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Old 04-15-2003, 07:59 AM
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Post pin on proportioning valve

Hi guys,
need to bleed my brakes, 2nd Gen Camaro (78 350cid to be precise), disc fronts, drum rears
proportioning valve / distribution block that the manual says I need to push in a pin to bleed the brakes, problem is the pin is jammed open and won't push in;

do I really need to push the pin in to bleed the brakes or does it just make it easier?

I can order one and fit it when it comes but I really need to get back on the road ASAP, any ideas?

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Old 04-15-2003, 09:45 AM
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I have changed brakes on a BUNCH of GMs and never pushed the pin. I always wondered what that pin was for. Guess that come from never reading instruction manuals!
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Old 04-16-2003, 12:42 AM
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cheers willys, that's what I thought,

does anyone know what that pin does anyhow?
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Old 04-16-2003, 04:56 AM
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I believe the pin is and indicator related to brake failure in one of the circuits of the dual system.
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Old 04-16-2003, 08:00 AM
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well, after a bit more searching (lucky I have nothing to do at work at the mo), in normal driving the proportioning valve supplies equal pressure to each wheel at gentle braking then splits 70/30 front and back under heavy braking

when bleeding, the mechanism that allows equal pressure to all wheels gets confused and cuts off supply to the front brakes meaning you can't bleed them, the pin stops this from happening.

Now, the pin locks the proportioning valve in one of 2 positions; either locked in the 50/50 front/back, or the 70/30 front/back

I'll take the car out for a spin after I get home and bleed them and I should be able to tell pretty quickly which one it is.
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Old 04-16-2003, 10:51 AM
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It occurs to me that somewhere in my dark past I read an instruction sheet or shop tech article that said for some cars,after installing a bench-bled master cylinder or breaking into the system, you should stomp the brake pedal several times before bleeding and adjusting. Perhaps this how the valve is centered on some vehicles without the exposed pin?
Worth a try, can't hurt.
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Old 04-16-2003, 12:14 PM
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[quote]Originally posted by andybird:
<strong>well, after a bit more searching (lucky I have nothing to do at work at the mo), in normal driving the proportioning valve supplies equal pressure to each wheel at gentle braking then splits 70/30 front and back under heavy braking

when bleeding, the mechanism that allows equal pressure to all wheels gets confused and cuts off supply to the front brakes meaning you can't bleed them, the pin stops this from happening.

Now, the pin locks the proportioning valve in one of 2 positions; either locked in the 50/50 front/back, or the 70/30 front/back

I'll take the car out for a spin after I get home and bleed them and I should be able to tell pretty quickly which one it is.</strong><hr></blockquote>

Thanx for the tip!
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Old 04-17-2003, 02:58 AM
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my problem is that the pin is rusted "in" so it's always in the in position (although I though it was the other way at first as I don't have a new one to compare against),
but driving the car, it seems to be stuck in the 70/30 position so that's ok (at least till the new one arrives anyhow)
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Old 04-17-2003, 03:07 AM
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Thanks to Hotrodders.com, I learn something every day. Our hot rodding Buds (Mates) across the way sure can make us get back into the books with their "forced" research!!

Thanks Andy.

Trees
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Old 04-17-2003, 05:47 AM
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well needs must when the the devil ****s on your cornflakes,

and I need to make sure I have the stopping power to offset the new found 411 lb/ft of torque

although I am becoming increasingly glad of this here intermernet thingy, I contacted a UK supplier of american car parts and they wanted roughly $200 for the valve and it would take 2-3 weeks to arrive (because they wanted to just put it in their next container that was due to come over), I contacted yearone.com, valve = $76, postage in 3-5 days = $36, plus taxes = $133
bargain!

[ April 17, 2003: Message edited by: andybird ]</p>
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Old 04-17-2003, 09:48 AM
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[quote]Originally posted by andybird:
<strong>well needs must when the the devil ****s on your cornflakes,

and I need to make sure I have the stopping power to offset the new found 411 lb/ft of torque

although I am becoming increasingly glad of this here intermernet thingy, I contacted a UK supplier of american car parts and they wanted roughly $200 for the valve and it would take 2-3 weeks to arrive (because they wanted to just put it in their next container that was due to come over), I contacted yearone.com, valve = $76, postage in 3-5 days = $36, plus taxes = $133
bargain!

[ April 17, 2003: Message edited by: andybird ]</strong><hr></blockquote>

I get mine at Pick-A-Part for $5!!
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