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1985 Chevrolet G20 Van dragging/pulling brakes has me stumped
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supercub
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PostPosted: Wed Aug 11, 2021 2:29 pm    Post subject: 1985 Chevrolet G20 Van dragging/pulling brakes has me stumped Reply with quote

So I've been having a front left brake issue with my '85 Chevy G20 Van for a while now. There was a slight pull to the left when braking for the past couple of months. The steering parts are tight and the alignment is good. Last week I replaced the pads, rotors, both calipers, and rubber brake hoses on both sides. I figured this would solve it but it did not. Actually I think its worse now than before. I can smell the hot brake on the left front after a drive. It's not hot enough to smoke but definitely hotter than the right side. With the front end raised, I can spin the right wheel and get about 1 1/2 to 2 rotations before it stops, but the left stops after about 1/2-3/4 turn with the same force. Thinking it was holding pressure somewhere in the front left, I cracked the bleeder as well as various other line fittings to that brake but the caliper does not release unless I physically force it back. I mounted the caliper without the pads and it slides back and forth very easily on the guide pins. There is a good solid stream of fluid while bleeding the caliper. I drove the van today and the pull/dragging from the left front seems to be getting worse and I started to feel a faint vibration while braking so it's parked for now so I don't ruin the rotor. I suppose maybe I got a bad left caliper but it seems like a real coincidence since that side was already having some trouble before the new parts. There is a disc/drum proportioning valve in the hydraulic system but I would think if that was messed up both front brakes would be having trouble. I'm really at a loss here as to what is wrong and I don't particularly just want to start throwing parts at it if I don't have to. Any ideas?
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Erik G
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PostPosted: Wed Aug 11, 2021 2:55 pm    Post subject: Re: 1985 Chevrolet G20 Van dragging/pulling brakes has me stumped Reply with quote

guide pins are a cheap easy thing to try. I find them bent on Chevy's all the time from people using a screwdriver and the old pad to push the caliper in for new pads. So common it's in the dorman or HELP section in every auto parts store. they should have brake caliper grease on them
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supercub
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PostPosted: Wed Aug 11, 2021 3:06 pm    Post subject: Re: 1985 Chevrolet G20 Van dragging/pulling brakes has me stumped Reply with quote

The guide pins came new with the caliper and are straight. They are greased. I mounted the caliper on the spindle without the pads and it slides very easily through it's whole range of motion. The old caliper with old pins (straight also) really slid hard even after I cleaned up and re-greased the original pins, which led me to replace the calipers with new ones. I actually found another set of new pins in my tool box that I was going to try but they are too small. I think they were for my old Astro van that I haven't had for 8 years. I'm bad about hanging onto crap, but that's a story for another time.
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mukluk
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PostPosted: Wed Aug 11, 2021 4:22 pm    Post subject: Re: 1985 Chevrolet G20 Van dragging/pulling brakes has me stumped Reply with quote

My money would be on you have/had some sediment or possibly rust particles floating around in the lines between the master and the calipers. This was pushed into the new calipers during the bleed after install and is now causing the left caliper piston(s) to stick.

I would recommend you disconnect the hoses from both calipers, completely flush all the old fluid out, and disassemble at least the left caliper to clean the piston(s) and caliper bore(s). Be sure to inspect the piston seal(s) for damage or imbedded debris as well while you have it apart.
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supercub
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PostPosted: Wed Aug 11, 2021 5:32 pm    Post subject: Re: 1985 Chevrolet G20 Van dragging/pulling brakes has me stumped Reply with quote

mukluk wrote:
My money would be on you have/had some sediment or possibly rust particles floating around in the lines between the master and the calipers. This was pushed into the new calipers during the bleed after install and is now causing the left caliper piston(s) to stick.

I would recommend you disconnect the hoses from both calipers, completely flush all the old fluid out, and disassemble at least the left caliper to clean the piston(s) and caliper bore(s). Be sure to inspect the piston seal(s) for damage or imbedded debris as well while you have it apart.


Now that you mention it, the fluid that I drained out of the old calipers after removing them did have a kind of weird grey tint to it. There is some really fine sediment in the bottom of the fluid reservoir for the front brakes. I did flush the fluid on the van about 4 years ago. The fluid in the for the rear brakes still looks good yet but the front brake fluid was surprisingly crummy looking before bleeding. I guess I'll give it a shot. I've actually never taken a caliper apart before, but it doesn't look too complicated.
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Krustybus
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PostPosted: Thu Aug 12, 2021 7:37 am    Post subject: Re: 1985 Chevrolet G20 Van dragging/pulling brakes has me stumped Reply with quote

You mentioned new guide pins, but not the bushings they go into. Nobody ever replaces those. They get hard, broken, sometimes turn to dust. Cheap and easy to replace. A little heat in the bushing area and a loose fitting drill bit to clean out the old bushing. I had the same light brake pull on my truck. New bushings, no pull.
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supercub
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PostPosted: Thu Aug 12, 2021 11:36 am    Post subject: Re: 1985 Chevrolet G20 Van dragging/pulling brakes has me stumped Reply with quote

Krustybus wrote:
You mentioned new guide pins, but not the bushings they go into. Nobody ever replaces those. They get hard, broken, sometimes turn to dust. Cheap and easy to replace. A little heat in the bushing area and a loose fitting drill bit to clean out the old bushing. I had the same light brake pull on my truck. New bushings, no pull.


The calipers came with new bushings. On the old calipers the pins barely moved in the bushings even after cleaning and lubing them, so I was pretty confident that was the problem. Unfortunately that doesn't seem to have been it. On my old Astro van, the rubber O-rings for the pins disintegrated to the point where the calipers would rattle around over bumps, but it didn't pull oddly enough.


Last edited by supercub on Thu Aug 12, 2021 12:02 pm; edited 1 time in total
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supercub
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PostPosted: Thu Aug 12, 2021 11:50 am    Post subject: Re: 1985 Chevrolet G20 Van dragging/pulling brakes has me stumped Reply with quote

I did what mukluk suggested and took apart the caliper. There was a little crap in there but not much. I let the reservoir drain down and then wiped all the residue out of the bottom of it. I then flushed through three reservoirs full of new fluid. I reinstalled the caliper and bled that. Overall it seems better but not 100%. Sometimes it stops nice and straight. Other times it will still pull slightly to the left, but not as bad as before. I jacked up the front end and spun the tires after driving it about 15 miles and the left spins about 2/3rds as many revolutions with the same force as the right. I checked the temps around the hub area of the front wheels and they are close, with the left running about 5-10 degrees hotter than the right. I was feeling too lazy to take the wheels off again to check actual rotor temps. I'm beginning to wonder if there is some trash in the proportioning valve that I can't get out. There is a separate outlet port for each front brake. The valve on this van doesn't look like you can take it apart to clean it out though. I may try taking off my proportioning valve and spraying what I can with brake cleaner and compressed air, or a new aftermarket GM disc/drum proportioning valve is about $50. I'm tired of bleeding brakes for today.
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