Rotor Thickness? (Brake issue - checking over everything.)

[Rein]

Posting this tonight (Saturday 12/14/19 - 2015H EST) in hopes of some information before I go out to attack again tomorrow morning.

’04 Astro RWD in the rust belt that is Cape Cod. My current goal is to fix my brakes. Finally acquired most of the tools necessary (including the elusive T55 this afternoon, which was missing from amongst all the others I’ve gotten here and there) and got the garage cleared out so I can work inside on a level surface. I suspect sticking caliper sliders are causing my issue, which is occurring at stopping speeds (stop signs, red lights, etc.) where brakes grab and pull to the right with a vibration/stuttering kind of sound (difficult to describe). If I pump the brake pedal rapidly the symptoms disappear (which is why I think it’s a caliper slider). I’m guessing it’s the left caliper that’s the culprit because it’s pulling to the right. At highway speeds no issues, except recently the pedal went much further down while braking one day and now, although I do have braking, it takes a bit more effort and there’s not a lot of room for the pedal to depress further (which is why I fixed my E-brake, at least for the time being - another story...).

Examining my front rotors the edges are so pitted (even when I used a wire brush/angle grinder down to bare metal) I couldn’t see any markings for minimum thickness. Can anyone tell me where I can find that information or what the acceptable minimum rotor thickness should be? These are the vented kind of rotors. The pads appear to be fairly new with decent hardware. Flex hoses and solid lines also appear to be in good shape except left side where the solid line nut is rusted away but connection still feels solid. There may be some fluid leaking there but I can’t tell yet - it’s too wet out and I have to dry everything up really well (put some air/heat on it) so I can detect any leaking. That fluid leak could explain brake pedal going down further recently. Reservoir was full last time I checked but I’ll have to look again in the morning. I thought the fluid looked OK but of course it could have absorbed water since it was added (no service records sucks). I thought the lines were steel but now I’m not sure - in some dry places up higher they turn to a verdigris green color but everywhere else they’re black.

Any info or thoughts appreciated on my brakes. (I know I’ve got to get back and followup with a couple of previous posts re: tools and wandering issue - my busiest time of year has finally come to an end so I have some breathing room and can catch up.)

I’ll check back first thing Sunday morning. Thanks folks!

[sixsix]

Yeah, well...
The Van deserves more, so do you.
Replace everything brake-wise with new parts.
Hubs, Calipers, Pads, clips, grease, Lines, etc, etc.

Anything else stopping you n' da' Van? Other cars and trucks ...
- maybe a ditch, tree, pole, wall or outhouse?



Mike

[Mmusicman]

Rotors aren't that expensive... just replace them.
Bought my last set of ACDelco's though Walmart

[Rein]

Yeah, well...
The Van deserves more, so do you.
Replace everything brake-wise with new parts.
Hubs, Calipers, Pads, clips, grease, Lines, etc, etc.

Anything else stopping you n' da' Van? Other cars and trucks ...
- maybe a ditch, tree, pole, wall or outhouse?



Mike

Thanks Mike, for the input. Unfortunately, I ain’t made a money, so I have to do what little I can when I’m able. For now, if I can put some elbow grease into it, I’ll try to lube or fix what’s broke and leave the rest. If I had enough $ to replace everything I would have had enough $ to purchase an A/S from down south where they aren’t rusted before I even get them.

[Rein]

Rotors aren't that expensive... just replace them.
Bought my last set of ACDelco's though Walmart

Thanks Scott. That was gonna be my next move, but I’m a detail kind of person and like to know specifics, especially for the future. I’m leaning towards these rotors ARE needing to be replaced, but only based on condition of the circumference - nothing else. I did measure them and was going to put that measurement in as an edit to my post but you guys just responded so I’ll do it now. Both rotors are at 29.xx mm thickness. There is no scoring or surface issues that I can detect and the insides (vented) seem to be fine.

[dchan51360]

[dchan51360]

Brakes for me are a “do not take short cuts” item.

But to each their own.

https://brakeperformance.com/brake-rotors/
Currently on slotted and dimpled rotor, semi metalic pads and very happy with them.
December is 35% off.

And replace the sliding pins on the calipers every time I do a brake job.

[WoodButcher]

Brakes for me are a “do not take short cuts” item.
But to each their own.
And replace the sliding pins on the calipers every time I do a brake job.

Get the hardware kit for the calipers as well, The bushings and "O" rings keep the calipers sliding and happy. When they go bad the symptoms you describe are common. Squeaking, sticking and dragging.

[Rein]

[quote="dchan51360”]

THANKS!!! That was exactly what I was looking for - just had no idea where to look. Now I know I should have checked parts supplier’s websites and, of course, I’ve already got AutoZone bookmarked in multiple places.

Those measurements confirm what I suspected - rotors are down at least 5/32nds from acceptable tolerance so definitely time to replace. I wouldn’t be surprised if they were warped as well.

Checked out lowest-priced at Walmart - $50/pair, which will do me fine - free shipping or free pickup. Works for me!

[Rein]

[/quote]
Get the hardware kit for the calipers as well, The bushings and "O" rings keep the calipers sliding and happy. When they go bad the symptoms you describe are common. Squeaking, sticking and dragging.[/quote]

Bruce

Hardware - oh yeah, absolutely, although I don’t know yet if I even need to replace pads and hardware since they look so good. Once I’ve got things apart and cleaned up I’ll know one way or the other, but all the bushings look and feel very good. If I have to I’ll certainly just get complete kits.

Also, I’ve been researching brake lubricants and determined Permatex Silicone Ceramic Extreme is the one for me. Following their instructions exactly.

[sixsix]

... Both rotors are at 29.xx mm thickness. There is no scoring or surface issues that I can detect and the insides (vented) seem to be fine.

29.00 mm = 1.142" ( which not coincidentally is the thickness of a new one )

" dchan51360 " , his chart shows that your thickness is still good...?

Gosh, maybe those discs are fine after all.



Mike

[Rein]

... Both rotors are at 29.xx mm thickness. There is no scoring or surface issues that I can detect and the insides (vented) seem to be fine.

29.00 mm = 1.142" ( which not coincidentally is the thickness of a new one )

" dchan51360 " , his chart shows that your thickness is still good...?

Gosh, maybe those discs are fine after all.



Mike

Mike

Don’t know what I was thinking when I compared my measurement to the AutoZone specs, but you’re correct! I just finished up the left front and got the van out of the garage and I’m pooped, dirty and hungry so it’ll have to wait until tomorrow morning for me to go out with the digital caliper and measure again just to make sure I didn’t post the wrong measurement originally.

My first-ever brake job! (Sort of…) Same symptoms - pedal to the floor to get any braking. Won’t know until I drive it if the other symptoms are gone, but I could push/pull the caliper in and out easily prior to mounting the tire. Small pile of rust on the garage floor. Cleaned all parts up either by hand/wire brush or on my bench grinder brush wheel (rotors are darn heavy!). Applied lube under and on top of pad hardware in/on pad ears and made sure pads slid in and out easily before completely reassembling. No lube anywhere it’s not supposed to be! I was surprised that the sliders and caliper bolts are all one piece after seeing a gazillion videos where they were two separate items. Cleaned off really well, wire-brushed on bench, cleaned out cavities really well with brake clean and double Q-tips and more brake clean until it ran clear. Lubed sliders per Permatex instructions. Also found interesting thin round SS covers on the pistons which I also removed and cleaned up well and lubed both sides before assembly (they had rust underneath). Pistons were sticking pretty good but not impossible to remove and had zero scoring or marks of any kind. Slider boots and piston boots appear in perfect condition. It’s possible pistons are not working well, but I won’t get into those until I’ve exhausted other areas first (like right front brake hardware and bleeding system).

As far as I’m concerned all the hardware seems in excellent condition so I’m leaning towards it just needed cleaning and lube and I need to bleed the system to get pedal back. Wire brushed and picked out around bleeder screw and banjo bolt in aid of getting those loose if I need to, although it’s only the bleeder screw I’ll need to loosen. I’m going to (carefully) use the propane torch/water quench method to make damn sure I don’t break them off! Hex socket to loosen at first (not 12-point). I found a really cool way to bleed using a modified hand sprayer/plastic hoses at the bleed screws so I can do it singlehanded without much fuss or equipment.

I won’t say my first-ever brake work has been fun, exactly, but I feel a whole lot more empowered than I did a year ago! I’ll keep reporting while I continue work on this to some sort of conclusion. Hopefully.

[dchan51360]

Sounds like you have a sticking caliper. Even if they feel smooth, very often the pins bind ever so slightly so that when you apply pressure the get out of alignment and you have the "pulling" to one side you describe. When you get your digital calipers out, measure the thickness of each of your brake pads. One of them may be significantly thinner or worn further. This will tell you which caliper is not moving freely.

Even though they "feel fine" I have learned that just enough wear, can cause them to mis-align and bind, but they will feel smooth. I now always put new sliding pins for the calipers when I do a brake job. I figure it's a cheap bit of preventative insurance. I think the AC Delco version was about $10.00-12.00.

If all the rest of the parts looked new and measure as almost new, I would suspect that the Previous owner, or mechanic that worked on it, decided to cut a few corners and not replace those parts when they replaced the pads any maybe rotors.

Depending on where in the rust belt you are, rust on the outer ring of the rotor can develop real fast. If it was not flaking apart and chipping away, you may be good.

You do need to find out why the pedal goes to the floor. Something is leaking somewhere. If there were just bubbles in the system, you should be able to pump the brakes and get them to firm up a little. May still feel mushy but if the brake pedal goes to the metal with out pushing back, you are not pushing against anything. if there are no visible leaks you may have an internal leak within the master cylinder. Do a complete bleed (all four wheels) and make sure to keep the master reservoir topped off. Then when complete if it's still going to the floor, you probably have a split in the seal inside the master cylinder that is keeping the piston from developing pressure.

[AstroWill]

Good job on not wasting money by replacing parts that probably don't need to be replaced. A thorough inspection is possible on virtually every part of the braking system with the exception of the hoses. Sometimes the hoses degrade from the inside out which you can't see visually but will still cause issues. Sometimes you won't be able to push much fluid through them, other times you can get the fluid to the slave cylinder but then it won't flow easily back to the master. They are one of those issues where if everything else looks good but you are having issues, suspect the hoses.

If you have a leak, that would be the absolute first thing to find/fix, nothing good comes out of a leaky brake system. You also stated that you don't know when the fluid was last changed, make sure that it gets a full bleed to get all of that old fluid out. It's amazing how much difference fresh fluid can make in the brake system.

Sounds like you are learning a lot and getting comfortable working on your van. That is great and you will become a much better owner/custodian of the vehicle as a result. Brakes aren't hard, though some steps are harder because of rust/corrosion depending on where your van has lived.

Lots of great information and help is available here. Noticing your year, I highly recommend the GM Techline eSI OVA edition with Virtualbox, it's the digital factory service manual that thoroughly covers your van! There are some links for setting up Virtualbox and such in my signature/profile.

Here is an example of what you will find in there:

04brake_rotor_thickness.pdf

(42.9 KiB) Downloaded 38 times

Welcome to the site!

[Rein]

HOW’D I MEASURE THAT ROTOR THICKNESS THIS MORNING WITHOUT BACKING THE VAN BACK INTO THE GARAGE (only flat, level place I’ve got) JACKING UP THE VAN AND REMOVING THE WHEEL?!!!

Smartypants that I am, I used my trusty Husky digital caliper. Turned it on, opened it up more than I expected I’d need, inserted into the only wheel slot open next to the only rotor surface exposed on both sides, rotated over the rotor, measured the thickness, reached in with other hand and (with juuuust enough room) pushed the power button on the caliper to turn it off. Removed caliper very carefully so as not to change setting, powered it back on and ran it down to zero. Reading was 29.75mm - pretty much what I was getting before. This confirms that the rotor is certainly within spec.

Until I can afford electric impact I have to remove tires the old fashioned way, with my 4-way speed wrench and muscle. Works fine but what a PITA to have to remove 6 nuts to get off the wheel cover and then 6 MORE lug nuts. GET ME BACK TO THE PREVIOUS WHEELS WITH 5 NUTS AND ONE SIMPLE, FLAT COVER REMOVABLE WITH A FLAT-BLADED SCREWDRIVER. I MISS MY SAFARI!!

More later when I have time to respond to the two previous wonderful replies.

[sixsix]

Oh, and there was another thing I forgot about the Disc Thickness Measurement.

The Pads will in some cases wear a 'Path' or Face Groove in the Disc Face.
There are sometimes 'Ridges' of Original Disc material ...
- that can maybe give a false OK measurement of 1.142".
- while not measuring the Width or thickness of the Wear area.

It is a tough measurement to Properly achieve with a caliper w/o offset Points.
Easiest when checked with an 'open' 0-1" ( 0-25.4mm ) Outside Micrometer.

I have seen 'Ridges' as high as .070" ( 1.8mm ) on one side with .050" on the other.



Mike

again... piecemeal brake purchases will be extensively higher than buying a 'Brake Kit'
just sayin'...

[Mmusicman]

^ CORRECT. Most brake shoes do not always ride against the very outside edge of the rotor (or certainly not evenly) .. leaving a high-point ridge. Brakes don't usually wear perfectly flat either. You may just be measuring the original thickness.. and you are certainly ONLY measuring the high points. There is more likely no way to accurately measure the actual wear with standard calipers.

[The Drummer]

Use C caliper ,or grind the rotor s edge down and mesure from there .

[Rein]

Yup, I was aware of the rotor edge thing going in (I’ve spent months researching all the things that need to be addressed with this van). Actually ground down that edge (which was extremely minimal) when I was cleaning them up, so the measurements I got were achieved as precisely as possible despite not having a C-style caliper. If I was concerned about getting a good measurement when I had the rotor off I would have inserted some shims to get me above the higher edges and then subtracted the thickness of the shims (washers, probably, or whatever I had laying around). I’m confident my measurements were extremely close, and certainly the rotors are within specs.

Prepping for an event on Saturday, but I got the Astro back into the garage at 0400H today (just as I was getting up and realized it was freakin’ snowin’ again!). D’oh! Warming up the space a bit with a couple very hot halogen lights I’ve got (I’ll bring in the electric heater when I get into it). Great for Winter, not so much for Summer (and yes I’ve been working on sourcing replacement LED bulbs for them). Hoping to get the whole van up on stands and start working on getting all the bleeders cleaned out and PBBlastered to see if I can actually bleed my ride and get less pedal travel and more response. Driving yesterday maybe 40 miles total in local traffic I only experienced one small grabbing reaction and no pulling or stuttering, so I think I’m on the right track. Brakes seemed somewhat improved. More later - Ginger Chewie dough is chilled enough - gotta go scoop the dough.

[AstroWill]

Sounds like you are on the right track, good job!

Just like everything mechanical in this world, eventually it requires maintenance, you will have your brake system in tip top shape in no time.