Hydroboost issues

[Eck]

So I got everything bolted up and fired it up. One of the bolts that attached the clocking bracket to the HB stripped out when I pushed in the pedal which then led to the “star clip” and plunger spring to pop out. I’ve gotten the bracket, bolts and MC all disconnected but now the piston and pedal is stuck in the down position.

If I reopen the hydroboost will it release pressure and allow the piston to come back up so I can reinstall the spring and plunger? Or is this indicating something else is going on? I’m VERY close to buying a hydroboost from a parts store with a lifetime warranty...


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[phyler]

I saw a post on this issue when I was looking for the rebuild info. There is something out of place. I'll look for the article.

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[Eck]

Took the hydroboost apart again and got everything installed again. I did not spend a ton of time bleeding the system but it seems like I’ve fixed the issues I was having. Fluid level doesn’t seem to be going down anymore and I don’t see any foaming or bubbles in the fluid.

However- I have two things going on that I could use some advise on.

1. The pedal rebound is pretty slow.

2. The brakes don’t work well. When I first installed before pulling it for the leak and new clocking bracket, the brakes locked up immediately when I put the pedal to the floor. Now the seem to just sort of engage. The new bracket is 1/2” instead of the 1/8” that was on there previously.

Do I need to lengthen the pushrod that goes from the HB to the brake pedal? Or is there another adjustment that needs to be made to make the throw further now that I’ve added 1/2” of space between the hydroboost and master cylinder?


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[Kinder]

Is the spacer between the MC and the booster? If yes then you’ll likely need to add something to take up the space that was created. Lengthening the rod from the pedal to the booster won’t solve this problem since it’s the rod out of the booster that isn’t engaging the MC correctly. I’m not sure if there is an off the shelf solution, I’ll look for something to link to.

[Eck]

Is the spacer between the MC and the booster? If yes then you’ll likely need to add something to take up the space that was created. Lengthening the rod from the pedal to the booster won’t solve this problem since it’s the rod out of the booster that isn’t engaging the MC correctly. I’m not sure if there is an off the shelf solution, I’ll look for something to link to.

Correct and that was my assumption as well. The MC I have had one that you added for power brakes vs manual brakes but when I added the 1/2” spacer- it obviously created a 1/2” lag. I haven’t been able to find anything off the shelf yet and it seems like the clocking bracket is a fairly common thing people are doing so I’m curious. Does it make more sense to have a longer rod on the hydroboost side or the master cylinder side?

Any thoughts on why the pedal rebound is so slow?


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[Justin]

The pushrod coming out of the hydroboos will need to be lengthened to correctly engage the back of the M/C. If I remember correctly, this is where I got my custom longer pushrod:

http://www.vancopbs.com/category_s/168.htm

Any local machine shop could make one easily, though. I'd get that in and see if you still have rebound issues. I'm wondering if the hydroboost partially relies on pressure from the M/C to return the brake pedal. Could also just be trapped air. Took a long time for mine to fully bleed when I did the swap. Either way, glad you're making progress.

[Eck]

So I ended up making a longer rod that goes in the Master Cylinder out of some 1/2 steel rod. The pedal is now very stiff and I’m able to lock up the brakes if I get on them.

I opted this route as it seemed like a lot less hassle than dealing on the hydroboost side. Also cost $8 for a 3ft rod.

I’d be interested to have someone compare mine to theirs as I’m a little surprised the Hydroboost doesn’t seem to give me the “ease” I was expecting. I still feel like I’ve gotta give it some good muscle to lock it up.


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[Justin]

You're welcome to swing by and drive mine. My pedal isn't super stiff, like manual brakes. It gets firm once it loads up, but there's still some hydraulic-y mush in it. Not a ton of feel compared to the little zippy cars I usually drive.

[ZOSO]

Interesting about the hard pedal. My buddies jeep has the same hard pedal where my bronco is really soft.

[phyler]

Do you know what size bore your master cylinder has? That can affect pedal feel.

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[Eck]

Do you know what size bore your master cylinder has? That can affect pedal feel.

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Looks to be a 1” bore.

This is what I bought. https://swperformanceparts.com/product/ ... B8QAvD_BwE


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[phyler]

Do you know what size bore your master cylinder has? That can affect pedal feel.

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Looks to be a 1” bore.

This is what I bought. https://swperformanceparts.com/product/ ... B8QAvD_BwE


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I wouldn't think that would be super stiff then. I've heard of it happening with the 1.25" bore.

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[Gunnibronco]

My original hboost had a very stiff/touchy pedal that locked up the brakes easily. I swapped from F150 calipers to the Tbird calipers to pull my bias forward and the pedal got significantly softer. It's a function of master cylinder, caliper, and rear wheel cylinder volume. I'm running the 2000ish Mustang m/c(1") Tbird calipers and 79 F150/Bronco rear brakes.

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[landshark]

My pedal is pretty stiff and easily locks up all four, but always fronts first. I don’t have any problems with the way the brakes work and you get used to it very quickly, it’s nice on the trail since you don’t have to ride the pedal. Iam using a proportion valve and the corvette master cylinder. My pedal rebound is instant.

I would suggest driving it for a while once you get the air out.

[Eck]

Thanks for all the feedback. I will drive it a bit and make sure all the air is out and see how it feels before making any tweeks. I haven't driven off my street and any faster than 30 mph so it could be much different once I actually give it a true road test.

[Eck]

Took it for a short drive and the brakes started to engage without pressing in the pedal. My initial guess is that the system pressurized more after driving it and started to engage the master cylinder. My plan is to grind down the pin I put into the MC a little more until that doesn’t happen.

On another note, my engine runs like crap. I had cut and made my own spark plug wires while I was doing the hydroboost so I need to check and test that all of them are working properly- and hopefully that will be the reason and an easy enough fix.


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[Eck]

I am a little perplexed. I am trying to dial in the Hydroboost to Master Cylinder engagement and I made a bullet to go into the Master Cylinder to take up the 1/2" of the spacer I installed. I had the truck propped up in the front and was able to spin the front tires freely so I took it for a test drive. After a short time, it seemed as though the brakes were engaging without depressing the brake pedal- making me think that maybe the hydraulic system is pressurizing and causing the rod from the hydroboost to engage the master cylinder. When I got back from the test drive, the front driver brake was g.

I propped the front end back up and turned the Bronco on and depressed the brake pedal about 20 times to try to pressurize the system again but the front tires still move freely. I am not sure how to determine how much to shorten the MC bullet since I can't seem to replicate the issue on jack stands.

Any advice?


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[Kinder]

A quick search yields a thread on CB.com. It looks like there needs to be a slight gap b/t the hydrobooster rod and the point of engagement on the back of the master. 1/16 inch is referenced, the OP just used washers. I’d say washers are a good starting point so the distance can be changed easily, then when you find the space needed take it out of the rod length.

https://classicbroncos.com/forums/showt ... p?t=270970