BUMP,,,,,,,,,BUMP,,,,,,,,


Ok, another guy with NO trans savy has a question. In the above quote, he states the engine "returns to idle". To me, this would mean that the trans is somehow unloading and freewheeling, letting the engine idle down even when going 60.

From my own experience with a GM od in my wifes old LeSabre, it did the same thing on long hills. I would let off and watch the tach drop from 2200 to 1300, then down to 600, then back up and back down, all the while picking up speed flying down Sunset point (Tony will know the hill! LOL)

Granted, with OD and very low numbered gears, the "affect" of engine breaking will be very hard to detect, but should the engine return to idle once he lets off the gas going 60?

Mark

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Lets just hope the "change" that we think we are getting does not end up being just "chump change"!

In response to J Mark , a 700R4 should down shift to 3rd gear when ever the throttle is in the closed position so you have engine braking . I would check your TV cable adjustment with a pressure gauge , at closed throttle to confirm that it is correctly adjusted .

I've never seen a 700 / 4l60 do that.

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Be kind to your children... some day they may be decide what nursing home to put you in

Jmark, do you mean to say that you didn't feel the affect of engine braking in your vehicle whatsoever, in overdrive? I'm not surprised and I don't think you were either.

You were able to watch your tach drop, fast68 said his engine returned to idle, but was he watching a tach, or were the effects of engine braking in high gear, assuming this is a c-6, just that minimal?

And woodz428 I would like to know, if in any of those ford manuals you have, does it give you a method to diagnose a no engine braking effect in high gear, for a 3 speed transmission?

Not no engine braking in 1st or 2nd, but no engine braking in high gear.

I have dozens of manuals around here, some that are 30 years old, and not a single one has any information on how to diagnose a no engine braking affect in high gear, for a three speed automatic.

Lots of info on engine braking in 1st and 2nd though. So why do you think that is?

Well, you did say you had built some transmissions, but you're no transmission guy, or you wouldn't be so stuck on this high gear engine braking thing.

And since you mentioned physics, let's talk physics.

The effect of motion is, momentum. Momentum is the product of the mass and velocity of an object and can be expressed as P=MV

The mass of a body determines the momentum of the body, at a given velocity and is a proportionality factor in the formula P=MV

And of course any discussion of physics would not be replete without the mention of inertia.

Sir Isaac newton's first law of motion states, in simple terms, a body in motion tends to remain in motion, a body at rest tends to remain at rest.

So let's tie all of this physics stuff into our discussion on engine braking.

Active engine braking, downshifting into a lower gear and foot off the gas pedal, allows the engine to gain a mechanical advantage, leverage, if you will, to dissipate power and slow the vehicle down. There goes that inertia thing.

When you downshift, it causes the engine to spin at a high angular velocity, increasing rpm's and reduces momentum and if you have your foot off the gas pedal, it should slow the vehicle down. Dynamically.

A less dynamic effect of engine braking would be, not downshifting, but instead, just lifting your foot off the gas pedal to allow the vehicle to slow down.

While this is also considered engine braking, it is more often referred to as engine drag. Which by the way, might sound familiar to you had you read the entire context of post #9.

Anyway, lifting your foot off of the gas pedal is not an active use of engine braking, but rather a passive, less dynamic approach to engine braking.

Thus the effects of engine braking, using the passive method and considering the laws of physics, could be viewed as negligible, as compared to the more dynamic active method.

This is why I say, you are not a transmission guy.

Over 30 years working in trans shops and not once did the subject of no engine braking in high gear, in a 3 speed transmission, ever come up, because of it's insignificance.

We talked about no engine braking problems, in 3 speeds, in first and second gear, but until now, never once about high gear.

I wonder if any of the other trans guys that contribute to this forum have ever tried to diagnose a no engine braking problem,in high gear, in a 3 speed.

Maybe I'm just wacked out of my skull. Maybe these types of discussions go on all of the time, in other trans shops across the country.

Tony, do you guys at your shop have many 3 speed, high gear, no engine braking problems?

Ok, now I'm done.

I'll go back to the OE post of the engine dropping to idle RPM when the gas pedal is lifted - trans in high gear (3rd) of this C-6.

There will be compression brake effect felt IF the trans converter is near a stock configuration. Obviously there are many variables that would change this effect.. gear ratio, tire size changes, steep hill, faulty torque converter sprag.

As I see it , when the gas pedal is lifted at say 55 - 65 mph(just a random speed I picked) ........ the trans remains in gear (3rd) . I doubt the trans is going into neutral. So this leads me to believe the converter would be the problem IF the engine returns to idle RPM as the gas pedal is lifted at speed.

Back in 1979 I was in West Virginia for a vacation. Weston WV area to be eggzack. My Aunt (then late 60's age) was driving us around to see the area. She commented on how her AMC Concord wagon must still have some good compression as the car would slow down (or not speed up) a bit on the down side of the hills as we drove. Even the old farm girl my Aunt was.... she knew of engine braking and what / when it happens.

Second eggzample: mid - late Mustang in the shop. Our AOD trans & mild stall RPM converter. The car drove like a turd from a stop. The car had poor gear ratio for performance, yet drove worse than it should... I noticed the engine would drop to near idle RPM at most speeds.

After we pulled the trans, pulled the converter out. The stator support snout had broken off the pump and was stuck in the converter.

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Be kind to your children... some day they may be decide what nursing home to put you in

OOOOOPS!

Briscoe and Tony.......

I'm not trying to beat this to death, just to understand the original question. Or maybe MY question. should the engine return to idle rpm when in 3rd gear and your foot off the gas when at a cruise speed?

From my own personal experience, with my 2 chevy trucks and my wifes caprice, I say no. The ONLY time my own truck did that was when the vac mod line was cracked. I could accelerate and maybe get it into second, but when I took my foot OFF the gas, the tach dropped to 600. When I stepped on the gas, the engine revved wildly until it matched the trans speed, then "hooked up" and accelerated more.

It seems to me that in a stock condition, no matter what trans is used, the engine should not drop to idle when off the gas pedal. My wifes 305 700r4 trans Caprice, when on the freeway in 4th and LU, will keep the engine speed up when my foot is OFF the gas pedal. (ok, it may drop 100 rpm) Granted, there is NO noticable decrease in VEHICLE speed because of the OD and gears, BUT the RPM does NOT drop to idle speed.

Personally, if the original posters statement about "returning to idle" is a factual statement, I believe he has some sort of problem with the trans or converter. I do not believe a normal functioning trans will do "whatever" to drop the engine speed to idle, while traveling down the freeway at 40 or 50 or whatever. But thats just me.

Mark

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Lets just hope the "change" that we think we are getting does not end up being just "chump change"!

This transmission has a problem - and since the subject seems to have been beaten to death, and the poster has since dumped the vehicle, my post will be brief.

There are several areas that can cause problems but most likely it is the forward clutches being either glazed or worn out. An older Ford shop manual, Section 17-01 will walk you through diagnostic tests. The hydraulic diagram will also help - I've included a copy from my '79 F350 Shop Manual. Photo quality isn't too good but the shop manual is ~30 years old



From experience - I've had 3 Fords with 460/C6 combos, I can attest to the fact that there is really not a lot of "compression" braking. You had to manually downshift to D-2 for good "compression" braking. Two of my three vehicles were P/U's were used to pull a 30', 8000# 5th wheel camper, the third, an LTD, pulled a 31', 9000# unit. The trans were never a problem - ever.

Heres a good disassembly 'first person' write up: http://www.fullsizebronco.com/forum...ead.php?t=98095


Dave W

Ok, maybe I'm not done.

Mark your right, If everything that fast 68 posted was correct, then yes, as Tony pointed out,that even his aunt could tell, some type of resistance should be felt. Engine braking, or engine drag, but some type of resistance.

So his engine rpms should not drop back to idle.

I doubted that they were. As I pointed out, fast68 seemed to be getting frustrated,and some of the stuff he was posting was pretty much "out there".

Voltaire wrote, that common sense is not so common. Based on fast68's post, I shot back that he would not feel engine braking in high gear.

So maybe he had a converter that was loose, or whatever.

It doesn't take a physics major to know that you should feel that resistance.

And even though I wrote that he should feel "resistance" and gave some reasons why he should, I still made that statement that he would not feel engine braking in high gear.

This was written from a transmission guys perspective, as usually our engine braking issues are with 1st or second, but like I've said before, you better be careful what you post on this site, a lot of sharp people visit this forum.

I don't want to beat this to death either, I am a little on the hard headed side though.

Tony and Mark, thank you for posting, your comments were somewhat of, a voice of reason. In other words, I like the logic.

Thanks Briscoe. Sometimes we get stuck in the symantics of what's being said and miss the point.

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Lets just hope the "change" that we think we are getting does not end up being just "chump change"!

i do engine and transmission rebuilds in my own shop on a fairly regular basis and am very familiar with the ford c-6 behind a 351M (have a heavily customized 79 everything new, some is stock).

The ford c6, at least everyone ive cracked open, have no overrun (freewheeling) cababilities when operating properly. In high gear at 1:1 ratio you won't feel much but the engine should not return to idle at 60 mph unless clutches are worn or torque converter is defective. The "engine braking" effect will not be great but should slow the vehicle down slightly. engine braking otherwise called compression braking is not as prominent as it is on diesel engines due to the lower compression ratios of the engine. when the throttle is closed and the transmission is operating properly, the air flow through the engine is virtually cut off, creating a vacuum of sorts in the compression chamber (cylinders), therefore slowing engine rpms down under load. On diesel engines this is enhanced by using a valve on the exhaust pipe making a "jake brake" which stops air flow out as well on half of the cylinders effectively slowing down the vehicle.

Mechanics is based on theory. When there is a problem is causes a piece of the theory to be flawed. translates to if you know how it is supposed to work you should be able to fix it.