Hydroboost Q&A

[72tutone]

Does the input rod from the pedal matter length matter much? I welded a coupler and just extended it to the stock pedal. Im not sure if I should have kept the original length or not.
Ive read that from a hydroboost its 6" from mounting flange to end of the input rod. This was out of a 93 Astro van

This is with a disc/drum original setup in my 72.

The length from the pivot to the center of the pedal is around 17". Then the brake input rod hole down is around 2 1/2 to 3". Im not sure if I should drill down a bit to get it to line up correctly or not. In addition add some extra metal if need be to move the pedal position a bit closer to the 6"


Should I retain the 6" input rod length to get the correct pressure on the MC? Or is it fine to extend the rod to the stock hole in the pedal assembly?

Thanks!

[mcm1209]

In for info!

[randy500]

You shouldn't weld any mechanical brake component unless your a very experienced and certified welder. Welds crack and fail.
You should couple it with mechanical means such as pins, threads or press fitting.

[mcm1209]

Originally Posted by randy500

You shouldn't weld any mechanical brake component unless your a very experienced and certified welder. Welds crack and fail.
You should couple it with mechanical means such as pins, threads or press fitting.

With that being said.. no welding period on these frames as far as suspension goes as well.

[1971Stepside]

I'm planning to keep my Astro input rod and have my brake pedal welded to extend far enough to reach the rod. Drill a new hole and put the pin through the pedal/rod.

[72tutone]

Originally Posted by 1971Stepside

I'm planning to keep my Astro input rod and have my brake pedal welded to extend far enough to reach the rod. Drill a new hole and put the pin through the pedal/rod.

That was my question. I understand about the clevis/hole etc. But, I wanted to know if the stock length 6" should be kept. Or its ok to extend the input rod to the original hole that exists on the brake pedal.

The welding concern would be that 6" input rod wont reach the pedal and I need to weld to the pedal a bracket, so as to move the pedal closer to the 6" original length.

Concerns about brake drag etc. Or is it really so much as the output rod needs to engage the MC correctly and the input rod really isnt much of a concern?

[72tutone]

Originally Posted by 1971Stepside

I'm planning to keep my Astro input rod and have my brake pedal welded to extend far enough to reach the rod. Drill a new hole and put the pin through the pedal/rod.

Do you know which year astro van your boost came from? I did have the stock input rod, but I cut it and put a coupler on with the factory adjustable rod on the end to adjust accordingly.

I still believe that this is to far of length for the factory on the astro van hydroboost.

I assume the brake pedal assembly comes out as one piece vs the pedal alone and can have a new hole drilled out into a bracket that is attached to the pedal.

[randy500]

Your question i believe is 2 fold and the 2 dont relate to each other.
1. Can you extend the hydroboost rod beyond 6” to meet the pedal or should you extend the pedal to the rod
2. Hydroboost rod location on pedal, ie: pedal ratio

1. On factory power brakes the booster rod holds the pedal away from the outward pedal stop, its perfectly fine for the hydroboost to do so too. Make a bolt on extension for the pedal if needed...or extend the hydroboost pushrod. Just make sure there is enough pedal travel to operate the hydroboost unit withiut the pedal hitting the floor.

2. Pedal ratio is important and so is geometry, find a happy medium. Currently the pedal ratio is approx. 17/2.75=6.18. Power brakes are usually in the 4 to 5 ratio...so move the hole down if needed.

[randy500]

High pedal ratio with hydroboost could make for very touchy brakes.

[1971Stepside]

Do you know which year astro van your boost came from?

Mine is from an 05 Astro Van. I didn’t want to cut off the existing rod and thread it because I plan to give this truck to one of my sons (neither knows how to work on them) and I wanted these parts to be easily interchangeable should something fail. This is why I want to add to the brake pedal. It will come out by itself.

[72tutone]

[QUOTE=randy500;8668495]High pedal ratio with hydroboost could make for very touchy brakes.[/QUOTE

Randy, thank you for replying. What is really strange is my 72 super had factory booster. This is why I'm scratching my head on the pedal ratio period from measuring down those numbers are very close. 17" and 2 and a 1/2 inches from pivot to hole.

If I'm not mistaken, trucks with boosters should have between 4: 1 and 5:1. Manual should have much higher than this

[randy500]

Factory booster has reduced pedal ratio from linkage at firewall bracket.

[72tutone]

Originally Posted by randy500

Factory booster has reduced pedal ratio from linkage at firewall bracket.

That's what I thought. Just trying to figure out why mine is so high. Again, its a factory cheyenne super with disc/drum and a 11" morraine factory booster.
That pivot mid point to mid pedal reaches 17". Then only a 2.5 or 3" from pivot to center of rod hole.

Head scratcher?

So, to confirm it doesnt matter if the input rod is longer than it was, just as long as there is sweep of the brake pedal and it doesnt hit the floor board?

As far as pedal ratio, this is something I need to look into for sure.


Accurate?

[randy500]

The pedals are all the same, the reduced pedal ratio is built into the power brake booster bracket pivot mechanism. You could measure it all out if you needed. Just accept its less than the pedal ratio I calculated before.

Yes just extend the rod in a safe manner and it will be fine.
You will want the pedal lower than it is at rest, similar to power brake pedal height.

I did this a couple years ago. I installed a 70's van booster (11" Delco dual diaphragm) directly on the firewall, almost like captain fab does with his bracket. The van booster has an eyelet attached to it for the brake pedal. I had to extend my pedal about 1.5' to connect to the eyelet.
I made it a direct shot, essentially inline with the factory pedal hole. I was concerned about the high pedal ratio too.
.
For me it worked out fine and here is why.
I used a 1.25' bore master cylinder (big bore master = higher pedal effort) because my front brake calipers are huge and take a lot of fluid volume (dana 60 4wd front axle)

I think captainfab makes a bracket for the hydroboost unit.
sample install I think of his bracket.
http://67-72chevytrucks.com/vboard/s...d.php?t=376045

[72tutone]

Ok yes I to also have a 1.25 MC bore. I will just extend the pedal and use the factory hole in the pedal if its not an issue.

I will try and get to 4:1 to 5:1