2003XC70 Why are brakes rock hard only in reverse?

carboncow · Post by **carboncow** » 08 Oct 2015, 15:49

We've had this issue for well over a year and it seems to be getting more regular. When the car is first started in the AM and we have to back out of the driveway the brakes are rock hard and the car feels like it's not going to stop...more pressure on the pedal doesn't seem to do much.

Now if the car is parked the other way in the driveway or on the street and I have to leave first thing in the AM traveling forward...never an issue.

Sometimes it seems if you give the car a lot more time to warm (and build pressure in the booster?) everything is fine.

eBrake works great and was replaced in the last few years and I don't think the issue started when it was replaced.

This is a new one to me and I've been doing brakes on my own cars for approx. 20+ years.

thanks.

Post by **jimmy57** » 08 Oct 2015, 18:44

That is exactly the symptoms if the vac pump isn't working. When started cold the cam positioning for lowered emissions plus the retarded ignition timing for speedier warmup mean very little engine vaccum. After 45 seconds the cam and ignition timing are adjusted and vacuum goes to a more normal level and vac pump is not needed.

If the vacuum pump switch is working right then with key on but engine not running, pumping brakes will make pump come on.

Post by **vtl** » 08 Oct 2015, 20:49

Do you hear a load buzz when the key is put into position II? This is brake assistance pump. As stated by jimmy57, it is likely dead.

Post by **jimmy57** » 08 Oct 2015, 22:10

31400692
31265825

The first number should be it. I think the second number is the older part number.

The gearing in reverse combined with elevated idle speed makes it seem worse in reverse. If you do a same temp, stone cold engine start and try it in D you will see it is very close the same level scarily hard to stop before the engine settings normalize.

carboncow · Post by **carboncow** » 09 Oct 2015, 21:59

Thanks guys. For some reason I'm not getting email notifications so getting here late.

I"m going to go listen for the buzz tomorrow. I seem to recall after shutting the car off that I would randomly hear a buzz I could not identify...and someone pointed out that it was mostly like that pump. I asked Jimmy in a post quite some time ago what the pump switch was as mine had fallen apart and I had it zip tied together...but could not identify it's purpose. That question should lead me to test that first.

I'll check for the buzz tomorrow. If non I figure I'll order a $60 switch off ebay unless you guys have a test to determine switch vs. pump. Between the two it sounds like a cheap fix to get the car safe for the wife again!