View Full Version : Hydroboost Pedal Feel - Should it feel this spongy

06/20/08, 09:29 PM
I have read all of the earlier posts about hydroboost and spongy pedals, but just can't seem to get mine to feel like I think it should. The truck actually stops great. What seems to bother me is once it stops I can continue to push the pedal to the floor - should I be able to do this? I figured eventually the pedal would stop travelling (before hitting the floor pan). Also, I noticed that with the truck turned off the pedal still feels spongy with alot of travel - shouldn't it feel just like manual brakes with the engine off?

I have got an astro unit mounted to a BC Broncos angle bracket. The MC is new from Napa (#101612 '80 Camaro disc/drum). All of the brake lines are new, the front calipers are new (ebay disc brake kit) and the rear wheel cylinders are new. The caliper bleeder screws are pointing up and the knuckle and calipers are properly clearanced.

I have bench bled to MC 3 times, bled the brakes manually 4 times and even bought the pump type pressure bleeder and bled them an additional 4 times with it. I can't seem to find anymore air in the system. The pedal still feels the same to me

Maybe I just don't know what this is supposed to feel like. Someone please tell me this is OK - I am a week away from finally driving this thing after 3 years.


06/20/08, 11:01 PM
Mine has a little sponge feel to it, well after the point of lockup.
Have you pumped the brakes to bleed off the accumulator? I think there is a hair of extra sponge in the manual mode, but it still works fine. Just the hydro servo moving a touch. Not EXACTLY like the old manual brakes, but if you didn't know how it originally was and drove without the hydro running you would feel as if they were just another set of manual brakes. I would call it normal.

06/21/08, 05:11 AM
My pedal is solid. Doesn't matter if it running or not. It just easier to push with the booster. I'd say there's probably still some air somewhere. Park on a decent hill. Maybe even some car ramps if your not on the road yet. Pump the brakes a few times with the engine off to purge any pressure left in the booster. Hold the brakes and see if the pedal moves or the rig does. If it does move you most likley have air somewhere in the lines. Do your caliper bleeders face up? They need to for bleeding.
We had to put 2 1/2 quarts of brake fluid through me buddies Heep before we got the final burp and good pedal feel.:o

06/21/08, 06:46 AM
Thanks for the replies

I forgot the accumulator gave me a few more assisted pumps with the engine off. Once I pumped enough to bleed off the accumulator the pedal firmed up a bit. I think my biggest concern was that I could push the pedal to the floor (when assisted) and yes, this was after the truck comes to a complete stop - other than that the truck stops really well

06/21/08, 07:05 AM
Thanks for the replies

I think my biggest concern was that I could push the pedal to the floor (when assisted) and yes, this was after the truck comes to a complete stop - other than that the truck stops really well

I hate to post this because I know how frustrating these things can be, but I think you still have some problem. IMO you should not be able to push the peddle to the floor. Mine will not go near that far. And if you can push it that far, seems to me that you may have some air in the actual brake circuit (not the hydra boost) or you have a master cylinder with not enough volume. I would keep working on it until the bottom of the peddle is about where it was without hydra boost. When mine had air in it still, I think it reacted very similar to what you are describing. To get mine bled well, I took a brake fluid bottle to the wheel I was bleeding and essentially recirculated the fluid until I could get no sign of air at all, then ran another half MC through each wheel.

06/21/08, 08:36 AM
I just completed mine and I have a very solid pedal feel. Definitly firm and I can't get it anywhere near the floor. At a stop with the engine running I get a litle vibration/push back on the pedal but other then that the pedal feels good both when the truck is running and when it's off.

Any chance you have a leak somewhere? Maybe it's letting air in the system.

Good luck.

06/21/08, 03:42 PM
I just completed mine and I have a very solid pedal feel. Definitly firm and I can't get it anywhere near the floor.

X2, I might have 1" or less of total travel. Not even close to the floor.

06/22/08, 09:28 AM
I can't find any leaks anywhere. I have alredy put 2 quarts of brake fluid thru the system while bleeding it. I get no air at all. I have done the manual (pump and hold bleeding) and used a pump style pressure bleeder and see no more air in the system.

The MC I am using is the same used by others on this forum for a disc/drum setup, so I believe it should have enough volume.

The most frustrating part is that the truck stops amazingly well. I have only tested on my street, but stops immediately from 30 mph with about 1 inch of pedal travel. The problem is that if I continue to press down really hard on the pedal (as if I still had manual brakes) the pedal slowly drops to the floor. It is a very slow, steady drop as if something is bleeding off fluid. The brake light turns on and I believe I can here the PS pump start making noise as I reach the floor.

I just want to drive this thing, but need to get comfortable with these brakes first.

06/22/08, 12:22 PM
So I ran a couple more tests.

I parked on a hill and shut off the engine. Pumped the brake pedal 10 times to bleed off the accumulator. Put the truck in neutral and held the pedal down until it went to the floor. I tried rocking the truck to see if it would roll and it would not move.

Second test was on the same hill, but the engine was running. Pushed the pedal to the floor. Put the truck in drive and hit the gas, while keeping my foot on the brake. Truck still would not move.

Seems like the brakes are working, but why can I push the pedal to the floor? Also tested a few panic stops on my driveway (will need to add proportioning valve in the future) and the truck stops great with little pedal effort or travel, but if I continue to keep my foot pressed on the pedal, it will slowly drop to the floor (takes maybe 5 seconds to reach the floor and I need to press really hard)


06/22/08, 01:29 PM
I had all kinds of issues like this until I got all of the air out of the hydaboost unit. When you push hard to the floor 5 times in a row and shut off the engine and check your PS fluid, does it drop any? If so you still have some air in your hydaboost unit or PS. The noise the pump makes is getting me to thinking that it is low on fluid maybe? Then again, in your case I am thinking it must involve the MC because when all is said and done the rod on the MC would have to be what is allowing the peddle to drop all the way to the floor. Is your MC new or used? Is it loosing any fluid at all?

06/22/08, 03:43 PM
Thanks Buldozer. I ran your test pumping the pedal 5 times and the PS fluid level did not change. I did not see any bubbles in the fluid and the pump made no noise. The pump is a new dual return unit from a 77 Lincoln. I even tried rebleeding the pump by jacking up the front end and turning the wheels lock to lock 5 times with the engine running. Still the issue remains

The MC is new as well and it not losing fluid.

I also pulled the rear wheels and drums to see if I was overextending the wheel cylinders, but all was dry with no leaks.

I can't believe I would still have air in the brake lines after all this, but it might be the case. I thought the pressure bleeder would have taken care of any remaining air, but maybe there is still some in there. I will try to do some more manual bleeding tonight (my wife will be pleased).

By the way after all this testing my brake warning light is on and won't go off, no matter how many times I try to center the pin - could this be indicating something?

Any more help would be appreciated

06/22/08, 04:31 PM
Anyone think I need to go back to NAPA and ask for another MC? After reading alot of past threads I am thinking maybe I got a bum MC.

06/22/08, 10:34 PM
IT's not your brakes, its the Hboost or the system itself.
I would suspect some dirt or other crap in the system allowing the leakdown.
A new or used Hboost?? Gotta ask, some guys buy new.
check the rod out the back of the Hboost for leaks. This is my suspicion
Also look in the steering pump for air bubbles. Bubbles are not good.
Suggestion - - - rebleed the hboost system, this time start with a loose low pressure line on the hboost and let it pump out about half a can of fluid.
Then do the bleed sequence again, get the instructions from Hydrotechs site and follow it religiously

06/23/08, 05:28 AM
Thanks for the reply TOFIC

Hboost unit is used from salvage yard. No leaks out of the rod at back. No bubbles in the PS pump.

When trying to clean out the hboost unit from the low pressure side do I pump by pressing on the brake pedal or do I need to spin the motor/PS pump?

I can't find the bleeding instructions on hydratechs site. Is it in their forums area (which is currently unavailable)?

06/23/08, 07:38 AM
I don't have hydroboost on my EB but...
at work we have a whole slew of new chevy trucks with hydroboost, and on almost all of them, the pedal is kinda spongy, and you can push the pedal to the floor. it's a little unnerving, but it's supposedly normal.

06/23/08, 10:17 AM
That is funny that you cant find the sequence, Paul Clarke at Hydrotech (he owns it) is great about this. Have another look or send him an email I know he will help.
short version
disconnect LP line start and idle engine for 1/2 can of fluid stop engine. reconnect line
refill can with fluid
put front axle on jack stands with wheels off the floor
start engine
turn steering back and forth a couple of times.
check PS pump for fluid level top up if needed
start engine, turn wheel back and forth again twice.
recheck fluid level top up if needed.
keep it up until no change in level
should firm everything up
My hboost is rock hard running and discharged I defy you to get it to go to the floor (mine is a 76 Ford unit, see article on side<<)

06/23/08, 11:11 AM
Mine has a little sponge feel to it, well after the point of lockup.

Mine have some sponge to them too. They've been that way with 3 different boosters (2 used, 1 new) and several different brake configurations. The only time I've had what I consider a "rock hard" pedal was several months ago when I was doing some testing of a prototype big front brake kit with 2 piston calipers. When I went back to my single piston Lincolns after completing my testing, it had its old feel again. I've gotten used to it and I know that although I can push my pedal to the floor if I really try, that point is well past lockup when the engine is running. Lars on this board has the identical setup to me (booster, master, and front/rear brakes) and his pedal is harder than mine. So I could imagine that I might have some air in my system somewhere.

Todd Z.

06/23/08, 11:14 AM
That is funny that you cant find the sequence, Paul Clarke at Hydrotech (he owns it) is great about this. Have another look or send him an email I know he will help.

Forums are down at the moment and Paul is unreachable via email or phone anymore. Unfortunate.

Todd Z.

06/23/08, 12:00 PM
If you think you are having any issues with the brakes - clamp off the front and rear brake lines at each axle. Put fuel line of a vise grips and clamp the rubber lines running to each axle. If you still have break issues it HAS be be at either the MC or Hydro unit. Sounds like your Hydro is in need of a rebuild..

06/23/08, 12:28 PM
Just to muddy the waters. I popped the rear brake line on my bronco the other day on accident and it leaked a fair amount of fluid from the rear lines and I would expect picked up some air before I clamped it off. I replaced the line and drove it around a bit without bleeding and my pedal was spongy but still stopped on a dime with the hydroboost. I rebled the system and now the brake is rock hard again.


06/23/08, 07:05 PM

I started your re-bleed procedure, but wanted to confirm something before I continue.

I disconnected the LP line from the PS pump and capped the PS pump connection. The other end of the line is still attached to the Hboost. I placed the hose in a jug and started the engine and let it idle. Nothing came out of the hose - is that OK?. I couldn't get anything to come out of the hose until I stepped on the brake pedal. Fluid flowed most when I had the pedal down. Once I let up it slowed to a trickle then stopped.

Just want to be sure this does not indicate a problem.


06/23/08, 10:50 PM
nope sounds good, keep going.
I am still betting on something in the system so continue.

07/05/08, 07:22 AM
So I finally got back at my brake issue. I ran throught TOFIC's flushing process 2 times and still had the same results. I swapped in another master cylinder and the sponginess went away - so it was either a problem MC or I did a better job bench bleeding it. I still can push the pedal to the floor, but it was well beyond the point of lockup and I literally push myself out of the seat doing it. If I get the urge one day, I might pull apart the hydroboost unit and rebuild it just to be sure there is not some lingering issue, but I drove the Bronco for an hour the other night and all went well

07/05/08, 04:42 PM

Glad to hear everything worked out. I currently have a BC setup in my bronco and I would like to convert it to an Astro hydroboost as well. Can you possibly post some pics of your set-up. It would be greatly appreciated


07/05/08, 05:06 PM
I have some pictures of the tee setup and the dual return
Also have some of the shifted hydroboost setup (mounted in clutch pedal location)
Want some of these pictures??
glad you found your problem, I trust you are enjoying the "stop on a dime, and get 9 cents change" style of braking??

07/05/08, 05:35 PM
Thanks TOFIC! Some pics of the tee and dual return would be great. I am looking to see how KDML mounted his Astro booster to his BC angles bracket.

Thanks again,

07/07/08, 08:37 PM
Pictures as requested.

Setup consists of BCB angle bracket, threaded rod couplers to space hydroboost off the bracket, homemade flat mounting plate and the astro hydroboost. I could not find a threaded rod end I liked to mate the hydroboost pushrod to the BCB bracket so I ordered a 3/8 rod end blank from McMaster-Carr (#6065K241) and drilled, shaved and threaded it to fit. I bought adaptors from Summit to convert the hydroboost high pressure fittings to -6an (part numbers were AER-FBM2608 and AER-FBM2609). If you have any specific questions or need other pictures let me know

Good luck

07/08/08, 01:29 AM
Excellent Pics! Thank you KDML