Slant Six Forum :: Trans Emergency

The 904 lock-up converters come in "low stall" (LS) and "high stall" (HS) versions, that's what the sticker refers to.

I tow my race car with our 66 Dart station wagon and it has a lock-up converter. What is "weak" about the set-up is that the friction surface in the converter is not real big and you can feel it slipping when it trys to engage under heavy load.

I know the car well enough to know that the trans will always go into lock at 40 mph, in drive... no matter what. I make sure to not be in a "high load" situation at the moment of lock-up. If it is under heavy load, I can feel the converter trying to lock but the RPMs don't drop and I feel it "chatter" as it slips. Let-off for a moment, it locks-up, get back into the throttle and it holds. I am sure that you could burn-up a converter fast if you stayed in it as it slipped and chattered, fighting the load to lock-up.

One thing to note is that the AT fluid get more "work" in these units so change it, along with the filter, at the service intervals. I always seem to find more friction "flakes" in the filter with the lock-up trannies but simply change the filter, pour-in new fluid and it keeps going.
DD

Author:	ceej [ Thu May 01, 2008 10:55 am ]
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LS= Low Stall HS= High Stall What those values are? I dunno. Found one reference that said "HS=High Stall 2400-2800 rpm LS=Low Stall 2000-2400 rpm" That may or may not apply to this application. CJ

Author:	Doc [ Thu May 01, 2008 11:34 am ]
Post subject:
Quote: Thanks, you guys are champs. The "lock-up" sticker on the converters have the letters "LS" on one and "HS" on the other. Are these significant in any way? The 904 lock-up converters come in "low stall" (LS) and "high stall" (HS) versions, that's what the sticker refers to. I tow my race car with our 66 Dart station wagon and it has a lock-up converter. What is "weak" about the set-up is that the friction surface in the converter is not real big and you can feel it slipping when it trys to engage under heavy load. I know the car well enough to know that the trans will always go into lock at 40 mph, in drive... no matter what. I make sure to not be in a "high load" situation at the moment of lock-up. If it is under heavy load, I can feel the converter trying to lock but the RPMs don't drop and I feel it "chatter" as it slips. Let-off for a moment, it locks-up, get back into the throttle and it holds. I am sure that you could burn-up a converter fast if you stayed in it as it slipped and chattered, fighting the load to lock-up. One thing to note is that the AT fluid get more "work" in these units so change it, along with the filter, at the service intervals. I always seem to find more friction "flakes" in the filter with the lock-up trannies but simply change the filter, pour-in new fluid and it keeps going. DD

Author:	polara pat [ Thu May 01, 2008 6:28 pm ]
Post subject:
Quote: The 904 lock-up converters come in "low stall" (LS) and "high stall" (HS) versions, that's what the sticker refers to. I tow my race car with our 66 Dart station wagon and it has a lock-up converter. What is "weak" about the set-up is that the friction surface in the converter is not real big and you can feel it slipping when it trys to engage under heavy load. I know the car well enough to know that the trans will always go into lock at 40 mph, in drive... no matter what. I make sure to not be in a "high load" situation at the moment of lock-up. If it is under heavy load, I can feel the converter trying to lock but the RPMs don't drop and I feel it "chatter" as it slips. Let-off for a moment, it locks-up, get back into the throttle and it holds. I am sure that you could burn-up a converter fast if you stayed in it as it slipped and chattered, fighting the load to lock-up. One thing to note is that the AT fluid get more "work" in these units so change it, along with the filter, at the service intervals. I always seem to find more friction "flakes" in the filter with the lock-up trannies but simply change the filter, pour-in new fluid and it keeps going. DD Well first off Doc, You have a Dart wagon that you tow your race car with and it's not in the Slant Wagons gallery? I'm a huge sucker for this kind of thing. I tow my race wagon with a matching 440 powered '67 Polara. People love it, but not as much as I do. Good tips on "playing" the lock-up chatter with throttle response. This really is brand new territory for me but I'm looking forward to seeing how it works. I went with the LS converter since it was the good one. I can't see needing a higher stall for the driving that I do. What are the potential MPG gains to be had from running one of these lock-up trannys?

Author:	SlantSixDan [ Thu May 01, 2008 7:29 pm ]
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Six percent highway fuel economy improvement relative to an otherwise-identical non-lockup trans. You can adjust the lockup road speed by means of the tension of the lockup control spring in the valve body. Stiffer spring = higher lockup road speed. The first couple years of lockup transmissions locked up early and tended to lug the engine, so a stiffer spring was released to raise the lockup speed from the original 40 mph to a more practical 50 mph or so. The higher line pressure required to overcome the stiffer lockup spring also engaged the lockup clutch more firmly. Doc, it sounds like you might have an early-production lockup spring in your trans.

Author:	Doc [ Fri May 02, 2008 10:14 am ]
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Quote: ... Doc, it sounds like you might have an early-production lockup spring in your trans... Yes, that is also my guess and I keep looking for that stiffer lock-up spring kit so keep me in mind if anyone come across one. I called TransGo a while back and they no longer had any. They did give me the spring's tension rating so I can "roll my own" the next time the trans pan comes off. DD

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Author:	SlantSixDan [ Fri May 02, 2008 11:49 am ]
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Quote: Quote: ... Doc, it sounds like you might have an early-production lockup spring in your trans... Yes, that is also my guess and I keep looking for that stiffer lock-up spring kit so keep me in mind if anyone come across one. Still available as a dealer item for under $4, part number 4202 672. Not sure what its tension is, but it's definitely the late-production (higher lockup speed) part. I am guessing you also could shim it, if you wanted to raise the lockup speed a little higher.

Author:	Doc [ Fri May 02, 2008 1:52 pm ]
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Thanks for the Mopar P/N, I will check with my local dealer. As I remember, the tension on this spring is pretty stiff so I'd be better-off buying one at the engineered rating instead of trying to shim my way into the correct tension.... and I don't really like doing valve body work because of all the ATF that drips onto you. DD

Author:	DusterIdiot [ Fri May 02, 2008 3:49 pm ]
Post subject:	Yep...
Quote: instead of trying to shim my way into the correct tension.... I remember quite a time back, when that's what the local tranny guys would do to these boxes (not fully understanding what needed to be done...), and never get them right... the car would go to lock up and shudder and shudder and the owner would complain like mad... Glad Dan has a part number. -D.Idiot

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