Power Brake Booster

wdhouser · Post by **wdhouser** » 14 Apr 2011, 14:41

2001 V70 Base - I just replaced my power brake booster and now the front brakes appear to be slightly engaged all the time. The appears to have no power, it does not appear to coast freely and the front brakes were very hot. I verified that i had the correct booster (w/o Dynamic Stability Traction control). The installation (thanks to instructions that were posted here) were almost perfect and the reassembly was a breeze. I verified that the I plugged in the ABS unit and none of the brake lines appear to be crimped.

Any ideas?

jda2000 · Post by **jda2000** » 14 Apr 2011, 17:41

did you buy new or used? did you forget the o-ring between the booster and master cylinder?

did you open the hydraulic lines? did you attach the vacuum line?

wdhouser · Post by **wdhouser** » 14 Apr 2011, 19:44

It was a reconditioned unit from NAPA. Did not foreget the O-ring, however, the old one was a flat O-ring, and the replacement was round. The round seem to fit very well.

Did not ope any hydraulic lines.

I'm not sure what you mean by the "vacuum" line? But I think everything else was reconnected.

jda2000 · Post by **jda2000** » 15 Apr 2011, 07:26

I usually recommend buying new rather than used or rebuilt.

Pricewise, the new unit is about $200 vs $150 + core charges for rebuilt, but the new one is an OEM ATE unit and comes with new brake pedal position sensor, new check valve, new o-ring plus 12 mos warranty.

If you hooked everything back correctly and its not working up to par, bite the bullet and send that unit back and get a new one

Post by **jimmy57** » 15 Apr 2011, 11:04

brakes hanging on wasn't the original problem was it?

wdhouser · Post by **wdhouser** » 15 Apr 2011, 14:26

The original problem was a hissing noise. Brakes worked fine. Disassembly was not easy, but reassembly was a piece of cake. I've checked all the hoses, brake lines, brake switch position and even measured the linkage and compared it to the original unit (4 1/4" from base to center of arm hole. Additionally the brake pedal has at least 1/16" play so it's not prematurely activating the brake booster. I must have done something either in the assembly or disassembly, but I can't figure out what it is. The booster is remanufactured. I new one cost $500 plus and this one from NAPA cost $200. If I take it to Volvo it's another $300 in labor. I appreciate everyone's help.

jda2000 · Post by **jda2000** » 16 Apr 2011, 14:06

I did the job myself a couple of months ago in my '01 V70T5 and a new ATE STC booster (not the DSCT) was $220 at FCPgroton, but with the 10% off mathhews site coupon, it was about $200 with free shipping.

Post by **chrism** » 16 Apr 2011, 17:02

Did you compare the length of the rod extrusion between the old booster and the new? Even though you have some free play between the pedal and the booster, I'm wondering if the front rod may be pushing against the master cylinder.

You could loosen the MS from the booster a few nut turns and see if the MS tends to push forward as you loosen the nuts. If it does seem to be pushing on the MS as you loosen it, keep loosening the nuts until it feels as though there's no push. Then while it's loose, jack up one front wheel and see if you can spin the wheel freely.

wdhouser · Post by **wdhouser** » 18 Apr 2011, 08:54

I did measure it and the distance on both extrusion rods from where they exit to the middle of the hole is 4 1/4". I jacked it up and the wheel rotated with some difficulty. I then pulled the brake pedal towards me and it spun a little more freely. I then unscrewedd the MS and it rotated even more freely but there does appear to be a rubbing noise and without exerting a lot of force the wheel rotates a little bit more than one revolution. Is that normal? It's beginning to sound like its the booster. Let me get your thoughts guys. Thank you everyone for your help.

Post by **chrism** » 18 Apr 2011, 10:21

...I then pulled the brake pedal towards me and it spun a little more freely...

It does sound as though something in the booster is not allowing the MS piston (or the pedal) to return all the way back home.

BTW - when you release the pedal, it's not uncommon to detect a very slight dragging of the pads on the rotor. But you should be able to spin the wheel fairly easily by hand.

Try the test again, but this time loosen the MS WITHOUT pulling back on the pedal. If loosening the MS alone results in the wheel spinning more freely, then you know the problem lies somewhere BETWEEN the pedal and the MS - like in the booster.