strange brake booster test results

[ejames82]

Hello,


I will be asking my question at other forums as well. I will share any relevant info I obtain.

I think I need a new brake booster. with the engine shut off, I pulled the booster-to-intake hose at the intake and sucked on it and it behaves strangely. I am able to suck air in an 'intermittent' sort of way. there is something inside that is blocking and unblocking the air as I apply suction. also, there is no half-way. either I am able to suck air easily or not at all.
according to several tutorials I have read around the internet, if I am able to suck any air, the booster is faulty. I don't see any way that a diaphram could be intact. I don't think that the check valve can cause this type of behavior.


there is another test where you:

'Depress the brake pedal several times with the engine off
and check that there is no change in the pedal reserve
distance.
Depress the brake pedal and start the engine. If the pedal
goes down slightly, operation is normal.'
for me, the pedal goes down more than 'slightly'. I think it goes down more than it should be.


this test:

'Start the engine and stop it after 1 or 2 minutes. Depress
the brake pedal several times slowly. If the pedal goes
down furthest the 1st time, but gradually rises after the
2nd or 3rd time, the booster is air tight.'
it seems to pass this test.

'Depress the brake pedal while the engine is running, and
stop the engine with the pedal depressed. If there is no
change in the pedal reserve travel after holding the pedal
for 30 seconds, the booster is air tight.'
the pedal seems to be sinking VERY SLOWLY within the 30 seconds.


any experience or expertise in this matter would be most appreciated.

 

[clivehorridge]

My only real experience with a brake servo was fluid leaking into the diaphragm, and ending up being sucked into the inlet manifold (not on an 80 mind).

The tests sound logical, but IMHO, if the diaphragm is leaking, it will leak big time. There's a lot of pressure on that rubber and the smallest hole would tear rapidly, I would have thought.

Any leak worth having would render the servo inoperative, and you would know about it, i.e. almost no brakes to speak of.

I've coasted down hill with the engine off before now, and it's like there's no brakes at all! (not recommended).

 

[ejames82]

clivehorridge,
I have read about the booster diagnosis's on several websites and how the brake pedal becomes rock hard and is almost unable to be pushed. but I am able to suck air (on and off, mind you) endlessly. supposedly this indicates that the booster's bad.
I have already ordered a new brake booster at rockauto. I will also be getting a new master cylinder. in any case, I will let everyone know the outcome. I WILL find the problem and report it. I just find it hard to believe that I am the first person ever to have a brake booster behave in this way (on-off suction), which is probably not the case. I am possibly the first person to ever tell about it.

I've coasted down hill with the engine off before now, and it's like there's no brakes at all!
be careful with that crazy driving. keep that engine running, please.

thanks for the reply.

 

[Dave Burgess]

If an 80 servo is anything like a the larger ones fitted to other 4x4s then it won't have a diaphragm in the flexible rubberised disc fixed at the edges and moving the middle, but will be a rigid disc with lip seals at the edges. If that fails ( I have seen a LR101 item cracked across the diameter) it fails to a point where there is no vacuum held at all. If the seals wear, the leak can give variable performance but shouldn't be catastrophic.

 

[ejames82]

thanks for that info, Dave Burgess. that could have been the case with this booster.

 

[ejames82]

input shaft on original is 1cm longer

more problems.

I received the booster, centric 88374. I purchased it from rockauto. the rockauto part number is 16088374.


the part looks great. it actually looks like it will go right in, but...


THE INPUT SHAFT THAT GOES TO THE PEDAL IS A CENTIMETER SHORTER THAN THE ORIGINAL BOOSTER. the original sticks out 13cm and the centric sticks out 12cm.
here are links to pictures, in case this site doesn't allow pictures.
http://postimg.org/image/pg8nus1xh/
http://postimg.org/image/f3d2uzoi1/



I haven't installed it. right now I am debating what I will do next. if I was to install it, it seems that the pedal would be further away, I would think, by a centimeter. perhaps this would cause the vehicle to have no brakes at all, though I don't think that would be the case.
I called rockauto and told them about it. their phone support is excellent, but they are just a distributor, they don't actually rebuild the parts. they couldn't give any info regarding the difference in the input shafts. I think they tried to contact the centric company, but were unable to do so. they did give me a website: centricparts.com

if I knew that I could easily exchange the input shaft from the original to the centric, and not void the warranty, I would make a go at it. I even told this to the rockauto person.

I am just wondering if there is something about these boosters that I am unaware of. like, for instance, perhaps the original booster would still have air in it that would make the shaft stick out a centimeter more, where the centric has no air in it. or something else about the device. just a thought. I know I am reaching.

maybe someone else on here has had the same type of thing happen and can tell what they did. my wife seems to think that I should put the part in and try it, and quite often she is right. she's not doing the work. and the work is nothing compared to getting into an accident.

this part is considerably cheaper than the comparable cardone part. I was really hoping that things would go smoothly, it would have been nice to get on here and say 'the part was perfect in every way, you get to save a few bucks'. who is to say that the cardone part wouldn't also be 12cm, the same as the centric.


any info or advice would be most appreciated.

 

[ejames82]

I took apart the part of the original booster where the input shaft enters the booster. I took pictures. if the site does not allow pictures, here are links to the pics.
I was hoping to find some way to exchange or adjust the shaft and/or assembly. It doesn't appear that it can easily be done. I even pulled on the shaft, but not too hard.
obviously, the manufacturer doesn't want the average joe to make changes.

I did not attempt to disassemble the remanufactured booster. there didn't seem to be a reason if I couldn't disassemble the original as well.


http://postimg.org/image/aasyw7r1h/
http://s26.postimg.org/jvclj3gdl/IMG_1555.jpg
look down in the input shaft spring

http://postimg.org/image/3lmfg75ph/
http://s26.postimg.org/uw7qo48mh/IMG_1557.jpg
side view input shaft

http://postimg.org/image/3znrfspt1/
http://s26.postimg.org/ssxbgg8tl/IMG_1558.jpg
el-cheapo clip

 

[Dave Burgess]

Is it 10mm shorter, or just in the clevis pin mounting/locking nut? The 12cm measurment seems at the same point as the bottom of the clevis pin thread, so they may be closer than you think.

Worth an email to check with the supplier before you take it apart and can't return it

 

[frank rabbets]

If the shaft is a different length then there may be other differences. The shaft comes up against a physical stop when out so just pull the short one to make sure it is fully out. There is most likely a circlip just inside the bore which retains the shaft washer. If you remove the circlip be careful as the shaft return spring will suddenly expand and might hit you in the face or ping round the garage.

If there is no circlip then the whole housing must be split but you might need special tools to undo the crimps unless the two halves rotate. Probably not worth pursueing if the housing needs to come apart.

 

[ejames82]

I decided to install the booster when I was told by a member at another site that he used a centric booster. it appears to be working ok. I put some 'chocks' in the yard to stop the car from moving in case the brakes didn't work and moved the car back and forth many, many times. and really put them to the test. I took it for a ride and the brakes stop the vehicle like they are supposed to.

there were some things that I didn't like about the experience (info for anybody else about to do this job):
1. the fact that the pushrod was 1cm short (of course).
2. the hidden screw that is under the reservoir. if it's not removed, you can't remove the reservoir. thank goodness the wife came out and saw me struggling with it and grabbed the new master cylinder and checked it out. the screw requires a very short stubby phillips screwdriver and I used vicegrips to clamp on to it for more turning leverage.
3. there is a bracket that secures the throttle cable that comes off the master cylinder that requires removing one 12mm bolt. it doesn't fit tight on the new master cylinder. seems that the new one is now not as big around.
4. due to the difference in the pushrod length. the brake light switch had to be re-adjusted. fortunately, this type of switch does not screw in like some I have seen. no need to disconnect the switch. just break loose and tighten the 14mm nuts.

thanks for the replies