GM hydro boost brakes for newbies like me....

chilliwak

Expedition Leader
Hello everyone. I am trying to locate all the parts and such to make my 1979 Chevy pick-up into a vehicle that has hydro boost brakes as opposed to vacuum brakes. Please post or repost any info you have here, including pics. I am a total new beginner to this issue so too much info is better than not enough. Thank you, Chilli..:)
 

ihatemybike

Explorer
With multiple Astro vans passing through my stable, I can say head to a junk yard and grab all of it. It looks pretty simple. Just a extra set of hoses and a different booster mounted.

There is a downside to the hydro booster, loose the power steering pump or line pressure you are back to manual steering and brakes. It's happened to me twice in 20 year and over a million miles of driving hydro boost vehicles.

First time the power steering pump went out, but I was playing in a snowy parking lot at the time and had the wheel at full lock. Had to drive home from Cleveland, with a van load of mountain biker, in a snow storm, with no power steering or brakes. Engine braking rules.

Second time I had an idler pulley seize up, shedding the serpentine belt, on the way to work. No alternator, no coolant circulation, no power steering or brakes. Van still managed to get me to work, back home and to the parts store. (roughly 40 miles) \m/

I love Astros.
 

superbuickguy

Explorer
beside the booster, you need a pump.... the pressure side can draw off the same line, but the return lines both have to go their own port on the pump (more specifically, to the reservoir). The issues with hydroboost is leaks - rubber hose degrade pretty quickly then start to leak... of course, if you have a diesel or turbos - you don't have enough vacuum to run vacuum assist.
 

elyon

New member
I spent the bucks and went with A Hydratech system. Upgraded to braided stainless lines. I bought an updated steering pump from Jegs.

Works like a champ! Gives me a lot of confidence in being able to stop this beast.

You have about 3 brake applications on the accumulator if the pump fails.
 

Larry

Bigassgas Explorer
I’ll repost some reference photos in this dedicated thread…

Here is a GM square body specific hydrobooster. The difference between the square body GM booster and Bosch boosters used on other GM, Ford, Dodge, etc. vehicles is the booster to firewall bracket, booster to pedal rod and booster to master cylinder rod. With enough fabrication a Bosch hydrobooster could be used from just about any vehicle although for an easier swap it is quicker and cleaner to just find one from the period correct GM truck when retrofitting to another GM truck.

1973-1991 GM square body truck, Suburban and K5 booster. This one happens to be a 1981-1991 unit with metric thread fittings. 1980 and older have standard SAE threads and are rather hard to find in salvage yards.
16376373795_8e0a8841d8_b.jpg


16188757338_d10f029209_b.jpg


The booster to firewall bracket that is unique from vehicle model to vehicle model but it can be removed by the large nut on the back side, which can be a SOB to get a wrench onto. The rod can be removed as well but it is tricky with a lock ring in there somewhere.
16381474702_8bd6e624d9_b.jpg


16350425876_5b79d70960_b.jpg


Contrary to popular belief, the power steering pump does NOT need to be replaced when retrofitting hydroboost. The big difference between a hydroboost power steering pump and a non-hydroboost pump is the fact the HB pump has two return ports in the reservoir. There is no harm in tying the two return lines together to reuse the non-hydroboost ps pump. In fact, GM tied the two return lines together on full-size G-vans and P-chassis motor home/step vans with hydroboost and only used a single port return at the pump. Also, there is no difference in pump pressures for hydroboost. ANY Saginaw pump used on GM trucks (some Dodges and some Fords) produce plenty of pressure to run hydroboost. Pressure is not built in the pump itself anyway, pressure is regulated by the pressure regulator that screws into the pump reservoir itself where the high pressure line screws into. Running high pressure is not always a good thing either as it can make the power steering feel too easy and light where the vehicle feel like the vehicle is driving on ice. Remember the big ole GM big body cars like Cadillacs, Buicks, and Olds of the late 60’s and 70’s where the steering wheel could practically be tossed from lock to lock with one hard whip of the steering wheel? Old big body Chryslers of the era were the same way. The difference was the pressure regulator screwed in to the pump. Many years ago I actually took one those regulators out of an old Cadillac ps pump and screwed it into the ps pump on my dad’s wrecker to help with steering boost. In the end, it came back out because the steering was just too overboosted and felt “light” driving down the road. A lot of ole hot rodders with old recirculating ball steering gears (like we use) modify the regulators to boost pressure or reduce pressure to stiffen up the steering to give more of a road car feel to the steering. All that said, it is not required to replace the ps pump (or regulator) to run hydroboost. Yes, some hydroboost power steering pumps will have a higher pressure regulator but that is not for the sake of hydroboost, but more to provide more steering assistance on the heavy vehicle hydroboost is usually found. For example, a GM truck with the snow plow prep package may have a higher pressure regulator to offset the weight of the plow hanging off the face of the truck and it just so happens that truck could have hydroboost.

This is how my K10 is plumbed with the return lines routed together. The return lines come together then out to an aux cooler then back to the return port on the pump. Same way GM had G-vans and P-chassis plumbed.
16381482762_e817e138b3_b.jpg


16381489982_a223f63e82_b.jpg


16381495932_6bda6afd35_b.jpg


Here is an example of how the power steering and hydroboost is plumbed on one of the trucks my company builds. The model shows a ZF p/s pump but we used the same plumbing on our older vehicles that ran Saginaw pump and Saginaw steering gears as well.
5240138026_38807a5462_b.jpg



Another item that is worth mentioning is the proper way to bleed power steering and hydroboost. Pretty much 90% of people think just starting the engine and turning the steering wheel back and forth is the proper method to bleed the system. The actual correct way to bleed the system according to steering engineers I work with is to lift the front wheels off the ground, start the engine and turn the steering wheel lock to lock 2 or 3 times then, turn off the engine, exit the vehicle and turn the wheels lock to lock about a dozen times by using the actual tire/wheel. The difference is the motion and pressures inside the box initiated by the movement of the pitman side of the gear box instead of the selector shaft side (steering wheel side). When it was explained to me it made perfect sense but I don’t recall all of the details but has something to do with creating high and low pressures inside the box to push the bubbles out. That procedure works great the first time, every time....


Another hydraulic assisted brake booster system that is pretty slick is the Bosch Hydromax unit. These are used on medium duty trucks in GVWR ranges up to where air brakes are required. The neat thing about these units is the fact if there is a loss in hydraulic pressure the electric motor will cycle to provide power brakes, whereas hydroboost uses an accumulator that is good for a pump or two after hydraulic pressure loss. You may have noticed a buzzing sound if you’ve rented a U-Haul truck or driven any other non-air brake medium duty truck in the past 10-15 years when you place your foot on the brake pedal with the engine off. That noise is the Hydromax motor running. With some fabricating and wiring these make for pretty slick units to retrofit too. I don't really see these units adding any more power to the brakes, they just add more safety if there is hydraulic pressure loss.
new-bosch-hydromax-power-brake-boosters-1.jpg
 

SlowJoe

New member
I have a 77 K20 with the manual transmission. I recently converted it to hydroboost with a unit that I got from Vanco ( http://www.vancopbs.com/category_s/66.htm ) The bracket he made to mount it to the firewall required slotting the holes to match up to the studs and I also had to open up the hole in the firewall a bit to accommodate the nut that Larry showed above and mentioned it is tough to get to. I told him about these issues and he seemed surprised, so maybe I got the wrong bracket somehow. It was not that hard to make it work and a round file, or dremel tool with a mill bit would make short work of it. It is just worth mentioning, I thought. My brake pedal already had a hole from the factory above the pin that the master cylinder hooks to. Apparently the pin got installed in the upper hole for hydroboost and in the lower hole for vacuum boost. I ground off the riveted portion from the back side of the pin and knocked it out of the hole. I then installed it in the upper hole and back welded it to make it permanent. The Vanco unit comes with the linkage that connects from the booster to the pedal and everything else you will need. The only thing you need to do is move your existing pin to the upper hole and weld it in place as I mentioned. According to Vanco the pump needs to put out 1200-1500 psi. You can either modify your pump if it is in good shape or replace it with a new one. Here is a link on how to modify it:

http://westtexasoffroad.homestead.co...rsteering.html

They also sell them with the modification done already, but it is easy to do and cheaper to do it yourself. Larry mentioned that the higher pressure is not necessary, so I certainly would try my stock pump out with it all to see how it works before bothering with any changes. My pump needed replacement anyhow, so it all fit into the big picture.

I thought it may be helpful to list some reasons as to why I decided to convert it in the first place. First of all, my master cylinder was leaking, and the leak was partially going into the booster. Both components needed replacement anyhow, so the time was as good as any.
Secondly, I often use my truck to haul heavy loads of firewood, trailers, tractors etc that it really could use some extra help stopping reliably. Leaving extra following distance is a good idea, but when some twit in a honda jumps in the space you are leaving for safety and slams on brakes, you better be able to do something about it. As it was, I was relying way too heavily on the trailer brakes in those circumstances.
Finally, I have a lot of experience driving other trucks with hydroboost, own a 2001 suburban with it and have always liked the extra stopping power that it provided. The great brakes on the Suburban really pointed out the inadequate brakes on the pickup and I finally made the swap.

So why the Vanco unit? It certainly is more money to do it the way I did, instead of the route Larry took with the salvage parts. I am definitely a salvage parts type of guy, but the main issue was time for me. I really did not feel like I should spend the time to locate an acceptable unit, and install it hoping that it would not have any leaks or other issues that I would have to spend time sorting out later. I am very busy currently and felt that I really did not have time to tweak things and get the cobwebs out of used parts. I suppose either path is just fine, but for my current circumstances, I felt this was the best route for me.

Anyhow, so far as the swap goes I believe it is pretty straight forward. I will attempt to give an overview of the various tasks involved with the swap.

As I mentioned above, the pin for the linkage has to be in the upper hole in the brake pedal. The pin is inserted in the hole and the back side is riveted from the factory. My truck already had the upper hole from the factory, and I have another spare set of pedals from a 1973 model that has both holes as well. Even if it did not have the upper hole from the factory, the hole could be drilled if necessary. The booster linkage needs to be as straight as possible, so it would just be a matter of holding it up to the correct position after the booster was installed, marking and drilling the pedal. Then put the pin in the correct hole and weld it to keep it in place. In case someone is not familiar, the pedal swings on a special bolt that has to be removed. The bracket / housing can all remain under the dash. If I had it to do over again, I would have ordered a new set of bushings from LMC for my clutch and brake pedals, but I was lucky enough to piece together a decent set since I had an extra pedal assembly. The plastic bushings are cheap and available though, so there is no reason not to get a set on hand prior to working on it.
Here is a link:
http://www.lmctruck.com/icatalog/cc/full.aspx?Page=155

Part #10 in the drawing shows the plastic bushings for the clutch pedal. They are the same for clutch and brake pedals, so for an automatic you only need 2 instead of 4 to do clutch and brake pedals.

Removing the old booster is not worthy of discussion, and the new booster fit into place just fine. Hopefully Vanco has his bracket situation sorted out since I mentioned it to him. I did remove the bracket from the booster to make the hole slotting process easier, but would not have been necessary other wise. The nut that holds the bracket onto the booster must be able to penetrate the firewall because the bracket mounts flush against it. The hole in my firewall had to be enlarged slightly to provide this clearance.

Once the booster/MC was bolted in place the brake lines are hooked up. The master cylinder I got had the holes for the lines swapped as compared to the old one. I asked him about this and he said it was normal to have to swap front/rear positions on the lines sometimes. The threads were correct, so no issues there. Then the routing for the hydraulic lines must be determined and cut to length. There is nothing really to mention about this except that you may want to consider plumbing in a cooler. Most vehicles that I have worked on that came with hydroboost from the factory come with a cooler, so I thought it best to install one. Vanco said this is strictly up to the individual, but since I was plumbing the lines I decided to go ahead and do it. After running it long enough to do the bleeding process, I was surprised at how quickly it had warmed up even without driving it. I used a small transmission cooler because I found a good price on it. Link: http://www.amazon.com/Hayden-Automotive-676-Rapid-Cool-Transmission/dp/B000C39CL8 I think most any cooler you come up with would be fine, so long as you have the space for it. It is good to take plenty of time to route and secure the hoses properly to avoid any chance of hoses vibrating against something that could create a hole in it. I over engineered mine and used bulkhead fittings to penetrate my radiator support because I just was not satisfied with the options for a route where nothing could hit them. I also used hard lines for the most part, but this was not necessary either. I tend to make things more involved than they really have to be sometimes, but I really hate having to go back and do something again because I didnt do it right the first time.

I was not aware of the bleeding technique that Larry mentioned above, and I did have a few times at first where I apparently had some air remaining in the system after bleeding it. It was not a big problem, but there were a few corners I had to make with no power steering. It worked it's self out and is fine now though.

All in all, I feel that it was a pretty simple swap and was pretty much bolt on. The hose routing for the cooler took a bit of time, but I really wanted it to be secure and out of the way. I am really happy with the results. So far, I have hauled one load of firewood with it since making the swap. It wasn't a terribly heavy load, but the extra braking power was great. I really should have done it years ago!

Here are a few pics of it all:







The picture below shows the supply line going into the steering box and the return line leaving it to go to the cooler. The line coming from the cooler can be seen going over the frame rail before it T's into the return line from the booster as it heads to the pump. I put some rubber hose on it as a chafe guard where it is close to the brake lines.






Here is a photo of the truck and my best helper!



 
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underdrive

jackwagon
SlowJoe, that is a very neat installation, love the cooling lines and bulkhead fittings going through the radiator support.
 

Larry

Bigassgas Explorer
SlowJoe, that is a very neat installation, love the cooling lines and bulkhead fittings going through the radiator support.

For sure! Nice install Joe! Love the bent tubing in the right places. Clean truck too!

Man, you have that timing advanced on that baby. Got a thumper cam in there?
 

underdrive

jackwagon
Oh, a few quick notes on the medium-duty Hydromax units:

1) while the electric backup pump is a nice touch, it is only capable of less than half the pressure as compared to what the unit will produce when running off the PS pump - at 400 lbs of input force (from the pedal) a Hydromax with a 2"-bore master cylinder will normally put out 2000psi of line pressure, in backup mode that drops to around 850psi. The real beauty of the electric pump is that it will rebuild pressure you use as you cycle the brakes on and off, whereas with the light-duty Hydroboost units whether nitrogen-charged (gold or blue accumulator) or spring-loaded (silver accumulator) you only get 2-3 brake applies and then you're done.

2) since I mentioned the 2" Hydromax master cylinder, that's actually the larger of the two available, the smaller is 1-3/4" bore. In comparison the largest master used on light-duty truck from the factory is 1-5/16". That is a rather large difference, and will make for one very short-travel pedal if a even a small Hydromax unit is used on a light-duty truck. And there really is no advantage to the swap other than the electric pump, as both the Hydroboost and the Hydromax are capable of over 2000 psi line pressure when floored, thus I doubt there will be any performance gains from a setup using a Hydromax to feed light-duty brakes.
 

barefoot boy

Observer
"The master cylinder I got had the holes for the lines swapped as compared to the old one. I asked him about this and he said it was normal to have to swap front/rear positions on the lines sometimes. The threads were correct, so no issues there."

So you are saying the front brake line attached to the new master cylinder where the rear brake line attached to the original master cylinder? If so, was this necessity based on the flare fitting size? Thanks.
 

underdrive

jackwagon
His factory master (JB6 RPO code?) most likely had the large chamber (front brakes) towards the radiator and the small chamber (rear brakes) towards the windshield. The JB7-spec (1-ton SRW and heavy 3/4-ton) master he appears to be running now has the small chamber towards the radiator and the large one towards the windshield. Both have 1/2" primary ports (front brakes) and 9/16" secondaries (rear brakes), so just some bending the brake lines around some is needed to have them line up with the new ports position when you switch one for the other.
 

SlowJoe

New member
Thanks to everyone for the compliments!

"The master cylinder I got had the holes for the lines swapped as compared to the old one. I asked him about this and he said it was normal to have to swap front/rear positions on the lines sometimes. The threads were correct, so no issues there."

So you are saying the front brake line attached to the new master cylinder where the rear brake line attached to the original master cylinder? If so, was this necessity based on the flare fitting size? Thanks.


The response from "underdrive" answers your question. The ports that the lines hook to are different threads, so they are not interchangeable. The front line must hook to the front, and the rear must hook to the rear. On the new cylinder these positions were reversed as compared to the old one, and required just a bit of bending to the lines to get them into the new positions. It was not a big deal, but I wanted to mention it so others would be aware if they were considering the swap.


Larry, the cam is stock right now. I put a goodwrench 350 in it, and when installing the distributor I didn't take the time to line it up in the normal orientation that is commonly seen. It runs good and I just wasn't bothered by it. My suburban has the 8.1. I like the power it produces but I don't think I will ever spend the money to upgrade to a big block in the pickup. I would like to get a bit more pulling power out of it with a cam swap or something, but it does a pretty good job as it is so upgrades are not on my short list at this time. Having the SM465 helps a lot with the pulling, so it helps to mitigate the power deficiency.
 

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