Recently I purchased a 2006 V70 FWD NA with M56 manual transmission and about 90K miles. The previous owner bought it for European delivery and it was shipped home to USA after a few years in Europe. Records that came with the car indicate it was mostly serviced at Volvo dealers.

The biggest issue I noticed before purchase was the car veering slightly when brakes were applied / released, perhaps due to worn struts or control arms. The car also veers slightly under throttle application / release.

Today I realized that the problem is partly from brakes - the right front and left rear rotors are not shiny and dont get warm after multiple hard stops. I dont think the RF and LR calipers are frozen or binding, if they were it is more likely that the rotors would be overheating. There are no dash warnings or ABS light to indicate a problem. With heavy brake application from 30-40 mph on a dry road surface, the left front tire starts to lock up and ABS activates only on that wheel. That is correct behavior, the LF skids because it is the brake that is mostly stopping the car.

The clutch master cylinder was replaced just before I bought the car. Perhaps air was introduced into brake lines during that repair ? I think there is some brake line pressure for the RF and LR calipers but not enough for significant braking.

First check will be the calipers to make sure they arent binding, then confirm that the pistons do move when brake pedal is pushed. Bleeding all calipers would probably be the next step.

Has anyone seen a problem where one half of the dual diagonal brake system doesnt work ? Which section of the master cylinder is for the RF / LR calipers ? I dont know if a problem in the ABS system can remove line pressure from the RF / LR circuit.


Thanks,

Mike

Finally got around to diagnosing the problem - it was caused by stuck valves in the ABS hydraulic block. The block has 2 valves for each brake caliper (8 valves total) plus 4 more valves related to traction and stability control.

The valves for each caliper are:

1. Inlet valve that is normally open, permitting fluid to pass to the caliper.

2. Outlet or dump valve that is normally closed. It opens when commanded by the ABS controller to reduce line pressure by dumping excess fluid to an accumulator and the ABS pump inlet.

In my case the normally open inlet valves for the RF and LR calipers were stuck closed, preventing fluid flow from the master cylinder to the associated calipers. The hydraulic block is a sealed unit that has little possibility of repair without specialized tooling. Xemodex in Canada sells remanufactured blocks for several hundred dollars. For $75 I obtained a used block from a local auto recycler and confirmed that all 12 valves were working before installing the block.

When the ABS controller/hydraulic unit is installed in a car, the valves (and pump) can be individually activated by a Vida/Dice system. A clicking noise will be heard if the valve being activated is not stuck. That is how I originally diagnosed the problem, after realizing that no fluid was flowing during attempted caliper bleeding.

To test the valve block on a workbench, I separated the ABS controller electronics module from the hydraulic block and used a solenoid coil similar to the coils in the ABS controller. An equivalent test setup could be created by removing a solenoid coil from a defunct ABS controller module and connecting the coil through a pushbutton switch to a 12v battery or power supply. Then a candidate hydraulic block could be quickly tested by placing the solenoid coil over each projecting valve sleeve and pulsing power to the coil. Clicking noise = valve OK, silence = stuck valve.

Depending on which valves are stuck, it is possible for a hydraulic block with seized valves to seem OK under normal non-ABS braking. However a stop with ABS activation would cause the brake circuit with seized valve to behave improperly.

Perhaps the valves in my original hydraulic block seized because the brake fluid was not flushed often enough by the previous owner. After all the work it took to understand and fix the problem I have incentive to regularly flush the brake lines.

Mike

Thanks for getting back to us. Good info.

I'm late to this threaad.

I agree that you should start with a 4 wheel brake bleed.

How is the brake peddle? is it soft, or does it drop down slowly when you step on it? It should be firm.

Who installed the new Brake MC? Don't assume it's OK.
It first needs bench bleeding.
Was it a new OEM unit or a remanufactured?
Beware remanufactured MC's many are junk since all that some do is replace seals. If the bore is corroded or worn it needs machining or a new sleeve installed. My sense is that with a MC, you bite the bullet and buy only new OEM. You might luck out at Ebay and find a good price.

Another thing can be shot flex brake lines. I'd replace with new rubber
and not stainless, since stainless invites electrolysis nearby.

Good luck, Bill

The easiest thing to do would be to bleed the brakes, all 4 of them. Make sure you have the proper fluid for 2006.

If that doesn't fix it, suspect the caliper and take a good look at the slides.

When I bought my 850, previous owner must have complained about noisy brakes. The pads were glued to the brake pistons with red RTV, along with glue on the pad hangers - the pads couldn't move! Of course the brakes didn't work and needed 2 new rear calipers, along with rotors.


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Keeping it running is better than buying new

For me this is a modern Volvo. Earlier dual circuit cars had a shuttle at the fluid distribution block which is designed to shut off a circuit that is faulty. That's why you have dual circuits. In this case one side may be faulty and the shuttle is doing its job. The shuttle may also need to be reset after brake work or pressure switch replacement. I'm sure someone can expand more on these comments. It could be a very simple fix.

“First check will be the calipers to make sure they arent binding, then confirm that the pistons do move when brake pedal is pushed. Bleeding all calipers would probably be the next step.”

That is exactly where I would start. I suspect that there might be air in the RF/LR hydraulic circuit. Perhaps the clutch master cylinder repair might have introduced the air and it wasn’t properly bled out?? Having a schematic of the brake/clutch hydraulic system would be helpful.

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Will I buy another Volvo??? We'll see....