Transmission / Brake Interaction (Feels like brakes are on in Reverse)

When starting the truck and going into Reverse there is an interaction with the brakes. Sometimes, the Truck won't coast backwards (even on a sloped driveway). Requires real throttle to move. The hack "fix" is to move through the gear positions to Drive. At that point, I usually I feel the brake pedal relax. Then if I cycle back to Reverse and everything is normal and the truck glides back freely. Occasionally I have to cycle to Drive more than once to get the brake pedal to relax.

I bought the truck used a couple of months ago. 2006 Tacoma 4WD, 4L, Automatic, 70K miles. The recurring issue happens when the car is "cold" (usually the first start in the morning). Also during colder weather the issue is much more pronounced. During warmer months this happened 1 in 4 morning starts. Now that it is colder (December) this happens every morning and during other starts. This is mostly a nuisance issue. Once I cycle the gears and get on with it, the truck is tip-top. No other problems. Transmission is great in all other situations (shifts smoothly etc).

I have seen some discussion of this issue in other internet forums but no clear answer. At first, I assumed this was something in the transmission. However, after months of experiencing this, there is clearly at least some interaction with the brakes based on the brake pedal feel. Is it the computer? Master brake cylinder?

Here is what I have done so far as I get the truck in good working order:

* Cleaned the transmission pan/filter and drain/filled Transmission with WS (several times to get most of the old fluid out). Set the ATF level carefully per proper procedure.
* Replaced front brake calipers/rotors and performed a brake bleed on all brakes.
* Adjusted the parking brake. And of course I have ensured the parking brake is fully released when this happens.

The $64,000 question is: What is causing this issue and how do I fix it? Any help is appreciated!

 

Can the drums/shoes be freezing? We don't wash cars at the dealership if it's too cold out.

 

Broken parking brake cable(s). You’re welcome

 

WRT freezing issues - Possible but most of the time cold does not mean freezing. This happens when it is 60 degrees (sometimes) and 34 deg F (very frequently). Also the brake pedal changes feel when cycling to drive tells me it is some kind of interaction with the Transmission... I think?

WRT broken parking brake cables... I don't think so. The parking brake works perfectly in other situations and the issue with the pedal feel seems to be key.

In the other Toyota forum that describes a similar issue (4 Runner) it was resolved by adding ATF. My ATF level is set to spec and I have tried adding 1/2 Qt above spec to see if that helped. I could "believe" that cycling the gears warms up the AT and that somehow triggers something in the computer that impacts the brake pedal feel.

I realize this could be apples and oranges but the description seems very similar to what is going on with me.

 

You may isolate the issue if you chock the front tires.
Then place jack stands under the rear axle , shift to Neutral, and then attempt to free spin the wheels.
This isn’t exactly a convenient way of checking. But it might help in diagnosing the issue?

 

The transmission is not interacting with the brakes. When you park on an incline and engage the parking brake the weight of the truck is resting on the brake shoe. Release the parking brake the weight of the truck is still on the shoe and that is preventing it from releasing. When you shift into drive that moves the vehicle forward enough to take the weight off the brake shoe and allow it to retract.

This is my theory.

 

@Jimmyh @TnShooter These are both good ideas / Theories. It gives me something to try to diagnose the problem (or at least eliminate some theories). I will run with those ideas and report back. Testing in Neutral is the key to both.

For what it is worth, my prevailing theory at the moment is that when going to reverse the Transmission is not properly "in gear", whatever that means. This could mean it is not warm enough, or not enough fluid in the torque converter (because of the incline) or some kind of mechanical misalignment from the shifter cable mechanism. Not sure. I don't know much (obviously) about the detailed inner workings of the AT. In any case working the shifter ultimately resolves the issue. One thing I can say for sure (I think), is the AT is cold at first and by working the shifter, helps to warm it up. Not saying it is a Temperature issue alone but that is a thought. And the truck computer definitely monitors transmission temperature. You can see it on the OBD readout.

Why I get the brake peddle relax when going into Drive is a bit of a mystery. It seems like the Truck computer reacts to going into Drive position and does something that gives that feel but it may not be directly related to the issue.

 

Could it be hill assist.

 

Operating conditions of hill-start assist control on the trucks with (TRD) Off-Road package.

When the following four conditions are met, the hill-start assist control will
operate:
●The shift lever is in a position other than P or N (when starting off forward/backward on an upward incline).
●The vehicle is stopped.
●The accelerator pedal is not depressed.
●The parking brake is not engaged.

Automatic system cancellation of hill-start assist control The hill-start assist control will turn off in any of the following situations:
●The shift lever is moved to P or N.
●The accelerator pedal is depressed.
●The parking brake is engaged.
●Approximately 2 seconds elapse after the brake pedal is released.

■When shifting the shift lever
●On vehicles with an automatic transmission, do not let the vehicle roll backward while the shift lever is in a driving position, or roll forward while the shift lever is in R. Doing so may cause the engine to stall or lead to poor brake and steering performance, resulting in an accident or damage to the vehicle.

 

One other thing to add to the list of possibilities is rear axle seals. If the seals leak gear oil onto the rear brake shoes they will stick to the inside of the drum after sitting even just overnight. It produces a symptom just as you described as well.

 

I’ve never seen this happen.
Not saying it can’t happen.

When mine leaked, it didn’t cause the shoes to stick.
I actually thought it made the rear brakes less effective and the E-brake to “slide” more before it caught.

The biggest problem was the gear oil all over the fender wells and inner wheel.
That stuff stinks, I don’t like the smell of it at all.

 

After several tests, I can give at least a partial answer. It is the rear brakes sticking. I ultimately nailed this down when the car was parked on a level surface (after the truck was sitting for some time in cold weather) and I was able to go straight to drive. The truck felt stuck (as in my usual driveway - reverse case). Going from Drive to Neutral (and back) had no effect. With some help tried to push the truck (in neutral) on a level surface and it was stuck. I next tried to pump the brakes a few times and everything fixed itself and I could drive normally.

As to why the brakes stick, I still have more to figure out. I understand the front disk brakes very well and the front wheels turn in neutral when the problem occurs (yes, I used a jack to figure this out). The details of rear shoe brakes / e-brake are unfamiliar to me. I don't see any leaks on the driveway so hopefully not the axle seal but uncertain for now. I will report back when I get to the bottom of the rear brake issue.

Thank you all for helping me get this far!

PS Thank you for the Hill Assist details. I checked that out as well and was able to go through the check list provided (i.e. when Hill assist is on) and conclude that this is not the problem since it did occasionally stick in Drive.

 

OK, so I finally got around to rebuilding my rear drum brakes: New drums, shoes, springs, cylinders etc. I used a kit from Rock Auto and followed the procedure in this excellent youtube - https://www.youtube.com/watch?v=3ru8E9iw7nM

It was a huge mess inside the drums and one of the drums took hours to remove because of rust. I am doubtful that the rear brakes had ever been serviced. I did back off the adjuster, release the ebrake and I tried to use the drum/bolt trick to get off the sticking drum. The bolts kept stripping when the forces got to high on the threads. From there I reverted to sledgehammer, pry bar, and liquid wrench AND the bolt trick working together (i.e. maximizing pressure with the bolts just before they strip and then sledgehammer + prying ultimately worked). Wow that was painful! (Note to self: take the drums off once a year and apply anti-seize and sand down the ridge in the drum as needed to prevent this mess from recurring.)

Now that I have new rear brake hardware installed my mysterious "transmission/brake interaction" has been completely resolved. Thank you all for your help! Specifically: @Jimmyh, @Jason J , @mlcc , @TnShooter @Steves104x4 104, @HAVOC . This site has been a very helpful resource because of you all.

 

I've had rotors/drums crack at that hole using the bolt method. Had to resort to the BFH method.

 

Good to hear you have it sorted out, Good job!

 

Look at the e-brake cables where they mount to the backing plate. They like to crack right there.