Engine vacuum cause of bad brakes? What's your vacuum pressure? (1 Viewer)

[bhardesty]

I'm trying to get a FZJ80 that's been sitting for 3 years back on the road. 1993 with just under 200k miles and 35's. Here's the work completed on the brakes:

New booster (budget brand)
ABS delete
LSPV delete
All 4 calipers/rotors/pads brand new
Vacuum bled many times

All of this led to a firm, not sinking pedal but lack of braking power, especially noticable with quick deceleration attempts.

I then measured the engine vacuum at 12 inHg (at the intake manifold port for the booster hose). Checked ignition timing and it was 10 degrees retarded! Changed to 6 degrees advanced and that gave me a 15 inHg vacuum reading. Also new intake manifold to booster hose, and timing chain tensioner. Checked for vacuum leaks and didn't find anything obvious.

Braking was much better but still far from right. No way I could make an emergency stop, maybe barely drivable.

MAIN QUESTION:
What are other people's vacuum readings? Is 15 inHg acceptable?

OTHER QUESTIONS:
Any idea how the timing could have changed that much? Sign of timing chain issue? Bad valve timing (separate of ignition timing) would explain this I believe.

Bad booster? It passes all FSM tests and has been replaced and I don't want to throw that kind of $ at it without advice. It is a budget brand though...

Is it possible that the EGR system could cause low vacuum?

Is a compression test the next step? Vacuum readings were steady, I don't suspect major engine issues.

I have a booster check valve and grommet on order, and have a vacuum pump that I can rig up to test the lower vacuum theory.

Thanks for your help!

 

[Dave 2000]

Run the engine for a minute. Switch off and press the brake pedal, release and press again, repeat until pedal goes hard. You should get around three vacuum assists before pedal goes hard.

Next, pump brake pedal until solid, with a little pressure still on the the pedal crank the engine, the brake pedal should be 'pulled' down. Next get a metre of rubber pipe, run the engine for a minute in a very quiet area and switch off. With one end of the pipe near your ear listen for leaks around the booster and listen for hissing sounds, if nothing restart and switch off and check again, this time though put the pipe around the push rod of the brake pedal where it goes into the booster.

If all the above is good, then check you adjusted the booster correctly before installing, if all is good then the booster is not at fault.

15 hg vacuum is a good number to be honest, so I would try all the above tests before looking anywhere else.

Regards

Dave

 

[Dusten]

15 in of mercury is pretty decent vacuum. 18-20 is more common on most vehicles but I don't think that extra 2-3" is going to change your braking in any noticable way.

My big cammed lightning made about 8" of vacuum at idle and the factory vacuum assist was still fine.

 

[bhardesty]

Thanks for the feedback, I should have time to do these tests and inspections later today, I'll report back. Also good to hear y'all think my vacuum is acceptable, that was keeping me up at night!

I'm thinking living at 7000' elevation is also contributing. The difference in atmospheric pressure is almost 7 inHg which would lower the pressure differential across the booster diaphragm by the same amount. I believe that the vacuum gauge I'm using operates independent of atmospheric pressure.

Does anybody have actual vacuum readings for the FZJ? I'd be curious to see the range from a fresh rebuild to 300+k miles.

 

[Dusten]

Thanks for the feedback, I should have time to do these tests and inspections later today, I'll report back. Also good to hear y'all think my vacuum is acceptable, that was keeping me up at night!

I'm thinking living at 7000' elevation is also contributing. The difference in atmospheric pressure is almost 7 inHg which would lower the pressure differential across the booster diaphragm by the same amount. I believe that the vacuum gauge I'm using operates independent of atmospheric pressure.

Does anybody have actual vacuum readings for the FZJ? I'd be curious to see the range from a fresh rebuild to 300+k miles.

It's unlikely you'll see much less vacuum on an old motor.

18-20" is pretty standard for a stock engine or almost any kind. And the fact you're at 7000' tells me you have no issues with vacuum

 

[bhardesty]

Dave's test results:
Build up vacuum, turn motor off, only get 1 pump of assisted brakes. Hold pedal, restart engine, pedal sinks like it should. Start motor, wait for vacuum to build, turn off, wait for 1 minute, still has 1 pump of assist. Carefully listened for leaks as described on both sides, none. I recently took the master off and confirmed the push rod length was set correctly.

I hooked up a vacuum pump and reservoir to the booster, pumped down to -20 inHg, valved off and removed the pump. Didn't leak down at all after a minute. Accelerated and hard stopped, first time I've heard the wheels lock up this whole time! So that worked.

Tried again with the motor vacuum hooked to the booster but used the parking brake and let it build vacuum, instead pressing on the pedal to shift into gear and lose my one pump of assist (I'm basically going back and forth 20ft in a shop). Felt much better, not nearly as good as the rigged -20inHg test, but acceptable I think.

So, it appears my booster is not leaking, the -15 inHg is good enough (as you told me, thanks), but my booster somehow has a smaller capacity? Seems like the 1 pump instead of 3 is the best clue so far.

 

[bhardesty]

Booster check valve and grommet came in. Installed and tested, no change.

 

[Dave 2000]

Seems a problem with booster capacity, the 80 diesel has two boosters, one for the brakes and one for the clutch. There is actually an extra reservoir to cope with the demand from the two boosters. Regardless, with one press of the brakes there is insufficient reserve for braking on you car, perhaps the booster size is not correct? Even if it bolts on correctly the actual physical size may be wrong, or there is an assembly issue inside. As an aside, do you have larger than stock wheels/tyres? Larger wheels/tyres increases the braking effort needed at the pedal to stop the vehicle within the same distance.

Regards

Dave

 

[bhardesty]

I ordered (another) booster last night. A reman Cardone 532728 unit with a 9.74 in diameter diaphragm. From what I read on MUD these are rebuilt OEM. Can anyone confirm that is the correct diameter?

I also ordered a new master cylinder because that is literally the last remaining moving part that isn't new.

I didn't say it before but I also did a full parking brake overhaul and rear axle seals/wheel bearings, this has been a long and expensive fix!

I am on 35's but that is not the issue, they were installed before this saga started.

The only other thing I can think to do is measure the fluid pressure at the calipers. I don't think there is a pinched line from inspection, and all calipers bled nicely.

 

[Kernal]

Did you consider a SEIKEN booster? Many on the 80 forum have had good luck with that brand.

New Seiken 44610-60792 brake booster?

I'm still trying to solve an old problem, soft brakes. I have replaced every item in the brake system and haven't solved the problem. I still believe it's the brake booster and installed two rebuilt Bendix booster from O'reily's. I have been looking at the new not rebuilt Seiken booster for...

forum.ih8mud.com

New Toyota Land Cruiser LX450 OEM Seiken Brake Booster with Gaskets 44610-60792

New 80 series, FZJ80, FJ80, 1991, 1992, 1993, 1994, 1995, 1996, 1997, brake, brake booster, OEM, Seiken, japan, 44610-60792

www.cruiseryard.com

 

[bhardesty]

Thanks for the links and advice, I somehow missed these threads in my search. I got a quote for $924 from the dealership then read the Cardone ones are rebuilt OEM and worked for $200 in other threads, didn't realize there was a middle ground option and all of the conflicting experiences.

I've ordered a Seiken and will be returning the Cardone, definitely one part I don't want to have to worry about failing!