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69 Chevelle abrupt braking

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phaan47

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Discussion starter · #1 ·
Hi,

At very slow speed the brakes really react abruptly. If I brake, not aggressive at all, the car stops abruptly.

With normal driving I don't feel there is a problem except I think I hear the brakes a bit approaching a stoplight when I slightly tap the brakes.

Front have discs and rear have drums. I checked the brakes as far as I can do that. The pads I think don't look to bad (see pictures). Fluid level is ok. What could it be? Sticky brakes? The rears look old.

Thanks
Paul
 

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#2 ·
I would look at the power booster. I had one go bad and it did exactly what you said. I knew it was the booster because of a variety of issues. If I touched the brakes and you thought I had slammed them. It would not do it all the time.
 
Discussion starter · #4 ·
I did a booster check where you pump the brakes 4-5 times and then start the engine with pressure on the brakes. After starting the engine the brakepedal does go down further so that would seem like with this test the booster is oke.
 
#5 ·
Make sure the rear brake shoes are adjusted out properly and just barely touching the drums. If they are adjusted too far inward, they can get cocked out of position when they start to be applied and actually cause what you are feeling as they partially grab and then get wedged against the drum.

Not saying that is the issue, but I've seen it happen.

Also, when this happens - does the car nosedive, or just stop abruptly? Do you get any wheels locking up that you can detect?
 
#6 ·
It is hard to tell in the pics. Are your shoes and brake hardware bone dry and dusty, or is there some slime from a leaking axle seal or wheel cylinder? If it is wet at all, replace the seals and shoes and throughly clean everything.
 
Discussion starter · #7 ·
lucifershammer said:
Make sure the rear brake shoes are adjusted out properly and just barely touching the drums. If they are adjusted too far inward, they can get cocked out of position when they start to be applied and actually cause what you are feeling as they partially grab and then get wedged against the drum.

Not saying that is the issue, but I've seen it happen.

Also, when this happens - does the car nosedive, or just stop abruptly? Do you get any wheels locking up that you can detect?
Click to expand...
Good tip thanks. I will check that. It does nosedive and I hear wheels locking up sometimes when this happens. I guess that would mean it is more a front brake issue I guess what you are perhaps getting at.

But during normal drive it doesn't seem to be an issue.
 
#9 ·
Has anything in the brake system been changed recently? Have they “always” been prone to “touchiness?”

One thought that crossed my mind was power booster rod depth. There is an inexpensive tool to check the rod depth out of the booster and into the master. Incorrect depth could lead to something like you are encountering. If booster has an adjustable pushrod, this will guide you to proper adjustment.

I know it has helped me a couple of times.

Image
 
Discussion starter · #12 ·
bccan said:
Has anything in the brake system been changed recently? Have they “always” been prone to “touchiness?”

One thought that crossed my mind was power booster rod depth. There is an inexpensive tool to check the rod depth out of the booster and into the master. Incorrect depth could lead to something like you are encountering. If booster has an adjustable pushrod, this will guide you to proper adjustment.

I know it has helped me a couple of times.

View attachment 795125
Click to expand...
I have to say that since I have the car (5 years) nothing has changed on the brake system and it has had this issue. Because it wasn't such a big deal while driving it normally it wasn't high on the to do list. It was not driven to much because we were still (very slowly :) ) finalizing the rebuilt. The tool you talk about I am not familiar with but will for sure look into that now.
 
Discussion starter · #15 ·

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Discussion starter · #17 ·
Well I did what lucifershammer wrote yesterday and adjusted the rear brake shoes to where they are just barely touching the drums (because the were not) and for now that is a big big improvement! I also cleaned and lubricated like 69SS454 wrote. I will check again next week to see if it is still good. Thanks and enjoy the weekend!
 
#18 ·
Problem is
Service flush and bleed brake fluid
emery tape rear linings' and drum surface
emery tape front discs both sides
wash rear linnings
adjust rear linnings till drag can be felt and heard

advanced
inspect caliper slides for wear and lubrication
wash and remove rust from front calipers ,, expanding corrosion grabs caliper pistons

DOES THE VEHICLE HAVE A DUAL DIAPHRAGM FITTED this will make the brakes sensitive
Factory fitted was 11 inch single ????
Over boosting makes pedal sensitive
 
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swampy 6x6
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