Another Hydroboost Conversion - Problem???


Senior Member
Nov 26, 2001
Alright, I went with the parts listed on the other conversion thread and ordered the parts through advance auto.

All is connected and tested. Results, when I am barely moving and I depress the brake pedal, the car stops immediately. However, if I boost up to say around 35 mph and try to lock them up, the pedal will go all the way to the floor without locking the wheels. The car will slow down but they will not lock up.

When sitting in the car at idle, I can depress the brakes and feel them solid to about half way or less than if I continue to depress the pedal I can take it down to the floor. This isn't right, is it?

I bled the brakes, gravity style, on all four corners. So is it possible the Master Cylinder may have an internal leak? By the way, I benched bled the cylinder, so no air bubbles after completion.

It is a reman, so you guys think it may be bad, as I don't know other than trying another one to determine if that is the issue. :confused:

If it is going all the way to the floor like that, I'd suspect a bad master. If you had a small amount of air in the lines, it would feel spongy. You should be able to sit at idle and hold it at a solid point with no further downward movement.

I have never had good luck gravity bleeding, but I don't think that is your problem anyway.
I suspect the same thing, so off to buy a new one this time. Going to try the newer version and see how that works.

I will update the thread when completed.


Good luck. Let us know what part number you end up going with and where you got it. I don't think Advance sells new masters for this conversion.
Ok so I went with the NM2220 as it was the only one available in my area. It's diffently larger than the the other Cardone reman I purchased.

So with this one now installed, the brake pedal feels correct and I cannot depress the brake pedal all the way to the floor (car off) like I was able to with the other one. So I think this one is good.

Now, I went with gravity bleeding the brakes but not sure If I did them long enough? Anyway, when I went to try the brakes, I had the same thing, with normal driving (slow) the brakes work but if I try to spped up and try to lock up the brakes, the pedab travels all the way to the floor.

So is this an indication of air still in the system? If I try to bleed the brakes with someone helping me to pump bleed them. I understand I should put a clamp at the proportioning valve. Question, I still have the cast iron one and not the brass one. However, I do see the pin at the end sticking out. Is that correct? If not, how do I get it to reseat? It's a pain in the ass to get a clamp in there, so I may have to come up with something else.


You might still have some air in the system, but I would think it would be spongy in any case no matter what your speed. Regardless, I bled mine with speed bleeder screws, so they don't require the constant open/close with pump method. I just ran a tube from the bleeder to a water bottle and pumped until there were no more bubbles.

The plunger on the proportioning valve MUST be depressed during the bleeding and it should remain there during normal operation. It isn't hard at all to get a clamp in there if you use the right kind. I used a woodworking slide jaw clamp, the with the pistol grip.

If you need to reset the proportioning valve, check here.
Does it only need to be reset if the brake light is on? Mine is not on.

I am going to try and get a clamp in there, but it seems like I need to remove the shift gear out of the way so I can get a clamp in there. :confused:

Anyway, I am going to try it and see how it goes. Hopefully air in the system is the issue.

If the pedal feels like a "rubber band" it's the booster. Been there---done that. :rolleyes: Get another booster. ---Keith
I just did a hydroboost conversion. When it came time to bleeding brakes, I used a reverse brake bleeder from Phoenix Brake Systems I got from Sears mail order for $139 plus shipping. (I've seen them about $15-$20 cheaper on eBay) With the reverse bleeder, all you do is open the bleeder screws 1 at a time, attach the hose that is connected to a hand squeezed pump which is fed by a bottle of brake fluid, take out some of the brake fluid in the reservoir and then activate the pump.

The idea is it pushes the fluid from the calipers upwards into the master cylinder, which also pushes up the air bubbles (law of physics). With this kit you can bleed the brakes all by yourself (1 man job), and you don't have to push in the button on the proportioning valve. (I didn't anyways). I did each bleeder screw 15-20 pumps, and checking the master cylinder as it would fill up with fluid injected in the pump. Then pull the hose off the bleeder screw, let the screw burp a little fluid and tighten down.

Took the car out and the braking power was very good. Darn near threw me thru the windshield. I also tried this when I had a powermaster set up and it was better with the reverse bleeder than it was before.

Hopefully this might be of some help to you with brake bleeding.
Well it seems I'm still having issues with the Hydroboost.

I returned both the Booster and the Master Cylinder. I received the replacements. I benched bled the MC until no more bubbles appeared.

Installed both items and bled the brakes using a hand held brake vacuum pump.

When I tried depressing the brake pedal, I can push it all the way to the floor. :confused:

Is that a sign of a bad MC?

I really want to get this going and it's driving me nuts.

What am I doing wrong or not doing? :rolleyes:

It is going to either be air in the lines or a bad master again. I have never had good luck bleeding with a vacuum pump. If you insist on doing it that way, you have to tape the threads on the bleeders to prevent air from getting sucked back in. Speed bleeders are really the way to go if you want to get a good bleed cheaply. Those Phoenix reverse bleeders are NICE, but it would take a lot of brake jobs to pay for itself. :)

If it were me and I was sure I bled the brakes by the book, I think I'd punt and get a NEW master. Remans are a crapshoot.
I was using a Mity Vac to bleed the brakes.

I am ordering the speed bleeders and try that first. If I still have the same problem, I will get yet another MC and try that.


Pedal to the floor, only with the engine running, or both with the engine running and without? If it goes to the floor without the engine running, bad master....only with the engine running, bad booster.
had the same problem got a new.not rebuilt master and bleed, bleed, bleed!turbonut85 helped me after dozen of ?,s.
With the car off, I cannot push the pedal to the floor. With the car on I can.

However, I am going to bleed the brakes again just to be sure. :rolleyes:

With the car off, I cannot push the pedal to the floor. With the car on I can.

However, I am going to bleed the brakes again just to be sure. :rolleyes:


Does the pedal feel like a "rubber band" until it gets down to around 2" off the floorboard? (WITH the engine running) If you let the car move slowly, can you still stop the car with alot of foot pressure?? These are all symptoms of a inoperative hydrobooster...not a bad master cylinder. If you have absolutely no brakes what-so-ever, and the pedal literally goes ALL THE WAY down to the floor without slowing the car AT ALL....that would indicate a problem with the master, an external brake line leak, or a very large volume of air in the brake system. If you have bled as you say you have...I would lean towards the booster being the issue. I know you have replaced it once already----but that's where I'd start, if it were me....and believe one time it WAS me. Like stated above, the boosters are remans as well, so there have been a number of issues with them as well as the reman masters. Unfortunately, you can't get this particular booster new anymore...only remans. It's a pain in the balls to keep returning them---I understand---but they are under warranty, so keep doing it until you get one that works. Good luck and post back what you find. ---Keith
Hydroboost conversions

Well, Hello Gentlemen! I have offered a lot of advice here, and I feel I started the hydroboost conversion thing. I get beat up a lot here, and don't know why. I don't know all the components you used, nor the master cyl piston size. We use NEW BOSCH units, and designed them to fit the car properly without cutting rods and brackets. We normally use a 1.125" master, but a 1" piston could be used. USUALLY when the hydroboost pedal drops, it is because of the P/S PUMP. The relief valve in the pump, can stick, causing this "pedal drop". This happens when the sediment of a 25 year old steering box washes up from the opening of the lines in the steering system. The air in the pump foams, and then floats the sediment up into the relief valve. It must be removed, cleaned, and the spring stretched. Rarely, because of the huge size of the crank pulley, the pump could be oversped, causing it to cavitate, and lose pressure. This occurs at over 6000rpm pump speed. It can reach 12,000 rpm beacuse of the pulley speeds.
Buying an ad

O.K. sure, But oddly enough, people here are buying junkyard vacuum boosters, junkyard hydroboosts, and cobbling them on. Thsis is UNSAFE in the hands of people inexperienced in brakes. Brakes are much more than "Slapping in a set of pads". I did not mention the name of my company, BTW. Readers here are buying junk, and then spend more time trying to figure out why they have MORE problems. BRAKE FAILURES can be DISASTROUS! I STARTED the Hydroboost swing here, and have offered advice for all brake problems here, free.
As an aside, I lost $40 MILLION from ex-employees who embezzled my inventory and CUSTOMER LIST to start a competing business, particularly selling REBUILT hydroboosts, claiming they were NEW. THAT is fraud. However, how does that void my knowledge or advice? Yes. I AM THE ONLY AUTHORIZED O.E. Distributor for NEW BOSCH Hydroboosts. WHY? How does that make me a bum? I would think that on this forum, some would believe Bosch's faith in MY company would bring in some respect. NO ONE here can match my 45 years, at 60-80 hours a week of working strictly on brakes on ALL vehicles could offer more thorough, and tried and true ADVICE. If so, step up.
BOSCH has sued both Hydratech and ABS in Federal Court for "Trademark Counterfeiting" and "False Advertising". It took a long time, but they are coming to defend my company.
Do I have lots of money" No. It's been a struggle because of the THEFT by my former employees. My advertising budeget is very slim.
I guess it's all about paying for an ad here. O.K. How much? How much to offer safe, quality brakes to the members here, so they have a choice of putting new units on their car, or going to the junkyard? It's their car, and their families lives at stake.
Understand there Bob...and that's why when I did my hydroboost conversion, I went and bought all the parts fresh that came on the hot air cars. Yes the brakes are an area not to skimp out on. I wasn't going to try to source an unknown conditioned brake part from the junkyard and try to make it work. I had a few offer me an Astro van models HB that required cutting/modifying of the brake pedal to master cylinder actuating rod. I'm not a fan of hacking something up to make it work if I can get a unit designed to fit on the car. Only real mod I had to do to make a hot air brake set up work on an intercooled car is to bend one of the power steering lines just a tad to fit into the power steering pump.

I know you did not mention the name of your company but I've read some of your posts which clearly shows you promoting your product. I think it's great you offer a solution to the "prone to fail when you least expect it and repairs will milk your wallet dry" Powermaster brake system. Perhaps you should become a vendor for this board. I'm not sure how it works but I'd assume it's some sort of sponsorship...meaning you pay Shane or Jay to help keep this board running and in turn they'll allow you to have a spot on the vendors page plus you can talk everything and anything about your product and no one can/will say anything...because you've paid your dues to keep this board afloat.