Hello All ,I have been working on a homebuilt tractor project for about a year now.It is 4 wheel drive 4 wheel steer ,I would
say it weighs around 1200 lbs.Power plant is a 3 cyl gas geo metro engine, which runs a 20 gallon pump 2000 psi @ 2200 rpm.That is plumbed to a single spool cross mfg valve,and to a hyd motor rated 2.8 ci rev with a max torque of 650 inch lbs,max speed 970.The motor connects to the input side a samurai transfer case which then goes to the front and rear axles.MY problem is the machine will just move itself on level ground and starts to shake when going down a slight incline.
I am starting to think maybe the motor is way under powered for the job,btw there is no case drain hooked up to the motor.
Does the torque of the motor seem to low?

What are the ratios in the transfer case, axles, tire size. Sounds a little weak, but it really depends on the ratios based on the above questions.

As for the shaking going down hill, the motor is probabally cavitating. Can you hold the brakes a little to keep the motor pushing instead of being pushed.

The hydraulic motor is on the small size. 650 in pounds torque is 54 ft pounds, through say 3 1/2 to 1 rear ends with 30 inch tires gives 126 pounds force.
The pump is too big for the motor you need about 10 gal/min. With the bigger pump the relief valve is probably opening and dropping the pressure to who knows what, should put a gauge on the line.
Gator could be right on the cavitating or the relief valve is opening and closing with the reduced load while on an incline.
Hope this of some help.

At some point you will probably need to put a counterbalance valve into the circuit.

about counter balance valve

more info

This will control the cavitation when you go down hill. The cavitation can quickly damage the hydraulic motor.

Chris

The transfer case is out of a sj410 with ratios of Hi = 1.58:1 Lo = 2.51:1,and 4:11 rear ends ,with 235 15 inch tires.
Looking back on this now ,it does seems the pump and motor should
have been in reverse for sizing,however the pump was given to me and I picked that motor because of its top rpm.
There is motor on sale at Princess Auto rated 14.1 ci ,2669 in lbs and max rpm 243. What do you think the top speed of this thing would be? looking for around 6-10 mph

I was just looking up the engine specs of the original 410 sami and it produced 54 ft lbs @ 3000 rpm.Because I don't have a transmission before the transfer case I am losing out on the torque needed to get me moving.
The motor I posted specs on rated @ 14.1 cu should require 22 gpm
to get max rpm ,if I did my math right.

Going to post my excel file here. Looks like 1200 would give you top speed of 19 mph in hi range and 12 mph in low range with a 35 inch diameter tire. You will have I assume a variable speed control such as https://www.surpluscenter.com/item.asp?item=9-4169-12&catname=hydraulic you may want to look at https://www.surpluscenter.com/ for your motor. I bought all mine on eBay however.

Ok... I could not download my file above hope you are able to.

Your ratios (I did not save the file after I put in the figures) are as follows 4.11, 1.58 and 1.588

or 2.51/1.58 So the last ratio give you the speed ect you would get when in low range. Let me know here if excel file loads if not I can email it to you.

Hey Clint , the file won't download for me either ,when you get a chance email . Thanks

OK where should I plumb in a gauge,between pump and valve ,or between ,valve and motor?

It is conventionly placed between the pump and the control valve but will work anywhere between the pump and the motor. If it is between the pump and the valve, it will show the backpressure of the system when the spool is in neutral. This is sometimes useful for troubleshooting. If there is a lot of pressure there (when in neutral) your filter may be plugging up or you hoses may be too small. This will generate un-necessary heat.

Chris

I'm running a 24ci/rev motor at 2000psi,driving a samurai transfer case and 4.11 axles.All I can tell you is it will spin the tires and dig a full bucket full of dirt with good breakout power.Not much on top speed but has good pushing power.It's good at snapping 1-1/4"dia axle shafts too.My guess if you are running 20gpm/2000psi and are barely moving,then a larger displacement motor would do it for you,torquewise..Off the cuff,i'd start with at least a 18ci/rev.The only thing a case drain benefits you is allowing you to run higher pressures on a more continuous basis,and it helps keep the motor cool by circulating more oil.Check eBay for a motor,there's always used ones for sale there.

there's a few on eBay right now, one 17ci/rev for 145.00. Char-Lynn motors

.numerous other ones for reasonable $$. I've even bought some that were supposedly 'cores for rebuild'-like the one in my loader-but have held up just fine for years now with no attention at all..Search on 'char-lynn'in the business/industrial section of ebay.

Thanks Guys for info. I went and bought the 14.1 ci/rev motor yesterday and installed it.It moves now and doesn't shudder going down inclines.It is alot slower,high range is just a fast walk ,but low should be good for snowblowing.
I am having trouble with the geo engine right now,when it warms up it dies out on me.Maybe an egr thing.Also I think I will need some sort of govenor or cruise control to keep the engine at a constant rpm.
Bunkclimber, is your hyd motor direct into the transfer case?

Bondeoca
We like pictures

I used a #60 1-strand roller chain to side drive it.A 30T sprocket on the motor and a 15T on the transfer input.I had to make a custom input shaft to support the side drive load on the transfer case input.The shaft rests in a roller bearing mounted to the frame,and the other end bolts to the input flange on the transfer case.The hyd motor bolts to a mount plate(1/2"thick)on the frame with an eccentric hole and slot so you can move the motor to take up slack in the chain.The motor has so much torque at 2000psi it ripped itself loose from the bracket twice already.I had to put heavy metal stops for the motor to push against to help lock it down.

Bunkclimber ,so you ended up haveing a 2 to 1 ratio on your input and that doubled your speed.That may be something I will have to do in the future,just not sure if I have enough room.
I will start a thread of this build as soon as I figure out how tp upload pics.Also I think my problem with the geo engine is the fuel pump.

hey if you replace the fuel pump stay away from the solenoid impulse type,I've heard lots of folks only get about 6mo out of them now because of the ethanol fuel content.Yet to be confirmed as the cause but three people so far told me that they tried 'universal clicky type'pumps and they dont last long...FWIW

Thanks Bunkclimber for the info. It is the fuel pump so I need to find one.
Also I noticed for the short time I had it running, it is quick to start and stop on the tcv. When in neutral it stops,so I assume it is a closed spool,and I would like to have it open so it will coast to a stop.
Maybe I can machine the spool that is in it now to be open center design.

The spools are honed to fit the valve body bore with pretty tight tolerances,one nick and you'll make a real mess at 2000psi.I'd save the present valve for a future project(you'll have more,trust me)and just buy the right motor valve.Brand Hydraulics makes a really nice motor spool control valve,you can get them from Surplus Center or Baileys.Really nice folks at Brand Hyd,helped me out with a valve blunder a few years back..great customer service.