Power steering loosing power

JClark · Feb 20, 2004

wh bob1,

On my way through town this morning I stopped by the dealership to tell them about your experience. The service manager said that seemed to be the same problem with mine. The pressure test results were at the bottom of the acceptable range so they have decided to add shims to the relief valve. He also said the used 4100 they have is doing the same thing.

The shims should arrive next week so I am hoping to have a fully functional tractor by next Friday.

Max front tire pressure for my R3s is 22 psi. I keep about 20 in them so I believe tire pressure is not the issue here. But like I mentioned upthread, if I pumped them up to about 40 psi I am sure steering would be easier.

Thanks for your information. I am a bit more confident now that the dealer is on the right track.

JClark · Feb 20, 2004

By the way, does everone know you can see parts diagrams online? Go to:

http://www.deere.com/en_US/groundscare/parts/orderparts.html

You have to enroll but it is worth it. It really helped me understand the hydraulics setup. You know what's worth a thousand words.

nailerguy · Feb 20, 2004

Jclark, now we are getting somewhere! With the pressure at the bottom of the acceptable range, the steering effort will suffer when you load the bucket. I am sure the lower pressure is due to the thinner fluid and that the shims in the relief valve will solve your problem.

Please guys do not misunderstand what I have been saying all along, the thinner fluid will work just fine in your tractor but the pressure will have to be adjusted to make up for the pumping losses and the fact that the thinner oil will go through the system relief and internal orifices much easier. Less backpressure = less pressure and evidently, in the steering system on a tractor it does'nt take much pressure loss to make a big difference.

Jclark, on a different note, you have been steadfast and loyal to your John Deere tractor even through the tough times the dealer and the RM gave you. For that (for what it is worth), you have earned my respect. Loyal people are getting to few these days (although there seem to be quite a few on this website), Happy tractoring.

Nailerguy

bigpete · Feb 20, 2004

jrlichina.

I gotta’ beg to differ….and from my conversations with a PhD' retired professor of engineering, and JD engineer in the ‘50s…my Father.

First, I'm not supporting the theory that the change in the tractors caster angle would be the sole cause of the problem, (nor would my Pop’), but there is merit to the principle. That is, a slight change to a reasonably neutral caster angle in a CUT under a heavy load might have a dramatic effect on steering effort. Lots of other factors here, most have been covered earlier, i.e. ballast, tire pressure, surface conditions, hydraulic oil pressure, etc. Pressure now being increased with shims... /forums/images/graemlins/grin.gif

Second, to your statements....

 Caster is important on higher speed vehicles like cars, trucks, and obviously race cars, but it is NOT an issue as it pertains to CUTs. 

Our slow-moving equipment is designed to carry a wide-ranging amount of weight in a variety of conditions, including slope, tilt, varying surface conditions, etc. Engineers spend an incredible amount of time testing and tweaking all of the steering dynamics in CUTS, not the least of which is caster angle. everything is BALANCED for safety, straight-line stability, and steering effort. Because of the fact that the tractor may creeping, or moving at over 10 MPH, and the fact that the front axle load can vary as much as 400% in a matter of moments, caster is more critical than ever and more sensitive than ever. Slight changes in a reasonably neutral caster condition, coupled with a dramatically increased load and even a slightly a modified downward thrust angle from the larger tires rear tire and inadequate ballast can make the steering effort increase exponentially

 In general caster comes into play when the vehicle is in motion not in static situations. 

This is simply incorrect. Caster is in play all steering conditions, dynamic and static. Changes in caster angle primarily affect two things: stability in motion and required steering effort from a static position. Camber is affected secondarily by changes in caster.

 The only time it would have an effect in a static situation is if the caster angle was changed drastically (greater than +- 20 degrees). 

An exaggerated 20 degree change in the caster angle, under load, and under-ballasted on a John Deere 4110 would render a very precarious stability condition in motion, and definately a completely inoperable steering condition from a static position. Whereas a 3 to 5 degree change might realistically have a dramatic effect on steering effort, ESPECIALLY from a static condition with inadequate ballast.

Most people know of caster, camber, and toe from automobile alignment training and discussions, but they are basic steering dynamic principles for racecars, bicycles, grocery carts, mining equipment, and little red wagons. If you consider the wide spectrum of steering applications from creeping mining equipment to an open-wheeled car going over 200 MPH, you will find the sensitivity level is exponentially greater at the ends of the spectrum. That is, a minor tweak to caster in a high speed car will have dramatic effects on stability, and a minor tweak to caster in a slow, heavily loaded vehicle will also have a dramatic effect, but in required steering effort.

I’ve even bored myself here, so I’ll just end by reminding everyone that JClark has (had?)to force his steering in static conditions, not while he’s moving. This symptom leads trained engineers to begin diagnosis by asking about these specific steering dynamics. I’m sure the RM was just parroting what an engineer told him, but that doesn’t make the principle absurd. It just isn’t the first blush answer anyone wanted to hear. The added pressure from the shims should overcome any possible imbalance from the changes to the steering and thrust dynamics. That's what we're all hoping for here, afterall. /forums/images/graemlins/grin.gif

Trev · Feb 20, 2004

( Most people know of caster, camber, and toe from automobile alignment training and discussions, but they are basic steering dynamic principles for racecars, bicycles, grocery carts, mining equipment, and little red wagons.)

Toe on a bicycle? You lost me on this one! /forums/images/graemlins/confused.gif

Bob

bigpete · Feb 20, 2004

Got me...scratch toe for two-wheeled vehicles. /forums/images/graemlins/blush.gif

However, a bike's front wheel can be out of "toe." It's just toe right, or toe left, that's all.... /forums/images/graemlins/wink.gif

jrlichina · Feb 20, 2004

bigpete

I believe I pretty must prefaced my statement with "in general" and my extreme example of excessive caster was just that, meant to be extreme. I agree with many of your statements. My main point was that the rear tires that are a couple inches larger in diameter would cause such a minor change in caster that it was not enough to cause the steering problem he is having. If you look at my earlier posts you'll see what I thought the problem was and how to actually diagnose the problem. I just didn't want to get too technical in my explanation. And believe it or not I'm an engineer too and I've designed and built several front suspensions for 4WD trucks and 2WD tractors. Thanks for your comments.

JerryG · Feb 21, 2004

However, shouldn't it go away if you take it out of 4wd? 
It would more than likely if and only if the relief and or the pump has not been damaged.
About the statement on caster, As far as caster goes it should have very little if any to do with the lack of steering response that is taking place. My points about stress would come in to play only when using FWA. There would be no pump or drive line stress in 2wd from the larger rear tires . What I have stated is only the way that I would think that JD would approach the problem. Any time there is a deviation from what is recommended or there is a modification to a piece of equipment, it is deemed as a situation where the warranty is void. I will say that I hope that Deere helps and tries to correct the problem whether it is because of the ratio imbalance or not.

bigpete · Feb 21, 2004

jrlichina and JerryG,

Yeah, the caster angle isn't the only problem. In fact it might not have anything to do with the problem at all. But a vehicle with a thoughtfully balanced suspension, such as a modern CUT, can be thrown out of balance and exhibit what one might call "functioning problems" in steering by even a small modification. When you look at the key changes to the machine from delivery day to reported problem, there are only two things that really changed--hydraulic fluid and filter, and bigger rear tires. Send those two factors to an engineer and he or she will begin to rule out the simple stuff. Since surface conditions, ballast, tire pressure, and modified steering dynamics from bigger rear tires are the obvious contributors to a possible steering problem, the engineer tells the RM to check working ballast, tire pressure, and get stock wheels back on the tractor. I think one of the bigger disappointments is the time it took to get pressure readings on the pump. I think it would be reasonable to expect a more responsive trouble-shooting process than JClark has seen.

Anyway, I often find myself jumping in on discussions or debates where people over-simplify or simply rule stuff out as ludicrous or absurd. We all really have limited information here and a good number of contributors in this thread have summarily dismissed adding bigger rear tires to the tractor as having no possible connection to increased steering effort. If the bigger tires do have a contributory effect on the increased steering effort, which I believe they might at some level, then it is most likely through a change in caster angle and a couple of other relational steering factors. You are absolutely correct that steering dynamics are very complicated, technical, and sometimes quirky. That's why we all might want to consider that the engineers that design tractors know a little about what they have told the RM to tell the customer.

Bottom line, if the increased pressure pushes through the increased effort, then JClark might have a tractor he is happy with. I'm all for biting the bullet in these situations and getting the tractor you really need. As long as the money works out.

JerryG · Feb 21, 2004

I think one of the bigger disappointments is the time it took to get pressure readings on the pump. I think it would be reasonable to expect a more responsive trouble-shooting process than JClark has seen. 
I am with you here. After checking the tire inflation pressure, the next thing should have been the pump pressure.

As far as front end geometry, If the larger tires ( IN 2wd ) effected it very much then 10s of thousands of farmers over the last 60 years woulld have had problems also. Every sence rubber tires were placed on tractors, larger rear tires have been placed on the rear of 2WD tractors. IN 2WD the larger rear tiires cause NO problem or very very minor ones to say the most . In 4WD it will mess things up.