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'98 V70 Hard Brake Pedal, "Popping" Sensation

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bmdubya1198
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'98 V70 Hard Brake Pedal, "Popping" Sensation

Post by bmdubya1198 » Fri Jun 08, 2018 10:20 am

Well I guess I'll finally give my daily a little attention to take my mind off of my projects!

I've had an issue for a while, probably since I changed my brakes about a year and a half ago, where the brake pedal just gets really hard sometimes. It's not too noticeable until I realize I'm putting most of my weight on the brake pedal just to stop the car from 35. The pedal is pretty stiff as it is, which is why it's not always immediately evident.
I've noticed it much more lately, especially on some of our rougher roads when I'm trying to slow down for construction and whatnot that it takes a lot of effort to slow down or stop and it feels like the ABS is kicking in (and it definitely has a few times).

The other issue that has been very noticeable is the brake pedal giving a "popping" sensation when it stiffens up. It feels like it's hitting steps while I depress it, and the brakes are less effective.

I don't know if it's an issue with how the brakes were bled (that was a project in itself, I could never get the pedal to feel "right," it was either way too soft and it went to the floor and the brakes barely worked or it was like it is now) or it's an issue with the booster. I have a feeling that the problem could be the check valve (is there only the one on the booster for 1998 models?). And just maybe that's what is causing that hiccup that my car has had since day 1, which interestingly enough happens most often while braking, and ONLY happens while I'm on the brakes (never done it while idling in neutral or park).

I just want my brakes to feel more linear than they are now. Plus, they seem to be too weak most of the time. I know the problem has to be within the power brake system (with the exception of the master cylinder, already replaced that a while back and it's not losing fluid) rather than the brakes at the wheels. Those have been completely redone, I replaced the seals in all four calipers as well as changed the front hoses and of course rotors and pads.

Sorry for the long winded and possibly scattered post, this is just one of those weird issues that I want to get taken care of. Is there a way to test the check valve, and am I that far off with that being the potential issue?


1998 V70 GLT Black/Beige 185,000 and counting
2000 V70R Venetian Red/Black 187k M56 swap in progress
1988 744 Turbo M46 Beige Metallic/Beige 188k- Gone but not forgotten
1999 Miata Sport 5 speed

scot850
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Re: '98 V70 Hard Brake Pedal, "Popping" Sensation

Post by scot850 » Fri Jun 08, 2018 10:29 am

Sounds like the booster may not be working.

Check the pipe to the booster from the inlet manifold has not split with age. Not all V70 P80's route the pipe the same, but it usually runs over under the battery tray and then under the airbox and up to the booster. If it has not been replaced then it makes sense to do that as they can crack with age.

2nd issue is the booster valve. It is a plastic valve that the booster pipe connects to. They can fail preventing vacuum holding in the booster. Pull one form a suitable junkyard car and swap it out and see if that makes a change.

3rd issue is how are the calipers? Rears are prone to seizing but fronts can too, especially when re-built units. Like axles re-built units are a crap shoot.

4th issue is when where the flexi-pipes last replaced? They can fail internally preventing all brakes working, and making it harder to bleed the system. A pressure system for bleeding the brakes like a Mity-vac (?) or similar really helps on these cars.

Neil.


2000 V70 R - still being an endless PITA
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2003 Toyota 4Runner V8 Limited
2015 Kia Sportage EX-L
1993 850 GLT -Sold
1998 V70 XC - Sold
1997 Volvo 850 SE NA - Went to niece in California - Sold
2000 V70 SE NA - New project and test bed - Sold

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Re: '98 V70 Hard Brake Pedal, "Popping" Sensation

Post by bmdubya1198 » Fri Jun 08, 2018 10:50 am

scot850 wrote:
Fri Jun 08, 2018 10:29 am
Sounds like the booster may not be working.

Check the pipe to the booster from the inlet manifold has not split with age. Not all V70 P80's route the pipe the same, but it usually runs over under the battery tray and then under the airbox and up to the booster. If it has not been replaced then it makes sense to do that as they can crack with age.

2nd issue is the booster valve. It is a plastic valve that the booster pipe connects to. They can fail preventing vacuum holding in the booster. Pull one form a suitable junkyard car and swap it out and see if that makes a change.

3rd issue is how are the calipers? Rears are prone to seizing but fronts can too, especially when re-built units. Like axles re-built units are a crap shoot.

4th issue is when where the flexi-pipes last replaced? They can fail internally preventing all brakes working, and making it harder to bleed the system. A pressure system for bleeding the brakes like a Mity-vac (?) or similar really helps on these cars.

Neil.
Thanks, I might go ahead and change out the booster vacuum hose anyway, as well as the check valve.

I redid the calipers myself, and the rears were pretty seized up. The front were not bad. I hear ya on the reman axles being a crap shoot... my Napa one has caused my transmission to leak from the output shaft since I put it in!

I changed the front flex hoses, the rears are original. They looked to be in good condition though, so that's part of the reason I haven't bothered.


1998 V70 GLT Black/Beige 185,000 and counting
2000 V70R Venetian Red/Black 187k M56 swap in progress
1988 744 Turbo M46 Beige Metallic/Beige 188k- Gone but not forgotten
1999 Miata Sport 5 speed

scot850
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Re: '98 V70 Hard Brake Pedal, "Popping" Sensation

Post by scot850 » Fri Jun 08, 2018 1:35 pm

As long as you get a good flow of fluid out the rear calipers when bleeding them then chances are the rear flexi's are probably ok.

Just make sure all the calipers are free, but I think the issue may be with the booster system.

Neil.


2000 V70 R - still being an endless PITA
2006 XC70
2003 Toyota 4Runner V8 Limited
2015 Kia Sportage EX-L
1993 850 GLT -Sold
1998 V70 XC - Sold
1997 Volvo 850 SE NA - Went to niece in California - Sold
2000 V70 SE NA - New project and test bed - Sold

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Re: '98 V70 Hard Brake Pedal, "Popping" Sensation

Post by FLXC90 » Fri Jun 08, 2018 2:24 pm

W; make your testing easier, get a piece of tubing you can run on top of the motor temporarily, then work on routing one the right way after you've done your diagnosis.


Current Volvos:
1998 V70 T5, 112k sat 5 years, still in mechanical coma (for sale )
2004 XC90 T6 AWD: 186k, 60 on transaxle ( traded in today)
1998 POS70 N/A: DD/training aid, 236k but really about 240k, I think...ABS module( passed on to son who sold it)

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bmdubya1198
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Re: '98 V70 Hard Brake Pedal, "Popping" Sensation

Post by bmdubya1198 » Fri Jun 08, 2018 2:28 pm

Same here, and I'm hoping a new check valve and hose will fix it.
Fluid flow at all four calipers was just fine. I used the Harbor Freight vacuum hand pump to bleed them.


1998 V70 GLT Black/Beige 185,000 and counting
2000 V70R Venetian Red/Black 187k M56 swap in progress
1988 744 Turbo M46 Beige Metallic/Beige 188k- Gone but not forgotten
1999 Miata Sport 5 speed

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bmdubya1198
Posts: 2227
Joined: Tue Dec 30, 2014 10:45 am
Year and Model: '98 V70 GLT
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Re: '98 V70 Hard Brake Pedal, "Popping" Sensation

Post by bmdubya1198 » Fri Jun 08, 2018 2:28 pm

FLXC90 wrote:
Fri Jun 08, 2018 2:24 pm
W; make your testing easier, get a piece of tubing you can run on top of the motor temporarily, then work on routing one the right way after you've done your diagnosis.
Good idea, that's probably exactly what I'll do!


1998 V70 GLT Black/Beige 185,000 and counting
2000 V70R Venetian Red/Black 187k M56 swap in progress
1988 744 Turbo M46 Beige Metallic/Beige 188k- Gone but not forgotten
1999 Miata Sport 5 speed

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