Hydro boost woes.....

[Rian_Colorado]

So.... the fun continues!

For the record - Forte Hydro boost. This has a 1" tandem brake master cylinder and a rear bias adjuster. Powered with a GM Saginaw power steering pump on a 427 - SBF. This is a pretty standard setup from Forte. I know many others have similar setups, so not sure what I'm doing wrong, or what I have "not right".

Setup the pushrod after discovering that the brakes would be maybe 15% "on" when motor was running. Got a tool to more accurately measure the internal shaft space. Total interior space was 4.5215. I shortened the shaft by .050 (per Mike), and used a digital caliper to set the shaft to 4.48 total. Re-installed the shaft / master cylinder etc. and re-bled the brakes.

Started the motor up!!.... ****, same problem as before, brakes are still dragging when the motor is on. SO... I start messing with the brake pedal, and lo and behold I can pull the pedal "up" towards the driver! However when I release it, it's like there's a vacuum pulling the pedal towards the floor?

I called the fine folks at Fortes, and they had me swap the high pressure lines from how I'd installed it. I Did that, and while it's "better" It still functions similarly. I can pull the pedal UP with my foot, and the car rolls freely, but after 10 seconds or so - it pulls the brakes on again.

All the while, the power steering seems to work appropriately? I've attempted to bleed the system of air, and I don't see any bubbles in the PS tank when turning the steering or activating the brakes

Long story short... I'm trying to see how others have plumbed their systems. Here are some pictures with labels for how I have the system set up now.
https://thefactoryfiveforum.com/attachment.php?attachmentid=218400&d=1756928911

PS rack:
https://thefactoryfiveforum.com/attachment.php?attachmentid=218399&d=1756928911



Let me know if anyone has things setup differently? or if anyone thinks the problem I've described above is from something OTHER than how it's plumbed?

Project always keeps you learning!
Rian

[canuck1]

I think your plumbing looks OK, as far as I can tell. Different model year sources for the booster and how it's clocked in the firewall can make it difficult to compare directly, but I'm pretty sure it's right. My car uses a Mustang hydrobooster and M/C where the booster is clocked so the reserve/emergency pressure can is mounted more or less on top.

Any chance you have any preload pressure on the pedal itself when starting the car? I know these units are very sensitive to any preload pressure either at the internal pushrod or at the one connected to the brake pedal. Any bind in the pedal movement that could impinge on the pedal's ability to return? Even a subtle bind can cause exactly the problems you're experiencing. Keep in mind some boosters will cause the pedal to rise very slightly at startup. If it contacts anything when this happens (a cross-tube, your foot) it will react as your describing. Other than that, kinks or obstructions in the return line can also lead to similar, hard to diagnose problems.

Sean

[Rian_Colorado]

Thanks Sean!

Forte had a similar thought regarding the pressure. I've triple checked it, and it's "loose" with the motor off, definitely NO pressure on it that I can find. It's not ever hitting the cross tube (where and how I have it set, it mechanically won't come out that far). In fact, when watching the pedal, as SOON as the motor turns over, the pedal moves toward the firewall.... NOT toward the driver (again, there's NO downward pressure on the pedal, It's literally moving in my hand, hanging freely)

What I AM beginning to look at is the output/low pressure side...

I have the output running into a "Y" The other input is the output from the power steering. Then the line runs to a fluid cooler, and finally back to the reservoir. I've noted several other folks systems that are plumbed the same, but now I'm thinking....

I might be getting some cross/feedback pressure on the low side where the Y is. ie - the power steering output "low pressure" is HIGHER than the output "low pressure" from the Power steering, and as such is putting a small amount of "back" pressure on the hydroboost - causing the system to apply a small amount of pressure on the brakes?

I'm guessing the solution is a check valve, or better yet, just dumping the output from the HB to a Y that's AT the reservoir, and NOT going through the cooler with the HB fluid.

Time to order more parts and build more hoses.......

[dbo_texas]

I feel your pain and hope you get it sorted. I've had a lot of difficulties with my hydroboost setup. I have it plumbed similar to yours, except I have the output from the PS pump going to the other port on they hydroboost (I guess like Forte's suggested when they had you swap the high pressure lines). Their install diagram HERE (https://fortesparts.com/technical-documents-instructions/?srsltid=AfmBOopSBx1NcRUuJi8FtzfHUq0-EypEEYgQzPHUigfehJT8cuHu3ta8) doesn't specify, so I'd guess it doesn't matter which of those two high pressure ports you use to connect to the PS pump output.

Here's a detailed diagram how mine is plumbed - using a Y-adapter on the return (from both hydroboost and PS rack), then going to an oil cooler.
https://thefactoryfiveforum.com/showthread.php?40632-ATX-MKIV-9644-Coyote-Build-Thread-(Index-Post-137)&p=573875&viewfull=1#post573875

[Rian_Colorado]

Hey Darryl -

I looked at your diagram a lot when installing mine, and I THINK I have isolated the problem (which COULD be a problem in your system as well if I'm right)

If you look at Canuck (Sean)s Diagram in this thread -

https://thefactoryfiveforum.com/showthread.php?50748-Hydroboost-with-power-steering-questions

you'll see that the diagram suggests that the output from the HB bypasses any connection to the fluid cooler, and directly returns to the reservoir (ie the "Y" is AFTER the cooler in the plumbing).

Both your system and Lidodrips appear to be plumbed with the Y "prior" to the cooler. I'm guessing that because you and Lidodrip both did yours with 10AN setups, that it's JUST enough that you're not having a slight flow restriction or even possibly back pressure fed to the HB unit. Since I did mine with all 6AN fittings, I'm having JUST enough of a restriction that I AM in fact encountering that issue. I ordered a Y connection today to replumb the low pressure return line from the HB directly to the reservoir

What really sold me that this IS the issue, is when I ran the car today, and watched the brake pedal.... the pedal MOVED when I turned the steering wheel from lock to lock (sometimes UP, and sometimes DOWN). NO WAY that should be happening in my opinion.....

This video explains it well - https://www.youtube.com/watch?v=6BReSzs7oec
I wish it had some pics or video to help explain, but if you visualize it while he's talking, you get the idea....

[rich grsc]

Either that or you have an issue with the hydro booster

[dbo_texas]

Hey Darryl -

I looked at your diagram a lot when installing mine, and I THINK I have isolated the problem (which COULD be a problem in your system as well if I'm right)

If you look at Canuck (Sean)s Diagram in this thread -

https://thefactoryfiveforum.com/showthread.php?50748-Hydroboost-with-power-steering-questions

you'll see that the diagram suggests that the output from the HB bypasses any connection to the fluid cooler, and directly returns to the reservoir (ie the "Y" is AFTER the cooler in the plumbing).

Both your system and Lidodrips appear to be plumbed with the Y "prior" to the cooler. I'm guessing that because you and Lidodrip both did yours with 10AN setups, that it's JUST enough that you're not having a slight flow restriction or even possibly back pressure fed to the HB unit. Since I did mine with all 6AN fittings, I'm having JUST enough of a restriction that I AM in fact encountering that issue. I ordered a Y connection today to replumb the low pressure return line from the HB directly to the reservoir

What really sold me that this IS the issue, is when I ran the car today, and watched the brake pedal.... the pedal MOVED when I turned the steering wheel from lock to lock (sometimes UP, and sometimes DOWN). NO WAY that should be happening in my opinion.....

This video explains it well - https://www.youtube.com/watch?v=6BReSzs7oec
I wish it had some pics or video to help explain, but if you visualize it while he's talking, you get the idea....

Uhg....now you got me worried there's a problem with how mine is set up. That Youtube video was helpful. I know Lidodrip has had his set up the same way as mine for several years without issue (putting the Y-adapter before the oil cooler, but using 10AN lines) to/from the oil cooler. I based my setup on his. But I can see where any pressure differential between the rack return and the hydroboost return could create a back-pressure in the hydroboost and mess with your brakes.

[canuck1]

Rian,

If you're correctly diagnosing an issue with impeded return line flow (sounds like that's what you're seeing), the best solution is to do away with the 'Y' junction altogether and add another fitting on to your pump reservoir so the hydroboost return and the return from the rack can both return to the reservoir separately. Many factory hydroboost cars have two fittings on the pump reservoir for exactly this reason. I'm not really a qualified hydraulic guy, but I wouldn't be surprised to find plumbing that works for one guy, doesn't work so well for another. There is undoubtedly some difference in pressure as well as flow between different pumps that could be enough to cause problems for some.

Sean

[Rian_Colorado]

Thanks for the input guys.
Sean, that's literally exactly what I'm planning on doing.

[Lidodrip]

Hello Rian,

Sorry to hear you are still having issues with your hydroboost system.

After I had adjusted my push rod to the correct length, my brake drag resolved and the system has functioned properly. I do not get any movement of the brake pedal when turning the steering wheel (just checked) nor do I feel any effect on steering or braking when doing both together. For all intents and purposes, they feel/behave as two separate systems.

I see two differences between our systems. We have different PS pumps (I have a KRC Coyote direct fit pump) and our return plumbing is different. Provided your PS pump is working appropriately, I doubt there is any reason to think different PS pumps would be an issue. I suspect you are heading down the right path with regards to focusing on the return plumbing. Both of our systems use return lines that Y together before the cooler to form a common return through the cooler and back to the PS pump. As you noted, your system has two 6AN lines coming together with a 6AN common return line and my system has two 6AN lines coming together with a 10AN common line. There is a substantial difference with regards to flow resistance between using a 6AN and 10AN common return line - Poiseuille's Law - http://hyperphysics.phy-astr.gsu.edu/hbase/ppois2.html#tub. Since your common return line is the same size as the two lines feeding into it, you will see a significant rise in pressure in the common return line in order to maintain flow - this may very well be causing your issue. This is not the case with a larger common line (10AN vs 6AN) because it can accommodate significantly higher flows at a given pressure difference. For reference, a 19% increase in radius size results in twice the flow at the same pressure difference. The radius of a 10AN line is approximately 75% larger.

It will be interesting to see what happens when you run separate PS and hydroboost return lines all the way back to the reservoir. If that doesn't solve your problem, then I would assume you have a bad hydroboost unit.

Good luck and keep us posted.

James

[Rian_Colorado]

Thanks for all of the feedback and input guys. Always good to know I'm not crazy!

So the solution worked as I'd hoped. Little plumbing adjustment, and re-making a hose or 2, and the brakes are now functioning as expected. Wondering if any others using this have a firmer pedal feel - thinking I might need to bleed the brakes further (I kinda hate watching pricey brake fluid go down the drain, but stopping IS important, so.....lol)
Ran a Y right at the return port on the reservoir and plumbed the return from the hydroboost directly to 1 side, and the return from the cooler to the other. After thinking about it a while, I'm definitely not worried about the fluid from the HB being that hot - much more of an issue with the steering, so totally happy to not fear any kind of pressure problem potential in my system. Hopefully this thread keeps others from making a dumb mistake later on.

Took her around the block, and had a nice sized grin on my face until I encountered some backfiring, followed by an unwelcome ticking sound. Thinking I have a timing issue (hopefully NOT a bent valve....) No idea how things could go from functioning totally normal, to out of whack that fast....

1 step forward and 5 steps back!

Rian

[danmas]

Damn! Feel you buddy.

[Lidodrip]

Glad to hear the hydroboost issue is solved - sorry to hear about the engine gremlins.

I found bleeding the Wilwood tandem MC a pain because my remote reservoirs are not attached to the MC (like most of the builds here). I had to bench bleed it while connected to my remote reservoirs when I separated it from the hydroboost to adjust the push rod length. Once the MC was bench bled, I found a pressure bleeder worked the best to finish the bleed process (fast and efficient)

Although unrelated to bleeding the brakes, the other thing that was key to proper function, was filing down the lower edge of the clevis that connects to the brake pedal. Without doing that, the pedal would not travel the full distance.

Keep marching on, it will be so worth it when you take your first street legal drive.

James

[dbo_texas]

Rian,
It appears I spoke too soon....I think I'm seeing the EXACT same issue as you. I've had a small leak on my rear brake, so I thought that was causing my pedal issues. But I fixed that this morning and the behavior is the same as you describe. With engine OFF, my brake pedal springs back up (brake lights turn off as soon as I lift my foot off the pedal). With engine running, when I push the brakes, I have a firm pedal and the brakes hold just fine, but the pedal doesn't return all the way up....it's just slightly still engaged (like you said...maybe 5-10% on mine). The brake lights stay on unless I lift the pedal up towards me with my toe. I think what I'm seeing is a pressure differential because of the "Y" adapter. Even though I'm using -10AN lines from the power steering, I think it's still causing issues.

For your fix, did you drill/tap a 2nd port in our PS reservoir (one for hydroboost, one for oil cooler)? Or did you mount your "Y" adapter directly to the PS reservoir and still run both returns to the adapter?

I think the ideal solution would be to add a 2nd port on the reservoir and just not use the Y-adapter at all. But in my setup, I'm using the KRC Coyote pump/reservoir and I don't want to drill into it. Even if I stick with a "Y" adapter I'll need to find a new one...the one I'm using now has two -6AN inputs and one -10AN output. If I move the adapter and mount it directly to the reservoir, I don't see how that solves the issue...as I'd have a -10AN return (from oil cooler) plus -6AN return (from hydroboost) going into a single -6AN port on the reservoir. Seems like a bottleneck still.

[CraigS]

I have no direct hydroboost experience so these are just some shot in the sky thoughts. What type of brake switch are you guys using? Does the pedal have to compress a spring pushrod to turn off the brake lights? Is there adjustment on the brake switch? Over the years I have had to adjust several brake switches to get things working correctly. I have also had to add a brake pedal return spring to assure that the pedal came up far enough to push against the brake switch. On FFRs it has also been somewhat common for the brake pedal arm to hit a cross tube as it comes up so the pushrod to the MC had to be adjusted shorter. While my experience is w/ vac boosters I know that there are two pushrod clearance specs. Pedal to booster and booster to MC. The second one can be a real pain to adjust. It's internal and usually needs some type of depth reading micrometer/caliper. If either of these clearance specs goes to zero the system doesn't work properly.

[dbo_texas]

I have no direct hydroboost experience so these are just some shot in the sky thoughts. What type of brake switch are you guys using? Does the pedal have to compress a spring pushrod to turn off the brake lights? Is there adjustment on the brake switch? Over the years I have had to adjust several brake switches to get things working correctly. I have also had to add a brake pedal return spring to assure that the pedal came up far enough to push against the brake switch. On FFRs it has also been somewhat common for the brake pedal arm to hit a cross tube as it comes up so the pushrod to the MC had to be adjusted shorter. While my experience is w/ vac boosters I know that there are two pushrod clearance specs. Pedal to booster and booster to MC. The second one can be a real pain to adjust. It's internal and usually needs some type of depth reading micrometer/caliper. If either of these clearance specs goes to zero the system doesn't work properly.

Thanks Craig. I've taken the hydroboost apart when I first got it and messed with the pushrod length until I got it dialed in per Forte's instructions. There is a very small gap between the pushrod and the master cylinder so I'm pretty sure I'm good there. I have the threaded rod going to the brake pedal arm adjusted so that the pedal arm is about 1/8" off the 3/4" frame tube when it's all the way toward the driver so there's no interference there. That is a major pain to adjust because it's super hard to turn that threaded rod (Forte just welds a bolt to the pushrod and there are no flats to grip). But I don't think that's the issue. My brake switch is the stock FFR switch switch...so yes it has some adjustability. I can pull it back so that it isn't "ON" when the brakes have a slight engagement. But I don't know that I want to do that. There's definitely some amount of pressure being applied to the brakes because with the car up on jack stands, engine off and in neutral, I can turn the rear wheels with my hand easily...but if the engine is running and I apply the brakes and then lift off, the brakes are still slightly engaged. I can turn the wheel but is is MUCH harder than before I cranked the engine. So some pressure is applied. The pedal also doesn't lift back all the way up on its own (hence the brake light switch still getting triggered). This just feels wrong.

Maybe just running the car will wear the pads down a bit so that they aren't gripping in this condition but I'm just not sure. What is telling is that is only does this with the engine on. If I kill the engine, the brakes are perfect (no pressure and the pedal springs back up). I suppose I could do as you suggest and add a spring to "lift" the pedal back up. Is that normal though? I've never heard of any builds needing something like that.

[CraigS]

I don't know if you would call a return spring normal or not but it would be worth a try. I used something similar to a carb spring and tied the end to something w/ a wire tie. That way I could adjust by tightening the tie to get just the right tension. Once the distance was worked out, then I made a metal bracket and drilled several holes for further adjustment if needed.

[Nigel Allen]

Can you take a look at a car with OEM hydro boost, or an exploded parts diagram. Perhaps a return spring is fitted on OEM installations?

I don't have any cars with hydro boost, but my daily drivers have a spring to hold the pedal at rest.
Good luck,

Nige

[CraigS]

I just checked our 2021 Honda Pilot. Sure enough it has a substantial brake return spring.
219178
As I was filing this pic on my PC I came across a shot that shows the one on my MkII FFR.
219179

[dbo_texas]

Thank for checking (and the suggestions). The hydroboost itself has a spring in it which should in theory push the pedal towards the driver seat - you can see it in the picture below. If what I'm interpreting as a very small vacuum force on the master cylinder is stronger than the force of this return spring, the brakes will stay engaged. I'm guessing that by adding and extra spring to the pedal, this would overcome the vacuum force and "pull" the pedal toward me, releasing the brakes in the process. I suppose it's worth a try....I should be able to very easily rig something up just for the sake of testing, then decide how to fix it permanently. Before I do this, I think I will first try changing my power steering plumbing and put my "Y-adapter" after the oil cooler instead of before it like I currently have.

Ignore the numbers....those were measurements from when I was adjusting the pushrod length (in my build post #95 (https://thefactoryfiveforum.com/showthread.php?40632-ATX-MKIV-9644-Coyote-Build-Thread-(Index-Post-137)&p=509214&viewfull=1#post509214)).
https://thefactoryfiveforum.com/attachment.php?attachmentid=175207&d=1668896798

[canuck1]

While it was common on many hydroboost vehicles (mostly diesel trucks) to have 2 return ports on the reservoir, Ford didn't bother for the 1996 Mustang Cobra. They simply used a 'T' which you can see underneath the reservoir in the attached diagram:

219195

I always recommend the 2nd return port on the reservoir when it's simply a factory style plastic tank because it's easy to do and eliminates most return flow issues. I just wanted to note that Ford didn't always see this as necessary. It CAN work with an inline 'T', provided it's plumbed similar to this diagram. My roadster's worked fine this way since 2005.

Sean

[dbo_texas]

While it was common on many hydroboost vehicles (mostly diesel trucks) to have 2 return ports on the reservoir, Ford didn't bother for the 1996 Mustang Cobra. They simply used a 'T' which you can see underneath the reservoir in the attached diagram:

219195

I always recommend the 2nd return port on the reservoir when it's simply a factory style plastic tank because it's easy to do and eliminates most return flow issues. I just wanted to note that Ford didn't always see this as necessary. It CAN work with an inline 'T', provided it's plumbed similar to this diagram. My roadster's worked fine this way since 2005.

Sean

Thanks for the inputs here. I'll give this a try and re-plumb my hoses, then report back. I just need to buy a few new adapters (already have the correct hoses).

[dbo_texas]

Well I didn't re-plumb my return line & y-adapter yet...haven't had the time. But in the meantime I did try 3D printing a little bracket so I could mount a spring on the brake pedal arm. I've been reading that this might not be the best idea and is most likely a band-aid fix for the real problem (likely culprit is pressure imbalance). But I wanted to try it anyways...so far seems to be working. I plan to still do the re-plumb and move the Y-adapter to after the oil cooler, but for now this seems to have done the trick. The brakes fully release after letting off the pedal. More details on my build thread post #335 (https://thefactoryfiveforum.com/showthread.php?40632-ATX-MKIV-9644-Coyote-Build-Thread-(Index-Post-137)&p=593257&viewfull=1#post593257).

https://thefactoryfiveforum.com/attachment.php?attachmentid=219908&d=1759936276


https://youtu.be/1JMMjdKw6CU