S10 Swap how to

[dsraven]

I use a bleeder like the lisle tool I got from princess auto. I use a nylon cable tie to ensure the hoses stay put and then place a longer section of clear urethane hose on the inlet and outlet, with the cable ties in place, on each hose so that the little bottle can become overfull and the fluid will simply drain down the extra hose instead of spray straight up out of the exit hole. you can buy different colored urethane hose, which is way more flexible than the vinyl hose that comes with, so you will easily know which hose is the inlet and outlet at a glance. I 1/2 fill the bottle, place that whole thing into an old coffee can so any spills or overflow will be contained. it is cheap, clean and works well for bleeding by yourself. when done, spill out the overflow, put the lid on the can and it is easy to store so dust and dirt stay out. I do enough brakes, usually, so I don't worry about draining, cleaning everything out etc but if you are just doing a single vehicle then it is good to clean it all up with brake clean and put it away.

[dsraven]

https://www.princessauto.com/en/brak...t/PA0002991081

you couls easily build one with an old pop bottle that would do the same thing. use hose that fits tightly over your bleeder screws heads. don't back the bleeder screws out too far or they will become air leakers through the threads of the screws.

[dsraven]

you can usually get a large bore syringe from a farm supply store or a feed supply outlet.

[Father&son56project]

Joedoh:

I used the tube in the jar method on all wheels, and also gave it a shot using a vacuum pump, but the problem persisted. After bleeding the system numerous times, there were absolutely no bubbles coming out but the pedal problem persisted. There are no leaks and I am not losing fluid from the reservoir, so this led me to suspect a master that was leaking internally at the seals. Rockauto had a clearout sale and I got a brand new one for under 22 bucks Canadian (about ¼ of what that same unit costs up here!).

Dsraven:

The new master is still sitting here in it’s box. I will definitely bench bleed it first, and based on your comments I suspect that it is in fact a step bore style. The manufacturer was very very clear about using their recommended bench bleeding system for step bore master cylinders (but they don’t bother to tell you what type they are selling you!). They include a video as well that shows the 2 ways to do it (either with a syringe (the fast way) or with a dowel (the slow way). I deleted the ABS (so no hidden bubbles there), but everything else is stock 1996 S10, including the routing of all lines.

I will post the results when I’m done. Thanks for the quick replies!

[dsraven]

a pedal that, when applied and held with equal pressure continued, slowly goes to the floor with no external leaks indicates an internal leak in the mastee cyl. good job diagnosing.

[Father&son56project]

Well, the brake situation is no better (and possibly a bit worse!). I replaced the master cylinder with a new one, and I followed the bench bleeding instructions very carefully. I also installed 2 new rear wheel cylinders as the old ones required way too much force on the bleeder screws to get them to properly seal. I bled the system again, and with the engine off the brake pedal is rock hard. Once I start the engine however, the pedal is mushy and sinks pretty much all the way down. With the old master cylinder I initially had a fairly firm pedal that sank slowly. With the new master I now have a mushy pedal that sinks fairly quickly. I was very careful with the bleeding process, following the correct order and opening the bleeders just enough to allow fluid escape, but not so far as to allow air past the threads.

There is however one weird thing going on. At the end of the combination valve there is a small rod that comes out and moves towards the firewall when firm pressure is applied to the brakes with the engine running. Here are 2 pics. The first shows where that rod is, and the 2nd shows the direction it goes under firm brake pressure (the direction I am pointing with my finger).











If anyone has a good diagnosis of my issue, I’d welcome it! No offence to all the well meaning members, but no wild guesses please. I’m at my wit’s end chasing down this mushy pedal.

Thanks!

[dsraven]

The combi valve has an automatic cut off in the case that one circuit of the brakes blows out and you have a major leak. You will likely need to center that internal valve located where the electrical part is. There is a tool used to keep the valve centered when you bleed the brakes otherwise the valve moves and closes one circuit. Google how the combination valve works and how to reset it, then try your brakes again

[dsraven]

It may be called a proportioning valve, combination valve or something else but either way there are a few good YouTube's on the subject. A few explain how they work. It is important to have the master cyl outlets plumbed correctly as well. Joedoh would be a good source for that or you could check an S10 at the wrecker or similar idea.

[dsraven]

One other thing to check, maybe you have already, is to ensure the pushrod from the booster to master has a little Freeplay so the master piston is allowed to fully retract. It would mean pulling the master away from the booster enough to do the pushrod length from the master mounting surface on the booster and likewise checking the depth of the depression in the master piston where the pushrod "pushes". Then compare the two. Should be a little play there.

[dsraven]

have you checked the booster for a vacuum leak or possibly a bad vacuum check valve at the booster?
pull the check valve out of the booster, disconnect the vacuum line and do a test to ensure it allows vacuum to flow one way and absolutely nothing goes back the other way
assemble the valve back to the booster like it was. now do a vacuum test on the booster to see if it holds a vacuum. simply apply a vacuum to the check valve and monitor to see if it drops in vacuum and listen for any air leaks at the inside of the truck around the booster pushrod, also around the grommet for the check valve.
question, engine idling, apply the brakes. does the engine rpm change at all? like it had a sudden vacuum leak to make up for?
is the pushrod from the pedal set up with some freeplay so as not to apply a slight pressure to the booster pushrod which would unseat the internal valve and "leak" vacuum?
maybe google how a vacuum brake booster operates for a little more theory on what could go wrong

[Father&son56project]

Dsraven:

Thanks for the suggestions! I ordered one of those tools to lock the rod in place during bleeding (but it’s a 10 day delivery). My combination valve appears to be the self centering type. As soon as you let off the brake, the rod returns to its normal position by itself. I tested the sending unit without any force on the brake pedal and there was no continuity (in other words the valve had self-centered and didn't activate the brake warning light).

As for the lines, my system is correct, and the lines follow the same paths as a stock ‘96 S10 does (It’s simply an S10 surrounded by an old body. It even has the S10 brake pedal assembly in it). The only difference is the ABS delete.

I have not yet checked the gap in the rod that sits between the booster and the master cylinder, but the booster/master combo was working when I bought the S10 and I had kept the pair bolted together when I disassembled the S10 so there shouldn’t be an issue there (but it’s not a difficult thing to check).

My engine idle does not change at all when the brakes are applied, and there are no obvious vacuum leaks (but I ran out of time and didn’t get to properly checking the booster and valve for a leak). I did however do some googling this eve, but what I found suggests that a vacuum leak in the booster would result in a hard pedal (my problem is the opposite). I will check it as you suggested anyhow, just to be safe.

The feeling I get when I press on the pedal is what you would expect if there was some air in the system. Given the lengths I have gone through to bleed this system, that pedal should be rock hard.

The saga continues!

[dsraven]

the booster to master pushrod gap could change since you have installed a new master cylinder, correct? not everything is equal and built exact so it is one thing to check possibly. while checking stuff, ensure te
he pedal to booster pushrod has some freeplay as this can mss with the booster operation if the valve inside the booster isn't centered. how do the calipers look. you say you replaced the rear wheel cylinders but have you checked the front calipers and their moving parts to ensure they are not getting hung up or are partially siezed? a good indicator of this is a set of brake pads that are worn more on one pad than the other. if the caliper slide mechanism is not allowing the caliper to slide then that could mess with the pedal feel between boosted or manual. another question for you is whether or not the master cylinder you removed due to an internal leak causing the slow drop to the floor, did it also leak some fluid out the rear of the master where the bore is? if so, some fluid may have made it's way into the booster and could cause problems. is your booster a dual diaphram type or a single diaphragm? singles are usually a larger overall size.
I removed a booster once that drained quite a bit of brake fluid out of the vacuum check valve port. this was caused by a leaky master cylinder at some point.
here is a link to some basic vac booster diagnostics.
https://axleaddict.com/auto-repair/B...-Booster-Check

[dsraven]

can you explain how you bench bled the new master? did you use a syringe and pressure bleed fluid back into the master cyl from the outlets? step bore masters can be a little tricky to bleed and that is usually the recomended way, reverse bleeding.
if you feel the master cyl was bled correctly with no room for air in the system anywhere, and the combi valve is centered allowing fluid to pass to both the front and rear circuits, and the brakes are all free moving with no sticking caliper slides etc, and the rear drums are adjusted properly with the park brake also adjusted properly, then it would seem to point the finger at the booster. a rock hard pedal with the engine off is a normal thing because the master cylinder for power brakes uses a larger bore size than a manual brake set up would so it normally requires more pedal effort. a spongy pedal only with the engine running suggests a possible issue that only rears it head with the added pressure that comes with the booster in play, like a poor brake hose or some other fault downstream of the master, or a booster issue. I would say check all the brake components like hoses, caliper slides, pads that may be hanging up, calipers for a sticking piston, wheels that don't spin freely (front wheels) brake shoes that are not adjusted properly etc. then check all the linkages from the pedal through to the master cyl pushrod. since we have to assume the booster functioned properly when it was in the S10 and the only difference is that it got moved to the old truck and the pedal system geometry may not be the same exactly or it maybe simply got bumbled around a bit and possibly a seal is not sealing like it should or a pushrod is bent etc etc. this is aside from removing the abs pump and changing the master cyl. arethere any brake line loops that may hold an air pocket? do the rubber lines swell when the brakes are applied with the engine running (when more line pressure can be had). there is a seal behind the master cylinder, do you recall if it was still in good shape? sometimes they can adhere to the master cylinder and become dislodged when the master is changed creating a leakage situation. there is also a seal at the pushrod from the pedals which usually also has a filter over it. maybe check that end as well. ensure the pushrod has a straight shot from the pedals so it isn't being forced out of alignment as the pedal is depressed as this can possibly unseat the booster valve which would cause constant boost and draw the pedal down and may also cause leakage issues. the booster you have is a dual diaphragm style I believe so there is twice the possibility for an internal leak I suppose. the booster is basically a pushrod that goes straight through to allow a link from the pedal to the master. it has the diaphragm in the middle, sealed in the can with vacuum applied to both sides. when the pedal is slightly moved forward there is a valve that unseats and allows atmosheric pressure onto the pedal side of the daiphragm. this makes the vacuum on the other side of the diaphragm want to pull the pushrod towards the master cyl which assists you to push the pedal down. when you hold the pedal at a given spot in the travel the valve seats and holds that differential of pressure on both sides of the pedal. with this in mind it kinda makes sense that possibly something is not quite right inside the booster, maybe there is a misaligned or slightly bent pushrod, a sticky internal valve, possibly brake fluid inside the booster has deteriorated rubber parts, possibly some dirt got inside the booster somehow? anyway, just some thoughts and ideas on things to check. I suppose you could also try reverse bleeding from each wheel but that requires a special tool, although some have made their own using a simple pump garden sprayer. you could google that. I think a reverse bleeder is available on amazon.ca for around a hundred bucks CAD.
https://www.brakebleeder.com/solutio.../how-it-works/
https://www.brakebleeder.com/solutio...eding-methods/

[dsraven]

https://www.amazon.ca/Motive-Product...0CJ5DV2I&psc=1

[dsraven]

something like the amazon bleeder would be easy to build yourself with princess auto parts. the reverse bleed. not too much worry that you would get crap from the calipers etc flushed back into the master cylinder since you have already flushed a whole bunch of fluid through the system already by the sounds of it.
just a thought, in case there is air in the system someplace. sounds like you have a hard pedal with the engine off though so things are kind of pointing towrds a booster issue
keep us posted onany new findings

[Father&son56project]

Some updates…..

My neighbour came over to give me a hand, which is good as he has been a licenced mechanic for 60 years. Yup, 60! Prior to him coming over I had done a bunch of things myself as well. Here is where I stand:

-Good vacuum from engine to power brake booster
-Good hose from engine to booster
-One way valve that connects hose to booster working properly
-Booster functioning properly (used the Axle Addict link, awesome guide!)
-All lines checked (despite them all being new-just in case). No problems, no ballooning of rubber lines, no weird loops where bubbles could get trapped (it’s the stock S10 routing)
-Entire system and every fitting checked-no leaks whatsoever
-Rear brakes checked, they are good (look to have been done fairly recently), properly adjusted and they function properly
-Parking brake checked-properly adjusted, functions properly
-Front brakes checked-functioning properly, movements are smooth, nothing sticks, pads are thick and wear is even everywhere
-Pedal assembly checked-nothing bent, no binding. A section of the S10 firewall had been transplanted, so the alignment of booster to pedal assembly was never changed (it’s again a complete, stock S10 assembly)
-The newly installed master cylinder was measured and checked against the old master cylinder-identical measurements obtained
-The seal where the master cylinder meets the booster was checked-looks good and it’s bone dry
-The seal/filter where the brake pedal rod enters the booster was checked-looks good and is dry
-Gap checked where brake pedal meets rod-all good, at rest there is a small gap so the pedal is not applying force to booster
-Gap checked where booster rod meets master cylinder-all good, there is a small gap there as well so the booster is not applying force to the master cylinder

Now it gets interesting. My mechanic neighbour told me to drive it around for a while, so I did. My laneway is long, and there is one very steep section, so I was able to apply brakes while steeply inclined both up and downhill, and on level ground. Once that was done there appeared to be some improvement however this test is really subjective. I hopped into my Honda and did the same and realized that under normal driving they both feel quite similar. There is of course still one problem to address……

That rod in the combination valve still moves backwards (towards the firewall) everytime the brakes are applied. Can air get stuck in that valve? It doesn’t matter if the engine is on or off, it moves every time you press the brake pedal. So my plan is this:

I have ordered the little device that locks the combination valve in place during bleeding and will have it next week. At that point I will use it and bleed the brakes again. If I’m lucky it will do the trick. If not, I will try a reverse bleed. If that is unsuccessful I will get some plugs for the various ports and I will isolate the front and rear brake systems for further testing. By this I mean I’ll seal off the front system and see how the brake pedal responds, then seal off the rear and do the same. I believe I’m closing in on a solution, and I will post the results.

Thanks again for all the help!

[joedoh]

Originally Posted by Father&son56project

That rod in the combination valve still moves backwards (towards the firewall) everytime the brakes are applied. Can air get stuck in that valve?

UGGH yes, I am just now reminded because of your question of the time I spent a week diagnosing soft pedal on a mazda truck, had the same combination valve. I bled it and no more problems.

and FWIW I call that valve a safety valve that keeps pressure on the fronts ig the line to the back rusts, and have not seen a benefit to even keeping it in the system. maybe it was for modulating the input to the ABS system but I run my lines straight to the brakes, no valve, take it out. I have probably 10 you can have for free if yours is broken somehow. (kidding)

[Tempest67]

and FWIW I call that valve a safety valve that keeps pressure on the fronts ig the line to the back rusts, and have not seen a benefit to even keeping it in the system. maybe it was for modulating the input to the ABS system but I run my lines straight to the brakes, no valve, take it out.


Really ??? I did not know that. I thought it was some kind of proportioning valve that was needed.......... I am now thinking of removing mine.

[joedoh]

it isnt a proportioning valve and even if it was, the configuration of my truck is completely different than a stock s10, motor moved back, cab moved back, it wouldnt be appropriate without adjusting anyway.

but the ones i have seen are safety valve so if you lose pressure on one end it locks to the other so you dont keep pumping fluid out the broken line/cylinder/hose. thats why it needs the spring in the middle. from a manufacturers liability standpoint, some people keep driving even with an obvious problem. that electrical connection sets the "brake" light on the dash

[dsraven]

maybe you could lose that valve and install an appropriate comination valve. it is a good idea to have something that will seperate the front to the rear in case of a blown line or some other brake emergency.

[joedoh]

Originally Posted by dsraven

maybe you could lose that valve and install an appropriate comination valve. it is a good idea to have something that will seperate the front to the rear in case of a blown line or some other brake emergency.

the s10 has this already, there is a 5 degree rearward tilt on the booster so the bulk of the fluid is biased to the front brakes (the rear chamber of the reservoir), and a slotted divider in the middle so if you lose either one of the dual circuits there is enough to get stopped on just the remaining circuit.

that valve is EXTRA security on top because (some) people are dumb and ignore problems, some will dump fluid in when they see the BRAKE light come on and the safety valve keeps them from just pumping it back out instead of investigating. I have seen rotorless brake discs because some people just metal-to-metal grind it completely away.

[JayB22]

I’m hoping someone can help me out with this. I’m trying to exhaust all efforts on keeping my 4wd drivetrain before ditching it to a 2WD setup. Sounds like when doing a sbc swap you need to move the engine back approx 7”. I’m doing so the transfer case hits a cross member. I’m looking at my frame and noticing that the cross member that it hits isn’t the one that is structural for the torsion bar suspension. It’s just a crossmember that seems to hold the skid plate on. I’m wondering if I can take this out and re mount it behind the cross member that holds the torsion bars in place? I here’s a fuel filter in the area that can be worked around. But also I have a cross member for the torsion bar suspension and a cross member for the 2 pc drive shaft about 16” behind it. Having both of these in place makes me wonder why I couldn’t just completely remove the skid plate cross member unless it’s for support for side to side movement on the top of the frame. But if that’s the case I could brace between my cab mounts and a brace across for the box mounts to make up for a his. I’m just hoping I can find a way to make this all work before ditching everything I have and starting over.

[joedoh]

it doesnt tie to the torsion crossmember on the bottom?


i found a picture of what i think is an EZ Chassis for a 4x4 s10, he notched it.

[JayB22]

Theres zero contact between that brace and the cross member that holds the torsion bar on. It also doesn’t touch the torsion bars in anyway. It has holes in it for the ebrake cable and for the torsion bars to go through. But it has no effect on them.

[joedoh]

neat. keep in mind though, as you cut, that the entire weight of the front half of the truck is carried right there in that couple inches of frame.