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Brakes work, but booster doesn't

Help, Advice and DIY Tutorials on Volvo's P80 platform cars -- Volvo's 1990s "bread and butter" cars -- powered by the ubiquitous and durable Volvo inline 5-cylinder engine.

1992 - 1997 850, including 850 R, 850 T-5R, 850 T-5, 850 GLT
1997 - 2000 S70, S70 AWD
1997 - 2000 V70, V70 AWD
1997 - 2000 V70-XC
1997 - 2004 C70

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Chasma
Posts: 5
Joined: 24 September 2017
Year and Model: 1994 850
Location: USA

Brakes work, but booster doesn't

Post by Chasma »

When I brake while driving, the booster starts, but gives out almost immediately, so I have to basically stomp on the pedal to actually stop. I tested the hose going to the booster, there's no leak.

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FLXC90
Posts: 1132
Joined: 18 August 2014
Year and Model: 98 V70 T5
Location: Florida Panhandle
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Post by FLXC90 »

sitting still do you hear a big chuff of air when you push the pedal?
normal failure mode is a hole in the diaphragm. Other way is hole in the outer housing, like rust-through.
Current Volvos:
1998 V70 T5, 112k sat 5 years, still in mechanical coma (finally at the top of the pile )
2004 XC90 T6 AWD: 186k, 60 on transaxle ( traded in )
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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Clemens
Posts: 1934
Joined: 3 September 2015
Year and Model: 96 855 R + 94 855 T5
Location: Austria
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Post by Clemens »

Just out pf curiosity: is it a gas powered volvo or one with the audi diesel? The diesels have a vacum pump that goes bad. I just had that on my VW Multivan.
Summer: 1996 855 R
Winter: 1994 855 T5M
Donor: 1995 854 10V

Chasma
Posts: 5
Joined: 24 September 2017
Year and Model: 1994 850
Location: USA

Post by Chasma »

FLXC90 wrote: 27 May 2018, 14:44 sitting still do you hear a big chuff of air when you push the pedal?
normal failure mode is a hole in the diaphragm. Other way is hole in the outer housing, like rust-through.
It sounds more like a squeaky toy could that be the same thing?

Chasma
Posts: 5
Joined: 24 September 2017
Year and Model: 1994 850
Location: USA

Post by Chasma »

Clemens wrote: 27 May 2018, 15:37 Just out pf curiosity: is it a gas powered volvo or one with the audi diesel? The diesels have a vacum pump that goes bad. I just had that on my VW Multivan.
Thanks, but it's gas powered.

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FLXC90
Posts: 1132
Joined: 18 August 2014
Year and Model: 98 V70 T5
Location: Florida Panhandle
Has thanked: 16 times
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Post by FLXC90 »

If you have a helper, one press brake, one listen for where the squeaker is. use a length of tubing as a stethoscope if necessary, to really nail it down, unless it is obviously inside the can. (booster)
Current Volvos:
1998 V70 T5, 112k sat 5 years, still in mechanical coma (finally at the top of the pile )
2004 XC90 T6 AWD: 186k, 60 on transaxle ( traded in )
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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