PT425 Wheel Motor Torque Increase - 30%

MossRoad · Nov 18, 2004

1. Can you retrofit a 425?
YES!
2. What would it cost?
LOTS!
3. Can you retrofit a 422?
SURE!
4. What would it cost?
SEE #2
5. Does the 422 gasoline engine have enough power to drive the bigger motors to full torque?
Hmmmm...
6. Who makes the motors
***** makes the motors.
 and can we buy them directly from the manufacturer
YES!
 and at what cost?
SEE #2
7. Are the mounting plates the same for old and new motors?
Hmmmm...
8. Do we really need it, or are we just being greedy?
YES! /forums/images/graemlins/grin.gif

BobRip · Nov 18, 2004

Thanks Moss. Those are really good answers. Your technical knowledge never ceases to amaze me, its almost as good as your sense of humor.

Take care, but not all of it.
Bob Rip

stray · Nov 18, 2004

A couple more questions.
Does the newer 425 have a larger pump to drive those wheel motors?
Will the newer 425 still do 8 mph at the same engine rpm?
If I did retro fit my 422 with the larger wheel motors how fast would my top speed be? Would it be like using a lower gear?
Hay maybe if they added a two speed gear box one could have the best of both worlds. LOL
I mean to say I am very happy with my 422.

MossRoad · Nov 18, 2004

In all seriousness, this has been discussed before. I think they said the top speed of the tractor was reduced a little to maybe like 7MPH or something. Have the specs changed on the website from 8MPH?

I would think that if you put torqueyer(more torqueful, man that's a tough word to make up) motors on there, you would have to lose some top end. But the benefits would be almost all positive.

The pump on the newer model is different in that it has a throughput shaft so that the PTO pumps can be put on in front of it and the engine can be on the rear of it. Also, the directional control appears to now be by the operation of a hydraulic valve under the treadle pedals as opposed to my cable operated lever on top of my pump. I do not know if the output of this newer puump is any different than the old pump.

A two speed gearbox would be nice. For our application, I believe it would have to be at the output of the pump and before the motors, so, it would most likely be some sort of two speed pump. One with high flow, low PSI and the other with low flow, but high PSI. Log splitter pumps come to mind, as they can be two speed pumps.

Another thing people have pondered is actual brakes on the PT400 series. Motors with hydraulic brakes internal have been discussed. After I had my wheel off a couple weeks ago and looking at the brake disk with slots for the parking brake, I think it would not be too hard to put an actual disk brake caliper in there. It could be hand operated similar to a motorcycle brake by a lever on the left side of the dash and would require just a small reservoir like a bike, as well. Couldn't be too expensive to add, maybe a couple hundred dollars and would suffice as a good emergency brake. The problem would be to fit the caliper inside the wheel. Again, motorcyle parts come to mind.

toy · Nov 19, 2004

While I was at pt in Tazwell a while back they had an older pt that they had taken the lifting arms off and put a forklift mast in its place. While I was looking at it I noticed that it had a hi range and a low range. I asked one of them, don't remember which one,about the hi and low range and he told me that the early ones had two speeds and I saw one in the trader for sale and they said that it had two speeds.

duane · Nov 19, 2004

You can increase the torque to the ground effect by decreasing the tire size from 23-10.5-12 to a 20-10-10. Changing the tire size will increase torque to the ground by 25%, but you lose 1 mph and 1.5" of ground clearance.

BobRip · Nov 19, 2004

I wonder if having lower tire pressure increases the torque. The tire would be flatter and there is then less distance to the center. This is kind of like putting on a smaller tire.

MossRoad · Nov 19, 2004

If you go too low on the pressure, you'll be more likely to pop the bead where the tire meets the rim. It's no fun getting the PT out of the woods on a flat.... I know. I ended up skidding it backwards on the rear tires and bucket to keep most of the dirt out of the rim. I took some photos and will post them in the next few days.

BobRip · Nov 21, 2004

Moss, the Power-Tracs have a mulitspeed system now. When you push on the treddle you actually change the displacement of the pump. A little push is low flow and higher pressure and as you push it further down you have effectively a continuously variable transmission with more flow and less pressure. I am far from a expert in this, so I don't understand exaclty why there is not more torque at low speed. maybe somebody esle can explain it.

BobRip · Nov 21, 2004

I have found a link which may explain this better. Look at the variable displacment pump here http://science.howstuffworks.com/backhoe-loader8.htm
I hope that I am doing this correctly