Rear Wheels locking up

Zachyfarms · Post by **Zachyfarms** » 19 Dec 2010, 20:50

Hi everyone, Im new to this site. My 98 s70 has been quite the project since i got it. Starting with the brakes.. The ABS light has been on for 2 years. used to be intermittent but went solid.. the brakes for last year have been locking up in rear Long before fronts even get close.. No matter road dirt or ice the rear wheel lock up before fronts when braking. I have always known braking to be somethin like 70% front to 30%rear. So what would be causing this. I have replaced pads and rotors front and rear checked all calipers for function. and Now the ABS i fixed with the awesome write up on soldering joints in ABS module and abs works perfect. But Rears still locking first..ABS kicks in properly but i can tell its the rears locking up not the fronts.. Before fixing abs it was nearly imposible to lock fronts but rears were skiding since i first touched the brake. I live in colorado and this concerns me because of the obvious ice plus rear tires locking equals same as pulling e brake. Sorry this was lengthy but what could my problem be dont know where to look everything seems to be working and now even the abs works.

Post by **jblackburn** » 19 Dec 2010, 21:30

I would try bleeding the brakes at all corners until you get fresh fluid out of the calipers - maybe there is water in the front lines. The S70 does bias light braking towards the back, but the fronts on my car are usually the first to start locking in most conditions.

aahmes57 · Post by **aahmes57** » 20 Dec 2010, 11:50

I'm also new to this site and it has been very helpful. I don't know if this applies or not however I recently had a similiar problem on a different make of car, actually truck. After trying and thinking of everything you probably thought of and tried, it was suggested to me to look at the cable that runs the emergency brake. Sure enough, the tube that the cable runs in was causing the cable to hang up and cause the brakes to stick on stay on.

Like I said, this may not apply at all since I'm unfamiliar of the Volvos e brake mechanics.

Post by **jblackburn** » 20 Dec 2010, 12:52

Actually, I could see how that could happen. It's braking more than normal if the E-brake shoes are dragging, and causing them to lock up before normal.

Mine shoes fell apart, locked my left tire, and dragged it along with no foot on the brake until the cable snapped outright. The backing falls away from the shoes and causes them to get stuck, which is a pretty common repair. Check out Lee's parking brake repair in the database for a how-to. I will tell you, though - it's not very fun.

Zachyfarms · Post by **Zachyfarms** » 20 Dec 2010, 13:53

i will try both. I did bleed brakes when i checked calipers a long while ago. But i will bleed it complete this time. thnak you for the suggestions

Post by **BEJinFbk** » 20 Dec 2010, 14:43

It may be worth your time to pull the rear rotors and inspect the e-brakes.

Post by **precopster** » 20 Dec 2010, 16:32

After eliminating all the above.

What sort of mileage have you done on the pads at the front? I'm leaning in this direction because I had a similar problem with my 960 which had a terrible hard pad compound at the front. This resulted in a rear braking bias which sometimes caused lockup. Do your wheels have the same amount of brake dust at the rear when comparing to the front? This is a fair (if somewhat rough) guide to the evenness of the braking. My 960 has even dust on all four wheras my 850 (with superior brakes) has much dirtier front wheels.

Have you tried a softer compound on the front brakes to re-apportion their braking strength?

Another factor can be tire choice. Old tires can be murderous to control. If the rear tires are old and the compound has hardened; there's your answer.

Post by **precopster** » 20 Dec 2010, 16:33

Keep us posted, thanks.

Zachyfarms · Post by **Zachyfarms** » 20 Dec 2010, 19:40

the rear wheels are completely black with dust every few weeks.. the front never have any dust..Can pad compound alone cause such a large rear bias. Would the proportioning valve cause something like this.. is it in master or somewhere inline.

Post by **precopster** » 20 Dec 2010, 22:48

Have no idea where this valve is. There's a fair amount of braking hardware under the bonnet. Are the discs glazed at the front? Are there grooves and lines on them? Pad compound as well as how these pads have been treated can cause irrepairable damage to the pedal feel and stopping performance. If there is little braking pressure at the front you won't be able to overheat the front discs on a repeated stopping run. Is this the case? Also can can you post photos of the discs?