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Hydroboost conversion questions

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gillis51

High Wheeler
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I’m considering converting my vacuum boost with a hydro boost. Vacuum boost is dying so I figure I may as well make the converstion. I’ve read most of the forums regarding the swap and think I understand what I need to do. I have been searching for a 92-94 Astro van in my area but haven’t found one yet. One local bone yard has a 2001 GMC Safari van with a hydro boost. I haven’t had the chance to swing by and see if it’s disk/drum. If it is will this system work?? Or did something drastic change between 92/94 and 2001.

It will be going into a 1979 Scout II with 345 4bbl currently with a 727 auto which may be swapped out witth a T19 4 speed. I am running 31" tires and have 3.54 gears. This vehicle is mostly a street cruiser, vey little if any off road.

Thanks
 

Dave Peters

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I used a booster from an 84 Lincoln; the linkage was the perfect length, but the bolt pattern is different, so the bottom holes have to be drilled through the fire wall. The stock fittings have nuts integrated into them and therfore must be reamed and nuts used which can be a pain to do. Now I would drill new holes in the Linc's that line up with the stock Scout ones.
The holes for the aluminium master are reversed with the brake lines exiting toward the block, but that's not really a problem as the lines are a ***** any way they face. I used the portioning valve the Scout had and it all seems to work. I've heard that masters can be bought facing the fender. When I tightened up the unit I didn't back the brake switch off and crushed it, necessitating the purchase of a new one. The one I got is for a Honda and is a perfect fit since the original, though a common type, wasn't in stock.
As I've noted in another thread I will be putting a second nipple in the tank of the pump to ensure the fluid gets back as soon as possible to avoid starvation. It should help keep the fluid a bit cooler, too.
Make sure the booster is fresh. Old is no problem- however, mine sat for years in the JY and the piston froze, forcing a buff job which may end up with a different booster being necessary. The bore of the Ford one is smaller than the GM, but the base looks the same so the GM head I have will go on the Ford base- some day.
All in all the switch was an ordeal but it's likely my fault in the way I went about it. However, it's great that I can tune the engine again!
 

Will Marsh

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It will be going into a 1979 Scout II with 345 4bbl currently with a 727 auto which may be swapped out witth a T19 4 speed. I am running 31" tires and have 3.54 gears. This vehicle is mostly a street cruiser, vey little if any off road.

Thanks

My question here would be "Why?"

You can buy a Reman booster with master cylinder from Autozone for $113. Bolt it on in a couple of hours and be fixed.

You'll spend at least that much on parts to fit the Hydroboost, and more hours than you want to, I'd guess at least 10, maybe more. For what?

Slightly better braking. IME, a late SII with front discs has plenty of brakes in stock form for 31" tires if they're working properly. Unless you intend to lift it and go to 35" or bigger tires, you're wasting your time and $$$ on a hydroboost conversion on a street rig.

YMMV,

Will Marsh
 

lindstromjd

Farmall Cub
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Apr 4, 2010
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Hurlburt Field, FL
I think the biggest reason to swap to a hydro-boost is if you have a diesel. The vacuum system on the diesels sucks (and therefore the power brakes, too), but on a gasser engine they work just fine.
 

fredsterra

Y-Block King
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I changed because #1 I have had my Scout about 10 years and have put 3 vac. boosters on it. And after driving one with Hydra Boost. Now having it on mine for about 2 years. The Hydra Boost brakes are far superior to vac.

In fact I would say the brakes on my 78 Scout with Hydra Boost are far better than my 07 F150 with 4 wheel disc.

After having it I would say this would be my first upgrade to any Scout.

Btw: I decided to go with a firewall spacer/apapter instead of drilling the firewall or cutting and welding the shaft.
 

hoosier

Farmall Cub
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Sep 16, 2004
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Jacksonville, FL
My Vacuum booster from Autozone went bad in 3 months. Went to Hydroboost and it's working great. Vacuum boost will stop the truck. Hydroboost will stop it a little better. It's just a gamble on how many vacuum boosters you'll swap out in the next 12 months.
 

Leeann

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Oct 25, 2006
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Don't quote me, but I think the 2001 is disk/disk, not disk/drum. You'll have to find an earlier Astro. I know the '95 is still disk/drum and I *think* the '97 is, too.
 

Dennis Bernth

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Wouldn't matter as long as you used the proper master cylinder and proportioning valve, the ones on the Scout now should work, I would assume the hydro boost is a hydro boost, the disk/drum difference is in the master and prop valve.
 

Randy Z.

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I changed because #1 I have had my Scout about 10 years and have put 3 vac. boosters on it. And after driving one with Hydra Boost. Now having it on mine for about 2 years. The Hydra Boost brakes are far superior to vac.

In fact I would say the brakes on my 78 Scout with Hydra Boost are far better than my 07 F150 with 4 wheel disc.

After having it I would say this would be my first upgrade to any Scout.

Yeah, definitely X-2 on this one. As good or better brakes than either late model 4/w disc vehicles I own. Cost locally was not that far out of line from a reman mc/boost combo. Installation was about 4 hours. It's worth it.
 

IH64Scout

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The hydroboost is the best option hands down, with junkyard parts and an afternoon you can have it swapped in for about $65 bucks! With little or big tires the hydroboost stops 10 times better than any vac boosted scout I've drive. Do it, you won't regret it!!

-Jon
 

scorp1us

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I'm in the middle of my hydroboost conversion.

Currently I am having some issues:
1. The adapter for the brake line. The prop valve (92 astro) has one large, one small. The scout had an adapter in the right direction but went to far (too big to). What should this adapter be?

I worry that the astro's prop valve is metric threading...

Price breakdown so far:
$40 Hydroboost unit (with MC, prop valve)
$7 Hydroboost hose
$8 1" square tube steel (36", enough for 4 sets)
$~4 stainless hardware.
$ ?? AN? adapter fitting, T, hose clamp x2
----------------------------
$59+??
 

Dennis Bernth

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I'm in the middle of my hydroboost conversion.

Currently I am having some issues:
1. The adapter for the brake line. The prop valve (92 astro) has one large, one small. The scout had an adapter in the right direction but went to far (too big to). What should this adapter be?

I worry that the astro's prop valve is metric threading...

Price breakdown so far:
$40 Hydroboost unit (with MC, prop valve)
$7 Hydroboost hose
$8 1" square tube steel (36", enough for 4 sets)
$~4 stainless hardware.
$ ?? AN? adapter fitting, T, hose clamp x2
----------------------------
$59+??

Did you just cut off the lines at the prop valve? If so, just use the fittings in the prop valve already with the Scout hard lines and reflare. If you didn't, even if the fittings are metric, the brake line sizes should be standard, and the metric fittings would be available at any decent parts store. If you don't have tools to flare and/or don't know how, then get someone that has quality tools and that does know how to do your lines. 'OK' isn't good enough on brakes....
 

scorp1us

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Did you just cut off the lines at the prop valve? If so, just use the fittings in the prop valve already with the Scout hard lines and reflare. If you didn't, even if the fittings are metric, the brake line sizes should be standard, and the metric fittings would be available at any decent parts store. If you don't have tools to flare and/or don't know how, then get someone that has quality tools and that does know how to do your lines. 'OK' isn't good enough on brakes....

No. I should have. But didn't think about that. Damn. And I went back to the JY to get my hose this weekend (lacked 16mm wrench to pull it last time) and my donor was gone! I ended up pulling a hose from a Ford (no joke!, pics to prove it)

I really do need to get a double flair tool. Never used one but they look simple enough.
 
Last edited:

fredsterra

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No. I should have. But didn't think about that. Damn. And I went back to the JY to get my hose this weekend (lacked 16mm wrench to pull it last time) and my donor was gone! I ended up pulling a hose from a Ford (no joke!, pics to prove it)

I really do need to get a double flair tool. Never used one but they look simple enough.

It's a handy tool to have! I have used mine a few times. And it's pretty easy to use.
 

Dennis Bernth

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OK, now I have some hydroboost questions. I just picked up (or I'll pick up the second two tomorrow morning anyway) three complete hydroboost units at my local JY for $100, with them doing the pulling. Originally they said $50 for the one they had on the shelf, but when I found two more Astro vans out back with complete units I guess I got the 'quantity price'. Two are complete with prop valves, one isn't, I think it had ABS and the lines were cut at the ABS computer. My question is, two of the units I got have the 'angled' mounting plate, and I need the 'straight' plate. I see the big nut on the back, and I've found the 'straight' plates on Ebay, but some of the listings say there is a special tool needed to remove that big nut. If so, where do I get one cheaper than the $49 one guy is selling them for, or will something else work? I know that the original vacuum booster on the D series was canted upwards for clearance with the engine, I don't know if I'll have to do that with the Hydroboost. My first thought was that I could cut out the center of the angled mounting plate and weld it back in reversed to make it similar to the way the vacuum booster is mounted on the D trucks, but I don't know if I really need to or not, I'll have to do some figuring. I think the plow Scout might be the first victim, the vacuum booster on it died and the pedal doesn't return now, so we'll see how that one goes.
 

Bill USN-1

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It's a nut. Just unscrew it.
IIRC there is also a snapring on it.
It has heavy knurles on the back so most don't reuse.
I have seen a spindle nut with the same threads work as a replacement.

The late astrovan angle plate works good for the old 80/800 firewall.

The hydro unit is smaller so I doubt it will need to be angled on the later vehicles.
Just get a truck/car resevior with a larger capacity to replace that little front astrovan one.
 

scorp1us

High Wheeler
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OK, now I have some hydroboost questions. I just picked up (or I'll pick up the second two tomorrow morning anyway) three complete hydroboost units at my local JY for $100, with them doing the pulling. Originally they said $50 for the one they had on the shelf, but when I found two more Astro vans out back with complete units I guess I got the 'quantity price'. Two are complete with prop valves, one isn't, I think it had ABS and the lines were cut at the ABS computer. My question is, two of the units I got have the 'angled' mounting plate, and I need the 'straight' plate. I see the big nut on the back, and I've found the 'straight' plates on Ebay, but some of the listings say there is a special tool needed to remove that big nut. If so, where do I get one cheaper than the $49 one guy is selling them for, or will something else work? I know that the original vacuum booster on the D series was canted upwards for clearance with the engine, I don't know if I'll have to do that with the Hydroboost. My first thought was that I could cut out the center of the angled mounting plate and weld it back in reversed to make it similar to the way the vacuum booster is mounted on the D trucks, but I don't know if I really need to or not, I'll have to do some figuring. I think the plow Scout might be the first victim, the vacuum booster on it died and the pedal doesn't return now, so we'll see how that one goes.

To make the plate take a 4.5" square plate of 1/8" steel. Drill 4 holes (3/8" plus a few mills for threads.) in a square that is 3.5" on a side (center to center) centerd o n the material. Between pairs holes (1.75") drill another hole (6 holes total). Somehow, drill your center hole. (Probably need to mill/cut). Take 2x 1" square tube steel (4.5" long) and transfer the pattern from the plate to the tube stee (for a spacer). The outer holes are for mounting the booster/plate to the tube steel spacers. The inner hole is for mounting to the firewall. Use 3/8 1" bolts for the plate/spacer mounting and 1.5-2" bolts for the center mounting holes to the firewall.

I found I had to adjust my pedal height with the 1" spacer. 1.5" of spacing would have kept it the original height. Now my brake sits just above the gas, whereas before it was even. The brake light switch has plenty of room either way. in this new configuration.

What I just described is to make a stock-style plate. You can modify it as need.

Removal of the snap ring is easy. To get the nut off, place the unit in a vice, with the nut in the jaws. Use a pipe wrench on the steel area for mounting nitrogen module... it won't take much. Once loose, it'll spin right off. The original plates are keyed at the center hole, so be mindful that the columns of 3 holes are vertical to the booster when you tighten.
 

Dennis Bernth

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It's a nut. Just unscrew it.
IIRC there is also a snapring on it.
It has heavy knurles on the back so most don't reuse.
I have seen a spindle nut with the same threads work as a replacement.

The late astrovan angle plate works good for the old 80/800 firewall.

The hydro unit is smaller so I doubt it will need to be angled on the later vehicles.
Just get a truck/car resevior with a larger capacity to replace that little front astrovan one.

Are you saying you don't reuse the nut? What holds the booster to the plate then, or am I misunderstanding you? The problem is that I don't think I can get to the nut with the angled plate, it's kind of recessed down in there, no way to get a box or open end wrench on it.
 

gillis51

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I found a 92 astro and am planning on pulling the hydro boost. What tools will I need and what will I want to take. Hydro boost pump, master cylinder, proportioning valve, mounting plate?, hoses? Anything else?

Thanks
 

Bill USN-1

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It has heavy knurles on the back so most don't reuse.
I have seen a spindle nut with the same threads work as a replacement.

You can split the nut very easily.
A small chisel or drill a small hole in the edge and then hit with a chisel.
Just like removing the retainer collar on a rear axle bearing.

I don't just press them off, I drill and split.
 
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