Just lifted a '95 with rear disc brakes, and now the brake pedal slowly sinks to the floor. I have bled all the calipers in the correct order, and have also bled the LSPV. After fitting a new master cylinder, the problem remains. The truck does stop well, but the pedal just sinks to the floor under pressure. Can the LSPV be contributing to this problem? I have not adjusted it in any way yet to compensate for the lift. Is this sinking pedal issue common to 80's?
LSPV question
- Thread starter agbuckle98
- Start date
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There is a common problem of getting all the air out of the ABS system when the master cylinder is changed. Do a search for the many discussions on how to fix it. I personally (luckily) have not dealt with the problem yet so must stop there.
The other problem may be a rubber brake line hose. Sometimes people will not remember to loosen the rear rubber brake line brackets (body to axle) so the rear axle could move all the way down when the springs were installed. If so, the line may get overly stretched and now is ballooning up when the brake is applied.
The other problem may be a rubber brake line hose. Sometimes people will not remember to loosen the rear rubber brake line brackets (body to axle) so the rear axle could move all the way down when the springs were installed. If so, the line may get overly stretched and now is ballooning up when the brake is applied.
If the brake pedal slowly sinks to the floor without you touching it, you have no pressure in the system. My guess would be a leak (either brake fluid out, or air in).
- Thread starter
- #4
It doesn't sink without pressure on it. I actually have to apply considerable pressure, but it does slowly sink away. When it reaches bottom, the brakes are still firmly applied though, even with throttle application there is no moving the truck.
Sounds like air in the lines somewhere, or a soft line that's bulging.
I'm 99% certain it's not on mine, as I've bled the brakes and checked the lines for leaks and bulges with the engine on and someone pressing the pedal. I'll report back once the kit comes in and I rebuild it.
- Thread starter
- #8
I thought about the soft lines bulging, but with a helper pumping the pedal while the truck is running, I inspected all of the soft lines and there was no bulging anywhere. As for air in the system, even if there was, you should still be able to pump the pedal up and hold it without it sinking.
- Thread starter
- #9
It is a brand new Aisin MC, it was bench bled before intallation. It's not unheard of to get faulty parts right out of the box, but i'm not willing to buy another one and go through the whole process all over again just yet.
Any updates on this yet? I took apart my master cylinder this weekend to rebuild it. I've bled the brakes on my truck a number of times and rebuilt all the calipers so I figured it would be pretty clean fluid inside. Not quite! There was a lot of sediment/gunk inside the master cylinder and the reservoir that came out when I dismantled it. After taking the MC apart I found that there was scoring on the internal pistons as well as on the cylinder wall so I now have a new MC on the way (which includes a new reservoir and cap too). Just wondering if you managed to resolve this problem so I know what to look out for when I install my MC.
