Soft brake

I have a 2004 Tundra 4x4 4.7 with 190200 miles, Owned since 2011. I occasionally tow a travel trailer or utility trailers with electric brakes. My brakes have been working good but the pedal is soft. I've changed the Master cylinder and the Vacuum booster. The pads, rotors, drums and the shoes are good and the system has been bled. No leaky calipers or wheel cylinders. I've done brakes on many other vehicles but this one stumps me. The ABS works when I stop on a slippery surface. The pedal never goes to the floor but should be stiffer. What am I missing?

 

I’ll start if the obvious - you did a 100% fluid swap?

 

Rear drum adjustment is key on these puppies. The rear shoes have to expand further if they aren’t adjusted properly and possibly giving you a soft feel

And welcome from the valley

 

Couple things: The cab type of your Tundra and the MC/booster combo you have is critical info when talking brakes. Show us a pic of your MC/booster combo and for crying out loud, tell us what cab type you've got.

@FrenchToasty is right - rear adjustment is so important to your braking experience there's an entire sticky thread dedicated to that alone. If your rears are working properly, sometimes setting/releasing your e-brake a few times will adjust the rears down and correct a myriad of issues.

Likewise, the process you use to bleed is key.

Also, did you bleed the LSPV? If yes, at what point in the process?

 

Extended cab.(small back seat) I'm going to try the parking brake tip and see if that helps. I bleed from R rear first then L rear then R front and L front.
Just tried the parking brake tip and I think I may have some improvement. Will update.

The truck is a workhorse and is dirty this time of year in North Idaho. I appreciate the rapid response to an issue troubling me for a while.

 

Ah. You need to bleed in this order:
RR > LR > LSPV > RF > LF


If you don't bleed the LSPV there can still be air between front and rear.

 

Welcome from LA (Lower Alabama)!

 

I second the LSPV bleed point. Air will consistently rise up the line from the axle to the frame. I actually do it first, than RR, then LR then LSPV again before doing fronts. Air being the biggest contributor to pedal softness when you are confident no leaky cylinders.

Make sure there is no droop in your parking brake cable when the parking brake is released. Although it sounds the rest of your system has been inspected, that cable stretches over time. The cable at the rear axle shouldn't droop when the parking brake is released. There are specs in the FSM for freeplay at the outer crank arm that connect the cable at the drum. Its adjustable at the crank, but usually isnt necessary. The turnbuckle on the drivers side frame rail has the most capacity to take up slack, any leftover slack can be adjusted at the floor pedal in the cab. Do the turnbuckle first, and don't mess with the parking brake pedal nut until you have exhausted the turnbuckle. There should be as few clicks as possible between released and paking brake applied at the pedal. Count the clicks. Ideally 6-8 clicks at the pedal, the fewer the better, this is from mremory you can look up the exact spec for clicks at the pedal on the FSM. Clean the pivots along cable route mostly at the rear axle, lube em up until they move freely.

Use the parking brake regularly. With proper tension on the parking cable, it will more effectively turn the star wheel tp keep your shoes as close as possible to the drum. The closer the shoes are to the drum the faster resistance builds at the pedal.

After that, if everything checks out, and you are still not happy, you can increse rear brake pressure at the LSPV shakle at the rear axle. Many threads on that, and it is in the manual. The rear drums are supposed to operate at 71 psi. The LSPV at the frame has internal valving with contact wear points. As you mentioned you are trailering, its possible you have excceded the wear limit on the contacts in the valve. When your springs compress under trailer tongue weight, the valve contact points engage and increase rear line pressure. They also wear down. With the bed/towball empty the valve may be returning too much pressure to the front, yielding lack of pedal feedback from low pressure at the rear. You may not be getting full pressure to the rear drums, but you don't have to mess with the LSPV valve. Put matchmarks on the shackle nuts at the rear axle. turn the top nut 1 turn, and then snug the bottom nut up to it. This could either take up slack in the valve or add line pressure of 11 psi to the rear, 11psi per full nut turn. Or some combination of the two until slack is removed. 11psi is a 15% increase in pressure at the rear drum. Thats a lot so drive test after each single nut turn. If you go too far you may get squat when braking while towing. If you find a shackle length that feels good empty bed, no tongue weight, remember to test run the next time you add a trailer, and make sure it doesn't squat under braking. If it does, go back to the shackle and do the reverse in 1/2 turn increments until ithe truck maintains level under braking while trailering. The sweet spot is there somewhere.

 

I found the parking break was not releasing. When I got under the truck the cables to the drums at the axle were slack. I pressed down on the park brake and the cable tightened but the parking brake didn’t hold the truck when I moved it.
I am going to remove the drums and investigate the park brake levers. FYI this truck’s not used much these past couple of years and has set for long periods. Being old, me and the truck, contributing to the problem. I have tried to be meticulous about maintaining it. It’s been a great truck and will probably be my last.

 

Thanks for the response and all of the pertinent information.

 

Common problem, especially when you don't use the brake often. Here's what you need:

https://www.rockauto.com/en/moreinfo.php?pk=4198851&cc=1426935&pt=20057&jsn=488

 

Tighten turnbuckle and bleed LSPV, RR, LR LSPV in that order, and test drive before digging into the drums. Less work. LSPV air is the common culprit next to parking brake cable slack.

 

More good information. Thanks again.

 

You can also jack the rear up and slowly adjust the stars on each side to bring the shoes closer to the drums, a slight drag isn’t the end of the world, better than being to loose

 

This is a temporary fix until pad wear increases distance between shoe and drum. Once the shoe wears away, if the parking brake isnt ratcheting the star, the air gap increases with shoe wear (increasing pedal softness), and you are right back where you started. Parking brake is essential to keeping the pad shoe close by constantly clicking the star when you park keeping freeplay at the drum minimal hence increasing the resistance at the pedal in the cab under braking.

 

I’ve also heard the self adjustment of the ebrake to shoes is kinda of a hopes and dreams kinda thing, that’s why I give her a few clicks every 5k or so

 

You can also disassemble the parking brake cranks, sand any rust off the pins and grease them back up. I do it every few years when they seize for lack of parking brake usage.

 

I haven't had a problem getting it to work.

Ive you are manually adjusting into extra shoe contact at the drum for pedal feel, maybe add a stronger return spring at the pedal and tighten the linkage bushings there. Might give you the pedal feel you are looking for. I wouldn't recomend doing it unles a vehicle is braking properly first. Might mask a safety issue.

 

I mean, in all fairness, if you live in the rust belt it very well can be! But if not, it should be an expected function of a properly working drum brake system.

 

Brakes are working better but the elements are getting to them and they use chemicals and salt on the roads here. I just went on Rock Auto and ordered new drums, shoes, parking brake kit, rotors, calipers and pads. Quite an expence but glad I can still do the work myself and have a shop to do it in. This will be a good spring project and everything will be brand new. Thanks to all again for taking the time to answer my questions.

 

Thanks for the question and all the informative answers. This thread has been helpful in learning about the brakes on my new, to me, truck.

 

Hopefully you have better luck than others with the drums. I've read more stories about new drums being out-of-round than I've read stories of perfect drums

(Most of those were with store brands and not OEM, but ... )

 

At this point, I think its a good idea to take the drums to a machinist and get them 'turned' before even trying to install.

And, in case the OP missed it, as several have commented, the E-brake self adjustment system is essential to your entire brake system working properly.


https://www.tundras.com/threads/rear-brake-adjustment-theory-and-practice.99575/