'87 SR5 Turbo Automatic has Really Soft Brakes
 

On my past two '87 SR5 Turbos (Automatic Tranny), I've had a hard time stopping the truck especially when pointed down hill in gear. If I'm at a redlight facing downhill waiting for it to turn, I feel like I have to literally stand on the pedal.

I think I need new rotors and pads, but am pretty sure those won't solve it.

Ideas:
1) Maybe it's the pads and rotors?
2) Maybe I have air in my brake lines?
3) Since mine are Turbo models, they should already have a larger brake master cylinder right?
4) And I've heard the 1" Brake Booster (Marlin, etc) won't help right?
https://www.roundforge.com/articles/...booster-specs/

Any ideas?

Have you looked to see what size you have in regards to the brake booster and master cylinder? It's easy to visually verify. If you're not leaking/losing fluid anywhere externally or internally, bleed the brakes maybe? You say you have to stand on the pedal, but what does the pedal feel like? A 30 year old booster could be failing too. Has the system been futzed with? Is the LSPV still attached and functioning correctly?
There's lots of things that need to be checked by you since you're in front of the truck.

Thanks. I haven't messed with the brakes much on my 1st gens. Answers:
- Have you looked to see what size you have in regards to the brake booster and master cylinder? It's easy to visually verify.
HOW? IS THERE A THREAD SOMEWHERE? I'LL DO A SEARCH.
- If you're not leaking/losing fluid anywhere externally or internally, bleed the brakes maybe?
AGREED
- You say you have to stand on the pedal, but what does the pedal feel like?
THE PEDAL FEELS OKAY - NOT TOO HARD OR SOFT. IT JUST TAKES A TON OF EFFORT TO STOP IT WHILE IN GEAR.
- Is the LSPV still attached and functioning correctly?
I WILL CHECK.

The size of the master is usually stamped on the side of it, should say 13/16, 7/8, 1, etc. The booster types are also listed in the link you posted, with pictures. Dual diaphragms have a step down in their shape toward the master cylinder.

Not too hard or soft on the pedal is subjective at best, but maybe you're not getting enough vacuum assist, maybe you have air in your lines. Maybe something auto trans specific? I don't know, never had an automatic anything. Maybe a lot of things. You've got a few things to check.

Yes^^^
Charles,
The transmission may still be tying to engage and drive forward even when you're on the brakes. Have you ever tried putting it in neutral while at stop facing downhill? Then we would be absolutely sure you are only struggling to stop the vehicle weight, not transmission trying to drive forward when you really want it to stop.

Also, there is a signal line from brake switch to ECU and ECT. I think they reduce fuel pressure OR injector output to help slow down the truck, AND tell ECT that you are trying to stop.
Please check IF you get 12V there when you press on brake.

FROM 1988 22RE SCHEMATIC

https://cimg1.ibsrv.net/gimg/www.yot...8751981257.png


https://cimg1.ibsrv.net/gimg/www.yot...7bb1c33999.png

https://cimg2.ibsrv.net/gimg/www.yot...eaefb3d5bb.png

Pull the wheels off and inspect your pads and rotors.

Jack the back pull the drums inspect your brake shoes and drums.

Do you use the Parking Brake to keep your rear brakes adjusted ??

if not that will lead to long pedal travel

A soft pedal does seem to be air in the lines or Rubber brake hoses blowing up like a balloon under pressure

Yes, the best troubleshooting tools are our senses; seeing, feeling, smelling...

​​​Good point because some people with auto trans don't bother using the e brake, especially those in flat terrain.

I don't think it necessarily has a larger master cylinder but a dual diaphragm brake booster

on my 94 I did the usual pad, etc. Still spongee brakes. Replaced the booster, stopped like a time.

so you keeping this one or dumping it?

Thanks. Did you go with a different or just new booster?

I'm actually planning on keeping this one - it will be my daily driver when I start my other project (a 4th gen King of the Hammers vehicle) - more to come on that!

I got really attached to my gray one and hated to see it go. This one has a rebuilt engine ($6K) less than a thousand miles ago, all the gauges work. Just needs a lot of aesthetics, brake work, tranny kick-down adjustment, and a new gasket on the rear diff. I'm also going to paint it Bronze Metallic and bought some '86 graphics for it - I've always loved that color and have never been able to find one.

I bought about 30 parts the other night online and am waiting for them to arrive. Current pic of the vehicle (when I towed it home last weekend) and the vehicle I want this one to look like (but with gray interior) when it is done attached!

Thanks RAD! I'm on it. Stay tuned.

Glad you found one to keep! Sounds like a keeper
I always liked that brown on a 1st gen
I bought an 86 (in 1986) put 120k on it in 4 years.
I saw it 2 years ago, a bit (OK a lot )worse for wear but it was still cruising around. Same license plate.

for the booster I bought a new one off Amazon.
it made a huge difference. Old one had a lot of corrosion on the inside due to a bad seal. Didnt see the damage until I removed the master cylinder.

I'm embarrassed to ask, but where is the ECT Module again? I looked in the passenger kick-plate and behind the glove box. I've forgotten where it is.

It is 13/16. Pic attached if it helps.

That's interesting. I've never seen one stamped with the old Toyota logo too. What about out back, is your LSPV there? I recently overhauled my entire brake system because I'm going to be doing some light hauling and the brakes were terrible. I found quite a few Micky mouse things going on underneath that I initially missed when I towed it home a few years ago. In the end, I replaced the master, booster, front calipers/rear cylinders, pads/shoes. I also had to repair two lines going to the front passenger side caliper that were hacked during an apparent LSPV delete. The fittings going into the "T" union were hacked off and there were compression fittings connecting the two lines. The pads on that side were worn wedge shaped, like only the front two pistons were working and the truck wanted to pull to the left on hard stops. Definitely go through everything on an unknown brake system. Not saying you need to throw new parts at everything like I did, but brakes are about as important as it gets, so make sure everything is in good order.

The booster was definitely bad on mine. I could press down and up on the pedal repeatedly and the idle would fluctuate. Now the idle is steady when I do that and the brakes are solid. This is something you can also easily test.

RAD, re-posting this from our other post on steering wheel vibrations in case it helps someone in the future:

I'm also beginning to wonder if these are all linked. I still need to check voltage at the ETC later today, but here are the current symptoms:

1) Steering wheel shakes while in gear at low RPM (AC off, pedal depressed) but goes away when AC is on or you press the pedal a little (or put it in P or N)
2) Braking is easier stopped downhill in N vs. D (but no or not much more than my 80 or 100 series land cruiser automatics)
3) If I'm going 50+/- MPH and press the pedal way down, the auto doesn't downshift out of Overdrive in Normal or ETC. I have to turn off Overdrive for it to downshift. I tried adjusting the kickdown cable yesterday and shifting is much smoother, but no affect on downshifting.

Just wondering if some/all of these are connected. The engine is completely rebuilt (nice and strong), but I do not know the condition of the tranny although it feels solid other than the lack of downshifting. I'll be diving into the ETC later today.

I still need to check voltage at ETC and make sure a faulty ECT Module isn't the issue later today.

Charles,I think you should start with these simple steps. A discussed in your "brake upgrade" thread, the Turbo seems to already have an upgraded brake compared to the 22RE.
​​​​​
I used OEM pads for front (provides most of the stopping power).
Used NAPA NON-premium shoes and cylinders in the back (provides less stopping power).

Lesson Learnt: The rear break cylinders are likely to leak after replacing the brake shoes. Here's why.

Don't forget that a vacuum brake booster needs good vacuum to work, if you have leaks your engine will run rough at low RPM and you will have to hit the brakes harder for them to work.
#1 are your rear brakes adjusted correctly (as mentioned)
#2 is the pedal spongy
#3 get a vacuum gauge and see what you get/check for leaks
#4 vacuum boosters can fail without causing the idle fluctuations when you hit the pedal

Are you running slightly oversized tires?

I've got about an extra inch on mine.

Definitely​​ not going to lock up the brake on accident in mine..

coupled with the mangled Bell cranks on the ebrake due to the routing of the cable around the rear lift. Setting the E-brake bends the crank, then doesn't release the rear pads fully. Er uh, bottom line check the brake isn't sticking a bit, this will wear down the pad.. A clear sign is you get one decent stop at the end of the driveway/block after using the ebrake.

Anyways there is also an IDL line from tps to ECT comp. Double check this one when you inspect the brake signal.

Also worth double checking the tps signal levels (voltage at ECU, key on engine stopped), throttle open should be around 5v and closed less than 1v (from memory, DBL check the book)

At 55 mph indicated you need to have 85% throttle to get the trans to drop down for acceleration.