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No rear brakes - Prop valve?

tsitalon1

Well-known member
Joined
Dec 29, 2010
Messages
309
Location
Montgomery Al
Hey guys,

Need a little help. My vr4 never seemed to stop as well as I would like and today I verified why.

No hydraulic pressure to the rear calipers at all.

The car is an ABS car so I am unsure if I need to replace the Prop valve, look for a blockage in the lines, or look at the ABS unit.

Any advice?
 

FlyingEagle

Staff member
Joined
Mar 5, 2005
Messages
1,635
Location
THE Ottawa
How was this confirmed?

Car in the air, wheels off the ground, someone pressing the pedal, while the rear tires are checked for brake application??

You could also flip up the caliper and make sure it moves when the pedal is pressed, just be careful to make sure that multiple pedal presss don't push it out too far. If you wedge something in between that won't damage surfaces, it will keep the piston from popping out.
Next use large channel lock pliers or a brake piston screw kit to push the piston back in .... oh, these cars probably have the "twist in/push in at the same time" rear calipers, so try using a set of large needle noise pliers and inward pressure (your hands are going to hate you and don't get stabby with your hands in case you slip) and make sure the caliper pistons will 1: Turn and 2: Retract.
Once caliper bore/piston movement is confirmed on both sides, then go to the next step.
Have someone operate the parking brake. Be sure to confirm the pistons move out, as they are acted upon with direct physical/mechanical operation of a pivot/arm inside the caliper. If during these tests you don't get movement from physical actuation of the piston directly, then try this.
Go with a bleed, but be very weary of old bleeder screws. Snap one and you are either attempting to drill/easy out the screw or putting on new calipers.
I've torched a myriad of screws, let them cool just enough from being cheery red, to then allow light pressure manipulation to crack them loose. Sometimes they don't play nice and require a few applications, and other times they require no heat at all.

Wrote a book, but just wanted to make sure the basics were covered.
 
Last edited:

tsitalon1

Well-known member
Joined
Dec 29, 2010
Messages
309
Location
Montgomery Al
Hey thanks for the reply.

Verified as such:

1. With rear wheel off the ground engine running and had someone step on brake pedal, rear wheels spinned freely.
2. Caliper pistons not stuck as I just rotated and pushed them in to replace the pads that day. (old pads had almost zero wear in 2+ years)
3. Attempted to bleed rear, assistant pumped and held brake pedal while I cracked open the bleeder - nothing came out.
4. Brake pedal feels normal and NOT spongy or soft.
5. Car stops ok (can lock up fronts) and is not dangerous - just feels like I'm missing 25-35% of my braking ability.

My only thoughts are Prop valve, rear lines, or ABS unit.

I'm leaning towards the Prop valve as a google search on the topic reveals several people (non-dsm folks) reporting a loss of rear breaks when Prop valves go bad. I read there is a built in safety feature in them to prevent catastrophic failure if the valve detects a large diff in pressure between front/rear (for leaks).

Has anyone here had these symptoms before with a GVR4 or DSM?
 

EHmotorsports

Well-known member
Joined
Sep 25, 2012
Messages
1,278
Location
Beaverton
Disconnect the caliper brake hoses to the back and see if fluid comes out. if it does replace rear calipers. if not work your way up to the prop valve.
 

tsitalon1

Well-known member
Joined
Dec 29, 2010
Messages
309
Location
Montgomery Al
EHmotorsports - No fluid when disconnecting rear calipers from brake hose and stepping on brake pedal. - Brake pedal also feels normal.

JNZTuning reports that the Prop valve isn't available for a 91 GVR4 with ABS...

Anyone know of another valve that will work? Anyone have one lying around they want to sell?

Looks like the prop valve only handles the rear brakes as the fronts as fed directly from the ABS unit.
 

FlyingEagle

Staff member
Joined
Mar 5, 2005
Messages
1,635
Location
THE Ottawa
Any 89-92 ABS equipped Galant (turbo or non-turbo) will have this. Manuals states they are the same for 89-92 Non-ABS, and TC/NA ABS. Split point 740 PSI, Decompression ratio 0.4
All other models of Galant, FWD or AWD (93) will not work, as they have a lower split point near the 5XX psi range.
 
Last edited:

ade

Well-known member
Joined
Aug 16, 2011
Messages
303
Location
Paumanok NY
i got one its purty ugly looking and i never used it while on the car but if u want it its yours. i just have to look for it.
 

tsitalon1

Well-known member
Joined
Dec 29, 2010
Messages
309
Location
Montgomery Al
Thanks guys, I found one from a gvr4.org member and should receive it soon.

I'll let you guys know if the deal falls through.

I'll also update this thread if the valve fixes the issue.
 

tsitalon1

Well-known member
Joined
Dec 29, 2010
Messages
309
Location
Montgomery Al
Turned out it was the ABS unit not passing fluid to the prop valve/rear.

Converted to non-abs and rears are working.

Thanks for the help guys.
 
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