Chasing brake symptoms that make the car shake.

So I'm getting a consistent and repeatable problem when driving more than about 10 miles in the e28. I drive it so infrequently now, I hadn't been thinking about it for a while and hadn't driven it many miles when I did so the issue hardly cropped up.

This saturday I took it to cars and coffee about 15 miles away in the big city. By the time I arrived at the event the car was slowing itself down when I let off the gas at parking lot speeds. On surface streets the issue manifests as a shaking steering wheel above 40 miles an hour and the higher the speed the more violent the wheel shakes any thing over 45 is dangerous and the shaking continues when braking until you get below 15 mph. Also while this is going on, the pedal feels like a brick, but no problems slowing down. The thing is, until the car warms up it drives perfectly, not of these symptoms are there at all.

Initially I thought the brake fluid just needed changed and that it probably has gotten some water in the system since I flushed it in 2011 or 2012. So today I flushed it again completely and took it out for a spin. Fine at first and after about 20 miles, same thing as before. Like every other time I limped it home brainstorming ideas. Two things came to mind. Least likely to me is the abs system is going bad and activating and staying active once the car warms up. Not likely in my opinion because the pedal never pulses like it would when abs is active. The second option I can figure is one of the calipers is sticking once the brake fluid warms up. On that idea when I got home I got my temp gun and shot each rotor right after I got there. temps in order I shot them df-293 pf-293 pr-274 dr-394. So I think the driver rear caliper is getting stuck mostly closed after I use the brakes after the car warms up. Is there something it may be that I am not aware of? I have already ordered the left rear caliper from rockauto because for 37 bucks it was worth it to throw money at. Obviously If it doesnt fix it throwing money at it will get me where it usually does.

First place I'd go is caliper.  

Probably has a combination of lot rot and sticky slide pins/pistons.

Start by taking temps right after a drive. If you have an ir thermometer, point it at each rotor and look for an outlier. If you don't have an ir thermometer, hold your hand to the center of the rim and look for a hot one.

I had similar on my 07 expedition, still did it after new calipers, wound up being the soft lines failing and acting like a one way valve. The heat from dragging killed a caliper and of course the pads/rotors were toast. 

If you haven't done the soft lines on the car in the last decade; add them to the list while you are in there.

old bmw calipers will get sticky, for sure. But, they are easy to rebuild (or replace). It could be a piston seized, or it could be the slide pins totally un-lubed and not sliding "back" after braking. For an e28, can probably find them dirt-cheap on RockAuto since I doubt there's much demand these days. 

And with the heat build-up, the pads would be overheading and leaving deposits on the rotors unevenly, causing shimmy when braking. 

assuming you're referring to your M5, front and rear Raybestos calipers on rockauto are like $35 each (plus core). Rotors are $10-20 (there are actually rotors on RA for that car that are THREE dollars!). Brake hoses are $5 each. I'd have no problem buying the "cheap" stuff (Centric C-Tek, Raybestos) - we use that stuff on our e30 rally car and its fine. Just invest in good pads (Hawk HPS are a good choice). Overall, you can do the whole brake system pretty much brand-new for like $300 for that car. 

Since I can't reply to two people by clicking reply, Apexcarver and irish44j, one of the things I was very happy to see when I bought the car initially, yes referring to my M5 in response to your statement, is that one of the previous owners had installed braided stainless steel brake lines. So assuming they are not the issue(and honestly they could be, but less likely) I am hopeful the raybestos caliper I ordered will be the fix, and yes the temp gun I used was an IR thermometer, thank you for that because I couldn't recall the proper name for it in my original post.

Caliper is sticking. Good chance the rotor is warped too. 

E28 nut here (currently own 4, have parted about that many). The actual brakes are a red herring. You should take a look at your suspension, particularly upper and lower control arm bushings. Also the center steering link idler arm has bushings that wear out and exacerbate an oscillation.

I recommend e31 8-series lower control arms. They're forged aluminum and come with a spherical bearing in place of the weak rubber bushing. Also moosehead engineering upper control arm bushings. You can buy them already pressed into the arms if you don't have a press.

Also, try mye28.com if you have other issues. The knowledge base there is incredible.

In reply to SVreX (Forum Supporter) :

rotor. I didnt even think about that. at least they are cheap.

In reply to Cactus :

I know where you are coming from. I have been a member on mye28.com since august 2010. the uca's, lca's center link, and idler arm have all been replaced. granted that was 9 years and 40,000 miles ago, but the main reason I don't think the front suspension et. al. is the issue is that up until the brakes start giving me issues, the suspension and steering is perfect and yes I mean perfect at any speed and condition. Even through the dreaded 44 to 52 mph shake that indicates the suspension needs attention, which is not there. Once it starts it will shake clear down till the car completely stops, then will clear up until about 28 to 30 mph then start again and get worse the faster you go, then lessen the slower you go until you stop. when the car sits till its cold(for example the next day) the issue goes away.

Never owned an E28, but I would tend to agree with the rest of the board that a sticking caliper is your most likely culprit. Especially since you seem to have the suspension route covered off, though nine years is enough that it's worth checking over. My E39 M5 had a very similar shimmy and it ended up being a seized front caliper in my case. I agree with the suggestions to replace that rear caliper, since it is cheap, along with new pads and rotors.

Caliper.  Definitely caliper.  And the associated rotor.

I sincerely doubt the suspension bushing issue based on your description.  I recall the drive home after buying my son's E39, and how the PO had mentioned the car needing lower control arms (tension struts), based on his mechanic's opinion.  The car had a pronounced shimmy as you applied the brakes at highway speeds.  All the while, I'm thinking "feels like brake rotors, but it's my first BMW, so what do I know?"

Get the car home and have my guy put in new control arms.  No difference.

Got the brake parts from FCP Euro and my son and I did the job ourselves. 

Car is perfect.

E39 owner here and my first thought is a bad bushing in the lower thrust arm but that doesn't explain the temperatures or the drag on the car. Stuck caliper.

And there it is. The other thing I didn't think of. Sticky slide pins.

Here's my plan. Provided the wife doesn't have a bunch of plans when I get off work today, I'm going to r&r the caliper slide pins and drive it until I determine it's fixed or park it and wait till the new caliper shows up. Either way I'll replace the caliper when it gets here because I'm sure the whole unit is original to the car so why not?

Interestingly last year I replaced the slide pins on both front calipers trying to get the problem to go away but didn't think about it being in the rear because my thoughts were steering is in the front dood, AND I had replaced the passenger rear caliper because the brakes were dragging on the inside a few years back. There again throwing money at a problem before taking the caliper apart because the real issue was the last time someone changed the rear pads the old bracket broke off inside the caliper and was shoving the new bracket and thus pad against the rotor. That was fun because I initially replaced the passenger front wheel bearing trying to chase that down. Oh how I love to throw money at cars.

I had the chance to take out the slide pins and clean and re-grease them but I wont be test driving today due to the incoming storm. I hate to get water on my clean car. Ha! but I did grab a couple of pics which I will upload shortly of the pins when they came out. dried up, hard grease was on them both and the bottom pin I had to get out with pliers, never a good sign. They are cleaned up, re-greased and installed. the one I had to grab with pliers did have a small gouge near the bottom by the threads so probably a good thing Im replacing the whole thing anyway. Pads looked good. Rotor looks fine (I know thats no real indication but it will do for now since I don't have a rotor at hand. ) Im sure Ill be able to get it out before the parts arrive.

This is both of them with old grease.  The one on the bottom required pliers to remove

Here they are cleaned up and ready to be greased.  Gouge is on the right one at the bottom. 

Update-I was able to take the M5 out for a good drive and determined that it is only partially fixed. The steering wheel no longer shakes at all under any braking, but when I was pulling in to my driveway it was slowing down way too fast for being in neutral and no brakes on. Rather than remove the slide pins and clean the area where they reside, Ill just send it back to rockauto when my new one gets here.  Thanks for the help and insight guys.

I've never owned a BMW. But you are describing classic brake problems which are common to almost all cars with disk brakes. 
 

The caliper sticks. Or the slides don't work. Those are effectively the same thing. Either way, the pad is remaining engaged with the rotor and dragging.
 

The dragging overheats the rotor.  It wears grooves into the rotor, but also warps it when it gets really hot.

The warped rotor causes the vibration in the steering when the brakes are applied, and sometimes a pulsing in the brake pedal.

The caliper (still dragging on the warped rotor) magnifies the vibration because as the dragging pad comes in contact with the high spot on the rotor, it causes more friction (which is the same thing as applying the brakes on only one side of only one wheel). As the wheel spins, you feel the steering respond every time the high spot in the rotor hits the pad (and the steering pulls in that direction because the opposite brake is not being applied). 
 

The heat and warping will continue to get worse. 
 

Glad to hear the sliders helped. But I'm still betting your rotor is warped. Cleaning and greasing the sliders enabled the caliper to slide more freely, so it's not dragging as much (or at all).  But the vibration was the rotor, and rotors don't unwarp themselves. 
 

I'd swap the pads and turn the pair of rotors. I'll bet it will be perfect.
 

In reply to SVreX (Forum Supporter) :

I would be in total agreement with you if the issue happened all the time the car was in motion. The difference is this issue is completely and predictably repeatable and until the braking system gets hot the brakes are completely normal at any speed and any condition. I have put in about 75 miles total chasing the issue.

I think I have it fixed. TL;DR at the end. I got the new caliper in last night and installed it this morning. Well don't be like me and not compare an item you receive before installing it because it made the problem go back to full on everything was wrong again. shaking wheel, hot brake rotor(100 degrees hotter than the fronts) slows down at slow speeds just like brake dragging. I get it home and take off both rear wheels to compare the sides. the calipers and slide bolts on the new caliper stick way, way out. like an inch. then I compare the unit I took off. the old one is physically smaller. number stamped on the old one is 35 the new one is 40. well crap. I remove the new caliper and push the old piston all the way down into its hole, which I hadn't done before and reinstall the old caliper so I can move the car around till I can find a right size new one. I bleed the brake line again and put everything back together. Then I decide to take it around the block. It feels pretty good, which I expected. Then I decide to take it to the next town and back and on the way home go the back way so if I have to drive slow I wont slow traffic down. Also the back way is twisty and fun as hell. I am able to go out and back at full speed no brake problems. Tomorrow Im going to take it on my full test route to see if it actually works for sure. I tested the temps when I got back and the problem brake was similar to the other rear brake and slightly lower than the fronts.

TL;DR -New caliper was wrong size and pushing in the piston seems to have fixed the old caliper.

Edit-I just went ahead and ordered new rotors and pads for the rear because why not? It can't hurt.

In reply to gunner (Forum Supporter) :

Braided lines are nice, but they can hide issues with the underlying material.  I'd plan on replacing those with OE pieces as the braided lines don't really help that much on the street.

In reply to gunner (Forum Supporter) :

The fact that it only happens when the brakes get hot does not rule out my explanation. 
 

Metal expands when heated. If your rotor is warped but has just barely enough clearance when cold to not bind the caliper, it would change whenever the rotor heated up. 
 

The vibration does not have to happen only when the car is in motion. It only has to happen when the rotor binds, which could be only when the rotor is heated.

The fact that the temperature is so much hotter almost certainly confirms it. 
 

Glad to hear you may have solved the issue. 

In reply to SVreX (Forum Supporter) :

Thats fair. I certainly did not take that into account. Hopefully the new rotors and pads will just be the icing on the cake then. I hope I did solve it because during my research today I found out no one has the correct sized caliper in stock. so thats awesome.

I took the car through the normal test loop and then home the back way. It's good. Glad to get that fixed. new pads and rotors will be installed when they arrive and im back to driving nirvana.

Alright. to cap this off I replaced the rear rotors and pads and removed the last of the issue completely. Then I bedded in the brakes and took it on a different test loop and man it is brilliant. Fixed!

Welp, I was wrong. Not Fixed. I figured it out at the beginning of the month after another drive and after learning that rear left calipers are currently not available, I rebuilt the one I had yesterday and took it for a drive, where I learned that it needed to be rebuilt but so does at least one of the front calipers. the good thing is the issue is not near as bad now, I can cruise at 60 even after it rears its ugly head, but it's still there. so I'll rebuild both front calipers then if that doesnt fix it, take it to the shop. At least I already own the front caliper rebuild kits so I can do it asap.

Ok its fixed. drives way different, much better. points me in another direction which Ill get to in a second. Rebuilt the passenger front caliper and wow getting four pots out is way more challenging than one. Compressed air shot out the piston nearest the port and not the rest. I got the brilliant idea of reinstalling the piston and clamping it in so it cant come out and got two other pistons out that way. the final piston took time and vice grips. reinstall was very straight forward.

Heres the other direction I mentioned. during disassembly, the lower  caliper bolt was loose enough that I was able to start loosening it by hand. usually I have to put the wrench on the bolt and hammer the wrench to start it. I dont like that. its possible I could have tightened up that bolt and fixed the issue completely, but since I wanted to do the rebuild, I didnt. So then I made sure they were at the proper torque and used threadlock when I reinstalled. I then tightened up the drivers side bolts, and I thought, you know, that shouldn't really be possible but I was glad I checked.

So thanks for following along, It's always a good day when I can wrench in the garage and get something fixed.