Brake pedal sinking Toyota Sienna

[GSCJR]

Do this:

1. Pump the brakes several times prior to starting the vehicle to see if your conditions persists, if it does, try step 2.
2. Allow the vehicle to roll in neutral as opposed to reverse or drive to monitor for any changes releated to engine vacuum (higher idle).

Keep us posted. The brakes on my Toyotas have never been awesome. In my opion the vehicles almost felt too heavy for the stopping power and I imagine with a Sienna, that would be amplified further. Hopefully you are able to determine if this is a hydraulic or mechanical issue.

 

[930.engineering]

After you have checked the MC, the booster including vacuum lines and have bled the entire system (ABS) thoroughly, so when you can exclude issues on them and if the problem still persists, I'd check the calipers' pistons for corrosion.

 

[supton]

On my Tundra I had a lack of brakes when the front pads seized. but once seized, the brakes simply did not recover, not until I took them apart and lubed back up. But I swear, the pedal was always mushy after I replaced a cylinder. Braking was good, just not as firm as when new(er).

Not sure why the pedal would be soft, then pump up. I would think a master cylinder would just be soft and stay soft, unless if bleeding off vacuum puts the piston in a different spot. I wonder if it's a bad rubber line? something that is restricting flow, it pumps up but slowly.

 

[jrvn]

air in the ABS system possibly, i had the same experience with my Tacoma, replaced the front pads myself and noticed right away a softer pedal, bled brakes myself numerous times still a soft pedal, took it to a Toyota dealer that had a BG brake machine and they bled the brakes with it for $128 i now have a pedal feel i can live with,

 

[JeffKeryk]

I like the way you renew your brake fluid. I always get a better pedal after a service.
I imagine you are using a pressure bleeder like a Motive Bleeder? They have served me well.
It does seem odd a master cylinder would go out so early but things seem to be pointing that way.

Good luck edyvw.

 

[The Critic]

Are your slide pins moving freely? The pin with the bushing on the front caliper tends to be very problematic on Toyota applications that take 1324 pads. The bushing will swell and cause the pin to get stuck; the pins fits very tightly even when new.

 

[edyvw]

I like the way you renew your brake fluid. I always get a better pedal after a service.
I imagine you are using a pressure bleeder like a Motive Bleeder? They have served me well.
It does seem odd a master cylinder would go out so early but things seem to be pointing that way.

Good luck edyvw.

Yeah, I use pressure bleeder, but Schwaben brand. Same thing.

Are your slide pins moving freely? The pin with the bushing on the front caliper tends to be very problematic on Toyota applications that take 1324 pads. The bushing will swell and cause the pin to get stuck; the pins fits very tightly even when new.

I disassembled everything few days ago and didn’t see issue with pins. However, didn’t lubricate them again. Now that you said this, I might take it down again and clean them, lubricate them and see. Thanx.

 

[The Critic]

Yeah, I use pressure bleeder, but Schwaben brand. Same thing.

I disassembled everything few days ago and didn’t see issue with pins. However, didn’t lubricate them again. Now that you said this, I might take it down again and clean them, lubricate them and see. Thanx.

You might need to replace that bushing. I hope you used the Toyota slide pin grease or silicone paste, and not something with moly.

 

[JeffKeryk]

Yeah, I use pressure bleeder, but Schwaben brand. Same thing.

I disassembled everything few days ago and didn’t see issue with pins. However, didn’t lubricate them again. Now that you said this, I might take it down again and clean them, lubricate them and see. Thanx.

Can you recall a point in time when the soft pedal started? Is it possible it was after a fluid service? I am just thinking outloud...
I would bleed them again. I'm sure you know what you are doing and are using a top quality tool, but it sounds like MC and/or air issue.
Again, good luck.

 

[edyvw]

Can you recall a point in time when the soft pedal started? Is it possible it was after a fluid service? I am just thinking outloud...
I would bleed them again. I'm sure you know what you are doing and are using a top quality tool, but it sounds like MC and/or air issue.
Again, good luck.

Yeah, it is before I flushed brakes few months back. So highly doubt it is that.
But, I will go and check sliding pins, do one more flush, just to eliminate those simple stuff.

 

[bbhero]

Lol. Ain’t happening.

Yeah don't blame you a bit....

They were horrible on the Sienna. Can't have that where you drive regularly.

 

[HangFire]

Have the brakes been bled using the Toyota ABS cycling procedure?

 

[billpace1956]

Ok guys,
I have a strange problem for some time. For several months in the morning or after 5-6hrs rest, brake pedal on 2015 Sienna is super soft, and barely stops getting out of garage on 7% grade. 2-3 braking attempts and things go back to normal. Thought first worn pads, as I sucked out any life out of them, installed Pagid pads, Element3 rotors, but same thing. I kept forgetting but last two weeks I was driving car more as I was upgrading suspension on BMW. So yesterday I decided to check pads as I was switching from winter to summer tires. In addition to discovering leaking strut, everything on calipers looked normal. All springs, retainers etc are there. No loss of fluid. Anyway, I decided to replace all hardware on pads, but nothing. Today same thing.
At this point I am suspecting that it is master cylinder. But, what is confusing me is that brakes are normal after few braking attempts. Actually, these Pagid pads are super responsive, nothing like mediocre OE ones.
Anyone? Trav? Critic?

I have a 2008 sienna that did the same thing. I told my mechanic about the problem and he replace the MC and the brake fluid. It STILL was like that!! I told him about it so he thought it was a defective MC. Took it out and got a free placement MC. It STILL took the brake pedal to the floor!! Ended up being the brake booster. This was in 2017. The brake booster at the time could only be had from the stealership for $1100.00 dollars. Fun times for sure. The problem was solved. I had 250,000 miles on the van at that time, it now has 363,781 miles on it now. The brake booster that was in the van when I bought the van was made by Aisin. Hope this helps. Thank You, Bill

 

[edyvw]

I have a 2008 sienna that did the same thing. I told my mechanic about the problem and he replace the MC and the brake fluid. It STILL was like that!! I told him about it so he thought it was a defective MC. Took it out and got a free placement MC. It STILL took the brake pedal to the floor!! Ended up being the brake booster. This was in 2017. The brake booster at the time could only be had from the stealership for $1100.00 dollars. Fun times for sure. The problem was solved. I had 250,000 miles on the van at that time, it now has 363,781 miles on it now. The brake booster that was in the van when I bought the van was made by Aisin. Hope this helps. Thank You, Bill

Thanx. I did not have time this week, to disassemble everything, but that is where I think the issue is.
I checked for codes, there was some ABS code in the system, so cleared that to see if it is going to come back.