Hydroboost troubleshooting

[TonyPDX]

Ok, I am stuck on this one. I rebuilt my entire brake system and now the hydroboost applys some presure to the brakes when I start the engine. It applys so much pressure it will hold the Bronco still on a small hill. If I turn the engine off it will imeadiatley roll down the hill like it should! I rebuilt my own hydroboost so I figured I did something wrong and bought a professionaly rebuilt one and swapped it in, but it does the same thing! What is going on? I disconnected the pushrod from the pedal to ensure it was not holding the pushrod in, that made no difference. The master cyilder and Hydroboost are both for a 78' Lincoln Mark so they should be compatible.

Help!!!! I want to drive this dam thing!

 

[elemetal]

You have pressure going to the brakes (duh) when its not supposed to be. Has to be an slightly open valve in the hydro unit due to mc/pushrod interference. Only other thing I can think of is too high of a input pressure from the ps pump forcing a valve open. Is the right pulley on the pump? Just trying to post up some possible causes.

 

[TOFIC]

Let me take a stab at it.
If both units are reacting the same (new and old) we can safely rule out the hydroboost unit itself. If both units react the same they cannot be the part at fault.
The accummulator on the unit should be good for one to three assisted stops. If you are not getting this reaction it is in the high pressure side of the system, it is not getting enough pressure. Check the output of your pump. Is your power steering acting correctly?
Another thing to check is the low pressure return line from the Hydroboost unit to the PS pump. If this is blocked or leaking it will cause really unique conditions in your system.
Check the actuating rod between the booster and the MC. Although I doubt this may be the problem have a look.
The pushrod should have little or no slop in it. I believe the setting is about 20 thousands of an inch.
If none of these conditions exist, I am confident it is your master cylinder. I used the old one off the Bronco and the one off the Lincoln and both work fine. Change out the MC for your old one off your Bronco and I will bet things will be fine.

TOFIC

 

[70bucks]

If you tee'd into your P/S return line for the hydroboost return you could have too much resistance. The resistance against the hydro return is what triggers the mechanical assist from the hydro boost. Try temporarily disconnecting the return line and hold the return so it re-enters the pump at the filler neck. (prolly need 2 people) Did you braze a return to your pump, or how are you handeling your pump return? Should be easy to check for petal free play on the brake pedal to rule out that posibility before disconnecting anything. Good luck

 

[TonyPDX]

Elemetal, Thanks for the reply. The push rod is the right one for this application as it is all for a 78' Lincoln, and when the engine is off there is no residual brake pressure so I don't believe this could be the cause.

Walker949, I have not tested the accumulator function, which should be a good thing to check so I will do that tonight. The power steering feels just fine and all the lines are new and plenty big for this application (AN 6). However I do have a cooler in the return line. It is a straight flow through design but I wonder if this could be an issue? Since the residual brake pressure goes away as soon as I turn the engine off I don't think the master cylinder could be the cause.

70bucks, thank you also for your reply. The return line shouldn't have too much resistance as I noted above it is all new AN-6 but I am going to check and see if that is the problem. I will disconnect the return line from the cooler and return it straight to the pump and see what I get....

Thanks again, for all you suggestions. Please keep them coming I want to get this fixed!

 

[toddz69]

Where is your return line plumbed in relation to where your cooler is in the return line? In other words, is it tee-d between the box and the cooler or between the cooler and the pump?

Sometimes the h-boost can act like you're describing if the h-boost return is tee-d in between the box and the cooler.

Todd Z.

 

[70bucks]

Hey Tony, what did you discover?

 

[TonyPDX]

Todd, I think you got it. I verified that pushrod was not the problem, and the brakes seem to act normal with the engine off. I finally was able to replace a seeping fitting and do some more testing last night. When the engine is started it actually pulls the pedal down about 1". Yes, the "T" is inline before the cooler, and I have verified there is substantial back pressure being fed to the hyrdobooster on the return/bleed line.

Do you think putting the "T" after the cooler with fix it or do I need to tap the P/S pump can for a second return line?

Thanks everyone, Tony

 

[lars]

Tony, I finished installing a hydroboost system in my Bronco about a week ago. I'm using the boost unit from a late Chevy 3/4 ton truck, with the same Dodge master cylinder as Todd uses. My pump is a Saginaw. At first I had the hydroboost drain line tee'd into the return line just above the pump (I have a cooler too, but it's upstream of the tee). I had all the problems you did. My pushrod setup is quite a bit different due to the master cylinder/h-boost combo; I machined an adjustable adapter so I could change the clearance/interference. Once I got the thing adjusted to the point that the brakes didn't drag with the engine running the pedal was unacceptably low. After reading this thread I pulled the pump and removed the reservoir. I had an old Saginaw canned ham reservoir in my junk pile. I used a hole saw to remove the return tube from that reservoir and welded it into the side of my good one in the same location as all the "hydroboost specific" pumps that I've seen. While I was at it I got rid of the piece of sh*t AGR pump that was dying anyway and stuck in a Saginaw pump from a hydroboost application (2002 Chevy pickup, which is the same as the one used on a 1980 Chevy pickup, it turns out). I also changed the adjustment on my adapter to get the pedal back. The new pump was quiet right away, and the system bled itself and started behaving after a couple of stops. The brake drag problem never came back. After several days of driving with it the pedal is still a little slow but it keeps getting better. I think the biggest reason for the improvement is the relocation of the drain line. You *really* don't want any back pressure into the hydroboost. The only problem I have now is that if I forget and apply the brakes as I used to do, I lock all 4 wheels.

Lars Pedersen

 

[TOFIC]

Tony:

A small tidbit I just learned the hard way.
After reading the posting I have the same T fitting in the return line. I wondered if this could be your problem.
I was walking through my "free" scrap yard and found a saginaw pump with dual return lines. Pump was pooched but the can was good. Took the can off the pump cleaned it up and put in on my good pump. Connected everything and tried the brakes. I got a little increase in power and lost an annoying seaping leak. You might want to try this modification.
TOFIC

 

[toddz69]

Todd, I think you got it. I verified that pushrod was not the problem, and the brakes seem to act normal with the engine off. I finally was able to replace a seeping fitting and do some more testing last night. When the engine is started it actually pulls the pedal down about 1". Yes, the "T" is inline before the cooler, and I have verified there is substantial back pressure being fed to the hyrdobooster on the return/bleed line.

Do you think putting the "T" after the cooler with fix it or do I need to tap the P/S pump can for a second return line?

Thanks everyone, Tony

The "T" after the cooler should fix it, but take Walker's suggestion and find a pump reservoir from one of the cars that originally had h-boost and swap that it.

Definite win on sano points vs. a "T" in the line!

Todd Z.

 

[heylouie00]

What have you guys done for the hi pressure hoses?

Make your own? Some application, maybe w/adapters? AN?

I have the explorer pump & EB Box.



Sorry for the hijack

--Craig

 

[TonyPDX]

Well I tested the system while holding the return line from the hydroboost going straight into the fill neck of the pump so I knew there would no back pressure on the line and guess what! The brakes don't self apply!
So, I pondered the rerouting of the return lines and the "T" only to I arrive at the same conclusion you guys suggested (two return ports).

I got two AN-6 bulkhead fittings and installed them in the pump reservoir. I drilled out the original return line tube and welded in one of the cut down bulk head fittings and drilled a new hole in the can to install the second bulkhead fitting. Now I have two returns and neither will require a hose clamp! I hope to get the whole thing reassembled tonight and test it.

Craig, I used Parker 919 SS hose and 90 series filed replaceable fittings to make up my lines. Any hose shop should be able to make up the hose you want for $20-$30 if you don't want to do it yourself. Take any old lines you have with you so they can see (and possibly reuse) your fittings.

Tony

 

[teqoso]

Hey guys which pumps have you used that helped with this swap. I did my install awhile ago, and everything that you guys are talking about is the same problem mine is having. I currently am running BC broncos steering pump. I am unsure whether it will accept two return lines. Can someone also include a photo of their setup to assist me visually. Thanks guys

 

[70bucks]

Hey guys which pumps have you used that helped with this swap. I did my install awhile ago, and everything that you guys are talking about is the same problem mine is having. I currently am running BC broncos steering pump. I am unsure whether it will accept two return lines. Can someone also include a photo of their setup to assist me visually. Thanks guys

I am currently running a saginaw pump so brazing an additional return line was fairly simple. The original set-up I used was a new ford style pump. I cut the top off pump and added t pieces of fuel filler hose so I could splice a piece of 2" pipe into the filler neck . Then I brazed a return line into it. It was ugly, but since it was a new Ford pump when I installed it I figured i'd use it up before buying the Saginaw. It also got rid of the pump whine.

As far as the question on hoses I was able to make up all the SAE stuff with Aeroquip parts. When it came to the hydroboost with the metric o-ring fittings I ended up having to buy new hoses and cut the ends off. If I did it again I'd shop for a boost that didn't have the goofy Ford fittings. Even the Hose Pros (they make aftermarket hyd hoses for the heavy equipment industry) who usually carry everything on the truck to cover all types of equip from US to Korean made couldn't match them up.

Hey, Todd Z. help me to understand how the location of the return line relative to the cooler changes the back pressure to the booster.

Good luck to all.

 

[TOFIC]

Regards to the question about the pumps with 2 returns.
I found mine in the free parts scrap yard. Out of a diesel pickup I believe.
The accumulated grime just reeked of diesel fuel. Was a Sagainaw pump.

TOFIC

 

[lars]

For a visual on a Saginaw pump with dual return ports, go to the Napa website http://www.napaonline.com/cgi-bin/ncommerce3/ExecMacro/NAPAonline/homepage.d2w/report and type in part no. NSP208726 in the "Napa Part No" search box on the left. Click on the product name description and you'll get a page with clickable pictures of a dual return Saginaw pump as used on a 1983 Chevy 3/4 ton diesel with hydroboost and without a/c. The a/c part matters only because the vehicles with a/c had a remote reservoir.

Otherwise, go to a junkyard and see if you can find a hydroboost-equipped vehicle, like walker949 suggested.

GM used the same Saginaw pump on all large hydroboost vehicles from at least 1980 to 2002 as best as I can tell. The can (reservoir) changed along the way, but that's it. The bare pump is part no. 20860 at Napa. That's what's in the assembly I described above.

You can get GM metric o-ring to JIC-6 adapters from Aeroquip. They are available online from Speedway motors, along with reusable JIC fittings and high pressure hose for power steering applications. They also have Aeroquip inverted flare to JIC adapters for the power steering box. Speedway's page with plumbing stuff is http://www.speedwaymotors.com/xq/as..._p.2/deptSearch_id.2/qx/prod_list_display.htm
For most GM hydroboost applications you'll need a GM 16mm to -6 and a GM 18mm to -6. If you have a Saginaw steering pump, the older ones were 5/8" inverted flare, the later (metric) ones were GM 16mm just like the h-boost.

The reason you can get some back pressure in the hydroboost drain line if you tee into the main return line is that there is a lot of fluid flowing in the return line, and even though the pressure is very low in that line, it's not zero. If it was zero, there would be no fluid flowing. One of those fluid mechanics concepts that takes a while to soak in, then suddenly it makes sense. If you *really* want to know, it's described by Bernoulli's equation.

 

[Unregistered]

The reason you can get some back pressure in the hydroboost drain line if you tee into the main return line is that there is a lot of fluid flowing in the return line, and even though the pressure is very low in that line, it's not zero. If it was zero, there would be no fluid flowing. One of those fluid mechanics concepts that takes a while to soak in, then suddenly it makes sense. If you *really* want to know, it's described by Bernoulli's equation.

I get the backpressure present in the PS return line, I don't understand affect the cooler placement in the return line has on the backpressure. Todd Z. has been pretty spot on with any of the posts I 've read of his, so i'm sure there is relevance to the statement, I'm just curious why.

 

[70bucks]

I get the backpressure present in the PS return line, I don't understand affect the cooler placement in the return line has on the backpressure. Todd Z. has been pretty spot on with any of the posts I 've read of his, so i'm sure there is relevance to the statement, I'm just curious why.

This is me soooooory,


Joe

 

[lars]

The cooler resists flow through it. Not much, but it makes a difference. So if you put the return tee for the hydroboost drain upstream of the cooler, then the hydroboost drain sees even more backpressure. If the tee is downstream of the cooler then the hydroboost doesn't see the additional backpressure, in which case having the cooler makes no difference. It seems that the best location for the hydroboost drain return is straight into the reservoir though. In that case the cooler is totally irrelevant.

On the subject of coolers, the junkyard is a great source for them. Ford used a stacked plate power steering cooler on a lot of later F series trucks. They are usually right behind the grille near the bumper. Kind of a PITA to get to, but my favorite local yard sells them to me for 5 bucks. They have metal tabs on them that make it easy to find a mounting spot in front of your Bronco's radiator.