so will update.
This is something a few of us looked at a while ago because we had all encountered the same problem on various cars .
A pressure bleeder cured the problem .
We concluded the problem is caused by the size of the piston in the master cylinder , its struggling to move enough fluid in partially filled systems, the swept volume is not large enough to compress the air sufficiently to force it through the system .
It's not a problem once the system is full of fluid as the fluid won't compress unless it overheats (boils, causing air bubbles)
A pressure bleeder cured the problem .
We concluded the problem is caused by the size of the piston in the master cylinder , its struggling to move enough fluid in partially filled systems, the swept volume is not large enough to compress the air sufficiently to force it through the system .
It's not a problem once the system is full of fluid as the fluid won't compress unless it overheats (boils, causing air bubbles)
This is something a few of us looked at a while ago because we had all encountered the same problem on various cars .
A pressure bleeder cured the problem .
We concluded the problem is caused by the size of the piston in the master cylinder , its struggling to move enough fluid in partially filled systems, the swept volume is not large enough to compress the air sufficiently to force it through the system .
It's not a problem once the system is full of fluid as the fluid won't compress unless it overheats (boils, causing air bubbles)
A pressure bleeder cured the problem .
We concluded the problem is caused by the size of the piston in the master cylinder , its struggling to move enough fluid in partially filled systems, the swept volume is not large enough to compress the air sufficiently to force it through the system .
It's not a problem once the system is full of fluid as the fluid won't compress unless it overheats (boils, causing air bubbles)
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