At a loss, 2 years of trying to figure out bad shake while braking

2001 Tacoma Prerunner 135k miles

I really need some answers on this and to get it fixed once and for all. Hoping some of you pros can help me get this fixed, I will try and explain in detail the problem I'm having and all I've tried so far.

Issue:
Bad shake/vibration while hard braking especially while braking downhill or pulling a trailer. It's not a slight vibration, it's bad and causing the whole truck to absorb it. While looking in my rear view I can see the bed moving so I suspect it's coming from the rear end and my local shop says the same. I do not feel the shaking in the wheel and my front end is tight with new ball joints and tie rods. Truck drives nice and straight. If I remember correctly this started while doing a full brake job on the truck, drums still in the rear.

What I've done so far:
-Disconnected all ABS components
-New disc brakes front
-New master cylinder
-New copper brake lines and hoses whole truck
-New rear drum brake kit with wheel cylinders and hardware
-ANOTHER set of drums and shoes ( to rule out defective 1st set or out of round drum )
-Full bleed many times

Not sure how to proceed here. I still think it's something going on with the rear drums. Or a bad suspension component somewhere? My truck has 135k miles and getting rusty, I am in upstate NY.

**UPDATE** Problem fixed, needed to install OEM drums see post #24

 

A good long braking effort (like riding brakes down a hill) can build up lots of heat and warp rotors. You're suspecting rear end, but if you hit a dead end there, a warped rotor can definitely cause a good shake/vibration under braking.

Good luck finding your gremlin!

 

Yeah I mean this sounds like textbook warped rotors. I can't imagine a bad u-joint or something because you'd likely experience that while under acceleration, so I'm just not sure. Perhaps knock out your front discs and pads once again to eliminate that from the list. Use OEM parts or quality aftermarket stuff like Hawk, brembo, etc. Doesn't have to be drilled and slotted and all that nonsense. Just use good parts.

 

Time to check for a bent rear axle shaft, or a bent front hub flange. You’ll need a dial indicator.

 

I agree with others that the description sounds like typical rotor warp, but if that's been eliminated then isolating the location is the next step.

For troubleshooting, you (or a shop willing to work with you) could use clamps on the hydraulic flex lines to isolate front vs. rear. There are tools specifically designed for this that won't damage a line in good condition.

I'd be taking the rear drums off and doing a visual inspection. Maybe replace if anything is even slightly questionable. Since rear drums last so long, they're often neglected.

I'd also go over all brake, suspension and steering components and make 200% sure that nothing is loose that shouldn't be.

 

My tires are a few years old and have plenty of life left. I could have them checked, but if they were the cause wouldn't I get some other type of problems even without braking?

Great tip, I will be buying the clamping tool to isolate my front and rear. Thanks!

 

Did you or the shop jack it up or on a lift and run it then slam the brakes on to see if it shows up.
Are your rear shocks or springs/eye bushings all good?
Frame straight and no rusted-out sections?
Now a loose front suspension (ball joints, tie rods, bearings, etc) could case vibration/shudder thru the whole truck on hard braking also.
Hard problem but seems maybe not the brakes after all you did and repeated.

 

What kind of shape are your shocks in? Has the truck been lifted, and do you have a rear anti-sway bar?

 

The fronts are new and the rear struts were replaced 30k miles ago. I was actually thinking they might be bad, or at least one. With the rear end jacked on the frame I can push up on the drivers side spring pretty easily and when I go to the pass side I cannot move it up at all. Maybe one is blown?

 

There are a couple of things I can think of. If you can find a long downhill road and there is no one else on it, you can use the parking brake to actuate the rear brakes only… keep your hand on the parking brake handle and keep it turned so that it doesnt “rachet lock” if that makes sense. Pull the handle and see if the vibration is present.

What I suspect more is that your load sensing proportining valve that is attached to the rear axle is defective. Is the truck lifted or does it have stock suspension.

The job of the load sensing proportioning valve is to allow more brake hydraulic pressure to the rear wheel cylinders when there is a load, that is the bed compresses the rear springs. If it is defective or the rod has been bent then the front disc’s are doing the majority of the stopping. Rear drums are just fine if they are adjusted properly.

I struggeled with this on my 3/4 ton Ram diesel pulling my 34’ 5th wheel, talk about scary, it would do the same thing, brakes shake and at the bottom of grades there was absolutly no brakes, theh front discs and pads were litterly smoking. I parked it until I could come up with a answer and a fix. After a month of inquiries to the “experts”, I discovered a service bulletin from Dodge acknowledging this and their recommendation was to remove the load sensing valve completly. Am I recomending this to you, no, just telling a story.

 

UPDATE:
I used a set of hose pinch clamps and pinched off the rear brake hose. The problem completely disappeared and my truck had zero shake and stopped nice and smooth SO it's a drum brake issue. Or possibly an issue with something else in the rear end that only presents itself when the rear brakes are functioning. I am betting it's the drums.

Has anyone installed the tacoma rear disc conversion kits I see are available and had success? I will have to find out exactly what kind of caliper/rotor/pad set they come with for future replacements. All they say is that they are "GM style" parts.

 

I forgot to include that in my post, the load sensing valve has been deleted and replaced with a Tee and still no improvement.

 

Try disconnecting the parking brake cable. I would think that if it's adjusted wrong or not releasing all the way it would cause 1 drum to drag or grab quicker than the other.

It's a Longshot but it's a free test, just takes a little time.

 

Yeah, I was going to say, almost all non OEM drums need to be turned right out of the box. I have experienced it twice now on my 1st gen Tundra.

China doesn’t make drums like they used to.

 

So after re-reading the posts you already changed drums so most have a 1-2 year warranty. Replacement free state out of round.
But you already did this once so....doubt drums. You don't have spacers or aftermarket rims do you as another area to look at.
Replace shocks if one blown first and retest with both rear brakes.
Pull on the rear axle and see is in/out or wiggle play or grinding/grating feeling pointing to wheel bearing.
Check for other worn/defective suspension components back there like springs, spring bushings, hangers, and frame.

If this did not fix it I would strip the entire rear brakes down (1 at a time for ref) and look at what you installed already several times.
You replaced the wheel cylinders (did you get the correct ones a s 2 bore sizes), shoes and springs actually installed all correctly (easy to put a springs in the wrong hole or location, retainer springs clips locked on, clean all levers and grease the pivots, unscrew the adjusters apart and clean/grease, check the parking brake cable, new stainless brake lines, then reassemble (get a diagram as other side may not be totally correct either) and then adjust them correctly. A disc conversion on an 01 is a costly approach and drums work fine.

I have no idea what deleting the rear prop valve has done to fix or make worse your issue or deleting ABS. Each time you change or alter OEM setup changes how the rears are designed to function.

 

Are you sure its not your rear leafs.....are you getting axle roll....
especially when loaded and compressed.

didnt real thru whole thread....but it looks like you've ruled out the obvious....

 

I do not know, we've yanked on the axle and leafs while the truck was up and didn't feel anything loose. It's a rusty truck and I'm sure there are worn bushings. The problem IS multiplied when I'm towing a trailer or have weight trying to slow down and stop. Just checking prices the leafs are expensive.

 

wait..... Did you do this at the same time as the problem started? If you removed the LSPV, and didn't install a manual valve, your rear brakes are getting too much pressure.