Shaking while braking

OK,
This might be a dumb post but my son has a 1999 toyota 4runner and I have done a lot of front end work. I have done a complete brake job front rotors and calipers,pads. I have done the rears as well changed drums, shoes and wheel cylinders. I have done the rack and pinion tie rod ends dog bones replaced. The truck shakes like a son of a gun when braking going down hill? and I checked wheel bearings too what could it be???

 

Warped rotors?

 

There are really only 3 things to check in this "shaking when braking" scenario. From the most likely to least, they are:

1. Warped front rotors. You mentioned that you've replaced the front rotors, but if you didn't use high quality replacements, they could have been warped out of the box. Additionally, the stock rotors on 3G T4R's are known to be a bit "thin," and warp easily, which is why a lot of folks do the Tundra Brake Upgrade. I say all this to say that you need to really verify that your rotors aren't warped, and don't warp when they heat up. (sometimes, you only get a shaking when the brakes are hot).
2. Out-of-round rear drums. If the drums aren't perfectly round, the shoes will drag unevenly. This is a lot like warped rotors up front, but with the "rear tech." Again, sounds like you've done everything in the rear, but maybe it's time to double check.
3. This can happen on the front or the rear, but you need to be sure that there is no debris between the rotors and the hub, and the rotors and the wheel. If there is, then they can rotate slightly out of plane, and that would give you a pulsating as well. I like to use a brass wire brush and brake cleaner to really smooth out all the surfaces that touch when I do a brake job, and I clean up the mating surface of the rotors/wheels each time I do a tire rotation. The same thing can happen in the rear with the drums, so check those as well.

If it does turn out to be warped rotors, this page has a great step-by-step guide (with pics) on the Tundra upgrade, as well as links to all the parts needed (at varying price points). OEM is best for the pads, but for the calipers you shouldn't pay the premium. Get them from your local parts store (ideally) or Amazon, which will give a lifetime warranty in case you ever need to replace them. And don't forget the upgraded lines, they make a big difference with the larger calipers.


https://adventuretaco.com/guide/step-by-step-tundra-brake-upgrade-on-a-tacoma-or-4runner/

 

Could be an uneven build up of brake pad material due to braking technique of driver.
Often caused by "hot hard stops". When rotors are hot from use, then the vehicle is stopped abruptly and foot pressure is maintained on brakes after wheels stop turning-pad material transfers to rotors.
These pad material built up areas continue to build up in normal or heavy braking. Making the pedal pulsating more noticable.
This is mistaken sometimes for heat warping of the steel rotor.

 

Did you use aftermarket rotors and pads?

I've found they warp almost immediately anymore and its very important you granny drive it for 400 miles with no hard stops.

I went back to TOYOTA rotors and pads from Duralast Gold Lifetime and it's night and day better.

 

Did you torque the wheels evenly and to spec after the brake job? Uneven torque can warp rotors.

If you have access to a dial indicator, can check rotor for runout.

I would be looking at other suspension items like lower control arms and ball joints, even though those don't normally cause a shake.

 

Post your alignment numbers & what type of tires you running? Does it do this in 4wd?

 

So since you replaced the rotors/drums and pads all around, but still have shake but only when braking, and checked wheel bearings, then maybe one or more of your wheel hubs, front or rear, is warped? Since your rotors mount directly onto the hub, if the hub is warped and you torque down your lug nuts, it could make your rotor not turn true. I've only seen wheel hubs warped by hitting something in a sideways manner, but I mean, sounds like you're down to the very last possible things it could be, and you didn't mention that yet. Good luck!

 

There is also one more possibility. Did you wire brush the hub before putting the rotor on? If you live in the rust belt, the rust on the hub causes the rotor not to fit flush. Go ahead, ask me how I know this.