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Old 06-05-2001, 06:49 PM
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Default how to tell if \"Torque Converter\" going bad?

i might be imagining things but it seems that my engine is turning higher rpm's than it use to when going about the same mph.

so it might be that i drive standards alot and love the engine compression braking "that my automatic don't have". fyi, this was my reason for going with the dual t-case swap, to be able to go slower down hills [img]/wwwthreads_images/icons/smile.gif[/img]

so, is there some way to troubleshoot my converter? or maybe someone can tell me what happens to make a torque converter "slip" more than when it is new?
fyi, i'm running a TH350...

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  #2  
Old 06-05-2001, 07:00 PM
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Default Re: how to tell if \"Torque Converter\" going bad?

I was working on a USMC HMMWV and it did the same thing, we rebuilt the tranny and it fixed the problem

JR
'94YJ,4cyl,33SX's,Locked F/R,NV4500,Soon to come:Wagoneer 44 Scout 44 & spools
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Old 06-06-2001, 11:02 AM
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Default Re: how to tell if \"Torque Converter\" going bad?

I've actually been meaning to ask this question to. My 727 tf seems like its slipping a little bit when I accelerate. The engine rpms go up, but there's a lag before the jeep starts rolling.

<font color=orange>--Laugh and the world laughs with you. Cry and the world laughs at you.
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Old 06-06-2001, 11:14 AM
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Default Re: how to tell if \"Torque Converter\" going bad?

A Torque converter ain't really doing too much untill you're at highway speeds of above about 42mph. If the RPM's stay high and the TC doesn't kick in you know there is a problem with the TC.

However, till the highway speed has been reached it's all clutch packs that are doing the work. If the transmission is slipping on roll-off it's usually time for a rebuild or a flush and new filter, in the least.

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Old 06-06-2001, 11:13 PM
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Default Re: how to tell if \"Torque Converter\" going bad?

thanks leve....I was afraid of that. I was planning on swapping in a 700r4. Guess it'll be sooner than later.

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Old 06-07-2001, 05:49 AM
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Default Re: how to tell if \"Torque Converter\" going bad?

thanks LEVE,
"A Torque converter ain't really doing too much untill you're at highway speeds of above about 42mph. If the RPM's stay high and the TC doesn't kick in you know there is a problem with the TC."

i'm not sure what you mean?
when you say "doesn't kick in" all i can think about is a lockup TC. i was reading {scary thing) and just can't imagine what could become less efficient.

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Old 06-07-2001, 07:33 AM
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Default Re: how to tell if \"Torque Converter\" going bad?

3/4TonYJ, you're right to question my answer above... as I was refrencing more of the "Lock Up" features of a Torque Converter (TC). I did not really want to get into a verbose discource on TCs so I glossed over the mundane aspects of the TC with the phrase "ain't really doing too much." and tried to diagnois the problem from the information given in the post. But since you caught me....

Let's look at the purpose of the TC. It's job is to de-couple and couple the engine to the transmission. I'm not a hydraulic engineer, but I do know a fair piece about electronics and guss what! Electronic and Hydraulic formulas are the same... only the names change! So I have to relate everything I know about TC's to electronics. It makes it a heck of a lot easier to me. The TC kind of reminds me of a slef regulated alternator, it's attempting to keep the balance between the drive load and the engine RPM's and providing enough coupling to keep the engine running. That's a lot to ask of a mechanical system. I find it a wonder!

So, when a vehicle slows to a stop, the car's engine can still run without killing the engine. This is done by the fluids not letting the TC couple all the engine's torque to the transmission. When the vehicle starts from that dead stop the TC increases the coupling to the transmission similiar to you letting up on the clutch. In fact that's what's happening... the hydraulics in the TC and the transmission are engaging and disengaging clutch packs, bands and hydraulic flow all the time to keep the vehicle moving...or conversely... stopping.

Usually a TC when it goes bad will not cause slipping, it shudders. It'll feel like a flywheel in need of resurfacing on a manual transmission. Most often when a TC goes bad the converter clutch will cause a slipping/gripping cylce. It's felt to the dirver like a washboard road when the engine decellerates or accelerates. An internal clutch pack that's worn will cause more even slipping on roll-off. It will get worse with each engage/disengage cycle. This is one reason the AT fluid is coloured red is to help diagnoiss this very problem. As the fluid ages it becomes darker in color. As it darkens, it's ability to work with the TC clutch is compromised. This is one of the reasons you have a cooler, to keep the AT fluid at it's peak longer. If it heats, it dies. Read the end of the post about lugging on a hill, it's death on AT fluid. Simply changing fluids and filtes help. Not because the filter provides more pressure, but because the properties of the new fluid are in effect agiain. That why you're hearing about the newer flush systems that COMPLETELY flush out all the old fluid from an AT. The cost is about $80, and a bargin if it saves your High Buck AOD from destruction.

A torque converer Lock Up is activated in one of two ways:

1. Moving vanes activated by centrifigual force (CF).

The force needed to move the vanes is determined by the engineering of the TC. As the CF increases the vanes move...

Drawback: You have little control, unless you install a shift kit, as to when the transmission's torque convter will engage.

Plus: It's a fairly simple system that is mechanical and it's free of having to know anything about engine load.

2. Electronic Activation.

This is the mode of choice for almost all newer vehicles.

If you've ever been lugging up a hill with a TC equiped transmision, gaining slowly on the hill (Oh ...like say I-84 in Wyoming... long hills that seem to go forever and fairly high elevation changes) just when you finally seem ahead of the game the TC kicks in. The RPM's drop and the vehicle slows down due to the excess load and then you've got to wind up the RPM's again. Then the cycle repeats. You're trapped! That's a lot of wear and tear on the transmission, engine, drive train and you're nerves.

So to avoid all that stuff... the smart engineers now start to figure in load, engine speed, vehicle speed and altitude. As if that ain't enough in some of the vehicles they even give you a little button to disable the TC lock up, if you desire for those long Wyoming hills. That's a nice touch, economy with choice. If the TC is engaged going downhill, it will provide some braking effect similiar to engine braking, less the slippage factor.

So, if I've explained this correctly, you'll have more questions than peace of mind. If not it's a clear as mud.

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Old 06-07-2001, 08:01 AM
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Default Re: how to tell if \"Torque Converter\" going bad?

Actualy Leve(I cant beleive I get to correct you) the clutches in an auto are engaged as soon as you put it in gear. The holding pressure on the clutches and bands does increase with rpm because the pump in the trans(driven by the 2 notches in the TC housing) increases pressure with rpm(there is a regulator to prevent too much pressure) to compensate for power increase. The trans is slipping because of worn bands,clutchs or low pump pressure. There is only one thing in the converter that could goe bad and that would be the sprag that prevents the TC inards from turning backwards.

3/4Ton...Take the truck to a reputable trans shop to be diagnosed. IT may sound like an aamco commercial but most transmissions don't need a full rebuild. Many times pumps wear out or the shift acumulators start leaking and don't allow the clutchs/bands to hold tightly. If the problem is dettected and repaired early you should be fine. If the trans is slipping and you wait, the clutchs/bands will wear themselvs out and you will need a complete rebuild.

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Old 06-07-2001, 09:28 AM
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Default Re: how to tell if \"Torque Converter\" going bad?

Actually JT, I think,in the grand scheme of things, I'm still correct in a jailhouse lawyer kinda way. You are correct about the bands and cltuches engaging when the put into gear. I have to give you that, however...

when the trnasmission is running up to, say freeway speeds and back down, the clutches and bands do engage and disengage, hence my terms: "the hydraulics in the TC and the transmission are engaging and disengaging clutch packs, bands and hydraulic flow all the time."

Your indication of a bad sprag would sure screw up a TC and I also thought of one other problem I've seen... but very rarely... and that's a broken vane in the TC. It's thrown about by the CF and the fluid and can make one heck of a racket or lodge itslef in the works and foul up fluid flow. In either case it compromises TC activity.



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Old 06-07-2001, 07:17 PM
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Default Re: how to tell if \"Torque Converter\" going bad?

thanks very much LEVE for all the info, (i know those long posts take some time)
i feel like i might be wasting everyones time but, i have 2 different automatics that i've posted about in the last month or so:
1. a 4L60E in my 97 Chevy 1/2ton (it had this shudder, that only happened under heavy load and while in overdrive, since changing the fluid (twice) myself. it has not been acting up)[img]/wwwthreads_images/icons/smile.gif[/img] and i think i will take it to an expert like "jimmythetech" mentioned when it starts up again.
2. a th350 in my YJ, this one has no problems at all (knock on wood) but did bring me to start this post. i think i'm making this up but the compression braking don't seem quit as good as it was when i first started running my dual transfercase setup, and this has led me to imagine that i might not be going as fast in 3rd gear at 2700 rpm's as i use to, (now my speedometer ain't hooked up) so i'm judging speed with my hair and keen sence of driveline vibrations [img]/wwwthreads_images/icons/smile.gif[/img]
thanks again.....

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