ABS Delete & Permanently Soft Pedal (2 Viewers)

[lumbee1]

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.

The LSPV has three lines going into it, the main line, the output line, and a sense line. The sense line is not necessary and it there in the event of a failure (from what I understand). I removed my sense line and installed a simple union and get full line pressure to the rear. I also installed a Willwood proportioning valve under the hood. I painted the W in Willwood to keep track of the number of turns and have it set to 6 turns from wide open to the rear.

The sense line is straight but I can't remember if the main line to the rear contains spirals or not. It's possible that you removed the wrong line to the LSPV.

 

[CaptBeardilocks]

I replaced all the brake lines in the whole truck. So I just ran a non-LSPV line to the rear split.

 

[CharlieS]

Not saying it is your issue, but I attributed my soft at the top pedal to all kinds of different things, but what ultimately fixed it was a new booster.

Mine is ABS/LSPV deleted too. I went down the road of lines (replaced all with Slee stainless); master cylinder, new OEM; repeated bleeding, and no improvement.

Then I had a booster failure on trail that forced replacement, and voila, fixed both my brake pedal firmness and my remaining rough idle issue.

I used the Sieken booster from CruiserYard, it comes with gaskets, and supports a iH8mud member business. It was 100% match to the original that I took out, down to the last stamping.

Out of curiosity, how does the diesel get vaccum to run the booster?

 

[CaptBeardilocks]

I have heard this before, that ARE rare instances where a soft pedal is fixed by a new booster.

The 1HDT has a vacuum pump run off the crank and a vacuum reservoir that gives you a bit if the engine dies or whatever.

I'm not sure of there's a way to test the vac that the pump is supposed to supply or oi the gas/diesel Boosters are in any way different from each other.

 

[RockJock82]

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!

Have you replaced or rebuilt the calipers? I noticed an improvement after changing out the old calipers.

 

[CaptBeardilocks]

Have you replaced or rebuilt the calipers? I noticed an improvement after changing out the old calipers.

Yes

 

[Izeloz]

I have a similar problem with my '91. I will be following to see what the resolution is. I suspect some wonkiness in my brake booster also.

 

[SNLC]

I have heard this before, that ARE rare instances where a soft pedal is fixed by a new booster.

The 1HDT has a vacuum pump run off the crank and a vacuum reservoir that gives you a bit if the engine dies or whatever.

I'm not sure of there's a way to test the vac that the pump is supposed to supply or oi the gas/diesel Boosters are in any way different from each other.

Yes just put a vacuum gauge on the rubber lines from pump to booster. You can tee it inline and test the booster too.

We just had a new booster fail out of the box. A simple vac test showed where the problem was.

Cheers

 

[CaptBeardilocks]

Yes just put a vacuum gauge on the rubber lines from pump to booster. You can tee it inline and test the booster too.

We just had a new booster fail out of the box. A simple vac test showed where the problem was.

Cheers

Test that vacuum is getting to the booster or that the booster is doing something in specific?

What range should the HDT vac pump be sucking? I seem to remember back in may Mercedes diesel days you were looking for something around 17in if the system was marginally healthy.

Thanks!

Seems more and more "new" parts need to be tested for functionality before use these days. Bummer.