danskelly

Hello all!

First-time poster, but I've been reading this forum a LOT recently after doing a complete rebuild of my 3VZE a couple of weeks ago.

Here is an issue that came with this truck when I bought it, and now have the time and energy to troubleshoot (ask for insight) it after finishing the rebuild.

Then traveling at speeds lower than perhaps 40mph, and the applying light pressure to the brake pedal, I get what can only be described as "tapping" on the pedal. The "tapping" rate is relative to the miles per hour, and it continues all the way down to about 5mph. Weird thing is, it does not "tap" at speeds higher than 40mph or so.

I've replaced the front rotors, calipers and pads (because they were worn, not necessarily for this issue.) I've visually and physically inspected the rear drums and shoes, and found nothing that would translate into a "tapping" on the brake pedal.

I've bled all four slave cylinders, and the ABS control valve thingy on top of the rear diff. (in that order)

During the rebuild I DID have the P/S pump disconnected, but I also bled that system.

Could there be more bleeding necessary, or do you think that there might be a bad part?

The "Rear ABS" light is not lit except when engine is off (as expected.)

Thoughts?

Thanks!

yayfortrees

I agree, that sounds possibly related to the ABS system. Maybe a bad or dirty sensor / connection?

Sorry I'm not of any more help, I'm sure others will post better suggestions.

Flash319

I would say it is not your abs. The ABS on these trucks don't work, they really do nothing.
Is the tapping a "pulse" on the pedal or is it a noise only?

If it is a noise it is more then likely the front pads tapping against the rotor. This can be caused by a brocken spring that holds the pads in the caliper pistons. If it is a pulse then I would say that something is out of round either the fron rotors (which you changed) or one of the drums.

Since you just bought the truck I would check that the back brakes where put together right and that the drums are round.

danskelly

I guess it could be called a "pulse" but I consider a pulsation as more of a "sine wave" vs. what it actually feels like... a "square wave." It definitely feels (and sounds) like a "tick."

Would out-of-round drums cause the above "square wave" ticking"? I know what a pulse feels like, but even when slowing down (around 10mph) no pulse... still a "tick."

Do I need some sort of tool to check to see if the drums are round? I usually just replace them if I'm suspicious. At this point, I'm not.

Flash319

Since your front is all new I would be looking to the back. Also since you say that it is more of a "square wave" I would also say back. This is because the back drums are very large and a flat spot may feel like a square wave.

You will need a way to spin the drum and a dial indicator to measure runout. I have a lathe so i just spin it up on there and see how it looks. Drums are not cheap so I understand where you are comming from.

The only way to eliminate the back is to plug the back port on the master cylinder and see if the pusle goes away. You may have to bleed again after so not a fun job.

I would also check that your e-brake is fully released. Make sure the actuator arms on the backing plates are loose and free. If not you may have one side dragging causing the pulse.

If you are hearing a ticking is it coming from the front or back? If it is from the front I bet it is just the pads dancing on the rotor. You may have some siezed pistons in one of the calipers. Toy calipers have 4 pistons, usually one or 2 sieze up without any noticable loose in performance but can cause a gap and then "tick tick tick".

danskelly

Yeah, looks like I have some fun diagnosing ahead of me. I just did a quick parts check, and I can re-do my rear system for about $175... Not too bad, but still will need to do a little saving. :-)

I don't hear a tick from the outside, but from the pedal. It coincides with the "tick" I feel on my foot. I don't hear anything from the front or rear brake components.

danskelly

Okay... I've done a tiny amount of diagnosis that has proven my theory.

I unplugged the ABS relay, and the ticking is gone! So, I have to say it IS an ABS issue. Any guesses to what component could cause this? I was gonna try throwing parts at it starting with the speed sensor, then the ABS relay... and hopefully not having to go to the $1,000 actuator.

yayfortrees

Why would you just throw parts at it? If you're rich like that, share some $$$ with me!

JK, but seriously, just start diagnosing some parts. I would start by checking resistances of sensors per FSM. Do the easiest things first, and hopefully it will be fixed without having to spend a lot of money on it.