96 Cobra Odd Steering System Noise

[Gears468]

Hello,

My son and I have just about gotten his 96 Cobra back on the road. One issue has us stumped and after trying every diagnostic we know and searching we don’t have a real answer. We would prefer to not start throwing parts at it, but maybe that is where we are at.

The steering system has the Ford rack and hydroboost. It has a Lares ‘new’ pump. We converted the lines to braided 6 AN on the pressure side. We are using Mercon V fluid. On startup all is quiet, but as the fluid heats up a low steady moan shows up and stays. The specific location of the noise is in the hydroboost which is weird to us. A moan would indicate air getting in the system in our experience.

We have vacuum bled the system multiple times and when rolling the steering lock to lock we consistently get air in the fluid separation canister when the rack is closing in on the lock, especially on the right. If we roll the wheel with engine off you can hear a pronounced gurgling from the pressure line from the hydroboost near the rack inlet. Once again right seems louder than turn left.

No leaks anywhere. The brakes work great and the steering assist is fine as well. It will make some noise at full lock when the bypass is working but nothing unusual. Just that nice low moan to accompany the 4v exhaust lol.

Is is possible the rack seals are failing and pulling in some air but not enough to leak? Or is the pump just a bad build? I have never seen a hydroboost fail but this one is 30 years old so maybe it is?

If helpful I can post up a video clip too.

Any thoughts are appreciated. Thanks.

Phil

 

[95opal]

Id look at the fittings on the pressure line since you said you changed them

 

[cobrajeff96]

Does the level in the reservoir change noticeably between cold engine off and when it's been operating for a while? This could indicate an air pocket and thus pump cavitation. Keep in mind that a groan can travel through the system and into a solid mass such as the hydroboost. Were you able to pressure test the new AN line before installing it? Summitt has an AN pressure test kit, it caps off one end of the AN line and the other has a schrader valve on it.

I never liked the Ford C-III style of pump. I went through three new Lares aluminum pumps a couple years ago, they all screamed above 3k rpm. I got rid of them all and went with the GM type-II pump and it's been great so far.

 

[Gears468]

Thanks for the replies. We did test the lines before install with that exact Summit kit you mentioned, but we will look at them again. I have no way to full pressure test at PS operating levels unfortunately. Maybe we can scrounge some decent OE hoses to see if that helps.

That makes sense on the noise seeming to come from the hydroboost, that is just where the air is camping out. The 96-98 hydroboost has that bleed screw on top of it, but I have never gotten any air from it.

The fluid level does change from cold start to operating temp. Typically it will go from mid line cold (hydroboost accumulator full) to MAX line hot. If you pump the brakes when cold the reservoir will read at MAX which is what I believe shop manual said is correct cold fill?

I hear you on Ford ps pump quality. We have considered fabbing a bracket to adapt a gm/saginaw pump to the teksid 4.6 block. Those pumps are bulletproof.

Phil

 

[cobrajeff96]

That's fine about the testing. You can just pump it to 100psi or more, throw it into a sink full of water and watch for bubbles for about a minute. Bubbles early on are normal because that's just on the surface. But after all the initial bubbles fizzle out, pay attention for any of them that might come from the hose ends.

Is it thick rubber power steering hose or PTFE lined SS braid hose?

The problem with air in any system is that it can exist just about anywhere and cause the symptoms. As the hydraulic fluid is essentially acting as like a Newton Cradle, the transfer from fluid to an air pocket is pretty much instantaneous and the pump cavitates no matter what. And what really sucks is that there could be an air leak somewhere, but fluid might not leak. The air will just slurp into the system due to the intensity of the flow (on the high side) that it'll carry fluid along with it and there'll never be indication of something wrong other than noise and possibly excess heat.

Speaking of which all of my Lares pumps screamed so much all the time that it put excess heat into the system. The cooler I installed into it was hot to the touch after even a short drive, it was insane. You couldn't put your hand on the heat exchanger for more than even a second. Fast forward to the GM type II pump setup, and the cooler is nowhere near hot even after a 30 min WOT slug fest on the autobahn with no cool-down. Most of the time it's just barely warm.

Anyways, try to ditch that C-III type of pump if you can. I went through one OEM iron which was actually not bad, but I also went through three re-man'd irons and three Lares aluminums - they all sucked. The irons at least didn't leak. The Lares aluminums.....one imploded spectacularly and the other two leaked after only 1,000 miles and were constantly screaming at 3k rpm and beyond.

 

[Gears468]

OK will do on the retest at 100psi. We used Aeroquip ends and PTFE SS hose. I am thinking it is what you are talking about being a air leak, but no fluid loss.

I see that Lee is making a CIII housing with Saginaw internals although it seems to be on backorder. It's not cheap, but I have used Tom's steering components with great success on other cars. That might be a good option for us if the lines test out good.

Thanks.

Phil

 

[Gears468]

Quick update, definitely something pulling in air. I did 100 total lock to lock sweeps in blocks of 5 with 3 brake pedal presses between. Engine off.

Every block of sweeps resulted in lots of bubbles, mostly small ones suspended in the reservoir. I'd give it 10-15 minutes and it would be clear and do some sweeps again, more bubbles each time.

I'll start process of elimination to see what fitting/component is the issue. I'll look at rack carefully as that is the last stop before the reservoir.

Phil

 

[Gears468]

Have a few updates, some progress but not a full solution yet..

1) pulled both high pressure ptfe lines and pressure tested at 130psi - all good.
2) I rerouted the lines so to follow factory path over top as opposed to under fender like we had before. I also capped the T and left hydroboost low pressure return line loose into the top of reservoir

Bleeding with engine off and front end jacked up in this configuration went well, bubbles stopped after about 30 slow sweeps with some pedal pressing in between.

Started car and ran to temp with front still jacked up, wheel sweeps and brakes applied periodically. No noise or air when front end unloaded which is a definite improvement.

Does anyone know the proper behavior for the hydroboost low pressure return flow? I saw basically a slow drip unless rack is at full lock. Then an ounce or so would come out. Very little came out when brakes applied.

Wheels on ground and test drive introduced some noise but much less than before. I believe our homemade T block of brass fittings was an issue but It also seems if the new pump and/or line adaptor fittings are restrictive. Stomping on brakes at idle will drop rpms and close to stalling. Full lock at very slow speeds also has this effect.

The brakes and steering both operated fine so we are still thinking rack and hydroboost are ok.

We are going to try fitting a set of Ford lines back in there instead of the lines we made next to see if that helps. I am also leaning towards a adding second return port on reservoir for hydroboost return.

Any thoughts are appreciated.

Thanks

Phil

 

[cobrajeff96]

The tee fitting is going to be restrictive to return flow for sure. A lot of people who've done things like Coyote swaps are finding this out over the recent years, those who've wanted power assist brakes but can't run the big vacuum canister (which is just about everyone). So since they're already in it for $$$ they do all custom installs with reservoirs that have two return ports so as to eliminate the tee junction.

Because when it comes down to both the rack and the hydroboost trying to send the excess pressure back to the reservoir, you have two flow vectors slamming into each other trying to get back to the reservoir at a sharp 90* angle, this in turn loads up the entire system is it's all one hydraulic circuit. This will surely not make it any easier on the pump because it's already trying to overcome friction resistance of the wheels on the ground as well as the hydroboost's spool valve (which actually isn't much).

When it comes down to a belt driven pump system, you will always be loading the motor and groaning at idle or dipping idle down when actuating any steering or brakes aggressively. So that's all normal.