Going Manual Brakes?

[Bowhunterbrown]

I have a 98 k2500 6.5 diesel suburbaan with 1 ton brake upgrade and abs delete. I am failry happy with current brakes...BUT I am always looking to modify/simplify and or upgrade things. Right now I have new stock MC and hydraulic (JD8?) brake booster. From what I read the booster provides about 4x braking power. Right now the pedal takes little effort to apply brakes...so I am wondering if I might be happy without the booster.

The benefts of deleting the power hydraulic brake booster would be simplicity, more room for a potential twin turb setup or large water to air intercooler setup, firmer pedal, less demand on stock power steering system.

Right now I am just spitballing. I want to know, can I simply bypass the brake booster as it is now to see what manual brakes even feel like? Can I simply reroute infeed to the out feed of power steering pump?

If testing it feels even close to acceptable, I will look into modifying stock brake pedal lever/pivot possibly different MC or even caliper swap, to get a little more manual brake power. I just want to see if it feels reasonable to pursue or not, assuming I can do a simple bypass of the booster.

 

[Will L.]

So you just need to get all alone on a racetrack or middle of nowhere, up to speed and turn of the key.

My race truck had manual steering because 1/4 mile didn’t need the steering, and I fit on a different box that was manual. And I tried running without a booster to save space and weight. In the words of the hilarious Chris Farley “HOLY SHNIKEYS!!!”. And the booster went back into use after 2 attempts.

You can reroute the lines to save some space. Even modify and move the system over to the left more with some creative brackets and pushrod- but plan on keeping that booster.

 

[Bowhunterbrown]

Hmmm....hadn't thought of that. I have a nice long quiet stretch of road right out my door. Will report back soon.

 

[Bowhunterbrown]

Interesting results. first couple tries I had decent braking and pedal still felt pretty soft then faded a little at end. Third try, from 5o mph, I killed engine and gave it a 1 and half count before applying brakes, this time braking felt pretty inadequate with a soft peddle and reduced braking power at wheels.

This isnt what I expected. I thought the pedal would frim up with the absence of the hyraulic boost. Instead things ere pretty mushy overall.

 

[Will L.]

Exactly. And remember the engine running is charging a boost in it. So there is some added thump the first couple times you hit the pedal. Take that system out and the mush is there, and you have to stand on the pedal. Something to test in day time is panic stopping. Buy a shorter belt and bypass the power pump steering all together.

Then after you have used your leg muscles about 30 times, try panic stops. You will 100% end the theory of manual braking. Seriously - don’t do this on public streets. Go somewhere like a racetrack. Do 60-0 stopping test on asphalt a few times, getting time & distance. Then swap back on the proper belt and do it again. On a race track where other drivers have same braking as you- its all good. Open public roads where paint rubbing is frowned on- not so much.

 

[1994ch]

Also remember that there is an accumulator in the system. So if you are testing the theory by just shutting off the engine, the accumulator will keep pressure on the boost system for several pedal applications. So pump the pedal a couple of times real quick and then push it in to try to stop................ as Will said.......... not fun. You have 3 points of contact with the truck: the back of your head, your hand on the steering wheel, and both feet on the brake pedal...... And it still won't stop very well.

I know this from experience having had the old PMD on my 6.5 go out on me a couple of times in traffic (almost hit a telephone pole once as I tried to pull off into a Bi-Lo parking lot.)

 

[SnowDrift]

I used to work for a local farmer that had a '78 F250 with no power steering and a manual transmission (Did I mention he ran 33x12.50-16.5 tires on it?). I was 16 when I started working for him and he never enjoyed it either. Back then, he complained about his shoulders bothering him. Later in life, they bothered him more. It wasn't a picnic.

 

[WarWagon]

The benefts of deleting the power hydraulic brake booster would be simplicity, more room for a potential twin turb setup or large water to air intercooler setup, firmer pedal, less demand on stock power steering system.

First rule of making more power is being able to STOP THE DAMMED THING!!! Otherwise you and your hard work gets pealed off a telephone pole. Death is the "Easy Way Out." as a lifetime of pain and countless surgeries including possible burn ward time can result from poor/INOP brakes allowing a "sudden stop" of some kind.

Firm pedal... This is signature GM Mediocre Mush for a brake system. It's better than a 1/2 ton. To eliminate "Mush" you need to look at brake line flex and then caliper flex. Look at what the 1999+ MY 4 wheel disc systems did for a start. Obsolete rear drum brakes G O N E. Also better calipers with more pistons.

That said: When was the last time you adjusted the rear drum brakes? You get a lot of pedal travel needing a hard stop in reverse to self adjust the stubborn 'maybe' self adjusters. I adjusted mine every other oil change aka every 5,000 miles.

The amount of pedal travel you would need is extreme if you eliminated the booster design. As noted above: it's a bad idea, a reason NHTSA takes engine failure/stalling seriously to the point of recall including requiring a Diesel injection system fail from water "oops without any warning" to continue to let the engine run rather than have a filter block water/fuel flow to save the system.

 

[Bowhunterbrown]

Ok. I hear you guys. I am learning things here. Good point about the accumulator. Seems a shorter belt bypassing the steering pump is best way to really test. I am fortunate to have a 2 mile straight stretch in front of the house in open flat rural area. It is nice for breaking new pads and rotors in.

I certainly wouldn't expect to be able to just delete power brake booster and be happy with brakes. I figured if it was even half way there to feeling reasonable, then the rest of the system could be optimized, like mc to caliper ratio, pedal leverage, brake line size, etc to get it to a place of respectable stopping power.
The thing that got me thinking on it was reading that the booster provides 4x boost Considering how effortless it is now. Seemed like doable.
Came across guys doing it on s10 and thought. Maybe it could be done on a bigger pig.

I rebuilt my entire drum brakes including new backing plates and went with 3.5" wide shoes on fresh drums with the the 1 ton wheel cylinder. I agree the auto adjust system doesn't seam to reliable. I adjusted mine recently after having overtightened one and seizing a drum

I recently deleted the abs and planned to install proportioning valve but on another guys suggestion ran it without prop valve and its pretty well balanced as is. If I stomp on it, the rears lock up just a hair before fronts, but not by much.

IF a robust manual system could be designed, it would actually be safer for the reasons you guys mentioned on the lack of brake power if pmd fails or hydraulic line fails, etc on power brake system. Wouldn't it?

I have access to a very talented machinist around the corner from me and recently seeing what he can do, has me thinking big on mods.

Why not a beefy eccentric cam as a lever to manually boost pedal force to a MC?

 

[Bowhunterbrown]

And I have been considering the gmt800 brake upgrade, BUT, IF there was a chance at making a manual system work great, I think that the two smaller piston calipers might be a move in the wrong direction of optimal mc piston/to caliper piston ratio for this theoretical manual brake setup.

 

[Will L.]

Hell no, don’t run without a proportioning valve. Ifnit wasnt needed, it wouldn’t be on ever car for street or racing. If you can’t find a replacement stock unit, you buy an adjustable one for sold by race shops.

It will never remain balanced. Up hill with a load, down hill no load,
High traction vs rainy day, etc. whoever told you that has no frickin clue what they are talking about.

 

[Bowhunterbrown]

Hell no, don’t run without a proportioning valve. Ifnit wasnt needed, it wouldn’t be on ever car for street or racing. If you can’t find a replacement stock unit, you buy an adjustable one for sold by race shops.

It will never remain balanced. Up hill with a load, down hill no load,
High traction vs rainy day, etc. whoever told you that has no frickin clue what they are talking about.

There is no load sensing proportioning valve on these stock.
Just the one tied into the abs module. Which sucjed in the suburbans, it was so front brake heavy that gm later provided an updated one in service bulletin.

Anyway, the braking on this thing right now with no proportioning valve, brakes extremely well. It's very well proportioned right outta the MC. I have a wilwood prop valve and some residual valves for the rear that I probably will go ahead and install next time I am in the brake system. But It's 3x better than stock proportioning valve setup already.

 

[WarWagon]

I recently deleted the abs

And here comes the back end around the front end. The #1 thing ABS did was keep the rear end IN-LINE rather than stepping out while allowing you to use the rest of the heavily loaded front wheel's stopping power. Unloaded pickups benefited the most. It's something I was reminded of years ago stopping hard in an old school van as the locked up rear started to step out on me as I had gotten used too ABS keeping me in-line.

The next question is what kind of an up-fitter would take the liability and remove the safety features on a vehicle like ABS?

On Mobility modified vehicles: Even with reduced effort braking and reduced or zero effort steering the ABS system stays. This includes hand throttle/brake controls. Additionally a high current electric powered hydraulic pump is installed to keep the power steering working in case of engine stall/failure. Hydroboost systems by design also have power brakes available from the backup pump.

If you are worried about engine stall then an electric backup pump system may be right for you. It's cost installed is likely more than your vehicle is worth with a full tank of fuel. Just saying you have options.

The removal of the proportioning valve ... This is becoming a safety hazard even on a race track. You are limiting your front brakes to the ability of the rear brakes. Loaded under some conditions your stopping distance has increased while the rear lock up risk is way higher. Stopping sideways before your increased braking distance plows you into something sideways isn't cool.

 

[GM Guy]

All this work to gut a reliable braking system and I bet you still have an automatic transmission.

If simplicity is the cornerstone to all your mods, I would think a manual swap would take precedence over everything else.

I guess call me crazy, but I always thought these had a good brake system. I really dont care how the pedal feels as long as it stops good, and it definitely does that, can lock them up on dry pavement were it not for the ABS.

Ive pulled Numerous trailers without brakes (either inop or never equipped with from new, heres looking at you farm header trailers) and so im putting alot of faith in the trucks brakes, and they do the job great.

ABS is up in the engine bay, dry and warm. unlike the crap location of the GMT800, down in the salt brine. PS cooler to keep from cooking out the hydroboost seals and hoses, unlike the diesel GMT800 which never had a cooler.

Most all of my high miled 6.5Ls are still rocking original hydroboost and steering components, including the 95 with 453K on it. cant say the same about my 06 Duramax, lack of cooler has cooked about everything PS fluid touches.

 

[Bowhunterbrown]

And here comes the back end around the front end. The #1 thing ABS did was keep the rear end IN-LINE rather than stepping out while allowing you to use the rest of the heavily loaded front wheel's stopping power. Unloaded pickups benefited the most. It's something I was reminded of years ago stopping hard in an old school van as the locked up rear started to step out on me as I had gotten used too ABS keeping me in-line.

The next question is what kind of an up-fitter would take the liability and remove the safety features on a vehicle like ABS?

I have had two different close calls, one potentially deadly when ABS system malfunctioned. One awd Toyota previa and one on my 98 suburban. Both vehicles getting up there in age. You could argue it is the owners responsibility to maintain the ABS system. I agree they work as intended if properly maintained, but I see trying to maintain these 25 year old systems as a losing battle. And when ABS malfunctions, it can be incredibly dangerous. But above all else, it is NOT HARD to brake safety without ABS. It's simple, keep safe distances, understand road conditions, and pay attention. I am also the only one that drives my suburban.
And on the Toyota Previa (350k miles by the way), I pulled the ABS fuse the day I almost got killed by that crap, which was about 8 years ago. Has been a pleasure to drive since. Completely rebuilt brakes (Except ABS fuse still out) front and rear last spring and it stops on a dime.

On Mobility modified vehicles: Even with reduced effort braking and reduced or zero effort steering the ABS system stays. This includes hand throttle/brake controls. Additionally a high current electric powered hydraulic pump is installed to keep the power steering working in case of engine stall/failure. Hydroboost systems by design also have power brakes available from the backup pump.

If you are worried about engine stall then an electric backup pump system may be right for you. It's cost installed is likely more than your vehicle is worth with a full tank of fuel. Just saying you have options.

I am not necessarily worried about engine stall, just pointing out that those guys ragging on safety of manual brakes are overlooking the safety issue inherent in hydro boost. Let's face it, engine stall at speed is a real possibility with a 20 plus year old pmd controlled rig.

The removal of the proportioning valve ... This is becoming a safety hazard even on a race track. You are limiting your front brakes to the ability of the rear brakes. Loaded under some conditions your stopping distance has increased while the rear lock up risk is way higher. Stopping sideways before your increased braking distance plows you into something sideways isn't cool.

The suburban I had was all front brake from the factory. Horrible.
With prop valve removed, the difference in line sizes between front and rear, and difference in caliper piston compared to wheel cylinder seem to result in a pretty well balanced system. I can lock them up from 45-50 and she skids to a hault in a very well mannered nature.
I swear, If you guys could drive my rig, you wouldn't be so hard up against this idea of ABS delete or prop valve delete.

All this work to gut a reliable braking system and I bet you still have an automatic transmission.

I have an automatic in the suburban at present yes, but I have an NV4500 out of donor 6.5 truck that will probably go in. I recently picked up a fourth 6.5 (a crew cab, manual) with bad motor. So I am debating which one becomes the simple beast and which one keeps all the comforts.

If simplicity is the cornerstone to all your mods, I would think a manual swap would take precedence over everything else.

I guess call me crazy, but I always thought these had a good brake system. I really dont care how the pedal feels as long as it stops good, and it definitely does that, can lock them up on dry pavement were it not for the ABS.

Yeah, my brakes aren't bad at all. The soft pedal feel doesn't bother me too much, it's more that I got to thinking if hydroboost offers 4x assist and my pedal feels pretty much effortless, then shoot, I could probably handle manual brakes, especially if optimized with some pedal pivot modification, MC bore size change etc.

Ive pulled Numerous trailers without brakes (either inop or never equipped with from new, heres looking at you farm header trailers) and so im putting alot of faith in the trucks brakes, and they do the job great.

ABS is up in the engine bay, dry and warm. unlike the crap location of the GMT800, down in the salt brine. PS cooler to keep from cooking out the hydroboost seals and hoses, unlike the diesel GMT800 which never had a cooler.

My 98 does not have PS cooler. When I resealed the ps pump and replaced some leaky lines I noticed my 96 parts truck had one. I almost swapped it over, but did not. Wish I had because after that, I had some bad tire wear (alignment shop nocked out factory tangs to allow full alignment adjustments, but didn't snug up the upper control bolts enough) the camber crept in slow enough that I had some bad wear on the new tires before I noticed. Anyway, with that camber in and bad wear, I noticed my power steering pump couldn't keep up well in parking lot type driving. Noticed it in the brakes too. Cooked the fluid.

I have got some new front end components going in before I put these new tires on. New power steering pump in hand that will go in when I engine swap soon. Definitely be adding a ps cooler in line at that point.

Most all of my high miled 6.5Ls are still rocking original hydroboost and steering components, including the 95 with 453K on it. cant say the same about my 06 Duramax, lack of cooler has cooked about everything PS fluid touches.

 

[GM Guy]

unless you bought your 98 new, im going to guess that a previous owner deleted it due to a leak or collision damage repair.

Outside of flushing the fluid occasionally which is a good idea ABS or not, im not aware of any routine maintenance that the ABS system requires?

Did that crew cab happen to come from central California?

 

[Stoney]

Just my 2 cents.. I've had nothing but problems with my truck for a handful of years now regarding the braking system. To this day I cannot figure it out, although honestly I don't have the budget to go buy a bunch of new parts at once. For some reason unbeknownst to me my brakes do not always fully release. I'm halfway convinced the hydroboost is not letting all the fluid back out at times. Or possibly something in the gearbox is putting back pressure on the hydroboost.. no clue....
Guys I'm here are going to argue with me but I think putting hydroboost on these trucks was a terrible idea.. a loop system that controls two of your most important functions steering and braking was not smart.. they should be independent from each other at least. If I understand your reasoning for simplicity, have you ever considered adapting the truck to a vacuum booster. Old school design. ?? I'm considering it myself just to separate the two systems but not sure if it would work properly or if the parts could be adapted to these trucks..
I will say I wish somebody on here would have made the suggestion to me a long time ago to use a shorter belt bypassing the power steering pump for diagnostic reasons... I think I'm going to try this myself. Just two ones and for all eliminate the possibility that it is something in the transmission that's causing the drag.

 

[ak diesel driver]

Can't do vacuum booster on a diesel unless you are using a vacuum pump

 

[Will L.]

I am not sure the belt driven vacuum pump produces enough volume of vacuum to operate a vacuum booster large enough for our system. Maybe electric ones could? But you need to know volume and iwc.

You would have to identify the vacuum booster that is big enough, then understand the volume and inches of water column (inverse of pressure) that it requires.

I never thought of it much- but I guess a second power steering pump to run just booster separate from the one running the steering box could be used. Not sure it would help in the diagnosis though.

More directly- having already known and severe issues in the brake system like a pinched off line making one wheel’s brake inactive… anyone recommending bypass for testing is from the dangerous to the insanity danger level. If a guy had a manual 4wd where you can test in low range 1st gear and letting off the throttle automatically slows the truck dramatically- that could lessen the risk. But you were already way into the danger zone.

And keep in mind- my idea of “try it to see” is almost like saying “F around and find out”. You were attempting diagnostic testing. It wouldn’t help you decide which part may be bad. He is thinking of permanent modifications- so for him to see how horrible it will do should show him “This is a bad idea”.

 

[GM Guy]

Just my 2 cents.. I've had nothing but problems with my truck for a handful of years now regarding the braking system. To this day I cannot figure it out, although honestly I don't have the budget to go buy a bunch of new parts at once. For some reason unbeknownst to me my brakes do not always fully release. I'm halfway convinced the hydroboost is not letting all the fluid back out at times. Or possibly something in the gearbox is putting back pressure on the hydroboost.. no clue....
Guys I'm here are going to argue with me but I think putting hydroboost on these trucks was a terrible idea.. a loop system that controls two of your most important functions steering and braking was not smart.. they should be independent from each other at least. If I understand your reasoning for simplicity, have you ever considered adapting the truck to a vacuum booster. Old school design. ?? I'm considering it myself just to separate the two systems but not sure if it would work properly or if the parts could be adapted to these trucks..
I will say I wish somebody on here would have made the suggestion to me a long time ago to use a shorter belt bypassing the power steering pump for diagnostic reasons... I think I'm going to try this myself. Just two ones and for all eliminate the possibility that it is something in the transmission that's causing the drag.

I'd suspect a rubber line failing internally that acts like a check valve, flap of rubber lays flat and lets the brake fluid push past and engage brakes, when pressure is released and fluid begins to exit, rubber flap flops into path of fluid and holds some back.

My unpopular opinion is that the pinch off tools that many shops use and the tool makers swear doesnt damage anything is what causes these hose failures.