98 S70 N/A MT, Brake Master Cylinder Replacement 9140251

[theWIFES_S70]

First things first: this is a messy job. Brake fluid will get everywhere. Proceed with that in mind. If you'd rather leave this to a shop, I don't think anyone should look down at that.

1. Identify the correct master cylinder.... Not as easy as it should be. Look at the nuts that screw into your master cylinder. If they are both the same size (11mm) then you need to order the master cylinder for cars without TRACS. If you have an 11mm nut (facing the front of the car) and another one that's larger towards the firewall, than you need to order the TRACS model master cylinder.

There are two master cylinders available from our usual parts suppliers. One is for cars with TRACS and one is for cars without TRACS.

Volvo Brake Master Cylinder (850 C70 S70 V70) - Cardone 11-2805
https://www.fcpeuro.com/products/volvo- ... car-112805

Volvo Brake Master Cylinder (850 C70 S70 V70) - Cardone 11-2843
https://www.fcpeuro.com/products/volvo- ... car-112843

I have had four of these in hand (including my busted one) so I spent some time looking at these two variations. Here is the only difference between the two...



I had mistakenly thought that this was a remanufacturing error. But it wasn't... It was a listing error. And information error!

2. Disconnect the brake pressure sensor electric connector, disconnect the (brake fluid sensor?) wire on top of the master cylinder. And move the relay box away. The extra room will be welcomed!

3. Place rags and napkins and paper towels over everything below the master cylinder. Go overboard. Trust me.

4. Drain as much brake fluid as you can from the reservoir. As soon as you remove the hose from the bottom of the reservoir, it will begin to drip profusely. I believe this is the hose that connects to my clutch master cylinder. (I'm not sure.) I didn't think fluid would come out of the reservoir so this probably cause a good 60% of the mess...

5. Crack the brake lines with a flare nut wrench. I used these great little Gearwrench Metric flex flare nut wrenches. The 11mm worked great. It flexed just enough to allow me to crack the nut without banging against the reservoir. Here's a picture of when I installed the new (wrong) master cylinder. I wouldn't remove the lines entirely until the bolts are removed so you can try to quickly remove it and quickly get the new master cylinder in there.


6. 13mm flex sockets will be your friend. Along with a six-inch extension, and a flex head 3/8 ratchet it's pretty easy to crack the bolts that secure the master cylinder to the brake booster. There are two bolts securing the master cylinder to the brake booster. I'm sure you could do this with short sockets and wobble sockets, but ever since I started using flex sockets stuff has just been so much easier. (I recommend a set of Metric Gearwrench Flex sockets.) NOTE: the napkins here are NOT ENOUGH.

7. OK, wiggle the old master cylinder out. It'll come out pretty easily. Try not to put to much stress on the brake lines. Once you have the old master cylinder out, swap some stuff over: take off the sensor with a 14mm combination wrench and disconnect the brake fluid reservoir by removing the T25 bolt that secures it. There are two gaskets that press into the master cylinder. They looked fine so I left them. I don't have any leaks right now so things should be alright...

8. Bolt the rebuilt master cylinder into the brake booster, but only hand thread it. Connect the brake line fitting closest to the firewall first. You'll have to move around the master cylinder in order to get the threads going. Take your time. It'll go in. Once you get it in, do the other. Again, take your time. Try not to put too much stress on the reservoir. This is why the flex head metric flare nut wrenches were really good here.

9. Once those lines are tight, get the master cylinder bolted on. Don't know how you would get a torque wrench in. Just know it has to be tight. Pay attention to how hard it was to crack the bolts. Use common sense here.

10. Reattach the clutch master cylinder hose and clamp it. I decided against using the original clamp and put in a worm gear one. The other one was kind of loose after all the years.

11. Fill up your master cylinder with DOT 4 Brake fluid. I used Pentosin Super4 two years ago. It turned really brown in that time. I put in Pentosin LV (lower viscosity) DOT 4 in there now. It costs more than Super 4 so hopefully its better!

12. Bleed the air from the master cylinder... I have been operating off this Scotty Kilmer video. I think I need to keep doing this. The pedal holds pressure when the car's off, it feels great, really hard. But it's not really working... I ran out of light so I'll finish up tomorrow. I also replaced the front brake lines with OE German lines so I probably introduced some air there, too. I'll bleed all four wheels and see if that gets the ball rolling (or gets the car stopping!)


13. Plan to bleed air from all four wheels. I tried to bleed the ABS pump but couldn't do it and ended up taking it to my mechanic. There are a lot of long videos about bleeding ABS pumps and master cylinders abd in one example the poster says you connect six feet of tubing from a bleeder screw to your master cylinder and you pump like crazy... don't know if that works. But I could imagine it working. Understand if undertake this job, you might not be able to bleed all the air out...

Thanks for all the support fellas!

[abscate]

Just a note on this. Anytime you crack a hose at the master cylinder you have to plan on bleeding at all four wheels to get air out. It is possible to bleed at the mc and get the air out, I've probably got an 80% success rate at this, but once in a while it's the full Monty. Upshot, make sure all bleeders are loose and workable before mc work.

[theWIFES_S70]

Thanks for the input! I didn't bleed the rear brakes so I'm off to do that now. I'm hoping I don't have to run a hose from a caliper to the master cylinder to bleed more air out, but who knows.

[abscate]

Just a note on acronym soup and parts here

From 99 on , traction control is called STC instead of TRACS. I suspect the mc changed too, I'll measure my mc ports and add that to the bastards thread.

Both 13mm Flare nuts measured on the ports of my 1999 with STC

[theWIFES_S70]

13mm??? Man, this is good to know.

Definitely check the nut size on your brake master cylinders before ordering parts!!

[abscate]

Just a note on acronym soup and parts here

From 99 on , traction control is called STC instead of TRACS. I suspect the mc changed too, I'll measure my mc ports and add that to the bastards thread.

Both 13mm Flare nuts measured on the ports of my 1999 with STC

This is fake internet news

There are both TRaCS and STC options on Volvo are in the P80 chassis. In 1999 you could have either. Source : cars in my driveway