68 c10 brake problems - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Gav2606 · 08-04-2018, 11:45 AM

Hi all. Ive got 68 c10 with s10 front discs and camaro rear axle with druns. I got in the truck this week and the brake pedal went to the floor. It was fine when i parked it up last time. Fluid level is good. It had dual master cylinder with a remote booster for the front brakes. Ive changed the master cylinder and no change. If i pump the pedal a few times a get a good pedal but leave it 3 seconds and then press it and goes to the floor again..i pumped them 40 times and the fluid level didnt drop and no visable leaks anywere. Could this be air in the system if the old master cylinder failed or any other ideas? The strange thing is dual system master cylinder i thought i would only loose front or rear not both. The brakes do work just right on the floor..

firedemon · 08-04-2018, 09:09 PM

sounds like air in the system

Gav2606 · 08-05-2018, 03:57 AM

Gav2606 · 08-05-2018, 04:05 AM

The block that the pipes go into. Is that a propertning valve. There is one hole with a bolt in it and its totally dry with no fluid coming out..is that correct? Also is the wire on the bottom for the brake warning light?

ncpetersc · 08-05-2018, 11:05 AM

Quote:

Originally Posted by Gav2606

The block that the pipes go into. Is that a propertning valve. There is one hole with a bolt in it and its totally dry with no fluid coming out..is that correct? Also is the wire on the bottom for the brake warning light?

That is the proportioning valve, the wire is for the break warning light, I have no idea if the "dry hole" is correct.

weq92f · 08-05-2018, 12:12 PM

Wow, I've never even seen a remote booster before.

The pumping action you describe indicates a failing MC plunger. What if you pump up the brake pedal and keep the pressure on it. Does it slowly find its way to the floor while you hold the pressure on the pedal?

Air in the lines would make for a spongy, mushy pedal because that air will compress where hydraulic fluid without any air will not.

-klb

**Steeveedee** · 08-05-2018, 12:47 PM

If you already replaced the master cylinder, the culprit is likely to be the slave cylinder in the booster is bypassing. I've never seen a setup like that before, BTW.

If it were mine, I'd be installing a conventional setup using the booster between the interior pushrod and the master cylinder. No offense, but that looks Mickey Mouse to me.

Gav2606 · 08-05-2018, 02:11 PM

Yeh i am thinking i should change it all to a more modern set up. Its how it was when i purchased it in the uk. Parts are not as easy to come by over here so may look at getting one shipped from rock autos. Yeh if i pump it up and hold it the peddle seems to stay there and not fade away.. it was a 2nd hand ms i fitted that my uncle had spare so no gaurentee its good.. thanks for the info..

68is4me · 08-06-2018, 12:18 PM

That complete setup just looks wrong. I would fix it right then see what the problems are. Is that even a proportioning valve? Is it up side down and backwards?

The factory disc drum prop valve should look like this.

08-04-2018, 11:45 AM	#1
Gav2606 Registered User Join Date: Apr 2018 Location: Highbridge Posts: 38	68 c10 brake problems Hi all. Ive got 68 c10 with s10 front discs and camaro rear axle with druns. I got in the truck this week and the brake pedal went to the floor. It was fine when i parked it up last time. Fluid level is good. It had dual master cylinder with a remote booster for the front brakes. Ive changed the master cylinder and no change. If i pump the pedal a few times a get a good pedal but leave it 3 seconds and then press it and goes to the floor again..i pumped them 40 times and the fluid level didnt drop and no visable leaks anywere. Could this be air in the system if the old master cylinder failed or any other ideas? The strange thing is dual system master cylinder i thought i would only loose front or rear not both. The brakes do work just right on the floor..

08-04-2018, 09:09 PM	#2
firedemon Registered User Join Date: Jun 2015 Location: @ Posts: 890	Re: 68 c10 brake problems sounds like air in the system

08-05-2018, 03:57 AM	#3
Gav2606 Registered User Join Date: Apr 2018 Location: Highbridge Posts: 38	Re: 68 c10 brake problems Last edited by Gav2606; 08-05-2018 at 04:03 AM.

08-05-2018, 04:05 AM	#4
Gav2606 Registered User Join Date: Apr 2018 Location: Highbridge Posts: 38	Re: 68 c10 brake problems The block that the pipes go into. Is that a propertning valve. There is one hole with a bolt in it and its totally dry with no fluid coming out..is that correct? Also is the wire on the bottom for the brake warning light?

08-05-2018, 12:12 PM	#6
weq92f Registered User Join Date: Oct 2016 Location: Dallas Texas Posts: 3,218	Re: 68 c10 brake problems Wow, I've never even seen a remote booster before. The pumping action you describe indicates a failing MC plunger. What if you pump up the brake pedal and keep the pressure on it. Does it slowly find its way to the floor while you hold the pressure on the pedal? Air in the lines would make for a spongy, mushy pedal because that air will compress where hydraulic fluid without any air will not. -klb __________________ 67 C10 fleet fuel injected '70 402, 700r4, 3.73 posi 07 335 sport turbo 6sp 94 Trans Am GT LT1 6sp posi -- sold after 22yrs 99 540 sport V8 6sp -- sold 73 240z L24 4sp -- given to friend 68 C10 step 350/350 3.73 open -- sold

08-05-2018, 12:47 PM	#7
Steeveedee Who Changed This? Join Date: Jan 2013 Location: Simi Valley, CA Posts: 10,676	Re: 68 c10 brake problems If you already replaced the master cylinder, the culprit is likely to be the slave cylinder in the booster is bypassing. I've never seen a setup like that before, BTW. If it were mine, I'd be installing a conventional setup using the booster between the interior pushrod and the master cylinder. No offense, but that looks Mickey Mouse to me. __________________ ~Steven '70 Chevy 3/4T Longhorn CST 402/400/3.56 Custom Camper Simi Valley, CA Last edited by Steeveedee; 08-05-2018 at 12:54 PM.

08-05-2018, 02:11 PM	#8
Gav2606 Registered User Join Date: Apr 2018 Location: Highbridge Posts: 38	Re: 68 c10 brake problems Yeh i am thinking i should change it all to a more modern set up. Its how it was when i purchased it in the uk. Parts are not as easy to come by over here so may look at getting one shipped from rock autos. Yeh if i pump it up and hold it the peddle seems to stay there and not fade away.. it was a 2nd hand ms i fitted that my uncle had spare so no gaurentee its good.. thanks for the info..

08-06-2018, 12:18 PM	#9
68is4me Registered User Join Date: Jun 2014 Location: lakefield,mn Posts: 566	Re: 68 c10 brake problems That complete setup just looks wrong. I would fix it right then see what the problems are. Is that even a proportioning valve? Is it up side down and backwards? The factory disc drum prop valve should look like this. Attached Images __________________ 68 c10 swb stepper 68 c10 swb stepper 67 c10 lwb 06 gmc duramax



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