Brake bleeding problem & Rear disc issues... anyone? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

75stepside · 03-27-2005, 11:10 PM

Trying to bleed out my truck this weekend: results front brakes, excellent pressure, rear brakes, so/so pressure. The front has great pressure; when you crack the bleeder, the fluid gushes out. In the rear, when crack the bleeder, the fluid drips out.

In my resto project, all lines, steel and rubber are new. I changed my porportioning value with one from a yard, b/c it was suspected to be the problem before with the rear having no pressure. The line going out of my master cylinder is 1/4" for both front and rear to the value. The line going out of the valve to the rear is 1/4". The master cylinder was replaced and bled.

Is is possible that I just have an air bubble in the middle of the system? Someone told me to lift the front of the truck up and let gravity work the air out...??? OR do I have a problem w/ my line setup? OR is it something w/ my rear disc setup???

boxrodz · 03-27-2005, 11:43 PM

In general, the disc/drum setups have less pressure at the rear wheels. One of the major brake companys that offer disc brake conversion kits for these trucks recommends upgrading the master cylinder to provide the needed pressure (and fluid) at the rear. I talked to TSM a while back and he didn't see a need to swap out the master cylinder. He said that they have done many rear disc brake conversions on 'delivery' trucks without any problems.

I swapped out my rubber brake hoses, disc calipers and wheel cylinders a couple of weeks ago. During the bleeding process, I noticed better flow in the front than the rear. Currently, I still have the stock rear drum brakes. While bleeding the rear, I had to be careful not to let air back into the lines.

I would try bleeding the rear again and watch for any air trying to get back into the system. BTW, did you have to bleed the master cylinder?

75stepside · 03-28-2005, 10:42 AM

Master cylinder was bled out. someone was telling me that there is a pin or something that has to be removed from the porportioning valve to get it to bleed correctly ???

boxrodz · 03-28-2005, 12:38 PM

Yes.
I'm not sure on your 75, but the metering pin covered by a rubber boot on the proportioning valve must be depressed. I was able to depress it with a block of wood. I also depressed the brake pedal a few times to release any vacuum in the system prior to bleeding.

84 PUMPKIN · 03-28-2005, 02:56 PM

I had the same problem on my '81 when I did the rear disc conversion. To make a REALLY long story short, I installed a new proportioning valve from In-line tube that was made for the disc/disc combo. Part #PR-101. It's a direct replacement and needs no adapters or extra fittings.

75stepside · 03-28-2005, 03:05 PM

where do you get this at!!?!? Is it a replacement for the factory porportioning valve?

edit... found it online... go google.com! http://www.inlinetube.com/Prop%20Valves/PR-101.htm

so, basically, you had the same issue, lame pressure to the rear?

boxrodz · 03-29-2005, 01:15 AM

Looks like the Inline Tube proportioning valve is what you're after since it will increase the pressure of the rear brakes (to 50%). I wonder if after installing the prop valve, an adjustable prop. valve will be needed to fine tune the rear disc brakes with respect to the front disc brakes.

84Pumpkin-
What conversion kit did you go with? How's the pedal travel with the rear disc brakes?

84 PUMPKIN · 03-29-2005, 11:21 AM

My '81 C10 has a kit that I purchased on ebay about 5 years ago.

My '79 K20 kit was also purchased on ebay about 2 years ago but from a different seller.

My '33 Coupe has a kit from Currie Enterprises.

Both trucks have stock master cylinders, brake lines, etc. The rear disc brakes and the proportioning valves are the only changes. The brakes are excellent and the pedals are nice and full. The Coupe has an adjustable valve due to the 502 under the hood. The rear brakes would lock up before the fronts so I had to adjust the pressure. The Coupe has manual 4WDB so the pedal has a different feel but the brakes are excellent.

75stepside · 03-29-2005, 11:47 AM

Just purchased my unit from In-line tube - great people to deal with... so, you dont have an adjustable valve on your c10 ? currently, i Have one on mine, mostly b/c i figured it needed it!?!?

84 PUMPKIN · 03-29-2005, 08:02 PM

No. I don't have an adjustable proportioning valve on either one of my trucks. If you have one already installed then I'd keep it because you can tweak the brakes to suit your driving style.

The crew at In-line tube are excellent to deal with. When I need anything related to brakes I call them first.

Hope the P/Valve does the trick.

boxrodz · 03-30-2005, 02:32 AM

Thanks for the info, 84Pumpkin. Coupes

with a 502

75Stepside - Let us know how you make out.

75stepside · 04-04-2005, 10:59 AM

Quote:

Originally Posted by 84 PUMPKIN

I had the same problem on my '81 when I did the rear disc conversion. To make a REALLY long story short, I installed a new proportioning valve from In-line tube that was made for the disc/disc combo. Part #PR-101. It's a direct replacement and needs no adapters or extra fittings.

Got my P-valve and got it in and the lines all bled out... may need a little more bleeding, but overall, worked out great. I have plenty of pressure to the rear... Question, is there any pin removing or anything like that when bleeding the system???

boxrodz · 04-05-2005, 02:15 AM

Good to hear that you got brake system all work out. I'm not aware of any pin other than the metering valve in the proportioning valve I mentioned before. I checked in the shop manual and did not see any mention of a 'pin'.

03-27-2005, 11:10 PM	#1
75stepside Proud Member Join Date: Nov 2002 Location: Pittsburgh, PA Posts: 741	Brake bleeding problem & Rear disc issues... anyone? Trying to bleed out my truck this weekend: results front brakes, excellent pressure, rear brakes, so/so pressure. The front has great pressure; when you crack the bleeder, the fluid gushes out. In the rear, when crack the bleeder, the fluid drips out. In my resto project, all lines, steel and rubber are new. I changed my porportioning value with one from a yard, b/c it was suspected to be the problem before with the rear having no pressure. The line going out of my master cylinder is 1/4" for both front and rear to the value. The line going out of the valve to the rear is 1/4". The master cylinder was replaced and bled. Is is possible that I just have an air bubble in the middle of the system? Someone told me to lift the front of the truck up and let gravity work the air out...??? OR do I have a problem w/ my line setup? OR is it something w/ my rear disc setup???

03-27-2005, 11:43 PM	#2
boxrodz Until Seventy Times Seven Join Date: Feb 2005 Location: Rocky Mountain Front Range Posts: 1,301	In general, the disc/drum setups have less pressure at the rear wheels. One of the major brake companys that offer disc brake conversion kits for these trucks recommends upgrading the master cylinder to provide the needed pressure (and fluid) at the rear. I talked to TSM a while back and he didn't see a need to swap out the master cylinder. He said that they have done many rear disc brake conversions on 'delivery' trucks without any problems. I swapped out my rubber brake hoses, disc calipers and wheel cylinders a couple of weeks ago. During the bleeding process, I noticed better flow in the front than the rear. Currently, I still have the stock rear drum brakes. While bleeding the rear, I had to be careful not to let air back into the lines. I would try bleeding the rear again and watch for any air trying to get back into the system. BTW, did you have to bleed the master cylinder? __________________ boxRODz 1983 C10 SWB Fleetside When two halves is gone, there's nuthin left. Two nothings is nuthin. That's mathematics son. You can argue with me but you can't argue with figures. Two half nothings is a whole nuthin...

03-28-2005, 12:38 PM	#4
boxrodz Until Seventy Times Seven Join Date: Feb 2005 Location: Rocky Mountain Front Range Posts: 1,301	Yes. I'm not sure on your 75, but the metering pin covered by a rubber boot on the proportioning valve must be depressed. I was able to depress it with a block of wood. I also depressed the brake pedal a few times to release any vacuum in the system prior to bleeding. __________________ boxRODz 1983 C10 SWB Fleetside When two halves is gone, there's nuthin left. Two nothings is nuthin. That's mathematics son. You can argue with me but you can't argue with figures. Two half nothings is a whole nuthin...

03-28-2005, 03:05 PM	#6
75stepside Proud Member Join Date: Nov 2002 Location: Pittsburgh, PA Posts: 741	where do you get this at!!?!? Is it a replacement for the factory porportioning valve? edit... found it online... go google.com! http://www.inlinetube.com/Prop%20Valves/PR-101.htm so, basically, you had the same issue, lame pressure to the rear? Last edited by 75stepside; 03-28-2005 at 03:11 PM.

03-29-2005, 01:15 AM	#7
boxrodz Until Seventy Times Seven Join Date: Feb 2005 Location: Rocky Mountain Front Range Posts: 1,301	Looks like the Inline Tube proportioning valve is what you're after since it will increase the pressure of the rear brakes (to 50%). I wonder if after installing the prop valve, an adjustable prop. valve will be needed to fine tune the rear disc brakes with respect to the front disc brakes. 84Pumpkin- What conversion kit did you go with? How's the pedal travel with the rear disc brakes? __________________ boxRODz 1983 C10 SWB Fleetside When two halves is gone, there's nuthin left. Two nothings is nuthin. That's mathematics son. You can argue with me but you can't argue with figures. Two half nothings is a whole nuthin...

03-28-2005, 10:42 AM	#3
75stepside Proud Member Join Date: Nov 2002 Location: Pittsburgh, PA Posts: 741	Master cylinder was bled out. someone was telling me that there is a pin or something that has to be removed from the porportioning valve to get it to bleed correctly ???

03-28-2005, 02:56 PM	#5
84 PUMPKIN Registered User Join Date: Oct 2004 Location: Alabama Posts: 166	I had the same problem on my '81 when I did the rear disc conversion. To make a REALLY long story short, I installed a new proportioning valve from In-line tube that was made for the disc/disc combo. Part #PR-101. It's a direct replacement and needs no adapters or extra fittings.

03-29-2005, 11:21 AM	#8
84 PUMPKIN Registered User Join Date: Oct 2004 Location: Alabama Posts: 166	My '81 C10 has a kit that I purchased on ebay about 5 years ago. My '79 K20 kit was also purchased on ebay about 2 years ago but from a different seller. My '33 Coupe has a kit from Currie Enterprises. Both trucks have stock master cylinders, brake lines, etc. The rear disc brakes and the proportioning valves are the only changes. The brakes are excellent and the pedals are nice and full. The Coupe has an adjustable valve due to the 502 under the hood. The rear brakes would lock up before the fronts so I had to adjust the pressure. The Coupe has manual 4WDB so the pedal has a different feel but the brakes are excellent.

03-29-2005, 11:47 AM	#9
75stepside Proud Member Join Date: Nov 2002 Location: Pittsburgh, PA Posts: 741	Just purchased my unit from In-line tube - great people to deal with... so, you dont have an adjustable valve on your c10 ? currently, i Have one on mine, mostly b/c i figured it needed it!?!?

03-29-2005, 08:02 PM	#10
84 PUMPKIN Registered User Join Date: Oct 2004 Location: Alabama Posts: 166	No. I don't have an adjustable proportioning valve on either one of my trucks. If you have one already installed then I'd keep it because you can tweak the brakes to suit your driving style. The crew at In-line tube are excellent to deal with. When I need anything related to brakes I call them first. Hope the P/Valve does the trick.

03-30-2005, 02:32 AM	#11
boxrodz Until Seventy Times Seven Join Date: Feb 2005 Location: Rocky Mountain Front Range Posts: 1,301	Thanks for the info, 84Pumpkin. Coupes with a 502 75Stepside - Let us know how you make out. __________________ boxRODz 1983 C10 SWB Fleetside When two halves is gone, there's nuthin left. Two nothings is nuthin. That's mathematics son. You can argue with me but you can't argue with figures. Two half nothings is a whole nuthin...

04-05-2005, 02:15 AM	#13
boxrodz Until Seventy Times Seven Join Date: Feb 2005 Location: Rocky Mountain Front Range Posts: 1,301	Good to hear that you got brake system all work out. I'm not aware of any pin other than the metering valve in the proportioning valve I mentioned before. I checked in the shop manual and did not see any mention of a 'pin'. __________________ boxRODz 1983 C10 SWB Fleetside When two halves is gone, there's nuthin left. Two nothings is nuthin. That's mathematics son. You can argue with me but you can't argue with figures. Two half nothings is a whole nuthin...



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