Brake Pedal Initially spongy then firms up (3 Viewers)

[obe12]

My 1994 LC 80 series brake pedal is initially spongy, 1st 1/4 pedal travel then firms up. The truck was this way from the day I bought it 12/2023. Now it would feel like rear brakes shoes out of adjustment on a rear drum brake truck.

Replaced all 4 calipers, Pads, Rotors, Stainless Steel brake hoses Frame to Axle and Axle to Calipers front and rear. Just replaced a New ASIAN master cylinder "ABS" option brakes rear full float, rear disc brakes. Pedal is identical to to before the 1/4 pedal spongy feel, and firms up. Old chev 88 year pickups were like this. My 100 is not that way at all.

When the truck was on jack stands and rear axle drooping it feels worse, load proportional valve reducing fluid pressure rot rear, the pedal feels linda the same symptom but worse.

Adjusted the level valve to get higher pressure when on the ground level, and pedal is better, but still spongy 1st 1/4 travel.

I do not know the characteristics of the 80 what's normal what's not. My 100 spoils me for better brakes.

Ok, please chime in....

All pressure bleed with pressure bleeder and bled ABS lines, Load ProP Valve and each Caliper. NO change, to how it was when I bought it 12/2023.

 

[Brav]

Usually that’s air in the system. Need do first bleed it.

 

[LandLocked93]

My 1994 LC 80 series brake pedal is initially spongy, 1st 1/4 pedal travel then firms up. The truck was this way from the day I bought it 12/2023. Now it would feel like rear brakes shoes out of adjustment on a rear drum brake truck.

Replaced all 4 calipers, Pads, Rotors, Stainless Steel brake hoses Frame to Axle and Axle to Calipers front and rear. Just replaced a New ASIAN master cylinder "ABS" option brakes rear full float, rear disc brakes. Pedal is identical to to before the 1/4 pedal spongy feel, and firms up. Old chev 88 year pickups were like this. My 100 is not that way at all.

When the truck was on jack stands and rear axle drooping it feels worse, load proportional valve reducing fluid pressure rot rear, the pedal feels linda the same symptom but worse.

Adjusted the level valve to get higher pressure when on the ground level, and pedal is better, but still spongy 1st 1/4 travel.

I do not know the characteristics of the 80 what's normal what's not. My 100 spoils me for better brakes.

Ok, please chime in....

All pressure bleed with pressure bleeder and bled ABS lines, Load ProP Valve and each Caliper. NO change, to how it was when I bought it 12/2023.

Not suggesting your bleed process is lacking.
But...take it to a brake shop that has a machine. Have them do a "brake service".
Then re-eval.

If no change, consider that other systems are different and adapt to it. It's like training to a new pistol.

While all the relevant features are there they may/could work differently from what you're used to.
Incorporate the differences and roll.

 

[White Sheep]

Sounds like your brake booster.

 

[ZetheGSD]

Just speaking from experience. I’ve bled brakes professionally for many years and my 80 was a conundrum. I went completely through the entire brake system with new parts. Same mushy-then hard pedal symptom. After everything was new and the system had been bled many many times with no bubbles, I was able to actuate the ABS module manually while pressure bleeding. I got brown fluid out of it. Pedal felt improved but performance was reduced…

Removed ABS and LSPV as a pair and now I enjoy incredible brakes!

 

[77mustard40]

^^^ ABS and LSPV delete was the best free mod I've done to my 80, night to day improvement in my brakes.

 

[LandCruisinMy93]

^^^^^ I also deleted the ABS and LSPV^^^^

 

[JoeCova]

How has break pad wear bin since the delete?

After seeing this thread I may delete mine as well.

 

[obe12]

It feels to me, the LSPV is the issue restricting fluid to rear brake calipers. The thing I considered, was wrong master cylinder was installed, rear drum brake option, therefore no residual valve internal in the master cylinder. To hold some brake fluid front backing up into the master cylinder, therfore apply brakes have to refill and pressurize the circuit therfore lower brake pedal, like out of adjusted rear brakes lowers pedal feel.

I used the Oem by VIN and got the Oem number for the mater cylinder Abs brakes, full float rear axle. Installed it no change, yes I have a positive pressure bleeder tool. Forces fluid through the mater cylinder.

Second, the LSPV valve can be delaying fluid pressure to rear calipers. I deleted it on my mini truck when added rear disc brakes and it required adjustable brake regulator and residue valve install for my mini.

Now this LC is heavier in the back than a mini pickup, therefore higher brake pressure could be ok and not swap ends on wet payment when braking.

I will look at deleting it and simplify my system, hate the pedal feel and Want it improved.

Tex

 

[obe12]

It feels to me, the LSPV is the issue restricting fluid to rear brake calipers. The thing I considered, was wrong master cylinder was installed, rear drum brake option, therefore no residual valve internal in the master cylinder. To hold some brake fluid front backing up into the master cylinder, therfore apply brakes have to refill and pressurize the circuit therfore lower brake pedal, like out of adjusted rear brakes lowers pedal feel.

I used the Oem by VIN and got the Oem number for the mater cylinder Abs brakes, full float rear axle. Installed it no change, yes I have a positive pressure bleeder tool. Forces fluid through the mater cylinder.

Second, the LSPV valve can be delaying fluid pressure to rear calipers. I deleted it on my mini truck when added rear disc brakes and it required adjustable brake regulator and residue valve install for my mini.

Now this LC is heavier in the back than a mini pickup, therefore higher brake pressure could be ok and not swap ends on wet payment when braking.

I will look at deleting it and simplify my system, hate the pedal feel and Want it improved.

Tex

Sorry, forgot to ask How did you delete the LSPV on the 80?

 

[77mustard40]

Here you go, I followed this thread and also replaced my failing booster at the same time

Yet another LSPV/ABS delete how to...

I finally had some time to get to this today. Figured I would take some pictures and do a write up. There is plenty of info here, but it is a bit scattered. This will go from the start to the end. Is it worth it? Absolutely! For all those that complain about the brakes, we have plenty of...

forum.ih8mud.com

 

[CrabCake]

This may sound simple, but something that I overlooked on mine...check your front wheel bearings! I did a front end refresh on mine and the brakes would get soft...first bump and they would pump up and be fine until driving a bit longer, then soft again on the first hit and then fine if I gave it an initial bump before real braking. Never went to the floor, but erratic on when it would do it, so I thought.

Basically, when you'd hit a bump or go around a curve, the rotor would press the pad/s back slightly in the caliper. First bump would re-set them, and subsequent braking was fine until you drove a bit more. Found out that my driver's wheel bearing had just a little play that I didn't bed properly with new wheel bearings/grease. Snugged it up after chasing this for several months and back to factory new feeling!

 

[obe12]

This may sound simple, but something that I overlooked on mine...check your front wheel bearings! I did a front end refresh on mine and the brakes would get soft...first bump and they would pump up and be fine until driving a bit longer, then soft again on the first hit and then fine if I gave it an initial bump before real braking. Never went to the floor, but erratic on when it would do it, so I thought.

Basically, when you'd hit a bump or go around a curve, the rotor would press the pad/s back slightly in the caliper. First bump would re-set them, and subsequent braking was fine until you drove a bit more. Found out that my driver's wheel bearing had just a little play that I didn't bed properly with new wheel bearings/grease. Snugged it up after chasing this for several months and back to factory new feeling!

Good point, mine are tight, just repacked and replaced new rotors, front and rear along with new calipers and stainless brake hoses.

Pedal is spongy without moving the truck.

consensus is trapped air in the ABS unit and LsPV valve restricting fluid pressure to rear.

My LC was owned by one for last 8 years and fluid was actually not that dirty. Aces him having it changed. I have NOT gotten rusty fluid like some has out of the bleeders.

Right now I am doing a motorcycle tip to see if I can get rid of the possible trapped air,

tie the brake lever applying brake pressure overnight. How it pushing the air out, I can’t tell you why it works, but it does. I have done this to a few bikes over the years and improves brake handle / pedal feel if they get a little spongy on initial application.

The ABS unit is high mounted, and I can see air getting trapped. I check the Service Manual for if there is a bleed procedure for this unit or short a connector to able to bleed, nothing like that.

A few posts owner have activated their ABS a few times rebleed brakes and gotten the spongy feeling fixed.

Others have removed the ABS and LsPV valve in back to rid the soft feel. Some have added an adjustable pressure regulator to the rear circuit to help prevent rear locking up earlier then front.

I had a mini truck, converted rear drum to rear disc, lifted and removed the LSPV valve non ABS.
It required a residue valve placed in line to the rear brakes from the master cylinder to keep pedal feel good, and also an adjustable regulator to prevent rear end lock up on wet pavement. Lookikg back yeah I had disc brakes with internal park brake calipers and never really like it. Park brake was not as good, brake performance over all to stock suffered on brake lock up or not.


I like to keep the ABS if I can, maybe make a longer rear bracket for LSPV valve, I just listed the truck 2-3 inches from its old ride height. If I wheeled all the time, maybe no ABS. Mine disables my ABS on center diff lock engagement too.

 

[flintknapper]

Consensus is trapped air in the ABS unit and LSPV valve restricting fluid pressure to rear.

^^^^^

Smart money says this is your issue. I battled mine for years before finally just deleting the ABS/LSPV and man what a difference.

****NOT**** suggesting you or anyone do the same.

Just saying a LOT of aging ABS systems suffer from air and old fluid being trapped in them. Despite my 'activating' the ABS many, many times in an attempt to clear it, it never really did much better.

I finally decided that I'd rather have a good, reliable braking system (that I control) over a poorly working (if at all) ABS system.

I grew up learning to drive and brake without ABS....so I don't miss it one bit. Brakes have never felt better in the 24 years I've owned my LC.