Vibration at 50 to 60 mph coasting in neutral after rear brake shoes

[ultred ragnusen]

Just replaced the rear brake shoes with the result of vibration at 50 to 60 mph which was unrelated to braking or the transmission where I'd like to learn from your experience what happened.

Balance:

Backoff: Adjust: Assemble: Gray Paste: ===========================================

1. Replaced just the brake shoes and tested at 50 to 60 mph where noticeable vibration occurred that wasn't there before the brake job.

1. This noticeable vibration was unrelated to braking events or to coasting downhill in neutral and was unrelated to road conditions.

2. All four wheels were previously balanced and originally put back in their original position after the initial repair as were the drums.

1. All six lug nuts on each wheel were torqued to 84 foot pounds using the classic star pattern. A thin coating of old (partially congealed) never-seize was applied to the rear hub to drum mating surface.

2. The main deviation from factory protocol was the common practice of adjusting the star wheel to the shortest position so that the drums go on easily and then lifting up on the emergency brake handle about a hundred times to adjust the parking brake to 7 clicks.

1. After an 18-mile test-drive loop, start to finish, to get to the highway and then to the first exit and back where half was highway and half were local roads, both drums "sizzled" a wet fingertip, perhaps the driver side drum more so than the passenger side drum.

2. The brake shoes had a gray pasty appearance, almost of leaking oil but no oil leaked on the brake shoes. =========================================== A. I rotated the tires front to back but they were balanced before so I don't see how that mattered afterward.

B. I very carefully torqued the six nuts on each wheel to 84 foot pounds, in a star pattern, with plenty of banging on the wheel assembly to jostle the seating position, although they were previously torqued to 84 foot pounds so I don't see how that mattered afterward.

C. I visually inspected the u-joints, wiggling them by hand, but I did not feel more than about a half millimeter or so of movement, but I don't know how much they're supposed to move - but they didn't change anyway.

D. I visually inspected the front and rear brakes, where no visual anomaly was seen, and wiped some of the never seize off, but it was a very thin layer anyway.

E. The only procedure I did very differently was that I explicitly followed the factory protocol for adjusting the brake shoes just prior to the drum replacement which was to mic the drum and mic the shoes and set the star adjustment to 1/2 mm (20 thousandths of an inch) smaller than the drum diameter.

F. I also left the parking brake adjustment loose at about 8 or 9 clicks instead of the 7 clicks (it still held the car on a hill but not as firm as did the first adjustment if the car was previously moving). =========================================== The procedure above "solved" the vibration problem.

The job is done but I would like to learn more about changing brake shoes. Do you have any idea what specifically had caused the vibration?

[trader_4]

I had my Mercedes in years ago for some work, I think it was brake work, but in the process they removed the wheels and put them back on. Driving home I had vibration at 60, where before it was perfectly fine. I took it back, they gave me the usual song and dance, nothing they did could have caused it, they don't move the wheels around, vibration could be from a driveshaft problem, etc. I took the car home, jacked it up, moved the tires from front to back, and Voila!, problem solved.

I don't think they were necessarily lying. For example, when taking the wheels off, no reason to move them around, more logical to just keep them where they are. But clearly the problem was not there before, was there after taking the wheels off and putting them back on, and was resolved by moving them from front to back. It's easy to try.

[ultred ragnusen]

That was similar to my experience!

I think it was either the tires moving from front to back, or, the shoes adjusted too tightly by the parking brake (can that even happen?) or maybe too much paste on the hub (but there wasn't all that much and I left most of it anyway) or the torquing of the lug nuts (although I torqued them both times - only I was more careful the second time).

A quick test would be to switch the tires back and see if the vibration returns.

Yup. It could be the tires being unbalanced, but I checked each one for static balance and they were dead on since I balanced them myself about a year ago and there was no vibration until now.

I've been rotating them every 4K miles and there wasn't any vibration then either.

The one thing that is very different is that the 18 mile test loop didn't heat up the drums too hot to touch when I did the job the second time, whereas the drums sizzled a wet finger on the vibration run.

[ultred ragnusen]

I mark the inside sidewall with the rotations, where each tire has had three rotations without any imbalance issue.

This tire, for example, went from Right Front to Left Rear to Left Front (and is now on the Left Rear).

I did inspect each tire for missing wheel weights but there were no missing weights, and I doubt cleaning out the pebbles which is standard before static balancing, made any difference.

[Clare Snyder]

Sure sounds like the rear shoes were not adjusted properly and the emergency brake was partly applied tp position the shoes which were allowed to "float", spontaniously and intermittently applying themselves.

When you properly adjusted the brake shoes they were properly positioned in the drum and did not "float", and therefore did not apply themselves.

You guys that insist on doing brake work on your cars without having a clue what you are doing SCARE me.

One of these days something SERIOUS will happen and someone will be killed, or worse yet, maimed for life.

[Paul in Houston TX]

Out of round drums and shoes were too tight. Or, shoes were too tight and grabbing.

[Clare Snyder]

No, the shoes were too loose and the cables were too tight

[Paul in Houston TX]

Ah! Immediately understood. Thanks for the insight.

[ultred ragnusen]

I want to learn so I appreciate the responses, where I realize you can only know what I thought to tell you, so it's hard to diagnose from afar.

After reflecting on Clare's answer, I think what he suggested is probably what happened as what he suggested "fits" the picture, although I'd like to understand better what he meant when he said "the shoes which were allowed to "float", spontaneously and intermittently applying themselves."

The evidence does seem to back up what Clare said, in that the drums were sizzling, and that the vibration was a "grabbing" type and not a "side-to-side wobble" like most tire shimmys are. So it was a weird different type of vibration that must have been occurring at slow speeds as well as fast speeds.

- But why would it only shudder at the fast speed? ===== I agree that it's very possible that Clare is correct when he said "the rear shoes were not adjusted properly", because when I used the factory adjustment procedure of 1/2 mm between the drum and shoes and then adjusting the parking brake by pulling up on it a few times, the vibration went away.

- But why didn't the procedure of putting the shoes on loosely and then adjusting the shoes via the parking brake work? ===== In the end, what Clare said seems to fit when he said: "When you properly adjusted the brake shoes they were properly positioned in the drum and did not "float", and therefore did not apply themselves."

- This fits that a. the drums were sizzling before and just warm now b. the vibration had an odd feel to it (but why only at speed?) c. original adjust was by pulling the parking brake a hundred times d. the gray paste on the shoes might have been drum metal flakes ===== I have to agree that I misunderstood how drum brakes work in that I thought the parking brake adjustment adjusted the brake shoes themselves, so I would just like to learn more about what Clare said when he said "the shoes were too loose and the cables were too tight"

- Was the vibration likely due to the specific combination of loose shoes and tight parking brake, or just to the fact that the shoes were too loose?

[Clare Snyder]

If the shoes are not adjusted properly and the hand brake cable pulls the shoes out to where they belong (giving a decent pedal) the shoes are not on their anchors (depends on the type of brake) and any suspension movement CAN tighten the cable, initiating a brake application. Also, on a "servo" type, or "self energizing" brake, if the leeding shoe "drifts" and contacts the drum, it "wedges" and aplies the trailing shoe as well. If it's not on the anchors, it Will drift. There MAY have been some low speed action, but the servo action would not be as strong at lower speeds so it may have been virtually un-noticeable

What vehicle are we talking about here?

[ultred ragnusen]

That must be it.

Once the leading shoe touched the drum, the trailing shoe must have been forced to follow, causing the grabbing.

It must have been happening all the time, but only noticeable at speed.

Thanks for explaining.

My big mistake was in thinking the parking brake adjusted the "final" position of the shoes.

[Clare Snyder]

On some it does - but then you need to manually adjust the handbrake (e-brake) linkage AFTER the shoes have adjusted - and this meansbacking off the e-brake adjustment first.

Youstill have not said what vehicle this is - and sincethere areSO MANY differentsetups for brakes, this is important information.

[ultred ragnusen]

Thank you for helping me understand what went wrong where I realize it's hard for you to help given the little information I know about it.

On this vehicle, braking in referse does not adjust the rear brakes. The continual adjustment of the rear brakes is only by the parking brake.

It's a 2002 Toyota Tacoma.

Mainly I ass-u-med that the parking brake would adjust the brake shoes, since that's what it does every day.

What I mostly want to understand is WHY the parking brake adjustment didn't work.

My main assumption was that the parking brake adjustment is the same as the manual star adjustment.

If that's correct, then I don't see how the parking brake adjustment is any different than twisting the star adjuster, but it apparently is (somehow).

That's my main confusion which I hope someone can help me better understand.

[Clare Snyder]

Look at

Note ther pin at the top. If the adjuster at the bottomis not adjusted long enough and the handbrake cable is too tight, the cable will hold the shoes out close tothe drum, giving a good pedal but the ends of the shoes are not in contact with the pin. One might br, or the other, but not both.

When the adjuster is properly adjusted and the cable is NOT too tight, both ends are against the pin untill the cyl expands, causing the leading shoe to contact the drum, and the friction of the liniung against the drum caused the shoe to rotate with the drum, carrying through the adjuster, and firmly wedging the rear shoe into the drum.

If the cable is too short it cannot adjust the shoes out far enough because the cable "false adjusts" the shoes.

The cable was too tight

It is

The cable was too tight

I hope this helps

And the automatic adkusters on a Taco are actuated by firmly applying the brakes in reverse. With the ebrake cables loose.

[ultred ragnusen]

That's basically the net effect. Thanks.

It's a lesson well learned to follow the factory procedure.

I don't know how people do this job without the large calipers though.

[Clare Snyder]

For years I've done it by trial and error - adjust the shoes to what I think is right, then dry-fit the drum - too loose, pull it off and adjust up. Don't fit? back it off and try again. Usually only a few minutes. Then fine adjust with the brake spoon. ALWAYS check the ebrake cables - and REPLACE if they are sticky - or you'll just end up doing the job again. Also make sure you have the wheel brake adjustment right BEFORE applying the e-brake -particularly if there is any chance it has a self adjusting e-brake linkage. Do it on a Ford Aerostar and you'll find out why REAL fast!! You'll spend half an hour backing off the cable adjuster - - - -

[ultred ragnusen]

I am very glad you explained the error which I agree with you that it was a big make for me to ass-u-me that since the daily automatic adjustment keeps the shoes adjusted, that a manual adjustment would do the same.

I also agree with you that there seem to be three major methods of determining the /initial/ adjustment, all of which use the manual star adjuster (and each of which has a flaw for noobs like I am).

1. As you said, one method is to repeatedly dry fit the drum from far too loose to just a teeny bit too tight, and then, as a final step, back off the star adjuster a bit.
2. A similar method is to put the drum on the vehicle once, and adjust the star adjuster until it just begins to feel friction.
3. The third method is to measure the width of the drum and the shoes to be about 1/2 mm (20 thousandths of an inch) difference.

Each method works, but all three have noob flaws:

1. You have to know what to feel for.
2. Again, you have to know what to feel for.
3. You have to have the tools to measure drum width to reasonable accuracy.

I thank you for helping me understand what caused the vibration at speed, which, as you said, I think it was that the shoes were too loose and the brake cable too tight. I don't understand exactly how but that combination caused a floating which caused the leading shoe to grab at speed which caused the wobble.

It's a good thing this was found on a short test run, and not after long term damage might have been incurred.

Thank you for your comprehensive explanation, where I apologize that I just don't understand everything you said about why the shoes were floating but that's my problem in comprehension and not yours in explanation.

[Clare Snyder]

When I was teaching the trade I would have had a brake unit in front of me, and you face to face - which would make the "understanding" a whole lot easier.

Next time you have a drum off, pull the emergency on part way and then lookat what has happened to the position of the shoes. Check closely before and after. then picture what would happen if the front shoe was "picked up" by the drum and consider the e-brake cable to be a spring. You'll get the picture.

[ultred ragnusen]

I agree with you that it must work the way you say, mechanically, but my brain is having trouble visualizing how all the pieces work together in that I know only how the pieces fit together, but I can't "touch" them and "push" them and "wiggle" them in my brain to see how they affect each other in real life.

Thanks for that explanation which is hard to write because you're describing a moving system with springs and interactions.

The key I learned is that the star adjustment step just can't be skipped!

To try to give back to the group for the kind help, here is the tool I made to make it easier to hold back the locking plate off the star adjuster. The wire came out of a hot water heater I took apart to see how it works inside, and it's about 6 to 8 inches long, where the critical part is the painted area that starts 1-3/8" from the end, and is 3/8" long, which I filed down to make an indent (since the whiteout paint wouldn't likely last long).

The tool is to push away the plate which locks the star wheel here:

This is all you see from behind, if your head was as thin as a cellphone:

The tool needs to go in deeper than a noob like me would think it needs to:

Once it touches the plate, you need to push another 3/8" inward:

Then you have to hold it in that position while you get a chisel:

This is what it looks like from the other side when its in position:

You will have measured the drum diameter already at around 11-1/2 inches:

You adjust shoes until they are 1/2mm (20 thousandths) less than drums: