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Old 07-03-2007, 11:17 AM
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My new 700R4

Hi Guys,

So I installed a rebuilt MADDOG 700R4 trans this spring. Everything is fine with so far. Yesterday, I meet a guy how said that you should use the drive and not OD to prolong the life of the transmission. I didn't know him from dirt so he could have been talking out his *** for all I know. Could you folks share your experinces with this issue if there is an issue?

Loco

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Old 07-03-2007, 11:30 AM
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I just got a 700r4 trans to, although the cars not running yet. Anyways I didn't get an OD trans not to use it. If I'd have wanted a 3 speed trans I would have bought a 3 speed. So even if it wears it out twice as fast (and I don't think it will make any diff) I'd still use the OD. The thing thats really hard on any automatic trans is the full throttle kick downs. If your going to need to down shift to make a pass, Down shift first then floor it.
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Old 07-03-2007, 11:39 AM
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My 90 model truck has 160K on it and it hardly ever has been in D.

Vince
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Old 07-03-2007, 11:49 AM
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I think this may have sometinkg to do with the earlier 700R4's, although we used them in some of our lighter Pickups (Fleet) and had a lot of Overdirve issues-could this possibly be before they offered the Tow/Haul mode?
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Old 07-03-2007, 02:16 PM
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Quote:
Originally Posted by daoldbuick
I just got a 700r4 trans to, although the cars not running yet. Anyways I didn't get an OD trans not to use it. If I'd have wanted a 3 speed trans I would have bought a 3 speed. So even if it wears it out twice as fast (and I don't think it will make any diff) I'd still use the OD. The thing thats really hard on any automatic trans is the full throttle kick downs. If your going to need to down shift to make a pass, Down shift first then floor it.
Actually you are incorrect, downshifting first, then accelerating is not how the transmission was designed.
A detent downshift is designed into the transmission and is OK, it is MUCH more detrimental to do a deceleration downshift than an acceleration downshift on almost all the automatic transmissions I am aware of, particularly GM autos.
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Old 07-03-2007, 02:17 PM
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To answer the original question,
You are fine to drive in OD under normal conditions. On the 700-R4 it is best to not tow in OD due to the additional strain placed on the already marginal 3-4 clutch pack.
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Old 07-03-2007, 03:55 PM
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quote
Actually you are incorrect, downshifting first, then accelerating is not how the transmission was designed.
A detent downshift is designed into the transmission and is OK, it is MUCH more detrimental to do a deceleration downshift than an acceleration downshift on almost all the automatic transmissions I am aware of, particularly GM autos.

I'm not sure I understand what you mean by "detrimental to do a deceleration downshift". Do not all automatic transmissions do this as a natural function every time you slow down? A "detent downshift" is a manual downshift right? I'm not a transmission builder thats for sure, but the chap with 30 years experience who built mine said the 3/4 clutch pack is the weakest link in the 700r4 and kicking it down into passing or "acceleration downshift at WOT is the hardest on it or any transmission. Now he never said to downshift first and then floor it but to me that seam the logical alternative. Jackshoe could you please explain your terms a little better so I know what you mean. Thanks
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Old 07-03-2007, 05:24 PM
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Scenario 1:
You are driving down the road at 55 mph and need to pass, you push the accelerator to the floor, the transmission automatically downshifts under acceleration to "passing gear". This can be a downshift from 4th to 3rd or in some cases 4th to 2nd with a 700-R4.

Scenario Two:
You are driving down the road at 55 mph, you need to pass, you let off the gas, downshift, and then accelerate. This is manually selecting a gear and if you let off the gas enough, it is a decel downshift.

Scenario Three:
You are slowing to a stop, as you slow down, the transmission downshifts automatically. This is a governed downshift under decel.



Scenario One is designed into the transmission. The engineers who designed it calibrated it so that it would make a detent or passing gear downshift so that the driver wouldn't have to manually command it. They did this to prevent damage to the engine and transmission and make the passing gear "automatic" as we expect from a factory automatic transmission.

Scenario Two is not what the trans is designed to do for several reasons I will explain later. Why would you need to manually downshift and then accelerate when the trans will already do it by itself?


Scenario Three is also part of the automatic function of the transmission designed into it. The transmission is an "automatic" so it must be in the proper gear. As you slow down, the trans doesn't downshift itself until it is below a certain road speed. It does this so you don't feel it downshift. The reason you don't feel it downshift is because when it does so, it usually freewheels internally on a sprag, and if not the input shaft speed will still be slow enough not to cause engine braking feel. This prevent damage to the internals. They also often don't downshift until almost at a complete stop unless you begin to accelerate, at which time it will downshift depending on the governor pressure, TV pressure on a 700-R4, etc.

One of the worst things you can do to an automatic transmission in most cases is to do a heavy deceleration downshift. That is to be at say 75+mph and downshift a 3 speed auto from 3rd to 2nd gear. On a 3 speed automatic the sprag is over-running and when you downshift it, it has to immediately lock. The fact that it immediately locks isn't an issue, as it does this on every 1-2 shift, but the load is different because instead of the the planetary sets being driven, they become the driving element.

On a 700-r4 specifically, a downshift from 4th to 3rd causes the overrun clutches to apply and the forward sprag, another somewhat weak area, to lock. The 2-4 band also releases. An detent downshift (under acceleration) isn't going to hurt it, but a manually commanded downshift under acceleration or deceleration can. Under deceleration, the sprag gets "hit" as I covered, but under an acceleration downshift, if it is automatic, the 2-4 band releases, the sprag locks by design, both being the same as an automatic detent downshift, but when you manually command it, the overrun frictions also must come one. This causes a momentarily drop in pressure that could potentially let the weak 3-4 clutches slip.

There isn't a problem with letting the trans do what it was designed to do, the only time it can be an issue is if the trans is shuttling, or making multiple shifts from 4-3-4, or even worse from 3-2-3.
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Old 07-05-2007, 06:12 AM
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Well,

That's what I'm talking about!! More knowledge than I could have gotten from just one ex-tow truck driver just paroled. Thank you gentlemen.

Loco

P.S. I'm sure many do but I never manually downshift an automatic.
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Old 07-05-2007, 10:01 PM
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Jakeshoe, This "shuttling" that you talk about, why does it do that and how can it be prevented? I own an 88 Iroc-Z and that is about the most annoyng thing in the world!!!
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Old 07-05-2007, 10:12 PM
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Shuttling was an issue on some of these units stock.

You can fix the issue with a valve body kit. A TransGo SK Jr or Reprogramming kit would likely help. I would first recommend checking TV cable adjustment, if it's a bit loose it could shuttle.

Also,
These transmissions will not stay on OD at WOT (stock) so if it is shuttling at high throttle opening and high speeds in 4th back to 3rd, etc. that would be normal.
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Old 07-05-2007, 11:17 PM
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Mad-dog Trannies

How long have you guys had the Mad dog trans. I am also a member of thirdgen.org because of my Camaro. Anyway they have been having the biggest issues with this guy. I am in the market for a trans and would like to know your opinion on them so I can make my desicion. Sorry spelling sucks
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