Low brake pedal when pressed first (1 Viewer)

[jayfrem]

Hi There

I have 1999 LC 100 with 150 K miles on it.
I noticed recently that when I press the brake pedal the first press seems a bit low and the second press immediately after seems to be a bit higher normal.

where do look for ? Could it I need to bleed the brake fluid to chase trapped air out ?

Almost 2 months ago replaced front wheel bearing.

I look at some other posts but no final solution posted.

Jay

 

[re_guderian]

Jay,

Check the obvious and cheap stuff first. What is your brake fluid level in the reservoir upon starting the truck? What is the condition of your front and rear brake pads? (don't discount the rears, on both my 100 series they wear faster than the fronts). What is the condition of your fluid itself - i.e. how long since a brake fluid flush has been performed?

 

[TXLX100]

Search on here. There is a DIY thread to remove the brake master cylinder piston and reinstall with new o-ring and some other bits. My 98 did this and has much firmer pedal now on first touch of pedal

 

[Spike555]

This is classic failing brake master cylinder symptoms.
It is loosing pressure when it is parked and you are pumping it back up with the first push of the pedal.
It will get worse until you loose all brake pressure. Could take years, could take weeks.
I'd take care of it ASAP.

 

[jayfrem]

Jay,

Check the obvious and cheap stuff first. What is your brake fluid level in the reservoir upon starting the truck? What is the condition of your front and rear brake pads? (don't discount the rears, on both my 100 series they wear faster than the fronts). What is the condition of your fluid itself - i.e. how long since a brake fluid flush has been performed?

Hi there fluid has been changed a yesr ago.
Front brake pads changed recently.
Rear pads still have half life in them.

For the brake master cylinder can its O ring be replaced or needs a full replacement if that is the problem ?

 

[jayfrem]

This is classic failing brake master cylinder symptoms.
It is loosing pressure when it is parked and you are pumping it back up with the first push of the pedal.
It will get worse until you loose all brake pressure. Could take years, could take weeks.
I'd take care of it ASAP.

The pedal is a bit lower on the first press even when driving.

Could the failure of brake master cylinder be sudden and loose all brakes suddently ?

 

[TXLX100]

Hi there fluid has been changed a yesr ago.
Front brake pads changed recently.
Rear pads still have half life in them.

For the brake master cylinder can its O ring be replaced or needs a full replacement if that is the problem ?

Google "ih8mud 100 series Master cylinder rebuild DIY" for the procedure. It worked for me, worth a shot before buying a new master cylinder or other components.

 

[2001LC]

A leak that suddenly allows fluid loss would result in no brake peddle pressure. Some areas to inspect: seal of master, seal of piston in each caliper (4 wheel), brake lines. Check for leaks, starting in cabin on firewall where peddle links to master.

Check level, read insertions on top of reservoir on how to.

Check booster pump function. Just like when check fluid level pump brake peddle 40 time with key off. Once booster has evacuated fluid into reservoir, turn key to on (do not start) and time how long it takes booster to stop, 30 to 40 seconds is good.

Master Cylinder Rebuild - DIY

 

[Spike555]

The pedal is a bit lower on the first press even when driving.

Could the failure of brake master cylinder be sudden and loose all brakes suddently ?

YES!! You have been warned by your truck of impending doom, you WILL eventually loose all brake pressure and not be able to stop.
If your parking brake is working you can slow with that, you s***f into neutral and slowing apply the parking brake to stop if you loose all brake pressure.
But you have been given a heads up.
I personally never rebuild master cylinders, I replace them.
I have NOT replaced one on one of these trucks.

 

[Landpimp]

I'd check the rear calipers, the wife's 99 had this same issue for quite a few years, finally traced it down to a bad slider in right rear caliper, replaced the slider and pedal is normal and has stayed normal for a year. It was taking the 1st pump to push the pads in, then it would be OK, till you used the brakes again, never bothered the wife but drove me nuts as my 2000 brakes were normal.

 

[Tareq]

I had ur problem 1 week ago, replaced rear pads with HAWK GREEN, stock rotors, bought same pads for the front but didnt install as they still had 50% mechanic said.

Flushed brakes in all 4 corners completely, and now it is stronger from the 1st press ,,, not as my previous BMW though

 

[f5driver]

I had similar symptoms. First press was weak and would go to the floor. Second pump would work fine. The problem was a front wheel retaining nut was loose. The staked washer broke and the nit backed off.

 

[jayfrem]

Thanks guys. My front wheel bearing needed adjustment.
Pedal is better altough a slight difference can be noticed between first press and second press.

Is it normal ?

 

[jayfrem]

Hey Guys

I am suffering again from a soft first pedal.

I am thinking to check in order:

1. wheel bearing

2. Rear Pads and sliders
Anyone know the rear sliders part # ?

3. Consider Master Cylinder rebuild

The first brake is not weak but a bit lower than the second press.

Thanks

Jay