Damper Plate Question
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Damper Plate Question

  1. #1
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    Default Damper Plate Question

    I'm going to use Dampener Plate, Dampner Plate, Damper Plate for search reasons. I did a search and found some info and it appeared that people spelled it differently. Hopefully if somebody else like me is searching in the future this will be helpful.

    The early 70's BBC motor is back in the boat and it's time to bolt up the TH400 transmission. The new setup is just like the old setup, a somewhat standard Chevy flywheel (not a flexplate). The current dampener plate is what appears to be a Borg Warner Standard Duty damper plate like the one shown below.

    The newly rebuilt motor should be good for around 600/600. At what point do I need to replace the "standard duty" damper plate with a "heavy duty" plate? If the standard duty plate is too weak for my new motor, is the Borg Warner "heavy duty" plate sufficient? If not, what plate do I run?

    Aloha

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    "It's HONDO, honey" Kyle's Avatar
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    In reality its called a torsional dampner; its purpose is to lessen the effects of the torque spikes felt at the input shaft at each firing impulse when the engine is running. Definately needed when not using a fluid coupling between the engine and trans. Those little springs really do work, it does the same job as the center of a clutch plate when the clutch is engaged on a manual trans. That being said, the bigger the HP the bigger the firing pulse, the stronger the springs that are needed. Just my $.02
    STEVE
    Last edited by old flat; 09-30-2008 at 10:32 AM. Reason: text

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    Is there some sort of horsepower or torque rating on these things? I understand reducing the shock loads by having the spring setup. I don't need a damper for use on a 1000+hp motor. At the same time I don't want to have any issues with what I've got now. If my existing standard duty damper will live in a heavy daycruiser with 600hp I'll run it. If using the standard duty deal is even questionable, which I'm guessing it might be, I'll spend the $$$ and run the correct parts. I guess what I need is some way to quantify standard duty and heavy duty.

    Aloha
    Last edited by AlohaJeff; 09-30-2008 at 12:02 PM.

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    Taking this one back to the top... still curious to know if anyone has some sort of knowledge on the dampener / dampner / torsional dampner plate HP and Torque capacity. What is a safe level for the standard duty versus the heavy duty?

    Thanks again!

    Aloha

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    Quote Originally Posted by AlohaJeff View Post
    Taking this one back to the top... still curious to know if anyone has some sort of knowledge on the dampener / dampner / torsional dampner plate HP and Torque capacity. What is a safe level for the standard duty versus the heavy duty?

    Thanks again!

    Aloha
    Well-- I know appx 700 Hp broke a standard plate. Not sure if it woulda been happy at 600 though..
    Is it just me or are toilet seats getting smaller?

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    Now we're talking... that's what I was wanting to hear. I've got +/- 600 hp now and have been hesitant to spend another $400 bucks on something I might not need. If 700 hp broke the standard dampener the heavy duty model apparently is something I do need. Half way to Catalina is not a place I want to be when I find out the standard duty piece ain't up to snuff.

    Aloha

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    FWIW- The standard plate broke at a high rpm 2nd/3rd shift (previous owner told me this).

    And when I was putting mine together, the thing I heard over and over was : "Make sure the play is right from tranny to dampner.."

    It's very much like the story of goldilocks:
    Too much is bad, Not enough is worse, and "just right" is what you're lookin' for..
    If no play, you'll take out your oil pump on the t-400 (and be very sad )..
    I forget what the correct play is (somebody may chime in here).. I'd hate to give you the wrong number.. I had too much gap and had to shim mine back about .200..
    Is it just me or are toilet seats getting smaller?

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    The reason I didn't want to change anything in my setup was it worked for years (lots of years) just the way it was. Over the trans input shaft there is conversion piece. It's notched at the pump end and splined at the dampener end. This conversion piece is spaced out with what appear to be two purpose built washers, they don't look like they act as a thrust washer as I can't see any noticeable wear on any surface. These are probably a 1/4" thick or so. I'm assuming that because it worked for as long as it did it must be assembled correctly. For all I know it's all wrong, but the very fact that it lasted this long leads to me to believe it's ok. If the thickness at the splined flange is any different or the offset of the disc itself is different on the heavy duty dampener I might have to re-shim the assembly. I might just run it as-is for a while and hope for the best.

    Out of curiosity... what sort of 2-3 shift took place? Is this a daycruiser or ??? Did it just shear and twist the disc or did the failure occur at the springs?

    Aloha

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    Yep-- The gap you need to maintain is that "wiggle" in the "washers" (what ever they are really called).. Too tight, dead tranny. Too loose (really testing the input splines-- not enough engaged).

    Mine was a blown cruiser when it blew up the plate. Don't know what broke other than made "alot of noise" and felt like the tranny was dead.

    I don't think I'd worry about it much unless you plan on hammerin' it outta the hole. As mine is a cruiser, I tend to roll it on plane then wack it.
    Is it just me or are toilet seats getting smaller?

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    Red face

    Jeff,
    Ritytity knew I'd chime in on this one. The dampener plate (standard) he mentioned actually lived for 20+ years in a blown (850 hp) ski race boat. When I owned the boat I was showing off with another (non hot boaters) couple in the boat and winged it to 7 grand in 2nd gear, then shifted it to 3rd (didn't back off). Instant neutral! I sure did impress them, ruined the entire day.
    Here's the funniest part. I pull the T-400 out and put the rush on a rebuild to my trans shop. I put it back in the boat.......still big neutral (with lots of the same noise). I had never even looked at or removed the dampener plate, which was destroyed at the internal plate and just spinning. Naturally I upgraded to the heavy duty one since I had to buy a new one anyway.
    So.....to answer your thread question, the standard dampener plate will most certainly hold up to 600 hp when shifted normally. Jocko
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    Here's a link

    At 600 hp you are on the edge with a standard plate imo if you are going to be shifting hard. The standard plates are not built to withstand this kind of power even though they may survive it if you're careful.

    The HD plates are large BW heavy application plates we machine down for Chevy Flywheel size and bolt pattern. They are thick and the springs are heavy. You may have to machine the center of your flywheel to clear the large fastening rivets on the HD plate. Dampener plates are much easier on the trans input shafts than solid type couplings. They absorb the shock. Anything bolted to the flywheel without springs or dampening in it is like a solid link and puts tremendous shift shock to the input shaft. Broken input shafts are no fun, I have had it happen. Let me know if I can help or answer any questions.

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    Default Hmmmm . . .

    I just sold one with a Velvetdrive transmission . . . I've seen them for sale on Ebay a lot . . . . the one I had looked just like the one in the pic . . . seemed to be kind of thin for high HP, plus all the bolt holes for different applications made me nervous as well, especially something designed to absorb shock . . .

    Just my 2 pesos

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