Questions with Hydroboost install

[ericwilkison]

I've just installed a hydroboost system that I pulled off of an Astro from the junk yard. So far the pedal feels weird. I've only tested in the garage / driveway so far. Applying the brakes is definitely working. Rolling slowly and pressing the pedal it stops quickly. Most of the pedal travel is very easy to push, almost too easy. However, when I press the brakes really hard the pedal goes gets stiff for a second or so at almost full pedal travel then gets easy again. It's almost like the boost is cutting out for a second. Has anyone seen similar symptoms?

Also, the pedal does not return as quickly as I'm used to. At a full stop if I press it in hard and then let off it takes 2 to 3 seconds to come all the way back up. Sitting stopped on an incline in my driveway when I let off the pedal I have feel a slight, but noticeable delay before the brakes let off and it starts rolling.

Some background info: The bronco is disk in front (Toms upgrade kit) and drum in rear. Before installing the hydroboost It was manual. I installed the boost because I'm moving up from 31" to 35" tires. I reused the stock master cylinder under the theory that it stopped well before, so the boost will simply help compensate for the larger tires.

 

[DirtDonk]

Did the master come from the same donor? If not, did you make sure to adjust the rod to fit the new master so it's at the specified setting?

And at any time was the master dismounted from the booster? If so, did you happen to push the pedal down without the master in contact?
Reason I ask about that last bit is that I've heard that you can basically ruin a hydro-boost unit to the point of it needing a full re-furb to work again.
Not sure what the symptoms are though. Thought I'd bring it up anyway in case anyone else knows for sure.

Good luck.

Paul

 

[thegreatjustino]

An Astro Van hydrobooster will have a short push rod that doesn't extend out beyond the booster.

The stock master cylinder will have a deep hole in the piston for a push rod.

If you didn't lengthen the push rod in the booster or put a slug in the piston of the MC to make the depth shallower, the brakes are never going to work right. The deep piston and short push rod will leave nearly an inch of gap between the back of the piston and push rod. The rod needs to make up for that gap before the brakes are applied at all which would give a very odd (and unnerving) pedal feel.

 

[ericwilkison]

I did make a longer pushrod between the boost and master cylinder. Cut down a vac booster rod from some random Ford at the junk yard. Found one with an adjuster screw on the end to get it just the right length.


As to Paul's comment, I do not remember stepping on the pedal without the mc. but I did not know that could be an issue, so I may have. Ive got a second booster unit, I went back to the yard to pickup houses and it was cheaper to grab the whole unit with hoses attached. Junk yards are weird. I may try swapping that in in and see if it helps.

Sent from my moto z4 using Tapatalk

 

[redfishtony]

Sounds like air in the system.

 

[DirtDonk]

That's a good point. How are the lines routed Eric? Any chance air can get caught in a high spot?
And if you had the pump open and especially if it was empty and all new fluid was put in, did you do the usual 99 and 44/100ths turns to the left and right with the tires slightly off the ground to purge any air?%)

If not, that would certainly be a good first thing to try. Before going to the trouble of swapping the unit out immediately.

Thanks Tony. Cooler minds might just prevail after all.
And by the way Eric, got a pic of this install? We love pics of new stuff. And to see what's going on under Bronco hoods anyway.

Paul

 

[ericwilkison]

Hey, Sorry for the late reply on this one the crud descended upon my household and knocked me out for the over the last week. Still hacking up a lung or two, but back at it at least

So back to the issue. The hydroboost unit just did not feel right. The more I played with it the more inconsistent it was. Sometime it would provide boost sometimes it wouldn't. I did the wheel lock to lock process to bleed the system multiple times. I started digging around on GM sites (I know it kind of made me feel dirty) and found these pages from a GM service manual regarding the hydroboost (attached for reference). I performed Accumulator Leakdown test and learned that it was not holding a charge at all. After shutting the engine off there was no power assist right away, little lone waiting an hour. I'm thinking the an internal seal, or check valve, or something was bad causing all the boost to come from the pump directly and nothing from the accumulator.

So, I swapped in the other unit I had and it is working much better. I took it for a quick drive around the block yesterday and very little pedal effort stops it on a dime. Almost too easy, but I think I can learn to live with that. When I had it apart I found that the master cylinder was leaking so I swapped over to the Astro MC. I've also attached a few pictures of the finished product.

Thanks for your help guys.

 

[unimogger]

Excellent follow up, thank you!

 

[bronconut73]

Looks like you have plenty of room between the booster and your valve covers....and those don't look like short valve covers....


Looks good with the Astro Van master cylinder.

It all looks good actually.

Bravo