Intermittent brake fade
#21
08-30-2019, 03:45 PM
I do not feel any type of ABS. Locked 'em up on pavement the other day. Got new rotors on the front but not sure if the sensors were ever cleaned and re-gapped. This low pedal thing is driving me nutz...
#22
08-30-2019, 10:01 PM
Looks similar the the abs plugs on the front hubs.
I have enclose 2 photos of what I think is the tranny abs plug. Confirm if you agree. After disconnecting that and the front abs wires AND pulling the fuse, it still happens. Only at low speed and only when turning. Stump city. Next step may be to just say f-it and convert to non abs...
#23
08-30-2019, 10:46 PM
Sorry, I was thinking about a 2wd and the speed sensor location.
On the 4x4 its on the drivers side top of the transfer case.
#24
08-30-2019, 10:52 PM
If you think its an ABS issue, I would look into the front hubs next.
Take the front wheels, calipers and rotors off....then spin the hubs to see if they are smooth. also check to see if they have any play in them.
When the bearings start going bad in the front hub it can throw some metal onto the front ABS sensors and act funky.
It may also help to remove the front sensors while you have it torn down to see if there is anything collecting on them. Just be very careful when removing the sensors are they are a snug fit and can break easily if you pry on them.
When I first bought my blazer the front hubs were bad and I could feel a bit of binding when turning them with everything else removed.
Take the front wheels, calipers and rotors off....then spin the hubs to see if they are smooth. also check to see if they have any play in them.
When the bearings start going bad in the front hub it can throw some metal onto the front ABS sensors and act funky.
It may also help to remove the front sensors while you have it torn down to see if there is anything collecting on them. Just be very careful when removing the sensors are they are a snug fit and can break easily if you pry on them.
When I first bought my blazer the front hubs were bad and I could feel a bit of binding when turning them with everything else removed.
#25
08-31-2019, 08:53 AM
If you think its an ABS issue, I would look into the front hubs next.
Take the front wheels, calipers and rotors off....then spin the hubs to see if they are smooth. also check to see if they have any play in them.
When the bearings start going bad in the front hub it can throw some metal onto the front ABS sensors and act funky.
It may also help to remove the front sensors while you have it torn down to see if there is anything collecting on them. Just be very careful when removing the sensors are they are a snug fit and can break easily if you pry on them.
When I first bought my blazer the front hubs were bad and I could feel a bit of binding when turning them with everything else removed.
Take the front wheels, calipers and rotors off....then spin the hubs to see if they are smooth. also check to see if they have any play in them.
When the bearings start going bad in the front hub it can throw some metal onto the front ABS sensors and act funky.
It may also help to remove the front sensors while you have it torn down to see if there is anything collecting on them. Just be very careful when removing the sensors are they are a snug fit and can break easily if you pry on them.
When I first bought my blazer the front hubs were bad and I could feel a bit of binding when turning them with everything else removed.
Yeah,I first thought it was ABS. But the symptoms seem to be persisting w/o ABS hooked up. Will look for the "other" wire off my xfer case and try again. Takin' the weekend off...
#26
09-04-2019, 11:44 AM
I have now disconnected as many ABS cables as I could find and also removed and unplugged the ABS unit from under the hood. The low pedal persists when the wheels are turned but not going straight. Always at low speed.
I have not tried going fast into a turn and giving them a try. Very baffling.
I have not tried going fast into a turn and giving them a try. Very baffling.
#27
09-04-2019, 11:46 AM
Following (because this is something I'd like to know how to fix if it every happened to me).
The only thing I could add is that I've done some thinking about the parking brakes and the circuit that overrides the daytime running lights (DRLs). Have you done any servicing on the parking brake pads? My understanding of the switch is that it is a simile contact switch so that its indicator light coming on or not could indicate something with the parking brake cable adjustment. BTW, the parking brake cable adjustment is separate from the parking brake shoe adjustment. That has to be done at the rear axle. I am familiar with the 4-wheel disk brakes system with the parking brake shoes on the inside of the rear rotors.
The only thing I could add is that I've done some thinking about the parking brakes and the circuit that overrides the daytime running lights (DRLs). Have you done any servicing on the parking brake pads? My understanding of the switch is that it is a simile contact switch so that its indicator light coming on or not could indicate something with the parking brake cable adjustment. BTW, the parking brake cable adjustment is separate from the parking brake shoe adjustment. That has to be done at the rear axle. I am familiar with the 4-wheel disk brakes system with the parking brake shoes on the inside of the rear rotors.
Thanks.
#28
01-06-2020, 11:59 PM
Eliminated ABS
Reviving this thread...
I completely removed the ABS. Converted to a Wilwood combination block with rear proportioning valve. Brakes all seem to work fine under normal conditions but STILL have brake fade after turning the steering wheel fully to one side or the other. Can't be unwanted ABS activation now since they are gone. Pulling my hair out over this and am back to square 1 trying to figure this out. Vacuum assist not leaking. New MC. New front brake hoses etc. Next step is to disconnect and plug front lines and try to recreate problem with only rear brakes. Trying to determine if mechanical or vacuum related.
On another note. Does it matter which brake line from the MC goes to the front or rear? Have heard about a primary and secondary piston but cannot find any intel for which goes where.
2001 ZR2 4 wheel discs.
Thanks again .
I completely removed the ABS. Converted to a Wilwood combination block with rear proportioning valve. Brakes all seem to work fine under normal conditions but STILL have brake fade after turning the steering wheel fully to one side or the other. Can't be unwanted ABS activation now since they are gone. Pulling my hair out over this and am back to square 1 trying to figure this out. Vacuum assist not leaking. New MC. New front brake hoses etc. Next step is to disconnect and plug front lines and try to recreate problem with only rear brakes. Trying to determine if mechanical or vacuum related.
On another note. Does it matter which brake line from the MC goes to the front or rear? Have heard about a primary and secondary piston but cannot find any intel for which goes where.
2001 ZR2 4 wheel discs.
Thanks again .
#29
01-07-2020, 06:02 AM
5 cents worth - brake fade means your pedal still goes to the floor sometimes? No leaks you said.
Does it have rear drum brakes?
I've been following up to here but now something came to my mind. You said it did it most of the times when you had backed up.
How about parking brake application?
This relates to rear drum brakes. When incorrectly assembled or with the incorrect brake pads it is possible for the pads to move around laterally. Means left and right seen in driving direction. Then they may slip off the brake actuators which then can fully extend without pressure.
Still the front should brake the vehicle. Not sure if your Blazer is diagonal or front and rear brake circuits.
Could it be that it is a mechanical failure where one or both of the rear brake pads slip off the rear actuator(s)?
I would look into the same at the front, making absolutely sure that all is to spec's.
Does it have rear drum brakes?
I've been following up to here but now something came to my mind. You said it did it most of the times when you had backed up.
How about parking brake application?
This relates to rear drum brakes. When incorrectly assembled or with the incorrect brake pads it is possible for the pads to move around laterally. Means left and right seen in driving direction. Then they may slip off the brake actuators which then can fully extend without pressure.
Still the front should brake the vehicle. Not sure if your Blazer is diagonal or front and rear brake circuits.
Could it be that it is a mechanical failure where one or both of the rear brake pads slip off the rear actuator(s)?
I would look into the same at the front, making absolutely sure that all is to spec's.
#30
01-07-2020, 07:30 AM
Reviving this thread...
I completely removed the ABS. Converted to a Wilwood combination block with rear proportioning valve. Brakes all seem to work fine under normal conditions but STILL have brake fade after turning the steering wheel fully to one side or the other. Can't be unwanted ABS activation now since they are gone. Pulling my hair out over this and am back to square 1 trying to figure this out. Vacuum assist not leaking. New MC. New front brake hoses etc. Next step is to disconnect and plug front lines and try to recreate problem with only rear brakes. Trying to determine if mechanical or vacuum related.
On another note. Does it matter which brake line from the MC goes to the front or rear? Have heard about a primary and secondary piston but cannot find any intel for which goes where.
2001 ZR2 4 wheel discs.
Thanks again .
I completely removed the ABS. Converted to a Wilwood combination block with rear proportioning valve. Brakes all seem to work fine under normal conditions but STILL have brake fade after turning the steering wheel fully to one side or the other. Can't be unwanted ABS activation now since they are gone. Pulling my hair out over this and am back to square 1 trying to figure this out. Vacuum assist not leaking. New MC. New front brake hoses etc. Next step is to disconnect and plug front lines and try to recreate problem with only rear brakes. Trying to determine if mechanical or vacuum related.
On another note. Does it matter which brake line from the MC goes to the front or rear? Have heard about a primary and secondary piston but cannot find any intel for which goes where.
2001 ZR2 4 wheel discs.
Thanks again .
Also it is important that the correct lines go into the master cylinder i.e. front and rear in the correct spots. The primary and secondary pistons are located inside the master cylinder and work like a proportioning valve using springs,seals and pistons within the master cylinder rather than having a separate valve.
I have been unable to work on my blazer as i am in the process of moving and its in storage for now. But my next step to troubleshooting my issue is to attempt to isolate the issue like described above by clamping brake hoses one at a time. Im beginning to think it may be a caliper issue, but im tired of throwing parts at it so i want to do some digging first.