ABS Delete & Permanently Soft Pedal (2 Viewers)

[CaptBeardilocks]

When I rebuilt my 80 5yrs ago (link in sig) I deleted the ABS system. Main reason was that the sensors/lines were ruined and I didn't think it was worth the money to try to replace it all. So the wisdom/benefits and or stupidity of ABS delete aside....

A lot was done at the same time. I swapped the 1FZ for a 1HDT etc etc etc. As far as brakes go I replaced literally every line in the truck from to back, the master cyl, calipers, and deleted the LSPV. I also manual-swapped it so I use the brakes a LOT less than I would in an Auto. And I probably would have chased this issue a lot harder a lot earlier if it was auto.

I now have over 50k miles on the build and I love the truck. But since day one the brakes have been a bit spongy. I've re-bled many times and last year I flushed the entire system again. The brakes work good (for a VERY heavy built truck, I live in it), but there's a lot of pedal travel and even then it's never very firm.

Two other things: If I press the pedal with the truck not running, it'll slowly go 90% of the way to the floor over a couple of seconds. And I do get a fair amount of vibration under heavy braking most, but not all, of the time.

The only thing I haven't changed out is the Booster. I also haven't adjusted the MC Rod since the ABS delete. I read somewhere (possibly an Aussie FB group) that certain booster failures can cause soft pedal instead of the typical "expected" really hard pedal. But that's only anecdotal.

Is there anything else I should have done when I deleted the ABS? Should I try to source a non-ABS booster & master? Is there a significant difference? Do I have a vacuum issue that is causing me the softer pedal, like a weak main booster hose? Is this a MC rod adjustment issue (I have never messed with one of those).

Thanks!

 

[CruiserDave]

Make sure you check those front wheel bearings for play. The vibration while braking only sometimes makes me think they could be loose. This can cause the calipers piston to get pushed back in causing longer pedal throw to engage the brakes. Also make sure you don't have a stuck caliper piston front or back as this could cause an inconsistent pedal feel.

 

[reklund5]

I had signifiant pedal feel improvement when I replace the booster on mine while the engine swap was happening last fall. That said....

I'd say to double check all your wheel bearings for play. if you have rubber flex lines, I've found it useful to use a pair of hose-pinch pliers on one corner at a time to try and isolate the problem to a specific caliper/stuck pads/loose bearing etc. You may try that as well. I've also seen questionable quality master cylinders and calipers from aftermarket suppliers. If you're not using OEM or known good parts, you might have to go back through those parts as well.

 

[CaptBeardilocks]

Make sure you check those front wheel bearings for play. The vibration while braking only sometimes makes me think they could be loose. This can cause the calipers piston to get pushed back in causing longer pedal throw to engage the brakes. Also make sure you don't have a stuck caliper piston front or back as this could cause an inconsistent pedal feel.

Front wheel bearings are good. I have been down that rabbit hole a few times.

Pad wear over the last 50k miles doesn't indicate any one caliper significantly dragging.

 

[CaptBeardilocks]

I had signifiant pedal feel improvement when I replace the booster on mine while the engine swap was happening last fall. That said....

I'd say to double check all your wheel bearings for play. if you have rubber flex lines, I've found it useful to use a pair of hose-pinch pliers on one corner at a time to try and isolate the problem to a specific caliper/stuck pads/loose bearing etc. You may try that as well. I've also seen questionable quality master cylinders and calipers from aftermarket suppliers. If you're not using OEM or known good parts, you might have to go back through those parts as well.

I check & re-pack wheel bearings yearly because the rig does see tough miles every year.

MC is OEM. Calipers are Napa, which was the best I could get when I rebuilt it because OEMs were NLA.

Rear Calipers are due for a pin lube/boots and maybe pads, but this issue has been happening since Day 1 on the build.

 

[HDJ80L]

Not sure if you did the classic pedal or pressure bleeding but when I re-filled and bled the brakes recently I had a soft pedal on the first drive. After a second round of bleeding the pedal was back to normal. I found that its important to close the bleeder screw quickly under a strong stream of brake fluid before moving to the next caliper. If you keep it open too long the stream weakens as the brake pedal is further depressed and air gets back into the caliper before you close it.

 

[CaptBeardilocks]

I don't think bleeding method is the issue. I pressure bled them once at the beginning when I noticed how soft the pedal was. Zero change. Since then the brakes have been bled, re-bled, flushed, bled again, re-bled again, etc. Multiple times over the last 50,000 miles. Pedal is always exactly the same. Zero change.

I believe it to be something other than air in the lines.

 

[lumbee1]

Which booster did you use? If the booster rod is too shallow, it can result in a lot of travel before braking begins.
Are you running stainless or new OEM lines between the axle and caliper and the frame to axle?
Is your brake fluid dropping over time? This could indicate a leak in the system when under pressure.
Do you still have your LSPV?

ABS was the source of my soft pedal. I had air in ABS that I couldn't get out even after bleeding a quart of brake fluid through the system.

 

[ChaseTruck]

...If I press the pedal with the truck not running, it'll slowly go 90% of the way to the floor over a couple of seconds...

If there are no leaks in the system, then in my mind that would point to a brake master cylinder with tired seals.

 

[CaptBeardilocks]

Which booster did you use? If the booster rod is too shallow, it can result in a lot of travel before braking begins.
Are you running stainless or new OEM lines between the axle and caliper and the frame to axle?
Is your brake fluid dropping over time? This could indicate a leak in the system when under pressure.
Do you still have your LSPV?

ABS was the source of my soft pedal. I had air in ABS that I couldn't get out even after bleeding a quart of brake fluid through the system.

Booster is the stock FZJ w/ABS booster. The truck I got the 1HDT out of was a RHD so no chance if swapping boosters in that sense.

OEM rubber lines everywhere. New at the time of the build.

Have never had to top up the brake fluid in 50k miles.

LSPV deleted as well.

It's not just that the pedal travel is far, it's also that when it starts to bite it's also soft. It definitely stops, it's just ... not quite normal. Lol.

 

[CaptBeardilocks]

If there are no leaks in the system, then in my mind that would point to a brake master cylinder with tired seals.

That's within the realm of possibility. Even new OEM parts don't seem to last like they used to.

I wish I could find the guy that I read that had similar symptoms and fixed it by replacing either the main vac hose or the booster. But from the replies her that would seem like a one-in-a-million failure type.

What's odd is that it has been perfectly consistent over the last 50k miles...

 

[Godwin]

You need to check the booster rod to MC distance and confirm that it is correct, and if not, adjust it until it is correct. This is an easy variable to rule out or an easy fix. Until you do this you'll be guessing at cause of symptoms.

 

[CaptBeardilocks]

I'll dig up the procedure on this and give it a try.

 

[rhc404]

Have you tried a more aggressive brake pad?

 

[TheBussman]

def check the booster rod first. I've seen a lot of different ways the LSPV has been deleted. One of my customers did it in such a way that air could not be bled from one of the lines he installed. one time there was a truck that had super warped rotors so bad that it was pushing the pistons back into the caliper and causing a low pedal.

 

[CaptBeardilocks]

def check the booster rod first. I've seen a lot of different ways the LSPV has been deleted. One of my customers did it in such a way that air could not be bled from one of the lines he installed. one time there was a truck that had super warped rotors so bad that it was pushing the pistons back into the caliper and causing a low pedal.

I definitely have to start with the rod. Not sure how it could have gotten out but I have to rule it out.

LSPV was deleted properly for sure. And def not warped rotors. I have heard that the alignment of the rod can cause shaking under braking, so I have to look at that as well.

Part of starting this thread was to suss out two main questions I had: 1) if deleting the ABS can cause any issues using the ABS MC & Booster, over non-ABS parts. 2) If a vacuum failure of some kind (collapsing hose, leak, weak vacuum, booster issue) could cause a soft pedal in some cases.

I was unaware the rod could be the cause, so ruling that out as soon as I can get in there.

 

[TheBussman]

I definitely have to start with the rod. Not sure how it could have gotten out but I have to rule it out.

LSPV was deleted properly for sure. And def not warped rotors. I have heard that the alignment of the rod can cause shaking under braking, so I have to look at that as well.

Part of starting this thread was to suss out two main questions I had: 1) if deleting the ABS can cause any issues using the ABS MC & Booster, over non-ABS parts. 2) If a vacuum failure of some kind (collapsing hose, leak, weak vacuum, booster issue) could cause a soft pedal in some cases.

I was unaware the rod could be the cause, so ruling that out as soon as I can get in there.

abs and non-abs have the same bore size, i had thought that the only difference was the port location.

are you using a manual propitiating valve in place of the LSPV?

weak vacuum or leaking booster will cause a hard pedal not soft.


brake lines can be capped of one by one to isolate front from rear and each corner if need be. one time i saw square cut seal on a caliper that was twisted around and the piston would retract too far each time the pedal was pressed.

 

[CaptBeardilocks]

No LSPV.

I think I got around the port location issue by rerouting a line. I think it was a spiral line and I carefully unwound one section and rerouted it. I should probably check that to make sure it's not a position that it could create an air trap of some kind.

Otherwise I would suspect an internal MC leak if it's not the rod.

I will add that, when the engine is off, the pedal will slowly depend most of the way to the floor. One or two pumps and it's back up to normal, engine still off. Not sure if that's indicative of anything.

 

[TheBussman]

most often internal seal failure of mastery cyl i know that you said it was already replaced. you can take both lines off and cap them. if it feels that same and the rod adjustment is correct the master is bad.

 

[CaptBeardilocks]

most often internal seal failure of mastery cyl i know that you said it was already replaced. you can take both lines off and cap them. if it feels that same and the rod adjustment is correct the master is bad.

Awesome, easy test. Thanks!

New parts seem to fail way more often than they used to. Would be odd that it hasn't gotten worse in 50k miles, but who knows. Good to suss it out now.