E30 + Purple Tag Steering Rack Issues

[Kobra 180]

First, a little context; I have an M52B28 swapped E30 touring project car.

I originally had a regular E36 rack installed. It was hooked up to the P/S pump with a stock E36 high pressure line, which was [poorly] bent to fit (routed around the back of the subframe). The return line was stock E36. I had no issues with this setup at all.

A few months ago, I got my hands on an E46 Purple tag rack. With the install, I figured I would replace the bent high pressure line with a custom one made with AN fittings. The new line routes between the subframe and sump, next to the low pressure cooling loop. Everything seemed to go smoothly with the install.


I bled the system by going from lock to lock with the front wheels in the air, first a few turns without the engine running, then several more with. I dropped the car on the ground and did a few more turns. At that point in time, with the car not moving, I believe the P/S felt fine.

I took the car for a quick drive around the block, and that when I started noticing the issue. It felt like the power steering assist was "lagging behind" my steering wheel input. And it seemed to be getting worse as I drove, so I quickly went home and turned it off. I assumed it was just a leak at one of the banjo bolts, but they all looked fine. I noticed some fluid had managed to get out of the reservoir via the vent hole. The fluid looked cloudy with lots of tiny bubbles. Perhaps it's just air trapped in the system? I attempted to bleed the system again, but nothing changed. I left the car to sit so the air bubbles would clear out of the fluid.

After more testing, the steering is still very heavy when turned, but if turned and held at a position, the power assist seems to "catch up" and the steering wheel goes light again. Possibly the result of an "air spring" somewhere in the system? The power steering pump doesn't seem to make any noise, although it is hard to hear with only headers for an exhaust.

I ran out of time to work on the car, and left it for a few months.

Last weekend I started her up again, hoping the issue had magically resolved itself. It hadn't.

So I'm thinking the issue exists with the purple tag rack, or my custom AN line. I threw away the old high pressure line, I can't easily swap that out. I still have the old E36 rack though, so I could swap that back in. But before I go through all that effort, I wanted to ask the community for input. Has anyone seen P/S behaviour like this before? 

Any help would be greatly appreciated.

Edited July 14, 2018 by Kobra
image link

[M3AN 4016]

Your pic isn't visible to me.

This is an interesting scenario... did you install a restrictor in your new return line?

https://www.bimmerforums.com/forum/showthread.php?1827109-WTB-Power-Steering-Hose-Limiter-Restrictor

http://www.bimmerboard.com/forums/posts/1176344

If you have fluid coming out of the vent hole on the reservoir and frothing in the reservoir then a restrictor may be required.

[Kobra 180]

Sorry, updated the image link.

I didn't create a new return line. It's still just a regular E36 one. The only new line is the high pressure line from the pump to the top hole on the rack.

Also, from all the research I've done, I've never heard of using a restrictor in this power steering rack swap. The leakage from the vent was only after the initial drive. Certainly hasn't done it since. I thought it was just caused by some air bubbles rushing into the reservoir. Maybe this is something to consider. 

Edited July 14, 2018 by Kobra

[M3AN 4016]

Audi, Porsche, Mercedes, BMW all use restrictors in various versions of their setups and I suspect it's common across other brands also.

BMW only added the restrictor in to later e36's and IIRC it was to address exactly the problem you're facing. Does the return line you're using have a crimp or hose clip of any description about half way along? If not it has no restrictor. You can just see it in the top of this pic...

If not that may be your issue but I can't be sure of course!

 

[Kobra 180]

My return line looks exactly like this. No restrictor in sight.

[M3AN 4016]

It's a difficult one. I can't recommend taking the system apart just to try a restrictor because I'm not sure that's the cause but it's the only suggestion I have.

I recall reading up about it when I did my E36 -> E46 swap also. I can't find all the info I read but I did find this just now which supports my recollection:

Quote

OEM Restrictor
We are commonly asked if we include the OEM BMW E36 M3 limiter / restrictor in our kits. The answer is yes and no. Our reservoir design is engineered to slow down the flow of fluid without causing aeration or spillover through the cap vent. BMW implemented the inline restrictor in the return hose as a patch or afterthought. With track abuse the stock system aerated and pushed fluid through the cap vent so when production started they pushed an inline restrictor in and called it a day.

Source: https://www.chasebays.com/products/chase-bays-power-steering-kit-bmw-e30-w-s50-s52

 

[Kobra 180]

Bump. Has anyone else got any ideas?

[Lucan 196]

So is your high pressure line from the pump to the rack DIYd with larger diameter fittings and pipe?

[Kobra 180]

The hose was made from -6AN "full flow" fittings\banjo bolts with 200 Series stainless hose from Aeroflow.

 I'm no AN host expert. I don't think it'll flow any less than the factory one, but I do think the hose could be a little small.

The symptoms make me think there is a flow restriction somewhere in the system. The rack was filthy when I picked it up, It could be dirt in the suck in there somewhere.

I took the belt off to check the P/S pump. It feels perfectly smooth, no noise.

I'll probably swap the E36 rack in this weekend to see if that fixes it. Otherwise it's the hose.

Edited July 19, 2018 by Kobra

[M3AN 4016]

Have you dismissed the (absence of a) restrictor as a possibility?

If you're flowing more fluid with the new hose and E46 rack (which has different internals to the E36 rack) you'll get the symptoms you're having. If the new rack flows freer than the E36 one (I don't know) and you're pushing more fluid through then the return line will be forcing more into the reservoir which is exactly what causes your symptoms.

If you're prepared to swap the E36 rack back in then what I'd do beforehand is drain the reservoir, disconnect the return line, shove a temporary restrictor in there then do it back up again and test it. Should be a lot less work than swapping rack and swapping racks might not pinpoint the problem (symptoms could go away if the E36 rack is more restrictive only to return again when you swap the E46 rack back in). Also swapping racks and eliminating the symptoms does not confirm the E46 rack is the problem.

 

[Kobra 180]

I'm not sure about the restrictor. Last weekend, I ran it for a few minutes going from lock to lock quickly. Even moving the steering wheel at slow speeds was difficult. But the fluid wasn't getting aerated at all. Perhaps the aeration I saw was from the initial bleeding of the system? The air bubbles in the reservoir could have pushed some fluid out of the vent. 

It feels like the system cannot flow enough fluid. I'm thinking the hose/fittings could be too small on the I.D.

3/8in. vs 1/2in. for the factory lines (not sure on this)

I could still try the restrictor easily. Perhaps a hose clamp around the return hose, and tighten it a bit.

[Kobra 180]

Actually, It looks like the high pressure line I choose should be fine. I found a picture of an OEM one cut apart.

Fairly small I.D. on the actual inner part.

Also, I found a few popular E36 AN hose kits that use -6AN fittings for the high pressure.

Edited July 19, 2018 by Kobra

[M3AN 4016]

BMW hoses are all metric to start with but I agree, that's unlikely to be your problem... the only issue would be if your new one was so narrow it created back pressure and that's highly unlikely.

Air bubbles and aeration are different things. If you have/had heaps of small bubbles in your PS fluid in the reservoir that's aerated fluid, if there were a few bigger bubbles that floated to the surface then they're just a natural result of the bleeding process. Aeration can only occur in the reservoir.

Based on your original symptoms also, fluid can only come out of the vent hole if the reservoir level is up there or there's massive agitation of the fluid (i.e. fluid being flicked around). It's pretty unlikely the fluid was that high so agitation is the primary suspect.

Agitation also happens to cause aeration.

The only thing that can can cause fluid agitation in the reservoir is the return line being over pressured. It's a closed system, the only other orifices are the vent hole (pressurised in your case) and the pump which is gravity fed and should have no back pressure at all.

Also, heavy steering is symptomatic of air in the system and if you're pumping aerated fluid through then that's to be expected.

Edit: that OEM hose is quite amazing, I had no idea the ID was so tiny.

 

Edited July 19, 2018 by M3AN

[Kobra 180]

The fluid certainly seems to stay clear now, no aeration. So not sure what that was all about.

I'll try adding a restrictor to the return hose tomorrow. If that doesn't help, I'm thinking it's dirt stuck in the system.

Thanks for your help, M3AN.

[Olaf 3317]

On 7/20/2018 at 8:14 PM, Kobra said:

The fluid certainly seems to stay clear now, no aeration. So not sure what that was all about.

I'll try adding a restrictor to the return hose tomorrow. If that doesn't help, I'm thinking it's dirt stuck in the system.

Thanks for your help, M3AN.

Holy thread revival!  What was the solution, @Kobra?

[Kobra 180]

Oh, it turned out my power steering pump was going bad. A replacement sorted out all issues.