Hey guys, attempted to install my new hydroboost unit today, but already ran into an issue...

The hydroboost unit was installed and bolted in place, but I have since removed it. When the brake pedal was in its relaxed position (fully up and against the rubber stopper), the clevis would reach the lower hole in the brake pedal and I was able to put the pin through it. However, my concern is that the clevis was barely holding on to the threads of the threaded rod coming out of the booster. If I moved the pedal down and off the rubber stopper, I could then thread the clevis on to the threaded rod some more, but then the pedal was much lower to the floor and no longer resting on the rubber stopper. It seems that the threaded rod from the booster unit is too short and needs to be longer? The instructions I received with the hydroboost unit says that there should be a minimum of 8 threads showing through the clevis, but when I did that, the brake pedal was no longer resting on the rubber stopper and had about 3/8" of gap between the pedal arm and the rubber stopper.

So, wondering what my options are? Should the pedal be lowered away from the rubber stopper? I think that I read somewhere that there should be a 1/4" or more of distance between the rubber stopper and the brake pedal arm? Is this correct? Or should I leave the pedal at its resting position against the rubber stopper and adjust the clevis outward? But then what do I do about the clevis barely holding on to the threads? I read in another thread that there is a longer threaded clevis that you can buy from McMaster Carr. Maybe this will be a solution to the adjustment issue?

Well, any insight from those of you that have run into this issue would be greatly appreciated. Thanks!

 

As long as the clevis has threads engaged thru out, I don't see an issue. 8 extra threads exposed does zilch.

 

I have heard that you need to adjust the rod so the pedal either does not touch the stopper or just barely touches. The booster can have issues if it is not allowed to return all the way. Check to see if the pedal has good travel, or stops before it gets to the floor once it's hooked up to the rod. I run my pedal a little lower and still have plenty of travel.

 

Thanks for the feedback guys. The C3 Corvette specific instructions I received with Hydroboost set-up is vague in the sense that it basically says to "adjust the brake pedal height as desired". What it didn't explain was whether or not the brake pedal should be adjusted with the brake pedal all the way up against the rubber stopper or if there was a specific reason to allow for lets say a 1/4" to 3/8" gap between the brake pedal arm and the rubber stopper. The instructions further went on to say "Double check for appropriate thread engagement at the clevis (8 thread minimum), then tighten down the brake pedal rod to clevis jam nut".

I definitely didn't feel comfortable with only having the clevis attached to the threaded rod by literally like 3 threads. So have been thinking on ways to either extend the threaded rod, or cut it short and install a threaded sleeve/coupler and attach to the clevis using additional threaded rod to make up for the distance cut from the booster rod. But the more I thought about doing that, the more "Bubba" it was beginning to sound. Lol

So after reading through several older threads tonight, I ended up taking the advice of forum members conclay and mysixtynine who recommended purchasing a longer clevis to help with this situation. It comes from McMaster Carr and basically has an additional 1/2" of thread attached to it. Think this should solve the issue of not having enough threads for the clevis to attach to and be able to properly adjust the pedal height.

For those of you in this same situation, below are the links referencing the information about the longer clevis...

https://www.mcmaster.com/#6071k14/=pjtnjb

https://www.corvetteforum.com/forums...post1585528198

 

I was thinking that the "minimum 8 thread" was to make sure that if the locker nut came loose, the rod could not back off far enough to disengage from the pedal completely. The pedal arm would hit up against the rubber stop before it could back far enough out for the rod to disengage and lose your brakes. With only a couple of threads there would be no safety margin and the rod could become separated. I think you are doing the right thing by obtaining the slightly longer rod.

 

Hi CG, I think you are spot on about the minimum 8 thread count that should should be protruding through the front side of the Clevis. I'm guessing that whomever wrote the instructions was trying to convey that the Clevis should be threaded on far enough so as to keep the Clevis in place in the event the jam nut breaks loose and the pedal pops forward. By doing this, there would be less of a chance for the threaded rod to become separated from the Clevis and lose brakes all together. The way my set-up is now may work, but there is barely any threads holding the Clevis in place and thus having the greater potential to separate from the rod. Instead of trying to modify things, going to go with the longer Clevis from McMaster-Carr. The additional 1/2" of thread should be exactly what it needs to make it safe...

 

You want to have about 1/2" of free-play in the brake pedal when it is in fully released state. Prior to braking, most folks put their foot on the brake pedal even though they haven't actually depressed it. If the Hydro-boost starts to brake as soon as the brake pedal is touched and you don't have that free-play 'cushion', you are going to have an "nervous" brake pedal.

Not sure if this condition is your concern, but thought I should share it.

 

Thanks for the info 7T1. I get what you are saying about the 1/2" of free play...I think? I am a bit slow sometimes, but thinking there is not a way to adjust the free play. I can however adjust pedal height and adjust the brake pedal down and away from the rubber stopper by a 1/2" or whatever. is this what you are referring to as free play?

 

Yes, you got it.

Even without the hydroboost, ALL brake pedals should have about 1/2" of free movement BEFORE any braking action takes place. So your pedal should have been set up that way. When adding the Hydroboost, you just want to match that strategy: adjust the start of Hydroboost action to begin after the pedal has been depressed about 1/2". Same result: no twitchy brakes!

 

Not meaning to step on any toes...BUT...

The position of the clevis on the threaded shaft of the hydroboost has nothing to do with the amount of free pedal travel. It can't...because regardless of any braking system. The clevis is held to the pedal via a pin and clip. And if it is threaded down or barely threaded in past the threads of the clevis. All this is doing is changing the pedal height position. That is all it is doing. Because if the pedal is set high or set low...when you press on it is is still performing the same exact function and that is not changing. When you press on the brake pedal..the shaft that will contact the master cylinder moves.

SO...unless the pin is a smaller diameter than the actual hole in the clevis....you will get some movement in that area...BUT...it does not matter how much or little you have the clevis threaded onto the threaded shaft....but obviously threaded down far enough to ensure you are utilizing all of the threads in the clevis.

The way to set the pedal travel is on the adjustment bolt that makes contact with the master cylinder. Due to not all master cylinders are exactly the same in this area....it is adjustable except for some GM vacuum brake boosters where they are not adjustable.

Measuring the depth of the master cylinder and using the contact surface or what ever is needed to achieve a measurement...and doing simple math...a person can find that IF they have the adjustment bolt (for example) 1/32" shorter. Then logic would dictate...that due to the length of the brake pedal in relation to the pivot point of the brake pedal...the pedal will move 'X' before it makes contact with the plunger in the master cylinder.

So...this is where you make your adjustments and you can fine tune your brakes accordingly.

I can tell you this. I have installed many Hydrotech systems and this car will stop like you have never felt before. Any any concerns you are worried about on the amount of your brake pedal travel when pressing on it will soon dissipate because the car will stop much sooner in the brake pedal stroke.

DUB

 

DUB..

Are you referencing "hydroboost" or the car's [regular] power steering? All I'm mentioning to the OP is that he doesn't want the hydroboost unit to start actuating until the brake pedal has been depressed a bit. However he does that is fine. If the hydroboost system has a 'dead action' area at the start of its movement, so be it. If it does NOT, something needs to be done mechanically to maintain that free-play on the brake pedal.

 

Here's my experience on this. The hydrobooster requires that the pedal rod is returned all the way when your foot is off the pedal, so if the pedal is hitting the upper bump stop before the booster is completely relaxed, it could make it twitchy or cause heat in the power steering fluid because the pump is trying to make pressure to give brake assist. That is not where the "free play" in the pedal comes from. The free play in the pedal is determined by how much the pedal travels before the master cylinder closes off the brake fluid return port. If the push rod from the booster going into the master cylinder is too short, you will have lots of pedal travel before you begin to have brakes. Too long of a rod there will make it so the brakes don't fully release, the brake fluid return port is blocked inside the master cylinder. In this case the brakes will overheat due to residual pressure build up and eventually lock up.

In the case above, the rod may have been cut a little short, or the adapter plate at the firewall too thick, but as long as it has the clevis fully threaded on and locked with the jam nut, there won't be a problem, your brake pedal is pushing on it, not trying to pull it off. The new longer clevis will give you more adjustment if you need it. Just make sure after adjustment of the clevis, you try to pull up on the pedal and it doesn't compress the bump stop, if it does, you may end up with the booster partly applied, but not necessarily the brakes. You may have to adjust the brake light switch on the pedal also.

 

You've explained this issue well...probably as you have some actual experience with the Hydroboost unit, and I was cautioning about a generic potential problem if the brake actuation is not set up properly.

Thanks for you clarification...

 

My comment was dealing with the same rod that '75 talked about that is adjustable that is coming out of the Hydroboost that contacts the master cylinder.

This same rod in a facotry vacuum brake booster still applies...IF it is adjustable...like what I wrote in my previous post.. it does not matter if it is Hydroboost or not. This rod must be set correctly.

So if 'spdrcr29' gets the main unit installed and the pedal is NOT actuating the unit due to the clevis is too far out.....and the brake pedal is actually pushing on the Hydroboost shaft becasue it is up against the stop for the brake pedal. Then it is up to the rod where the master cylinder is is where he can get the brakes adjusted correctly.

When I do these Hydroboost systems...for whatever it is worth. I always make sure I bring the brake pedal back to the hole in the clevis so I know the pedal is NOT causing for a problem.

DUB

 

'75, 7T1, & DUB,

Thanks so much for all of your feedback. This hydroboost system is new to me, so pretty much learning as I go. Each of your responses have been very helpful and I do appreciate it. Spent yesterday afternoon reinstalling the hydroboost unit with the new brake clevis from McMaster-Carr as well as plumbed the lines from the p/s pump, to the unit, and the rack & pinion set-up. Haven't filled with fluid yet, but at least its all installed.

I think that '75 is correct about the thickness of the adapter plate at the firewall. I'm guessing that if it would have been a tad thinner, I would have been able to get the clevis threaded on to the booster rod a few more threads. Regardless though, having the new, longer clevis installed makes me feel much better about being threaded on far enough so as to not only make it safe, but also to have the ability to adjust pedal height as needed. As far as pedal height, I currently have the pedal adjusted not quite a 1/4" away from the rubber stopper. I realize that I will probably have to fine tune it later, but suppose its a good starting point for now...

While reading through the instructions received with the Hydroboost unit I found that it didn't give any specific instruction on how to adjust pedal height other than to basically say " adjust as needed". It also didn't give and reference to indicate if the rod from the hydroboost unit to the master cylinder was adjustable. I ordered the unit with the long/deep rod set-up and also purchased a Wilwood M/C with a 1 1/8" bore to go with it.

Although I have yet to take any measurements as DUB suggested, I did notice that when I test-fitted the m/c to the hydroboost unit, there was no resistance to putting the m/c in place, meaning that it bolted on with zero effort. With that said, I'm guessing that the hydroboost push rod is somewhat short inside the bore to the m/c and not actually pressing on the m/c piston. This area is now what I understand to be where the "free play" can be adjusted. Again, the instructions said nothing about the m/c push rod adjustment, so I guess it could be taken as "bolt on the m/c and you're good to go"?
DUB's response has me thinking that may not be the case. So, I understand that measurements are needed to see exactly how much "free play" there currently is, but can anyone tell me if the push rod coming out of the hydroboost unit to the m/c is supposed to be adjustable? I attempted to twist and pull it with very little force, but the rod did not seem to want to move outward at all. Any ideas?

 

I have not seen a hydro-boost with an adjustable rod, I think you bolt it together and what you get is what you get. There needs to be some play there. I recall the vacuum boosters pre 77 had an adjustable rod, but I have not seen it on later models.

 

If when you fit the Willwood master cylinder the hydroboost assembly and you did NOT feel resistance. Then you do not have to worry about this area of the system. Because you are not actually beginning to move the valving in the master cylinder....thus beginning to apply the front brakes.

If your pin that goes into the master cylinder is NOT adjustable. Then you are at the mercy of how deep the pocket in the Willwood master cylinder is. A person could assume that all master cylinders should follow basic engineering guidelines in this area...but sometimes the company making them makes it to what they want.

Once you get your clevis in the way you want it...and the system bleed and working. I am sure you are going to be amazed.

Not that this matters but I like to use the Royal Purple power steering fluid due to it does no foam up bad at all.

And..it may be too late for this. But if you car where in my shop. Instead of getting another clevis. I would install another bolt and nut into the clevis and weld the nut to the clevis so it is now giving me more threads. Take that bolt back out....thread my jamb nut onto the Hydroboost and them install the newly modified clevis.

And...general rule of thumb. When a part is being threaded onto a threaded shaft or whatever. All you need to get to maximum strength for the threaded rod is enough threads that equals the threaded rod diameter., So if the threaded rod is 3/8" wide...all you need is 3/8" of threads going into it. More is better...if achievable. But not less that the width of the rod.

DUB

 

Thanks for this info. Was considering just using standard AC Delco Power Steering Fluid from the local Chevy Dealer, but sounds like the Royal Purple may be worth looking into. I've included a link below. Is this what you are referring to? As for welding a nut on the back of the clevis, it crossed my mind...but don't own a welder or know anyone who does. Would have been the cheaper route to go vs. purchasing one. Oh well. The one from McMaster-Carr worked out just fine.

https://www.summitracing.com/parts/r...FQoKaQod22QKYQ

 

YEP...that is the power steering fluid I use due to the system does take a bit of time to get bled out..and the last thing I need is foaming fluid.

DUB

 

Perfect. Think I'll order some.
Thank you sir...