88SR5runner

Hello everyone ,

This is my first post, but I've been around doing plenty of research the last couple of months and was hoping your guys experience could help me out. In September I purchased a 1988 4runner SR5 with 114 k miles on it . It's a 5 speed 22re that sat with occasional run time for the last 14 years. When I bought it , it was covered in scale rust with blown out fuel and brake lines. Long story short to my problem , I have almost replaced every brake component only to have the same effect. The pedal is rock hard with the engine off , but running it falls to the floor. It activates the brakes almost to the point of locking up , but only when the pedal is bottomed out. I haven't experienced this truck with good brakes, but I know it's far from correct. I replaced almost all the brake lines including the flex lines, and replaced the rear wheel cylinders and adjusted the drums to the point of dragging. I replaced the driver side caliper due to a destroyed bleeder and the passenger side operates with no sign of leaks. The pads have plenty of meat and there isn't any play in the wheel bearings. I replaced the master cylinder with an aisin and the booster seems to work well with all the usual tests. It holds vacuum, and drops the pedal at start up. I've bench bled the master both on and off the truck and all the bleed points flow fluid for hours without any air. Ive bled the correct order dr,pr,pf,df,lspv. I used the tried and true 2 person method and also made a pressure bleeder out of a 1/2 gallon garden sprayer at 20 psi. No matter how much I bleed the pedal goes to the floor while running. I even went so far to isolate the front and rear brake circuits with plugs including the bypass line , but the pedal still falls. With both ports plugged on the master, the pedal is firm with the engine running , but I don't know if the volume only in the master cylinder is enough to prove anything. I don't think the master is faulty, but I don't know what else it could be. I also adjusted the pedal and the booster rod to almost no play. It feels like the time I put into these damn brakes I could of done a concourse level restoration. Could it really be an air pocket from hell stuck some where? Any tips or advice would be extremely appreciated, I feel like this little runner is getting the best of me.

Co_94_PU

iTrader: (-1)

Hmm seems pretty thoroughly gone over. But it doesn't take much of a leak or restriction to throw things off. You'll have to start at the beginning with the mechanical system. I think unless someone sees something we both missed.

First a simple q&a, you used quality new fittings and lines of the proper size? Exactly which parts have you replaced or adjusted? (list form please not paragraphs, it's easier to follow and double check)

Pedal height, ​​​​​​Using a builders square with the 90° face towards the pedal, firmly press it to the floor and slide the face to meet the pedal, lock it down with the thumbscrew and post the measurement please.

Bracket fatigue, using a flashlight look along the pedal bracket for any cracks, and that it is fully and firmly against the inside of the firewall.

Deformations of mechanicals, using a flashlight look for a deformed pedal arm (paint fully intact), the bushing should have little to no play(where the pedal rotates on the bracket arms), push rods is straight and true with no bends or obstruction.

Worn and warped parts, ​​​​​measure and post, Front rotor thicknesses, rear drum inner diameters. Take three to four measurements equally spaced along the rotor circumference, also take at least two measurements of the drums (12-6, and 9-3) and post averages.

Inspect for proper pad return, measure starting clearance between pad material to braking surfaces at each wheel, start the engine and pump up the brake line pressure untill it's near its maximum (pedal firms up), release the pedal and stop the engine and again measure clearences between pads and braking surfaces, wait several minutes and repeat measurements. (Taking photos from the same angle and camera placement is probably the easiest way to gauge this part)

Line leaks, clean and dry all junctions and dust with cornstarch, again pump the line pressure to it's maximum with the engine running. Inspect for any signs of moisture in the dusting.

​​​​​
Inspect the rubber, piston and cylinder wall, supple and smooth with zero cracks tears or scratches, outer boots are dry with no signs of leaks. Piston rings intact supple no tears or scratches, cylinder bores show no signs of contact to pistons no scratches or debris.

​​​​by now you should have found several issues varying from minor to major and each repair should show improvements. When/if you disconnect the various valves and joints make sure each is cleaned and cleared of any internal build up which impedes flow volume..

If you don't find anything obvious above and there are no improvements. you'll want to proceed with the pressure tests, cap off the lines and testing for lines that bulge and waste hydraulic pressure.

88SR5runner

Thank you for all that info , I'm going to go through all of that and get back asap, I should mention that the pedal goes to the floor with no resistance. It barely applies the brakes through its travel , but really only has an effect when it bottoms out.

wyoming9

iTrader: (1)

You say this never had good brakes since you bought it.

Does anything lead you to think the Master Cylinder or Booster was changed ??

If Yes possible that the Rod is out of adjustment

Second no mention of the LSPV ( Load Sensing Proportioning valve) has this been removed or replaced with a manual valve

Even a small piece of grit can allow air to be drawn in in any of the threaded connections

You don`t mention replacing the drums it might just be a omission .

If they were not replaced were they measured ??

a few more ideas

When one of my way word project Toyota`s show up all the brake hardware and hydraulics gets replaced

Co_94_PU

iTrader: (-1)

I forgot to mention what fixed my soft brakes from the PO!


​​​​​​mine was a bent arm on the right rear e brake lever, the bell crank arm, it was mangled by an installation of a block lift which interferes with the cable.

It's an easy fix and check, make sure it's straight and between the protrusion/guide on the backplate.

88SR5runner

Thanks guys, I'll rewrite what I've done so it's easier to see

Replaced
Wheel cylinders- Wagner
Sections of brake line - pre flared napa
Both front flex lines - unknown origin came with truck
Driver front caliper - napa
Master cylinder- new aisin

Adjusted
Rear drums to point of dragging
Brake pedal
Booster rod
Lspv to full activation (all the way up)

I bought the truck with the front brake line blown out right above the tee on the passenger side, so I have never felt them work correctly. After I changed the damaged line I bled the brakes with the 2 person method , but forgot to put a block under the pedal. When I finished bleeding the pedal went to the floor with no resistance, but still engaged the brakes , but not at full potential. I figured I damaged the master cylinder which looked in bad shape anyway so I replaced it with a new aisin unit. I bench bled it and put it in and bled the brakes only to have the same issue. I then changed the wheel cylinders because I took the drums off to inspect , the shoes have plenty of meat and the drums didn't have any grooves or ridges. I didn't measure them , but with them adjusted and the truck off it took very little travel of the pedal for them to engage, so I figured it they were good and didn't have to overextended to meet the shoes. I checked the parking brake arms and they are straight and look in good order , as well as the brake pedal arm and bushings. The brake booster is labeled bendix , which would lead me to think it was changed? But it checks out with all the tests.

The only thing that stood out to me was bleeding the master cylinder. Both in and out of the truck , it only took a couple of cycles to get all the air out, even after minutes of pushing. Videos I see online show that it takes a lot more effort. Maybe I just get lucky ? Or unlucky? The lspv works the brakes and bleeds as well as all 4 corners so I believe it is good as well

coryc85

Can you check to see if the front calipers were perhaps swapped out for the V6 calipers? The V6 calipers have 1 of the pistons bigger on each side of caliper, which would require more volume...although probably doesn't explain why plugging the front port doesn't firm up the pedal.

edit: my post wasn't clear. The 4cyl calipers have 1 big and 1 small piston on each side, but v6 ones have 2 big pistons. Slim chance but worth a check. Just saw Wyomings post about bleeders and thats worth a check too.

wyoming9

iTrader: (1)

Calipers did not get put on upside down by chance makes it impossible to get the air out??

Just a thought while rereading this thread

If it was done before you bought the truck it might have been so easy to even consider the possibility I know I would not think of it till I had a problem getting the brakes to have a good pedal

88SR5runner

Ok so I checked out the calipers and they both have different sized pistons on each side , so they are correct for the master cylinder. They are also mounted bleeder up. Has anyone else had a hard time with air trapped in the master cylinder? Would it also be possible to have trapped air but bleed properly without air bubbles?

85TRD4runner

Hi there 88SR5runner, when I rebuilt the brake calipers on my 85 runner and got them mounted back on the truck I had one heck of a time trying to get the system bled properly. What ended up fixing it for me was deleting the LSPV and replacing it with a manual proportioning valve. When I took apart my LSPV it was kind of obvious that it was my problem, as it was full of rust and the internal piston was frozen. Apparently this is a somewhat common problem. Also, I did have to fight the master cylinder a bit to get an air bubble out that was stuck in the reservoir feed tube that fed the front brake lines. Heres a pic of where the air was trapped. Hope this helps you.

wyoming9

iTrader: (1)

For what it is worth I don`t recall ever bleeding a Master cylinder

Other then to lubricate the internal parts

A poor connection or bad bleeder allowing Air to be pulled in

88SR5runner

I didn't bench bleed the first couple times, and thought the no pedal resistance was the result. I'm going to try taking the lspv out of the equation and see what happens.

88SR5runner

So I spent 2 hours on the runner today, but still haven't found a solution . I replaced the other caliper hoping it would help , but didn't have an effect. I ran a new line straight to the rear flex line and completely removed the lspv. With the front and rear circuits isolated the pedal still goes to the floor without resistance, but now with the lspv removed the pedal drops even lower. I can lock the rear brakes up in gravel , but the front is still weak. Is it possible that the new aisin master cylinder is defective? I'm going to try an autozone one tomorrow just to rule it out.

Co_94_PU

iTrader: (-1)

Since you don't have the brake kit(tools) required to do pressure tests. I'd like to suggest you use a process of elimination, grab a handful of caps, plugs, and a couple flex lines to isolate the line section and junctions.

Cap off all four lines at the wheels and test the whole line system at once. If that's solid you know it's one of the cylinders and can test each one individually, if all the cylinders seem suspect it's the volume issue that was mentioned above and you'll need a bigger bore master. If not you can work over the lines one by one add a section and test.

88SR5runner

Hey guys, so here's an update after a while. I purchased a plethora of 10mm inverted fittings that converted to -3an with caps. That seemed to be about the only way to make caps for the metric lines. I capped off the master and the pedal was rock hard both running and off, I proceeded through every joint in the lines in both the front and rear circuits. All was done without the lspv. The pedal was high and stiff on every inch of the brake lines until I introduced any of the 4 wheels. Even when it was only 1 wheel cylinder or 1 caliper the pedal had no resistance till it bottomed out. Is it possible the new aisin master is bad , but only with the calipers or wheel cylinders connected? I would think the seal in the master would let fluid past no matter what was connected in the system if it was faulty ? I'd hate to buy another new master only to have the same problems. Could it be that a bone stock 4 cylinder brake system needs a larger volume master? Any input would be greatly appreciated.

Co_94_PU

iTrader: (-1)

Your bore and stroke of the master needs to be adequately matched to the slaves.

It's not very clear that you had the wheel cylinders hooked directly to the master. You are certain it's not the flex lines bulging? Certain none of the balancer valves are active?

Sounds like you got the wrong master cylinder when you replaced it. For what it's worth, in the future remember it's way easy to change out the seals on these and there is really no reason to get a "rebuilt" unit from the big box part store unless you damaged the bore.

I really prefer to keep my original parts in any case rather than get to CORE money. However at least keep your original to compare with the new parts until you know they are functioning and functionally identical.. it's "good practice"

88SR5runner

Yes I described that I capped all all the lines at all 4 corners right at the point of attachment. This included all the flex lines with a firm pedal. I tested each wheel individually meaning only one wheel cylinder was attached to the system and the pedal was soft. I apologize for the redundancy , but it's seems odd to me that a stock brake system needs a increased bore master to function properly. The master I removed was a 7/8 bore , and so is the one I installed. I searched and it seemed the general concensus was to replace with a new aisin unit so that was the path I took. I guess my next step is to try a v6 unit.

88SR5runner

My mistake both the old master and the new are 13/16 bore

Co_94_PU

iTrader: (-1)

Do you still have access to the originals? If so you can compare the stroke lengths, that won't be entirely accurate if they had been replaced before with incorrect parts.

It's pretty common for the big box parts store to give you whatever you plop on the counter regardless of what should be there..


Assuming you have the correct parts. See my original post regarding pedal adjustment. As well someone else suggested checking the adjustment of the push rod..

It's also possible you got the wrong pads in the "right box" it happens way to often!

88SR5runner

Ok so here's another painful update. I got a new aisin 1 inch master and threw it on. I bench bled it , bled all 4 corners well fired it up and still have no pedal. The brakes still engage , but not 100 percent and the pedal has no resistance. In my first post I wrote how I checked and adjusted the pedal and booster and I even rechecked. There is very little travel in the pedal before I feel the booster rod start to push the master. With a single diapgram shouldn't the pedal be harder to push ? It almost feels like the pedal is weaker now. I'm really at a loss for what to do next. There are no leaks , the rear drums are adjusted, but the brake pedal has no resistance.