Break problems advice. (1 Viewer)

[lcrva]

I have been plagued with weak brakes. I have to jam the pedal super hard to stop and I can’t stop fast enough to get the ABS to ever activate. (Can’t remove it by law here).

What have I checked:
1. Brake booster seems to work and pulls a vacuum.

2. Replaced master cylinder and bench bleed it.

3. Bleed all the brakes and the partitioning valve several times. The brake fluid looked dirty but all replaced and problem remains.

4. I don’t notice any significant ballooning of the lines.



I am ruining out of ideas and money, any advice on what I can test next? Thanks for any help you can give.

 

[voodu3]

Have you tried using a pressure bleeder? The abs system is hard to get all of the air out. Do you know that the abs works? When you put the transfer case in low gear does the light come on? Also what year is your LC?

 

[Malleus]

You can try bleeding the ABS directly (post #35); although it isn't guaranteed to fix the problem, some have found it helpful. I have fought this same problem on two of my three 80s ('94 and '95) for years. Using a Motive pressure bleeder is helpful, IME (the BA-10 is a must, though), but after replacing every wear part on one of them, and bleeding to replace the fluid, I'm convinced there is a small leak in the system, likely at a fitting, that I haven't found. The braking performance is improved after all the work I've done, and acceptable, buy it's not as good as my daily driver 80.

Bottom line is that if you've done everything that you feel is reasonable, and your brakes still aren't what you think they should be, you have a leak somewhere sucking air into your lines. You may find it with soapy water, but if it's really small, you may not be able to distinguish it from the bubbles in the soap. (It's too bad there isn't a flourescent dye for brake fluid; oh, wait, there is)

My next step, which is a problem for the winter actually, is to put a manifold and gauge system together, as described in the FSM, so that I can simultaneously check all five pressure points, downstream of the master and ABS, at once. This is a tool project that's been on the back burner here for a while now. I'm trying to develop a system that can be readily assembled, inexpensively, so that anyone can do this. More to follow on that.

 

[Rusty Marlin]

Couple of ideas.
Have you pulled the slider pins on the rear brakes and cleaned and regreased them?
How do you know the LSVP is actually working? is it leaking, is it stuck?
Have you taken it on grass or gravel and jammed the brakes on hard enough to cycle the ABS system?

 

[ColoradoBoy]

Couple of ideas.
Have you pulled the slider pins on the rear brakes and cleaned and regreased them?
How do you know the LSVP is actually working? is it leaking, is it stuck?
Have you taken it on grass or gravel and jammed the brakes on hard enough to cycle the ABS system?

^^^

My initial thought was if you have looked at the calipers (F & R) and verified that nothing is stuck or frozen as well. I'm going thru my whole system now- it is amazing how much crap accumulates in there if you don't maintain regularly. I'm trying to get out of the habit of letting things be just because nothing is giving me grief at the moment...

 

[lcrva]

Have you tried using a pressure bleeder? The abs system is hard to get all of the air out. Do you know that the abs works? When you put the transfer case in low gear does the light come on? Also what year is your LC?

I have tried a vacuum bleeder. I have pulled 2+quarts through I am definitely being fresh brake fluid out of all the bleed points. But No I have not done a pressure bleeder.

I do not know 100% the ABS works. No
Lights or codes. Trying to find some grass I can destroy to try. I can’t get it to brake hard enough on pavement to break traction.

I need to test in low range.
Car is a 1996. Thanks!

 

[lcrva]

You can try bleeding the ABS directly (post #35); although it isn't guaranteed to fix the problem, some have found it helpful. I have fought this same problem on two of my three 80s ('94 and '95) for years. Using a Motive pressure bleeder is helpful, IME (the BA-10 is a must, though), but after replacing every wear part on one of them, and bleeding to replace the fluid, I'm convinced there is a small leak in the system, likely at a fitting, that I haven't found. The braking performance is improved after all the work I've done, and acceptable, buy it's not as good as my daily driver 80.

Bottom line is that if you've done everything that you feel is reasonable, and your brakes still aren't what you think they should be, you have a leak somewhere sucking air into your lines. You may find it with soapy water, but if it's really small, you may not be able to distinguish it from the bubbles in the soap. (It's too bad there isn't a flourescent dye for brake fluid; oh, wait, there is)

My next step, which is a problem for the winter actually, is to put a manifold and gauge system together, as described in the FSM, so that I can simultaneously check all five pressure points, downstream of the master and ABS, at once. This is a tool project that's been on the back burner here for a while now. I'm trying to develop a system that can be readily assembled, inexpensively, so that anyone can do this. More to follow on that.

I consider it being a leak, but don’t you think if there is a leak I would have improvement after bleeding the system at least for a few hours?
Thanks for the information. I’m gonna try that.

 

[lcrva]

You can try bleeding the ABS directly (post #35); although it isn't guaranteed to fix the problem, some have found it helpful. I have fought this same problem on two of my three 80s ('94 and '95) for years. Using a Motive pressure bleeder is helpful, IME (the BA-10 is a must, though), but after replacing every wear part on one of them, and bleeding to replace the fluid, I'm convinced there is a small leak in the system, likely at a fitting, that I haven't found. The braking performance is improved after all the work I've done, and acceptable, buy it's not as good as my daily driver 80.

Bottom line is that if you've done everything that you feel is reasonable, and your brakes still aren't what you think they should be, you have a leak somewhere sucking air into your lines. You may find it with soapy water, but if it's really small, you may not be able to distinguish it from the bubbles in the soap. (It's too bad there isn't a flourescent dye for brake fluid; oh, wait, there is)

My next step, which is a problem for the winter actually, is to put a manifold and gauge system together, as described in the FSM, so that I can simultaneously check all five pressure points, downstream of the master and ABS, at once. This is a tool project that's been on the back burner here for a while now. I'm trying to develop a system that can be readily assembled, inexpensively, so that anyone can do this. More to follow on that.

 

[lcrva]

I have been plagued with weak brakes. I have to jam the pedal super hard to stop and I can’t stop fast enough to get the ABS to ever activate. (Can’t remove it by law here).

What have I checked:
1. Brake booster seems to work and pulls a vacuum.

2. Replaced master cylinder and bench bleed it.

3. Bleed all the brakes and the partitioning valve several times. The brake fluid looked dirty but all replaced and problem remains.

4. I don’t notice any significant ballooning of the lines.



I am ruining out of ideas and money, any advice on what I can test next? Thanks for any help you can give.

Update:
I activated the ABS with a battery. No change.

Abs light does come on with Low range.

 

[lcrva]

Couple of ideas.
Have you pulled the slider pins on the rear brakes and cleaned and regreased them?
How do you know the LSVP is actually working? is it leaking, is it stuck?
Have you taken it on grass or gravel and jammed the brakes on hard enough to cycle the ABS system?

These are my next steps. Just a guess but I feel like it’s not working well enough in the front. Nose does not dip down like most cars when heavy braking.

 

[lcrva]

Have you tried using a pressure bleeder? The abs system is hard to get all of the air out. Do you know that the abs works? When you put the transfer case in low gear does the light come on? Also what year is your LC?

Light does come on.

 

[lcrva]

I have tried a vacuum bleeder. I have pulled 2+quarts through I am definitely being fresh brake fluid out of all the bleed points. But No I have not done a pressure bleeder.

I do not know 100% the ABS works. No
Lights or codes. Trying to find some grass I can destroy to try. I can’t get it to brake hard enough on pavement to break traction.

I need to test in low range.
Car is a 1996. Thanks!

Next steps and welcome any advice…..
I think I will get new pads. That way I can check and lube the calipers and eliminate it having the wrong pads on there.

 

[Malleus]

I consider it being a leak, but don’t you think if there is a leak I would have improvement after bleeding the system at least for a few hours?
Thanks for the information. I’m gonna try that.

Not really. The brake system is a low pressure system, but still pressurized, when it's active (when your foot's on the pedal). Any vent to the atmosphere is going to reduce the pressure enough to be felt.

IME, pads do make a difference. I haven't tried every pad on the market, but I've tried the auto parts stores' brands and none of them were as good as Toyota branded pads; they're all I've used for years now. I've found I can get by with aftermarket pads on the front (if I have to), but I've never been able to get any pads, other than Toyota pads, to fit the rear calipers, without grinding the flashing off of them.

You've probably done this, but it's important to move the actuator (the long rod) up and down (once each way and hold it there) when you bleed the proportioning valve, or else you can get air trapped in the chamber. It's noted in the service manual. This won't make your front brakes any better, though, since the master has separate chambers for the front and rear circuits. It is possible that trapped air can move around in the system, though, so it's always a good practice.

I've attached my annotated and bookmarked brake repair section (from the 1995 Toyota service manual). It includes the entire brake section (BR-1 thru BR-63, with ABS and troubleshooting sections. Hope it helps.

 

[Malleus]

This chart tells you how the proportioning valve should be set, but also gives you an indication of target working pressures:

I would consider the first case to be dragging my foot on the pedal (just enough pressure to keep it from moving with a 1000rpm engine load). The third case is a panic stop. Unless you're trying to balance the valve, you can ignore the second case; it's there just so that the technician can see the valve is starting to open.

In any case, you should be able to generate the maximum pressure indicated. If you can't, there a system leak.

 

[lcrva]

This chart tells you how the proportioning valve should be set, but also gives you an indication of target working pressures:

View attachment 3710692

I would consider the first case to be dragging my foot on the pedal (just enough pressure to keep it from moving with a 1000rpm engine load). The third case is a panic stop. Unless you're trying to balance the valve, you can ignore the second case; it's there just so that the technician can see the valve it starting to open.

In any case, you should be able to generate the maximum pressure indicated. If you can't, there a system leak.

This is excellent information thanks so much for taking the time.

 

[ColoradoBoy]

Next steps and welcome any advice…..
I think I will get new pads. That way I can check and lube the calipers and eliminate it having the wrong pads on there.

Going back to posts #4 & 5. I would pull the calipers & verify you don't have any frozen pistons if the pads look OK. It sounds to me that you may be too focused on the ABS when the mechanical functionality of brake system may be at fault.
Good luck on your quest to get it fixed. Keep us posted!

 

[lcrva]

Not really. The brake system is a low pressure system, but still pressurized, when it's active (when your foot's on the pedal). Any vent to the atmosphere is going to reduce the pressure enough to be felt.

IME, pads do make a difference. I haven't tried every pad on the market, but I've tried the auto parts stores' brands and none of them were as good as Toyota branded pads; they're all I've used for years now. I've found I can get by with aftermarket pads on the front (if I have to), but I've never been able to get any pads, other than Toyota pads, to fit the rear calipers, without grinding the flashing off of them.

You've probably done this, but it's important to move the actuator (the long rod) up and down (once each way and hold it there) when you bleed the proportioning valve, or else you can get air trapped in the chamber. It's noted in the service manual. This won't make your front brakes any better, though, since the master has separate chambers for the front and rear circuits. It is possible that trapped air can move around in the system, though, so it's always a good practice.

I've attached my annotated and bookmarked brake repair section (from the 1995 Toyota service manual). It includes the entire brake section (BR-1 thru BR-63, with ABS and troubleshooting sections. Hope it

Going back to posts #4 & 5. I would pull the calipers & verify you don't have any frozen pistons if the pads look OK. It sounds to me that you may be too focused on the ABS when the mechanical functionality of brake system may be at fault.
Good luck on your quest to get it fixed. Keep us posted!

I agree that’s the next step I’m gonna do. I’m just curious if I should make the leap to replace the brake lines as well. They’re pretty old.

 

[NorthWA]

Just my two cents but I’ve never had much luck with vacuum brake bleeders. I do use a pressurized bleeder though.

 

[ColoradoBoy]

I agree that’s the next step I’m gonna do. I’m just curious if I should make the leaf to replace the brake lines as well. They’re pretty old.

Yes- I would replace the brake hoses as well. 30 year old parts...
My thought was to just bite the bullet & do it all at once- it's time. (doing this myself right now).
Cheers!

 

[ChaseTruck]

Measuring brake efficiency by estimating the nose dive will be an exercise in frustration - look at the front suspension geometry of the ‘80.

It’s stated that high pedal pressure is needed, and in the same breath I read that the brake booster seemed to work ‘because it’s pulling vacuum’. Something doesn’t jive here. The vacuum is courtesy of the engine running, the booster doesn’t pull anything.

Frozen calipers are a possibility - does the vehicle track straight under braking? If so, either all four calipers are frozen equally, or something else is afoot. From what I’ve read, I’d go after the booster.