Hydroboost pushrod angle, teardown and questions

[ksagis]

I was continuing on my journey on digging deeper into brake systems and finally got to the teardown of the hydroboost that I got from @catfan (not a Bosch, just a random unit to learn from), poked around on my pedal travel, and spent time looking a cutaways of hydroboosts online.

I'll start with some specifics on my rig: the hydroboost is a Bosch unit from Hydratech and is mounted directly on firewall (no offset bracket or bellcrank, I think maybe @toddz69 worked with Hydratech for the development of this design). The brake pedal adjustment turnbuckle goes into directly into the hydroboost. There is about 7 degrees of angle built into the firewall bracket to clear the EFI, so this results in about 7 degrees lateral angle on pedal pushrod to hydro input. On the output of the hydro to MC, I machined a hydro to MC pushrod to minimize the gap between the hydro and MC cup, maybe a max of 0.020" of gap there.

With engine off, there is about 0.5" of virtually no resistance to pedal movement, then maybe another 0.25" of travel that feels like compressing a spring, with continued pedal pressure feeling like its building hydraulic pressure in MC (these numbers are at pedal, which translate to approx 0.083" and 0.041" at hydro input shaft, so it's actually not a lot of travel at the hydro). I have all the bushings on the pedal shaft and the pushrod eyelet, so there is virtually no slop in the brake pedal going into hydro - I can see movement at the pedal translating to movement at the input shaft.

Now to questions:

1. Does anybody have a working HB on the bench that they can press input shaft to see if that directly translates into movement at the power piston?
2. When people adjust their linkage, do they take out the initial free play in the hydro, or do they set the adjustment rod with the hydro fully relaxed? I feel like its safest to have it fully relaxed but curious what others are doing? (I'm going to check if this is same with engine running later today)
3. Does anybody know if the part number for the Bosch HB with a threaded input shaft? @Apogee comments here about removing the collar and swaging it back on, has anybody done that and can share more details?
4. I've asked this before and can't tell if it's internet garbage or truth - any knowledgeable opinions on off angles wearing out the hydro input shaft seals significantly faster? My gut opinion is small angles aren't significant, i.e. 7 degrees at 20 lbs of pedal pressure is about 15 lbs of side load on hydro). @jamesroney configured a system with about 5-7 degrees here so didn't seem to worry him much and clearly Hydratech thinks its okay since they have 7 degrees of off angle. Todd has commented that he periodically notices weeping in that area, even for straight line action setups.

P.S. If I was guessing, the initial range of no resistance would be compressing the light spring on the output of the power piston and the second range of higher resistance is compressing the spring on the input rod to activate the spool valve. But that would say I was way off on setting my gap to MC and just don't think I was at 0.083" when I custom fitted to make it less than 0.020". Maybe the 0.083" is a combination of the roughly 0.020" of gap, plus covering up the transfer ports in the MC, but even that seems like a lot.

 

[bigmuddy]

If I might ask, where did you get the firewall mounting bracket?

 

[ksagis]

If I might ask, where did you get the firewall mounting bracket?

Comes with Hydratech kits

 

[ksagis]

Well, poked around internet and couldn't find a Bosch PN with threaded rod, did find the debuild instructions for Bendix (think same as Bosch?) HB that references a stupidly simple tool to just pry it out.

This threaded input rod might fit in place of removed input rod.

 

[catfan]

Well, poked around internet and couldn't find a Bosch PN with threaded rod, did find the debuild instructions for Bendix (think same as Bosch?) HB that references a stupidly simple tool to just pry it out.

This threaded input rod might fit in place of removed input rod.

That h-boost I sent you I tried to to get that rod off but had no luck. I tried putting it in a vise with push rod hanging
down and put a rod through the hole and used a hammer . I didn't want to mess it up so I gave up . I saw that tool
mentioned on a Chevy forum I think .

 

[EPB72]

Another option for #3.. cut off the pedal loop off the input rod and thread the end 3/8 24 is what worked for me,, with the loop gone you will be able to remove from housing and install seal on input ..you will have to make a seal installer it’s a stretch fit cup type seal ,, ,,, I made my own firewall bracket it’s straight off firewall works for me.. the HB unit came off a customers 06 2500 GMC 6.0l. HD was leaking on the output side and the replacement was a new unit from the dealer so no core,, resealed with pirate jack kit works great .

 

[ksagis]

That h-boost I sent you I tried to to get that rod off but had no luck. I tried putting it in a vise with push rod hanging
down and put a rod through the hole and used a hammer . I didn't want to mess it up so I gave up . I saw that tool
mentioned on a Chevy forum I think .

That tool is stupid expensive on Ebay for an original one, there might be a market for a reproduction of it.

I tend to think a prying motion versus an impact from hammer would be more effective in removing it. There are some notes in the debuild paper I posted about sometimes needing to rework the collar post reinstall ala the comments from Apogee in the linked thread. I couldn’t find any replacement swage collars.

 

[ksagis]

Another option for #3.. cut off the pedal loop off the input rod and thread the end 3/8 24 is what worked for me,, with the loop gone you will be able to remove from housing and install seal on input ..you will have to make a seal installer it’s a stretch fit cup type seal ,, ,,, I made my own firewall bracket it’s straight off firewall works for me.. the HB unit came off a customers 06 2500 GMC 6.0l. HD was leaking on the output side and the replacement was a new unit from the dealer so no core,, resealed with pirate jack kit works great .

Good advice, from glancing at the rod it wasn’t obvious to me the diameter would support the major of a 3/8 thread. Will look again tomorrow.

That looks like a GM MC, would you happen to know the width of the MC bolt pattern? There’s a bazzlion Bosch PNs and for the life of me I can’t tell the difference in them (other than maybe the mounting plate)

 

[toddz69]

Good advice, from glancing at the rod it wasn’t obvious to me the diameter would support the major of a 3/8 thread. Will look again tomorrow.

I think the booster you have might be the one that I sent to @catfan years ago? I'm not sure. But yeah, in any case, it's a Super Duty unit and you can cut the eyelet off and thread the pushrod. I've done that with several myself. Not all the pushrod diameters support a 3/8" thread but the SD unit do.

That looks like a GM MC, would you happen to know the width of the MC bolt pattern? There’s a bazzlion Bosch PNs and for the life of me I can’t tell the difference in them (other than maybe the mounting plate)

If it's GM, it'll be 3.4" bolt pattern. Fords and Chryslers for the most part are 3.2". Handy mnemonic - I always think of '32 Fords (3.2") to remember the bolt spacing.

Todd Z.

 

[Madgyver]

my angled astroboost

 

[Glass Pony]

Here's my HB kit with the 351 spec. from Hydratech. The bracket is angled some for clearance.

 

[EPB72]

I think the booster you have might be the one that I sent to @catfan years ago? I'm not sure. But yeah, in any case, it's a Super Duty unit and you can cut the eyelet off and thread the pushrod. I've done that with several myself. Not all the pushrod diameters support a 3/8" thread but the SD unit do.


If it's GM, it'll be 3.4" bolt pattern. Fords and Chryslers for the most part are 3.2". Handy mnemonic - I always think of '32 Fords (3.2") to remember the bolt spacing.

Todd Z.

Correct its a Camero MC with the wider bolt pattern,,,,,,, the spacer to rotate MC/HB 90 degrees and output pushrod came from if I remember Tallon,, that kent moore tool if a remember correctly there was another piece to it there is also a tool for redoing the swedge.

 

[ksagis]

Per question 2 above, the pedal is definitely different with engine running than my notes above, with the engine running, the pedal feels the same for about one inch of travel. And after thinking about it a bit, unless the pedal is backed up to a stop, increasing the length of the pushrod is only going to raise the pedal versus apply any pressure to HB input shaft.

Question for @EPB72 and @Glass Pony, I'm assuming the reason you clocked the HB 90 deg CCW (accumulator at 11 oclock) is to get better access to the lines? Only reason I can see since then you need to use the adapter at MC to get back to horizontal MC posts.

EPB72, not sure what you mean about making a seal installer tool, from looking at my debuilt unit, the seals look like a simple soft good type seal that I expected one could slide over the input shaft. Is the tool to only protect the seal during install, or something else to expand, etc?

 

[EPB72]

Per question 2 above, the pedal is definitely different with engine running than my notes above, with the engine running, the pedal feels the same for about one inch of travel. And after thinking about it a bit, unless the pedal is backed up to a stop, increasing the length of the pushrod is only going to raise the pedal versus apply any pressure to HB input shaft.

Question for @EPB72 and @Glass Pony, I'm assuming the reason you clocked the HB 90 deg CCW (accumulator at 11 oclock) is to get better access to the lines? Only reason I can see since then you need to use the adapter at MC to get back to horizontal MC posts.

EPB72, not sure what you mean about making a seal installer tool, from looking at my debuilt unit, the seals look like a simple soft good type seal that I expected one could slide over the input shaft. Is the tool to only protect the seal during install, or something else to expand, etc?

Correct on the HB clocking,, thers also an install tool but made my own tool, used an old marker housing and made to fit the seal is soft seal but prone to rolling if . So tool is tapered and you get the seal up into position just to the edge with tool at groove in input U just have nudge it to drop in ,,

 

[ksagis]

Few more bits of info in case helpful to others downstream.

To my knowledge this was a SuperDuty unit that went from Todd, to Catfan, to me. Looks to me the outside of this unit looks different than the Bosch units typically sourced by the vendor and HBs from Astros, Mustangs, etc, others may have better eyes.

It's definitely a bit of a pain to press the eyelet out of the input rod swage area, if I was going to rebuild a HB, I'd cut the end, thread, and use a turnbuckle. Feels like it might be easier, less prone to workmanship on a critical part, and give some future flexibility.

EPB72's advice for the input seals replacement technique is excellent, when I first glanced at them, I thought they were orings, but they are cup seals. They are a annoying to work without a tool like he suggests.

The input rod OD is 0.350" in the second section, and 0.500" in the last section (right before eyelet).

One can replace the accumulator alone if it has leaked done without replacing the entire HB by removing the snap ring. You can see it removed in one of the pics.

If anybody knows what vehicle to source a HB with a threaded rod already in place, etc, I'd love to know a vehicle or PN. Doesn't seem like all the vendors would be swapping the input rods after taking them into stock so feels like they aren't unicorns.

 

[ntsqd]

One of the things that I noticed in the cut-away drawing above is that the input push-rod enters the main shaft thru a bit of a funnel. That is to say that the designer limited the max operating input rod angle. They likely had a good reason for doing that and I expect that so long as your system doesn't exceed that max angularity that it's good to go.
That's assuming and inline loop. Not sure what to think of the offset loop supplied in my FSB's H-B conversion kit.

 

[Glass Pony]

Question for @EPB72 and @Glass Pony, I'm assuming the reason you clocked the HB 90 deg CCW (accumulator at 11 oclock) is to get better access to the lines? Only reason I can see since then you need to use the adapter at MC to get back to horizontal MC posts.

That's the way it was clocked from Hydratech. It worked the way it was with my application, so I went with it.

 

[bmc69]

cut the eyelet off and thread the pushrod. I've done that with several myself.

Todd Z.

that's what I've done to nearly my hboost units.

 

[ksagis]

I connected a couple of brains cells after looking at the parts some more and thinking about @ntsqd post above. I never understood why some of the push rods have the offset hole since it doesn't actually change the line of action and eliminate the side force. I think what it does it keep the rod straight so the OD of the push rod can't bind on the ID of the HB where the pushrod enters the HB.

For the SD unit I'm poking around on, the ID of the HB case where the rod enters is 0.540" with the second area of rod being 0.350". I have no idea of what stroke they design the HB too but using 0.75" stroke for math purposes, that results in a 6.9 degree angle before the rod starts to run into the ID of HB case.

And giving credit where credit is due, when I went back and was looking for the picture of an offset pushrod, that's exactly what ntsqd posted here on one of my older threads.

I'll starting to think the actual reason of the off-angle being bad is actually the potential of interference versus the seal wear often cited as the reason.

Edit: added pic of an offset pushrod

 

[ksagis]

Was poking around for a HB PN that came with threaded rod over coffee and came across this link from Paul at Hydratech on removing the rod. Nothing super new but thought I'd pass it on. Also created a PDF and attached it in case the link goes away.

As posted earlier, seems like cutting and threading the rod is easiest/best approach.