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Unread 07-15-2013, 09:47 AM   #1
zjosh93
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Power steering reservoir o-ring

I'm getting an occasional seep from the o-ring on my power steering reservoir. If I work on the Jeep it will sometimes leak a few drops a day for like a week. I think the pump is original and the nipple on the reservoir has shrunk somewhat so the o-ring barely seals. When I work on it I probably lean on it and disturb the seal.

I put a new o-ring on it and it felt like there wasn't a lot of compression on the o-ring when I put it back together. I just bought a new reservoir from Dorman but I've read that the o-ring they include is too small. Seems odd for Dorman but I don't want to get it all apart and have the wrong o-ring.

Does anyone have the dimensions of the stock o-ring? How about the durometer of the stock o-ring rubber? I'd like to order a stock o-ring for the new reservoir and a slightly bigger one from McMaster Carr for the old reservoir.

RockAuto only sells the stock o-ring in the pump rebuild kit and I already rebuilt my pump with it to get the o-ring I have now.

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Unread 07-15-2013, 01:15 PM   #2
zjosh93
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I looked around online and it looks like the o-ring has a diameter of 0.067". I can measure the reservoir to get the maximum internal diameter. Does anyone have a spare 4.0 pump around to measure the inner diameter of the fitting where the o-ring sits on the pump? I want to make sure the o-ring has the proper amount of crush to seal well.
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Unread 07-15-2013, 04:21 PM   #3
coralman
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Can't help you but would be very interested in what you find. I would think a Viton o ring would be your best bet though.
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Unread 07-15-2013, 08:43 PM   #4
moldeck
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I may have one in my garage, I will look when I get home.
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Unread 07-15-2013, 09:09 PM   #5
zjosh93
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Quote:
Originally Posted by moldeck View Post
I may have one in my garage, I will look when I get home.
Awesome thanks!

I've been researching o-rings in the Parker handbook. Too much info but it looks like I need to keep the compression around 22%-30%. Probably stick with nitrile.

EDIT: http://www.parker.com/literature/ORD...g_Handbook.pdf
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Unread 07-16-2013, 09:41 AM   #6
ghiotom
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There is no way your o-ring has a diameter of 0.067". Maybe you meant thickness? When my PS was leaking I thought it might be the o-ring, so I took it out and measured it as 7/16" X 1/16".
I think that was OD, but not sure.
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Unread 07-16-2013, 12:18 PM   #7
zjosh93
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Yes, I meant the width of the cross section of the ring. I'm not sure that's right though, I just got that from the description of that o-ring from some website while I was searching. The one that came with my new reservoir looks like it's probably 3/32" width and 7/16" for the inner diameter sounds right. I'm going to get my micrometer tonight and get some real measurements.
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Unread 07-16-2013, 04:28 PM   #8
moldeck
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I have an extra tank but it did not have the O-ring on it. Sorry.
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Unread 07-16-2013, 05:39 PM   #9
coralman
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Only reason I said viton is I think they stand up to heat better.
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Unread 07-16-2013, 08:54 PM   #10
zjosh93
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Thanks coralman I meant Viton, I was checking out o-rings on the mcmastercarr website.

These are the measurements I got off the o-ring that came with my new reservoir:
Outer diameter - 0.760"
Inner diameter - 0.550"
Width - 0.110"

I measured the width with a screw type micrometer because my digital caliper kept compressing the rubber to much. It was easier to feel the rubber with the micrometer. The caliper was giving me 0.101" for what it's worth.

I measured the plastic nipple on the reservoir and it was 0.592". This means that the radial stretch is 7.64% which is actually beyond the recommended 1%-5%.

My guess is that this is actually a metric o-ring with an inner diameter of 14 mm (0.551") and a width of 3 mm (0.118"). The plastic nipple is right at 15 mm (0.590"). Mcmastercarr sells a pack of 14 viton o-rings in this size for $7.

I might get around to swapping the new reservoir over this Sunday and I'll measure the bore on the pump and the amount of distortion in my old reservoir to see what o-rings are available for those of us with old reservoirs.

At first look it seems that a 1/8" width, 5/8" inner diameter o-ring might work for an old reservoir. This assumes that the reservoir has shrunk until the factory o-ring has no stretch over the plastic nipple. With this o-ring, assuming the pump bore is 19 mm, you get 3% stretch radially, and 25% compression. That's right about perfect but I still need to double check how much the old reservoir has shrunk and what the bore diameter is. My old reservoir nipple as visibly cone shaped from shrinking under the o-ring.
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Unread 07-17-2013, 03:41 AM   #11
coralman
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Looks like you were very thorough on your research. If mcmaster has part numbers please post them,as this kind of thing could come in pretty handy. I know that when my pump went out originally I tried a rebuilt pump with my old resevoir and could not stop a leak at that point. Looked at dorman resevoirs and they looked too funky for me to try, or at least the one I was shown. But the problem may have been a mismatched oring all along. Good job zjosh!
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Unread 07-20-2013, 10:17 AM   #12
zjosh93
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I replaced the power steering reservoir last night and was able to get the final measurements I needed.

The bore diameter on the pump is 0.766 in (19.5 mm). With a nipple diameter of 0.592 in (15 mm) the ring gap is 0.087 in.

Ideally the linear stretch of the o-ring would be 1%-5%. Unfortunately the closest standard o-rings are 9/16 in with a stretch of 5.2% and 14 mm with a stretch of 7.1%

Ideally the amount of compression on the o-ring would be 10%-40%. With a ring gap of 0.087 in that's 0.096 in - 0.122 in. Standard o-rings are available in 0.103 in (nominally 3/32), 2.5 mm (0.098 in), and 3 mm (0.0118 in).

I could not find actual specs for the stock o ring but from my measurements the stock ring is 14 mm inner diameter and about 2.8 mm wide. It's pretty hard to measure the width of the ring because the rubber compresses so that 2.8 mm may be 3 mm. The stock o-ring has 7% stretch and 36% compression. In theory that's a bit too much stretch but good compression.

The o-ring that I pulled off my old pump came in a power steering pump rebuild kit. It seemed a little hard and I measured the width at 2.67 mm. It would definitely seep at times. It may be that the spring clips that hold the reservoir to to pump side load the o-ring.

I'm going to order some 3 mm X 14 mm o-rings and see what measurements I get from them. It may be that the only real option is to get harder o-rings since thicker o-rings that will work aren't really available.
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Unread 07-30-2013, 10:29 PM   #13
zjosh93
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I got the 14 mm x 3 mm o-rings in today. They are a legitimate 3 mm wide. The stock o-rings I had measured 2.8 and 2.67 mm that's 26% and 21% crush. The 3 mm ring will have 36% crush. that's at the upper limit of the 10% - 40% ideal o-ring crush but it will probably work better than the stock ones especially since the stock rings seem to be a non-standard size. If mine starts leaking again or I have any reason to take the pump off I'll try one of these out.

Of course we learned in another thread that part of the infamous leaky reservoir may be faulty venting on the caps.
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Unread 07-31-2013, 08:12 AM   #14
coralman
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Post the part numbers if any josh. Thanks!
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Unread 07-31-2013, 10:22 AM   #15
zjosh93
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McMaster-Carr part number 9263K722

A pack of ten was $7.06 with around $5 for shipping. I have not tried these yet so there could be other issues with them. The math works though.
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