Brake issue I can’t figure out

[SpenserAK]

This applies to any vehicle, but since this is the only auto forum I’m on (80 series), figured I would throw it out here. Google didn’t turn up anything I didn’t already know, and nothing to help my issue.

Done lots of brake jobs, familiar with the system, etc, but feeling stumped here. Hoping I’m an idiot and it’s right under my nose. Recently picked up a 5VZ ‘98 from a competent mechanic friend. He did brakes and a thorough bleed, but it needed a new booster which he hadn’t yet installed. I did that yesterday, adjusted the little plunger for the master so the brakes behaved properly. Took it for a spin, felt proper, thought I was done. Easy. But today, it’s acting up. I believe the booster is functioning properly, but now my reservoir is acting like I have a leak somewhere. Pedal pumps up nice and firm with the engine off, no fluid loss. With engine on, thus booster doing its job, pedal doesn’t do much until it gets close to the floor, and I lose fluid from the res with each pump. Can’t find any leaks at the four corners, master and nearby lines are dry, booster is dry, nothing else visible. I’ve gone through enough fluid to expect to see something somewhere, whether on the vehicle or the ground, but that’s not the case.

Before the new booster, I had no symptoms of a leak at all - no fluid loss from res. All I can deduce is that when the (now functioning) booster is doing its job when the engine is running, it’s pushing fluid out somewhere new, but I can’t find anything for the life of me. If it’s a leak, it’s hiding like a mofo. Even with engine off and no booster, shouldn’t I still lose some fluid when I keep pumping? Please tell me I’m having a brain fart and missing something

 

[gnob]

Are you sure the master isn't failing into the booster ? If you don't have an external leak, tbats the only place fluid can go.

Or that pushrod is out of adjustment. Ive never had reason to adjust tgat rod between the two

 

[Learning Outdoors]

(Yes I know it's an old thread but...)

Summary (for the TLDR crowd): An ABS module can fail without the dash light warning. The brake pedal will travel almost to the floor before engaging. Techs/mechanics may misdiagnose as 'air', dirty fluid, failed brake cylinder, or vacuum booster problem. Removing the ABS fuse will tell you right away.

Just adding to the knowledge base for the 1998 ABS system. Bought my 98 from the original owner with 190K and at 250K, the brake pedal started feeling mushy. Tundra upgrade with full service of fluid, hardware, etc. Barely any change. Went back multiple times. Changed out the vacuum booster and master cylinder with all new OEM. Barely any change. It actually began to feel dangerous since the pedal went almost to the floor. Several visits over an 18 month period and all I could get was 'adjustments' and 'change fluids'. Nope.

Thanks to this forum and other online info, the ABS was suspect and it's a doozy if you want to buy the control module / valve body or whatever it's called. Just running the diagnostics is time consuming and even the Toyota techs from a private shop overlooked this angle. Why? Because the ABS light never, ever came on. Bulb and circuits were fine but the ABS failed without triggering the light. So, instead of spending $1300 I did what other have done. Disconnected the ABS fuse in the fuse box. (The 'correct' way is to unbolt the entire box and disassemble the fuse base for the ABS because it's bolted.) You can skip the correct way and use dikes to clip the fuse out from the top. Then, disassemble the dash and remove the ABS warning bulb. Done. I'm not positive but lots of sources say the OEM ABS module / body is no longer available but I've not verified that so YMMV.

If you drive long enough, you'll know that judicious reading of road conditions, braking finesse, and awareness will allow you to live perfectly well without the ABS. Might not be the sort of route you want to take but I was surprised the ABS turned out to be the problem.

Brake pedal is super firm and engages beautifully the first 3/4 inch of travel. Amazing.

 

[SpenserAK]

Thanks. I've never felt like I "need" ABS & have certainly had non-ABS vehicles before, so not afraid to get rid of it.

Was just getting into this new-to-me truck when I posted. Tons of work since, all-around. Related, though - did tundra brakes w/ new hoses not long ago, and reinstalled OEM booster (which was not the problem). A nice slow thorough bleed & new brakes helped (good power). Have a new master to install, but haven't yet. Pedal still travels further than normal, but doesn't have the "going to the floor" feeling anymore. After daily driving for a while, it's either weak seals in master, or ABS. I've done all things short of replacing those two. Out of town now, but will get to the master before winter & see if it changes. If not, gotta be ABS. Pedal behavior still has me leaning that way. Either way, at least I can stop well now. Could live with this indefinitely, but working toward normal.

 

[trashboy]

interested in this thread, since mine has the same symptoms and i did a complete brake job/flush. if your issue is resolved with the master install let us know

 

[Learning Outdoors]

Most recent thing I finally did with my brakes left me speechless for two reasons. First, one car has been serviced at the same shop for brakes for no less than 15 years and nobody ever thought to replace the front brake rubber hoses. It's a reputable shop but when they finally noticed the hoses and told me, they were well past the 'cracked' stage. Second, the other car has been serviced for about three years. Ditto on the brake work but again, nobody thought to include hose replacement on any of the brake services. I told them to leave them for me to do (and save myself $350 per car!).

My son's 98 4Runner had cracked front brake hoses and my 98 did too so I figured do both on a Saturday morning. Unbelievably, his OEM hoses were factory stamped at 05/1998 and mine were date stamped at 11/1997! Presumably, the hoses can fail but these had not failed after 26 years! On the other hand, some of the posts on this website say that when a hose isn't rigid enough, there will be some loss of function that could show as a squishy pedal and so on. Did not upgrade to anything and stuck with the basic rubber hoses (both sides are the same PN).

Short version of the story. After replacing master cylinder, booster, and all four wheels worth of hydraulics... if your brakes still suck, remember to do the rubber hoses. If the brakes still suck, it's probably your ABS module. Disconnect the fuse (requires disassembly of the fuse box) and regain full function of the brake system.

 

[aztoyman]

My daughter had a 97, one daughter in law had a 98 and the other daughter in law had a 99. ALL 3 went through this $hit. Ultimately It was the ABS. Too expensive to fix so they all ended up traded in.

 

[SpenserAK]

Most recent thing I finally did with my brakes left me speechless for two reasons. First, one car has been serviced at the same shop for brakes for no less than 15 years and nobody ever thought to replace the front brake rubber hoses. It's a reputable shop but when they finally noticed the hoses and told me, they were well past the 'cracked' stage. Second, the other car has been serviced for about three years. Ditto on the brake work but again, nobody thought to include hose replacement on any of the brake services. I told them to leave them for me to do (and save myself $350 per car!).

My son's 98 4Runner had cracked front brake hoses and my 98 did too so I figured do both on a Saturday morning. Unbelievably, his OEM hoses were factory stamped at 05/1998 and mine were date stamped at 11/1997! Presumably, the hoses can fail but these had not failed after 26 years! On the other hand, some of the posts on this website say that when a hose isn't rigid enough, there will be some loss of function that could show as a squishy pedal and so on. Did not upgrade to anything and stuck with the basic rubber hoses (both sides are the same PN).

Short version of the story. After replacing master cylinder, booster, and all four wheels worth of hydraulics... if your brakes still suck, remember to do the rubber hoses. If the brakes still suck, it's probably your ABS module. Disconnect the fuse (requires disassembly of the fuse box) and regain full function of the brake system.

Brake hoses were something I learned about early on when getting into working on vehicles. I replaced the rubber lines when I did the tundra upgrade - they were original.

Since my braking function improved notably with that job, master is still sitting on the shelf, hah. I'm still guessing ABS related, but it may be a while before I find out.