TF999 and the torque converter

[Jerry Bransford]

There's a Jeeper on one of the boards suggesting that the cure for braking issues with TF-999 auto-equipped TJs many of you are having is simply to change the rpm at which the torque converter locks up.

He said the braking problem is caused by "the stall speed on the torque converter is set way to low, and the advantage of being able to slip the converter and multiply the crawl ratio is not really being used to nearly its potential."

I know you can do that with 700R4 and TH350 trannys but is that doable on the TF-999? He's claiming "any auto tranny guru" can do it. Is he blowing smoke on the TF-999?

I've even wondered if you could prevent it from locking up like I could with an old Blazer I used to drive where the torque converter lock-up was electrially actuated. Maybe a switch in the circuit could take care of the issue?

Sorry if all this sounds unusually naive for me.

[Robert J. Yates]

Jerry,
First off - its officially a 32RH, not a 999 and while the guy is somewhat correct on his premise, its not complete as the idea is to actually be able to invoke the lockup for the torque convertor to gain compression braking on decents. Wiring up a switch on this tranny to lock the TQ up while in 1st gear is, according to sources much more adept at this stuff than myself, quite involved. I know Hellbender was looking at it for awhile but don't know what came of it.

As far as most of us are concerned, there are no issues with lock up or stall for climbing stuff - most all of our Jeeps do quite well at this once a deep pan is installed. So much so that the limitations of the stock suspension geometry quickly make themselves apparent.

[mrblaine]

Jerry, try this first.

Take two identical jeeps. One being auto equipped and the other being manual.

Start both of them down the street side by side, have the manual guy push in the clutch when they reach 30 mph and the auto guy let off the gas.

Which one will slow down the fastest without the application of brakes?

This is not an auto vs. manual thread starter. This is a mechanical discussion. Keep it that way or stay out of the thread.

[Jerry Bransford]

I wasn't clear guys, sorry, it's not compression braking that I'm referring to, it's getting it to stop with the regular foot brakes when you're in 4Lo. Like the problems that prompted both of you to begin upgrading your brakes.

[Robert J. Yates]

Not sure what you are getting at then as I'm sure I would not want a higher stall speed for the TC - it seems about perfect for climbing stuff. I would rather upgrade my brakes than upset that balance.

Think about it this way - if the lockup were enabled in 1st gear 4WD low,you would stall your rig if you came to a stop, same as with a manual if you didn't push in the clutch so as I said earlier, its not the TQ that you are talking about, its the lock-up mechanism.

[Jerry Bransford]

I know next to nothing about autos Robert so it probably is the lock-up that I'm referring to, which I thought was inside the torque converter.

The discussion is about how difficult it is to stop an automatic-equipped Jeep with ultra-low gearing when it's in 4Lo. The individual I'm discussing it with said it is an easy matter of adjusting where lockup occurs, rpm-wise. Then he said that "any auto tranny guru" would be able to easily fix it so that the common difficulty in braking with an automatic when in 4Lo with low gearing was no longer an issue.

I figured with as much effort as you, Blaine, and others are putting into your brakes to get around this braking issue, that it couldn't be as simple as he's making it out to be.

[Robert J. Yates]

Hmmm,
If it were so easy, I think that we would have heard more about it being done. The fact that I have yet to hear of anyone, or at least a regular joe jeeper kind of guy, who has successfully accomplished this, while not the end all of absolute proof , leads me to believe it is fairly difficult to accomplish. Think about what Blaine told you for a bit it will come around for you to what I am talking about.

[Jerry Bransford]

Originally posted by Robert J. Yates
Think about what Blaine told you for a bit it will come around for you to what I am talking about.

Thanks Robert, that's what I was thinking... that if it were that easy you and Blaine would have been all over it long ago.

I have read and re-read what Blaine wrote but I am not getting what he meant since it seems he is talking about compression braking.

[sethmark]

Originally posted by mrblaine
Jerry, try this first.

Take two identical jeeps. One being auto equipped and the other being manual.

Start both of them down the street side by side, have the manual guy push in the clutch when they reach 30 mph and the auto guy let off the gas.

Which one will slow down the fastest without the application of brakes?

This is not an auto vs. manual thread starter. This is a mechanical discussion. Keep it that way or stay out of the thread.

Honestly blaine, I would bet a tire that it depends on what gear the manual guy winds up in. If I could get there in 2nd (I don't remember if I can or can't) I guarantee it'll slow FAST. If I get there and am in 5th, its gonna be a different story, for sure.

What's the lesson here? I want to learn.

[mrblaine]

Originally posted by Jerry Bransford
I wasn't clear guys, sorry, it's not compression braking that I'm referring to, it's getting it to stop with the regular foot brakes when you're in 4Lo. Like the problems that prompted both of you to begin upgrading your brakes.

I understood what you meant, and what the guy was talking about. The fact that the auto has compression braking is the majority of the problem. When you let off the throttle, the engine does not drop to idle like it does with the manual. Engines only produce full vacuum at idle. So between the two scenarios, only the manual has full vacuum to actuate the vacuum booster.

I can't prove this theory yet, but given the circumstances, it is the only one I can come up with to account for the discrepancy in braking ability given that autos are assisting in the braking with the engine and the manuals generally aren't. Every manual I have driven and every manual driver I have ridden with always pushes in the clutch at the same time they hit the brake pedal.

It was not 4-lo that prompted any of my brake upgrades. It was 35" tires.

[mrblaine]

Originally posted by sethmark
Honestly blaine, I would bet a tire that it depends on what gear the manual guy winds up in. If I could get there in 2nd (I don't remember if I can or can't) I guarantee it'll slow FAST. If I get there and am in 5th, its gonna be a different story, for sure.

What's the lesson here? I want to learn.

The problem is that manual guys generally don't leave the clutch out. They push it in at the same time they step on the brakes. Try it for me and see if you subconsciously do it.

[Jerry Bransford]

Then based on what you say Blaine, perhaps disconnecting the vacuum-actuated brake booster from the engine's vacuum system and connecting it to an aux vacuum pump like is used for backup in aircraft would be the trick cure. They're small, operate off 12 volts, and do nothing but provide an alternate source of vacuum for several critical aircraft instruments.

[Jason L Williams]

Originally posted by mrblaine
The problem is that manual guys generally don't leave the clutch out. They push it in at the same time they step on the brakes. Try it for me and see if you subconsciously do it.

All the way home last night, I was pondering your original test. I figured if the answer would be the auto driver would slow first as he (or she) has the engine slowing them down. The manual driver has just disconnected the engine from the drivetrain. Therefore, the manual would just coast. No resistance so to speak.
Kinda like my first accident. I pushed in both pedals and it felt as if the truck just shot forward before the brakes started working.
That's probably why I don't push in the clutch until I'm just about to stop. I've always figured it helps prolong the life of the brakes using the engine help slow down. Kinda like an auto.

[mrblaine]

Originally posted by Jason L Williams
All the way home last night, I was pondering your original test. I figured if the answer would be the auto driver would slow first as he (or she) has the engine slowing them down. The manual driver has just disconnected the engine from the drivetrain. Therefore, the manual would just coast. No resistance so to speak.
Kinda like my first accident. I pushed in both pedals and it felt as if the truck just shot forward before the brakes started working.
That's probably why I don't push in the clutch until I'm just about to stop. I've always figured it helps prolong the life of the brakes using the engine help slow down. Kinda like an auto.

That's the way I figure it. I pondered that for awhile in response to people saying that the auto "drove" through the brakes. How can it do that if it is attempting to go to idle as soon as the throttle is released?

I would also guess that you are not typical and most manual drivers push in the clutch at or nearly at the same time they step on the brake pedal.

[TJRON]

Originally posted by mrblaine

I would also guess that you are not typical and most manual drivers push in the clutch at or nearly at the same time they step on the brake pedal.

Now I see why you don't laike manuals. You never learned how to drive one. Only an idiot would put the clutch in while slowing down. The clutch is used to start, stop and shift gears. Period.

[sethmark]

Blaine,
As I thought about our conversation, I realized that basically Ron is right. I never touch the clutch except for those three events. On road braking is never done out of gear, except for coming to a stop at a traffic light, and then its only at the last minute.

s.

[mrblaine]

Originally posted by TJRON
Now I see why you don't laike manuals. You never learned how to drive one. Only an idiot would put the clutch in while slowing down. The clutch is used to start, stop and shift gears. Period.

Alright then, please explain why two jeeps with identical braking systems have drastically different stopping characteristics with the only difference being the tranny.

When you let off the throttle with either one, the engine attempts to go to idle and applies compression braking.

I said it was theory, I did not say it was absolute.

Idiot looking to learn something here.

[Art Welch]

Originally posted by sethmark
Blaine,
As I thought about our conversation, I realized that basically Ron is right. I never touch the clutch except for those three events. On road braking is never done out of gear, except for coming to a stop at a traffic light, and then its only at the last minute.
s.

Same here.

For those that do pop the clutch in at the same time as the brake pedal Blaine's theory w/ regard to available vacuum makes sense to me.

Off road I know that if I'm in 1st gear 4lo and try to come to a complete stop without disengaging the clutch it won't happen despite the best effort of my brakes. That's with low gears but also with brakes that I believe are slightly larger than necessary for the weight of my vehicle in normal conditions.

Isn't the situation the same with the auto and the torque converter? To the auto tranny naive it seems like it functions the same way as a clutch and as long as it's engaged it will be much more difficult to stop.

I'm just trying to learn something here, not start a rant as Jeff put it.

[sethmark]

Originally posted by mrblaine
Alright then, please explain why two jeeps with identical braking systems have drastically different stopping characteristics with the only difference being the tranny.

When you let off the throttle with either one, the engine attempts to go to idle and applies compression braking.

I said it was theory, I did not say it was absolute.

Idiot looking to learn something here.

Beats me. Does the torque converter somehow rob vacuum from the motor?

[karstman]

I understand what the guy is talking about with regards to running a loose converter to improve braking at ~slow speeds~, and I've experienced it, BUT not in a jeep. I've swapped out the converter in my chevelle on 4 occasions to match different camshafts I had decided to run. In the end I was running a custom 9" converter with a stall speed around 3000 RPM. If the car is sitting on a hill, facing uphill, idling, in any forward gear, and you let off the brake, it will roll backwards with ease while still engaged in the forward gear. The converter is too loose to transfer any torque to the input of the tranny. In fact, you will not move forward until you get the motor up over 2500 rpm's or so. It is VERY loose at the low end, just as if you had your foot on a clutch. I can see where this may alleviate the engine driving over the brakes at slow speed because the converter is "engaging" (for lack of a better term) just off idle. Jill's TJ is an auto and I've noticed that the converter does indeed have a very low stall speed. It starts transferring torque at idle, because if you take your foot off the brake it will begin to roll forward on it's own.

Jerry - To my knowledge, you can not "adjust" the stall speed of a torque converter. You have to replace the converter with a different unit, or at least this was my experience with TH350's. I have never played around with a 999 much, so perhaps I should just sit back and be quiet, but what fun is that.

I have to disagree with the engine vacuum idea though. Vacuum is not solely dependant on engine RPM. It's a combo of RPM and intake airflow. When decelerating you have moderate RPM's but the air intake is cut drastically because the throttle is closed. That should produce more than enough vacuum to activate the booster. If I'm wrong on this, one option you could look into is a vacuum reservior. 1/4 mile folks run them all the time to run power brakes and big camshafts.

[TJRON]

I think we're talking about several different things here.
On the street: There's not much difference in stopping power. The engine will slow either down. You can down shift either one for more engine braking but the manual has more gears to help out. In an emergency stop I think they would be equal.
Coming down a steep hill: The manual has more gears and the direct link to the engine. I think the term "slush box" comes in here.
On the rocks: Manuals rarely apply the brakes with the gas on unless they have too high gearing and are using a hand throttle. Even then not too often.
Normally we have one foot on the gas and the other ready to apply or slip the clutch. To make an immediate stop on an obstacle we hit both the brake and clutch at the same time.
I understand what makes an auto easier to drive on the rocks is the ability to keep some pressure on the throttle and use the brake to regulate speed. To stop just apply more brake and let off the gas. If it's still in gear the engine is still trying to go. With low gearing the brakes are working hard.
The brakes are probably mostly over ridden when going over difficult obstacles with too much throttle applied and usung the brakes at the same time.
Does this make sense?

[John]

Originally posted by mrblaine

When you let off the throttle with either one, the engine attempts to go to idle and applies compression braking.

This isn't right. I drive my YJ with a manual and my wife's WJ with an auto. Right by my house there's one of those speed trap radar things that tells you how fast you're going and flashes at you if you're too fast (15 mph zone).
I enter it's line of sight with both Jeeps going faster then posted and can just let off the throttle of the manual equiped one and it drops speed pretty fast. With the auto I have to apply the brakes of the Jeep will continue along at the same speed it was at for the length of the road (less then a 1/4 mile)
I'll have to try this with hitting the clutch tonight when I go home and watch the results.

[TJRON]

Originally posted by John
With the auto I have to apply the brakes of the Jeep will continue along at the same speed it was at for the length of the road (less then a 1/4 mile)
I'll have to try this with hitting the clutch tonight when I go home and watch the results.

You might also try pulling the auto down into second gear and see what happens? Low gear if you're brave.

[MJR]

With the brakes I had on my XJ originally I would just bump the shifter into neutral so the engine and automatic were not still applying power at the same time. This is also the same essential thing as pushing in the clutch on a manual. The booster also has a check valve to hold vacumn which will be the most Hg after the last pedal application. The booster stores enough to allow safe braking if the engine dies too. Bottom line I believe that the automatic is simply applying engine torque all the time.

[Robert J. Yates]

Given my experience with the hydorboost, I don't think that vacume is the issue here.

As somebody else said, the TJ tranny seems to apply torque just off idle which is great for clmibing stuff but lousy for braking.