Jump to content

Brake vacuum problem


jackmac

Recommended Posts

Hi all

Having a problem with a lack of vacuum assistance on my 300tdi 90 (conversion, running td5 axles with vented front disks for what it's worth) . Having to absolutely stand on the brakes to slow down, it's not great. 

So far I've replaced the brake servo with a brand new one (not blue box, replaced o ring to master cylinder as well), tested that there is vacuum, tested the one way valve. Nothing has worked! Pumping the pedal until hard when the engine is off, then maintaining pressure as I start the engine and the brake pedal doesn't change at all. When I checked the vacuum I wasn't sure how strong it's meant to be, I found it much more noticeable with the engine a couple of hundred rpm above idle. 

Incidentally I also noticed when I changed the brake pads a couple of weeks ago that it took a herculean effort to push the pistons back in, which isn't a problem I've had before. The caliper pistons don't look that bad to me either. Not sure if that could be connected? 

Link to comment
Share on other sites

12 minutes ago, western said:

Read you replaced the servo, have you adjusted the servo pushrod ? if not that could give you a long pedal 

 

The pedal is actually hard quite early, I'm sure it's a vacuum issue because of the lack of change starting the engine having exhausted the vacuum. Not adjusted that though I wasn't aware it was an option, I'll have a look

Link to comment
Share on other sites

On 18/09/2017 at 10:09 PM, Retroanaconda said:

If you exhaust the vacuum, then start the engine and rev it a bit does it change at all then?

Just checked this, no difference. The servo is definitely holding vacuum because I started her up and left running for about 15 seconds, stopped engine and removed the vacuum pipe from the servo. There was a very clear hiss and a pop as I removed the pipe

Link to comment
Share on other sites

On 18/09/2017 at 6:02 PM, jackmac said:

Incidentally I also noticed when I changed the brake pads a couple of weeks ago that it took a herculean effort to push the pistons back in, which isn't a problem I've had before. The caliper pistons don't look that bad to me either. Not sure if that could be connected? 

I'd focus on this aspect if I were you, and leave worrying about the vaccum pump for the moment. Unless the pistons are rediculously rusty, this can only be the result of some sort of blockage in the system. 

Link to comment
Share on other sites

1 hour ago, nickwilliams said:

I'd focus on this aspect if I were you, and leave worrying about the vaccum pump for the moment. Unless the pistons are rediculously rusty, this can only be the result of some sort of blockage in the system. 

I'm going to drain all the brake fluid and replace the 2 front flexi lines as I've got extended ones waiting to go on, will give it a flush through and make sure it's all clear. 

Replacing the master cylinder having spoken to a friend who had the same issue, and I've also found an old topic on here with the same symptoms that was apparently fixed by changing the master cylinder. Fingers crossed 

Link to comment
Share on other sites

On ‎18‎/‎09‎/‎2017 at 8:30 PM, jackmac said:

It is working, I can feel some vacuum at idle - just it works a lot better above that. I'm not sure how strong it should feel? Using the very non scientific method of sticking my finger over the vacuum pipe

I had a bit the same problem, braking power was very low, took the vacuum pump off and it was missing a gasket.. So I assume it was not 100% vacuum. Put a new gasket in place and fixed.

Link to comment
Share on other sites

  • 4 years later...

So we are having masive brake problems so when we are sat with engine off the pedal feels okay then we run the engine on a test drive and the brake pedal on first pump feels good then take your foot of and pump again and nothing we have changed the servo all the cylinders shoes checked the vaccine pump is all good and no splits in pipes I’m now completely lost any help ???? 

Link to comment
Share on other sites

  • 2 weeks later...
On 11/20/2021 at 1:13 PM, Kaci said:

So we are having masive brake problems so when we are sat with engine off the pedal feels okay then we run the engine on a test drive and the brake pedal on first pump feels good then take your foot of and pump again and nothing we have changed the servo all the cylinders shoes checked the vaccine pump is all good and no splits in pipes I’m now completely lost any help ???? 

Have you rebuilt the Master Cylinder and put a seal in the wrong way round? 

Link to comment
Share on other sites

On 9/18/2017 at 6:02 PM, jackmac said:

Hi all

Having a problem with a lack of vacuum assistance on my 300tdi 90 (conversion, running td5 axles with vented front disks for what it's worth) . Having to absolutely stand on the brakes to slow down, it's not great. 

So far I've replaced the brake servo with a brand new one (not blue box, replaced o ring to master cylinder as well), tested that there is vacuum, tested the one way valve. Nothing has worked! Pumping the pedal until hard when the engine is off, then maintaining pressure as I start the engine and the brake pedal doesn't change at all. When I checked the vacuum I wasn't sure how strong it's meant to be, I found it much more noticeable with the engine a couple of hundred rpm above idle. 

Incidentally I also noticed when I changed the brake pads a couple of weeks ago that it took a herculean effort to push the pistons back in, which isn't a problem I've had before. The caliper pistons don't look that bad to me either. Not sure if that could be connected? 

The vacuum pump At idle should make a red swollen ring on the pad of your thumb and hurt enough that you remove said thumb. 

The brake pedal should sink on start-up as vacuum servo assistance is delivered. 

Exercise the front pads with a pry bar and someone pressing Hard on the peddle, they could be jammed and you only have rear brakes. 

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...

Important Information

We use cookies to ensure you get the best experience. By using our website you agree to our Cookie Policy