Brake pedal Pulses when stopped while in Drive or Reverse. Not when in Park

Previous owner did the stoptech slotted rotor and 2010 4runner caliper upgrade.

When I asked him about the pulse break pedal he played dumb or simply didn’t know. Besides that and a slight whine from what I think or hope is the diff when at high speed and feathering the throttle those were the only two issues I could find so I bought it and trying to work those out.

Going to have someone sit in the truck and hold the brake while I snoop around some more. Thinking of just throwing a brake booster at it just yo rule that out. Couldn’t hurt I guess.

 

Not a mechanic....but could the vibration be caused by something unrelated to the brake system, like a minor imbalance in the drive shaft?

 

Yeah, when OP said that the pulses are distinct, regular, quite fast, fairly strong, occur when the vehicle is parked -- and that they continue even with ABS disabled at the fuses -- it gets me to thinking that the most-likely source is something around the engine output shaft or torque converter input, that is somehow being coupled into the braking system.

OP can you refresh our memory again? When vehicle is stopped, w/ engine idling, which transmission selector settings does it occur in?

Suggest you try every setting carefully & methodically, i.e. Park, Drive, Reverse, 1 / 2 / 3, and Neutral, for at least 10 full seconds each. (Or longer if needed to allow for settling.) Of course w/ e-brake set and foot on the brake to keep the vehicle from moving at all.

 

It could be something else and I’m thinking that is the case. It’s not the driveshaft because it only pulses/vibrates when at a stop. Not moving, not braking, not driving but when transmission is in Drive or Reverse I feel it. Maybe a transmission.

 

Try all the different transmission settings carefully.

 

Park: RPM around 800/900. No pulse/vibe with foot on brake or with foot off

Reverse: RPM drops to about 600 and pulse constant with foot on brake applied the emergency brake and take foot off pedal and it continues. If I hold brake pedal and give it some gas at around 900/1000 RPM pulse and sound goes away.

Neutral: RPM stays around 700/800 and the pulse is not a prevalent is there sometime and not other times.

Drive/4/3/2/L: RPM about 600 and has most pronounced pulse/vibe and sound. Apply the gas and it all goes away around 900/1000. Let off the gas and it returns. Is also felt and heard of I apply the parking brake and left off the brake pedal. Again giving it some gas and foot off brake pedal parking brake on around 900RPM it goes away.

 

Interesting. By using the e-brake as part of your testing it seems like you may have eliminated the normal braking system as being the possible root/origin of the issue. The fact that the pulsing goes away with increasing RPM is also interesting.

I wonder if automatic transmissions have some kind of hydraulic bypass loop in them which keeps a small amount of trans. fluid circulating at idle RPM, but then gets shut off (i.e. the bypass is deactivated) when RPMs increase. (When it's time to carry the full power available in the fluid torque converter through to the gear sets.)

Separately from that guess, it's also possible it's some sort of shaft imbalance or bearing vibration which is only excited at lower rpms.

 

Broken motor mount results in this and other vibrations in some other marquees. Especially when stopped in gear.

Get under and pry around the motor and trans mounts and see if you can find a split rubber. Free, easy, and possibly the problem

 

It continues when in park, foot off the brake, e-brake engaged. I agree that this test pretty much eliminates the braking system as the culprit.

Seems like it is a certain RPM problem. Maybe pull and check or replace spark plugs? My 2011 recommends spark plugs every 30k. If you don't know when they were done, it might be a good simple maintenance item to do. Only buy from an in-person retailer or dealership. Counterfeit plugs are a real thing and more common than you would think. Stick with NGK or Denso copper plugs (what was originally installed). If you pull half NGK and half Denso plugs, then you really have a problem (indicating that the plugs are original from the factory and never bee replaced).

For giggles, check the line from the booster to the intake manifold. I doubt that is your issue, but a simple and quick check.

Other than that, I'm leaning toward something in the transmission section....not necessarily the transmission, but something around it like the torque converter.

Speaking of pretty standard maintenance, have you replaced gear oil in the front/rear diff and xfer case if you have one? I'm not saying that is remotely close to related to the issue, but something good to do on a new to you truck. I'd probably have the dealership flush the transmission as a next step in troubleshooting the issue. If you don't want to pay the dealership prices, there is a DIY here on how to do it. At a bare minimum, check the fluid level to make sure it is full.

 

Still have not found anything that just stands out. I may just change the motor and tranny mounts as it can’t hurt and that’s not too pricey. I’ll report back as I replace one thing at a time and solve the issue.

 

Gonna have to get under there and get somebody to put it in and out of gear … sounds like something is touching the body somewhere

 

If you haven't already, be sure to carefully check the transmission fluid level, according to spec if possible (i.e. when it is fully warmed up, I believe around 175ºF.) I have seen an automatic transmission do weird low-speed shudder things when underfilled.

 

Transmission check temp is 97-115F for the A750 trans.

 

Is that fluid temp? Or temp measures on the outside casing using a laser thermometer?

 

I would absolutely want to check the trans fluid level/condition, and maybe check torque converter to flywheel bolt torque.

 

That's fluid temp measured at the temp sensor in the transmission, pan temp will be slightly lower.

 

Older cars used to do this when their trans. fluid got low or old. The torque converter would partially engage and it would be trying to pull the car forward. I would definitely check the fluid level and condition

 

There is a process. You can find it on TW, but basically you perform a set of monkey maneuvers (rub head, scratch belly, type dance) that will get the Trans light on the dash to flash when the fluid temp is in the proper range.

Edit: https://www.tacomaworld.com/threads/how-to-drain-refill-automatic-transmission.63851/

 

Hey OP.....any resolution on this yet?

 

Dirty throttle plate and intake??