Any Volvo techs on here? re: brakes

Shappy · Post by **Shappy** » 25 Feb 2020, 13:28

I need to understand what is going on with my '99 V70 brakes. Most of the time they work just fine, but a couple of times each trip when I apply the brakes the pedal is very high and very hard, with no apparent braking effect. I then must pump and/or press harder to get the brakes to resume normal operation. I'm guessing the problem must be one of 3 possible components - the check valve, the position sensor, or the booster itself. I don't want to replace all 3 and discover the problem is something else. I'd like to understand why it is happening before throwing time and parts at it. Car has ~100k miles on it and is all original. Suggestions please?

: VolvoRR4.jpg (268.92 KiB) Viewed 1324 times

THANKS!!!

Post by **RickHaleParker** » 25 Feb 2020, 14:58

Are you losing brake fluid?

Post by **BEJinFbk** » 25 Feb 2020, 15:54

Possibility #4 - Are you getting any ABS warning lights?
( Just to make sure, does the ABS warning light come on
in self check mode just before you crank the engine over? )

Post by **abscate** » 25 Feb 2020, 18:51

The brake vacuum hose can chafe on the rear engine mount and bleed vacuum. Have a good look at the hose by removing it. There is an ejector pump which makes vacuum even under boost ( if you have a turbo) which ca also leak

Check valves and ejectors are available, I believe the brake boosters are not

I have two spares though, and traverse GTO quarterly

Post by **bmdubya1198** » 26 Feb 2020, 07:54

Check for any vacuum leaks first, make sure that big brake booster vacuum hose is in good shape and isn't chafed. Definitely check that ejector valve if your car is turbo, I've had one fail on me before while driving... not fun!

It's probably a good idea to change the check valve at this point anyway, I wouldn't be surprised if that's what's failing being that it seems your problem is intermittent.

Post by **scot850** » 26 Feb 2020, 10:52

Not sure what happened to my post response on this. There is a one way vacuum valve on the end of the hose into the brake booster/servo. These can start to fail with age. Pain to get into change but too expensive.

Neil.

Post by **jimmy57** » 26 Feb 2020, 10:57

To test for vaccum source problems, check valve or the vaccum ejector boost pump device: Start car and verify brake feel and function is normal. Drive car on a safe low traffic road. Get o 60-80 KPH and then coast for 2 seconds and then apply brakes to see if they are fine. If they feel hard as you describe then you have a more difficult to diagnose problem, likely the booster. If the brakes are fine then go on to next test. Accelerate briskly and while accelerating depress pedal a shot distance twist and then let off accel pedal and AT THE SAME TIME brake. If the brakes are now high and hard then the booster vaccuum supply system needs to be checked and replaced. Two seconds of coast will build aa lot of vacuum and would mask vac supply issues. WHen you accelerate there is no engine vaccum on a turbo engine car and depressing brake a couple of strokes bleeds off residual vacuum in booster. Applying brakes immediately will require vaccum for booster function before any vaccum is supplied by engine. The check valve on front of booster where supply line from engine connects holds vacuum in booster until needed. The ejector device mentioned is effectively a venturi through which some flows while under boost pressure from turbo and it causes suction through an orifice and is a backup vacuum source during acceleration or any other high throttle application driving. The way you describe problem points to both of these item in the vaccum supply failing as it would take check valve not doing its task of keeping stored vacuum present and the ejector not making vacuum to get that sudden brake apply with high and hard pedal to occur. That assumes the high and hard pedal is only happening on those instances where you apply brakes suddenly instead of a less rushed easy apply when you brske casually.

Post by **scot850** » 26 Feb 2020, 12:14

Great explanation jimmy57 of how to test this. I need to try this on my 'R' as occasionally I get a hard peddle on start up and reversing out of the garage. Once running there are no issues.

Many thanks.

Neil.

Post by **abscate** » 26 Feb 2020, 13:18

scot850 wrote: ↑26 Feb 2020, 12:14 Great explanation jimmy57 of how to test this. I need to try this on my 'R' as occasionally I get a hard peddle on start up and reversing out of the garage. Once running there are no issues.

Many thanks.

Neil.

Are you waiting for it to come off high idle? The Cars with VVT use it to inject extra air for idle burn (reduced emissions) which kills the manifold vacuum.

Like most things that are Volvo deep dive, I learned that from jimmy here.

Shappy · Post by **Shappy** » 04 Mar 2020, 19:42

THANKS for all the inputs here! I will work though them methodically once weather improves. Mine is non-turbo if that makes the suggested processes/sequences any different. I will start by removing and inspecting the hose to the check valve. Jimmy57 - not sure what you mean by "shot distance twist and let off".... ?? Yes the problem occurs well after driving for awhile.