Clutch pressure switch testing
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Thread: Clutch pressure switch testing

  1. #1
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    Clutch pressure switch testing

    For all the folks who are having shifting issues with their transmissions, for whom drain/refill cycles doesn't improve, one of few non-invasive possible solutions are shift solenoids and clutch pressure switches. Many have found through trial and error that the clutch pressure switches are maintenance items, and recommend their replacement. It kept bugging me however, that nobody ever mentioned a means of testing said switches, at least as a means of being confident in finding the "smoking gun" to a problem.

    I'm in a unique position in that I have a set of clutch pressure switches from the old trans I just removed and 2 new ones that I'm planning to install. So I figured, why not test the new and compare to the old?

    Here's the test setup: It consists of a portable air tank, a 1/2" tee, and other fittings cobbled together along with a 0-60 psi pressure gauge (better resolution than the 0-160 psi gauge on the air tank). The fitting used for installing the clutch pressure switch was a 1/2" brass plug drilled and tapped to accept the switch.


    Since this is a pressure switch, the idea is that the switch closes once the pressure goes above a certain upper threshold (i.e. zero resistance) and opens once the pressure drops below a certain lower threshold (infinite resistance). To perform the test, I attach the leads of a multimeter to the switch as shown, then air up the portable air tank just like you would a car tire. I then record the pressure required to close the switch as well as how far I have to drop the pressure before the switch opens. Here's my results from measuring a set of new switches:

    P/N 28600-P7W-003 (Brown): Closes at ~23 psi, opens at ~17.5 psi
    P/N 28600-P7Z-003 (Black) : Closes at ~30 psi, opens at ~24 psi

    Since I only tested one set of new switches, I don't know what the tolerance ought to be on the closing/opening pressures. My old black switch closed and opened within about 2psi of the new switches. However, it registered 3 ohms when closed instead of 0.1 like the new switches, and there was a very small pressure window (about 1 psi or less) over which it varied between 3 and 6 ohms. My old brown switch was clearly defective and likely the culprit in some shifting problems, as it sometimes registered 200 ohms, sometimes 90, but was highly inconsistent.

    I think what my testing confirms is that these clutch pressure switches are indeed maintenance items, but for diagnostic purposes, you CAN test the switches fairly easily to confirm or deny their likely culpability in a shifting problem. The main item to look for is that it behaves likes a switch (low resistance when closed). However, you DO need the ability to apply pressure to the switch in order to test, as they are of the "normally open" variety (i.e. infinite resistance at atmospheric pressure)

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  3. #2
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    When my trans was bad and eventually threw a code I pulled all the switches and eventually found one plugged with a combination of whitish plastic looking and aluminum colored material, cleaning it got rid of the code and allowed it to go on a little while longer before shifts got so harsh the tires would spin on wet pavement. All switches were working though. After watching the excellent videos you posted in the other thread where he shows the valves being stuck, and knowing most who remove the switches find them working, I'm wondering if the stuck valves have any relationship to the switches or the stuck valves are due to poor design or lack of filtering.
    https://www.odyclub.com/forums/24-199...-part-one.html

    In the first video he was drilling a bypass hole for torque converter, but I see as many or more complaints of 3rd clutch failures which he didn't mention. I'll assume the friction material is what's showing up on our magnetic drain plugs. I now have a Jasper with 27k miles on it (170k on van) and still get the same black collection on the drain plug as I did with the OEM. I'm not comfortable with the magnefine, seems to me too small to be trusted to not plug. At least my fluid has looked perfect on every drain with the new trans, I bought my van new and at 30k the trans fluid looked like crud and Honda did nothing to help. That guy seems extremely knowledgeable and conscientious about Honda trans, lucky are those who live near him. I'll have to look if he has any videos on fluid type and filters.

  4. #3
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    You're right - if you pull the CPC switches and they're plugged, that's definitely indicative of a different major problem that won't have a non-invasive solution most likely. Also, working switches certainly doesn't imply working valves as you've pointed out. My testing is limited to the electrical aspects of the switch in the presence of applied pressure.

    Supposedly, the magnefines have a bypass so that if the filter clogs, you still get full (but unfiltered) flow, and still benefit from the fluid passing by the magnet and still picking up some stuff. Of course, I haven't done any testing myself, nor have I cut one apart yet to evaluate the plausibility of the claim.

    There's also an upgraded filter for the transmission (the one that goes INSIDE the trans) as well (the outside is metal rather than plastic, but the filter is supposedly improved). I'll be ordering that one for the upcoming rebuild of my old trans. I believe a search on youtube for "upgraded honda transmission filter" or something similar should yield a video of it.

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  6. #4
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    I replaced my pressure switches about 3 months before the tranny started acting up so much I knew it was time for a rebuild. I kept the eleven year old switches and of course have the ones with about 3 months of use. So I tested them all.

    The eleven year old switches;
    P/N 28600-P7W-003 (Brown): Closes at ~30 psi, opens at ~20 psi with about .1 ohm of resistance when closed
    P/N 28600-P7Z-003 (Black) : Closes at ~35 psi, opens at ~28 psi with wandering resistance in the 150 ohms range, if I tapped on it I could get it to ~50ohms

    The switches with three months of service;
    P/N 28600-P7W-003 (Brown): Closes at ~28 psi, opens at ~18 psi with about .1 ohm of resistance when closed
    P/N 28600-P7Z-003 (Black) : Closes at ~33 psi, opens at ~26 psi with about .1 ohm of resistance when closed

    So my switches appear to be functioning properly for the time being, but as you can see and as webbch has pointed out they do go bad. webbch had a bad P7W and my old P7Z was not making good contact when closed. Aparantly Honda has gone to work on the problem and superceded the old switches. 28600-P7W-003 has been replaced by 28600-P7W-013 and 28600-P7Z-003 replaced by 28600-P7Z-013.

    Thanks webbch for testing the new switches and sharing this info. There was no test data or pressure ranges given for these switches in the alldatadiy.com manual. I feel a little better about leaving them in during my rebuild, as I have plenty of other things to purchase for it.

  7. #5
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    Quote Originally Posted by David57 View Post
    ***snip***
    There was no test data or pressure ranges given for these switches in the alldatadiy.com manual.
    ***snip***
    Ditto for the Honda shop manual.

    Thanks to you and webbch for creating benchmarks at least.

    Dave
    2002 Odyssey EX Fern (Granite) Green
    Honda hood protector, stainless steel flex brake lines, Honda block heater, AC condenser screen, Zymol wax
    151,000 miles/243,000 kilometres; original transmission; Amsoil MV ATF since 79,000 miles/127,000 kilometres; Magnefine aux ATF filter; Honda aux ATF cooler; 19 drain and fills

  8. #6
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    Since they are relatively cheap and easy to replace, I think "loading them inside a part canon" should be considered viable option when you are have shifting problem.

  9. #7
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    why a black and brown switch? i thought the 2nd and 3rd pressure switches where the same part number for 2001 ody

  10. #8
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    They are indeed the same part on a 2001 Ody.

    See discussion here: https://www.odyclub.com/forums/24-199...itch-part.html

    Dave
    2002 Odyssey EX Fern (Granite) Green
    Honda hood protector, stainless steel flex brake lines, Honda block heater, AC condenser screen, Zymol wax
    151,000 miles/243,000 kilometres; original transmission; Amsoil MV ATF since 79,000 miles/127,000 kilometres; Magnefine aux ATF filter; Honda aux ATF cooler; 19 drain and fills

  11. #9
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    I am currently battling 2nd gear pressure switch on my 1999. After getting bad 1->2 shift, I replaced it at about 175K miles; After 50K miles aka at 220K , started having similar problems; so replace them again with updated Honda part; Now in less than 5K miles, the problem is back.

    I have old switch in my hand. The inside diameter is about 4mm. With the spec of 35 psi to close, it does not take much force from the other end of the ball point refill to trip the switch. The transmission has to be shedding huge amount of material to get 4mm diameter switch internals to clog! If that was happening, fluid color and smell would be obvious.

    Only possible explanation is that the pressure switches can go out of the calibration easily and the actual pressure at which they open or close is extremely critical to the shifting if SOMETHING ELSE IS ALSO WRONG WITH THE TRANSMISSION.

    Autos are black magic to me; some of the educated guesses that I am making may be completely bogus!
    Last edited by sontakke; 09-04-2015 at 01:18 PM.

  12. #10
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    I just discovered something very interesting!

    The updated switch has only 2.5mm internal passage and doing the ball point refill test (or red brake cleaner tube!) test on it, it was very difficult to close. It also felt littler easier to close on subsequent attempts. I sprayed brake cleaner inside but there was no debris inside. Afterwards, it felt way too stiff on the first attempt and little less stiff subsequently.

    I am going to stock up on the old revision pressure switches just in case I have to keep on changing them more often! But first I have to figure out who to change it :-(

  13. #11
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    Just a heads up on my 2002 Odyssey I ordered both 3rd and 4th pressure switches part numbers 28600-RKE-004 and 28600-P7Z-013, I got the 28600-RKE-004 with the white colored connector but instead of part 28600-P7Z-013 they sent me 28610-RKE-004 which has the same black colored connector like the discontinued part. There was a note in the parts list I received from Majestic Honda and a google search says it's for an Odyssey, so heads up 28610-RKE-004 is the new updated switch with the black connector

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