rob76turbo

Copied from DIY forum:
Hi everyone, so just installed a 3" lift on my 05 CS. Put the tires back on, left most of the suspension bolts hand tight to let it settle. Put the tires back on and took it for a VERY slow drive around my block to again - let everything settle. Next step is put back up on lift and tighten / torque all the suspension bolts / nuts to proper torque setting. Anyway, as I backed out of my driveway, the brake pedal in incredibly hard to press and even when pressing really hard, there is not a lot so stopping power. Any ideas?

As usual, thanks to all the Rennlist guru's for help!!

TRINITONY

If it were a 957 I'd tell ya to check the brake booster hose going from vacuum pump on the passenger side. That was the culprit when I lost my brakes.

Petza914

Like Tony says, sounds like you're not getting any vacuum assist. Either that or the master cylinder is damaged.

rob76turbo

@Triniton where is that hose located off the brake booster (upper or lower side / left or right)? Do you have to remove the windshield wiper cowling to get to it? I just reinstalled it!!
Thanks!

TRINITONY

rob76turbo

Thanks again. The vacuum hose was split in exactly the same place as the one in the video. Now need to buy some 1/2" ID hose and a couple of clamps.

hopsis

100% the same place here. I fixed it last weekend but haven't had the chance to go for a drive yet. I'm confident about the repair but the error message remains, I'm hoping it will clear itself after a while.

I initially got some cheap clear pvc hose but that would collapse almost shut under vacuum. Don't do what I did, get stronger hose, something like heater or fuel hose.

Petza914

Brake booster hose is a special reinforced hose designed to specifically prevent collapse under vacuum. I don't know what size.it is on the Cayennes, but if the same size, here's a part number for a couple.feet.od trh booster hose for a 928.

hopsis

Good to know. Inner diameter in this case and application is 13mm or 1/2" whichever way You want to put it.

It's actually useful to understand that a lot of engine hoses will handle positive pressure just fine but will not hold vacuum. And vice versa.

rob76turbo

Ran into the same problem again, but on a different Cayenne. I took a look at the brake booster vacuum hose and it seems to be intact. I am thinking it could be the Brake Booster Vacuum Air Pump itself.
Is there a way to test if the Brake booster Vacuum Air Pump is working and or faulty?

As always, thanks!!

Crozzer

Mighty vac. Connect to tee in small lines coming from vacuum pump passsnger side rear of v8. (Remove rubber cap, insert adapter from might vac.

Should read 17-20 in hg when running. Should hold 20 virtually indefinitely. If you have leaks or low pressure try the different circuits off the tee. (Search my posts or DIY for lots of info and pics).

smoke machine super helpful. You’ll wish you had one eventually. I got the autool.

pump and that thick hose to the brake booster are unfortunately common failure points on the platform. As are many other PCV and control or vacuum lines.

rob76turbo

Thank you Crozzer!!!

95_993

I found the same hard plastic line cracked while I was changing the coolant expansion tank.

I slide a 1/2” piece of heat shrink tubing over the cracked, hit it with the heat gun….done.

rob76turbo

Well it turns out it could be something entirely different. When I reinstalled the intake I cracked one of the vacuum fitting on the back completely off. I suspect that lack of vacuum across all those hoses is the culprit. Putting it all back together (with a new intake manifold). I report when it’s all buttoned up.