hydro boost install

[coxfmly]

I just pulled a hydro boost unit off of a wreck that isn't leaking and looks relatively new. before I swap it out do I need to lube the input shaft which goes into the brake booster? any special prep prior to install and are there any differences in power steering fluids?

thanks

[DmaxMaverick]

Nothing special. It doesn't hurt to slobber some grease on the shaft ends, and whatever linkage you can reach while under there.

Use a quality name brand synthetic ATF (Mobil-1, Amsoil, Redline, etc.). Don't waste double the money on inferior PS fluid. If you are only replacing the HB unit, flush the system with fresh ATF. Remove the HB return line and route into a container (use an extension hose at the nipple). Overfill the reservoir, idle the engine, and pump the brakes and turn the wheel lock to lock. When you hear the pump complain (growl or whine), stop the engine, refill, and repeat. Do this until the fluid coming out is the same as going in (2 qts. or more). Replace the return line, top off, and motor on.

[rustyk]

I've become somewhat of a reluctant "expert" in bleeding Hydroboost, as I've had the system apart several times in the past year: Replaced 3 pumps (2 Saginaw/Nexteer defective with broken shafts), the HB unit itself, and the HB-operated shaft brake. With the engine in the rear, my lines are about 25' from the pump to the HB, so bleeding is no fun.

I agree with dMax except for one part of the procedure: Don't wait for the pump to complain; if it gets that far, air can be reintroduced into the system.

Use a clear or translucent container and a clear hose. Do the procedure dMax recommends, but stop the engine after a couple of cycles. Top off the reservoir, wait 10 minutes, and repeat until no more bubbles can be seen. Waiting is an important part, so the entrained air can migrate to HB unit where the return line can purge it.

The system does self-bleed, but it's best to start as air-free as possible; because the HB is the system high point, using dMax's technique works very well.

[DmaxMaverick]

Thanks for the reply, Rusty. The system in a pickup/SUV will absolutely bleed itself, and very quickly. The pump is low, the output is up, and the steering box return is up to the pump. Your application is unique, and bleeding could be an issue in your case with the components and miles of tubing all at near level fluid travel. I've done this hundreds of times on trucks for years (an exaggeration, of course, but more than I can count....maybe). The process is the same, from a 1982, all the way up to current model Duramax trucks.

[coxfmly]

I will tackle this in the morning and let you know how things go.
Thanks again for all of your help

[rustyk]

Thanks for the reply, Rusty. The system in a pickup/SUV will absolutely bleed itself, and very quickly. The pump is low, the output is up, and the steering box return is up to the pump. Your application is unique, and bleeding could be an issue in your case with the components and miles of tubing all at near level fluid travel. I've done this hundreds of times on trucks for years (an exaggeration, of course, but more than I can count....maybe). The process is the same, from a 1982, all the way up to current model Duramax trucks.

Sometimes I envy the simplicity of the systems in "normal" vehicles . Owners of those envy the access I have to my engine (the engine room is 4'x6') .

[DmaxMaverick]

Sometimes I envy the simplicity of the systems in "normal" vehicles . Owners of those envy the access I have to my engine (the engine room is 4'x6') .

For your application, it would be ideal to have an external fluid reservoir, with a sight glass or level indicator. You have the room for it, and it would negate any air/cavitation issue. Servicing/flushing would be a piece of cake.

[coxfmly]

Help...
I pulled the Hydro Boost unit off of my 94, and upon inspection I noticed the brake pedal shaft has a different shaft (end) opening size than my replacement. The replacement unit (wrecking yard find) has a smaller end opening. Both units look identical subject to the shaft hole.

It looks like the original shaft has an opening of approximately .620 with the replacement unit at .570. The brake pedal has a stepped shaft from .500 to .580. I could massage the I.D. of the replacement end opening .020 to make it fit, but I don't want to do anything crazy. I would assume the I.D. of the shaft is there for a reason, other years or applications.

The original unit had a lot of play on the arm. What should I look for or should I just buy another replacement (new) unit?

Thanks again,

[DmaxMaverick]

While all the HB units are the same in design and function, there are subtle differences over the years, dependent on application. If the one you have doesn't fit, I do not suggest modifying it. Even if it does fit, verify it is compatible for your truck. If you get one that does fit, but you are unsure of the application, thoroughly test your steering and braking systems after the install.

The HB units are the pressure/flow manager for the entire power brake/steering system. Depending on model and year, the steering systems have changed, and have different requirements. Make sure you replace with the correct series unit. Even the same year and model may different, comparing SSS (Speed Sensitive Steering) to non SSS equipped trucks (this was an option for some years/models)

I don't have part numbers on hand. Look up various models/years and compare part numbers.

[coxfmly]

Looks like its shopping time, Thanks

[coxfmly]

Dmax,
Picked up a rebuilt unit from Napa for $170. flushed the system with Valvoline synthetic ATF and I'm back on the road. Thanks for all of your help....

[DmaxMaverick]

You're welcome. Glad to hear it's behind you.