pump pressure 801.4

[kid_rock]

Hi all, I have an old 801.4 jcb. I have operated it since 1992ish. I inherited it from my late father. About 12 years ago he asked the guy who did our fitting to put a new pump on it. I told him that it wasn't the pump, but changed it anyway!

Anyway the left track is slow in both directions. I have checked the pump pressures. It is a triple pump and the readings are 250, 150 and 200 bar. The slow track is on the section pushing 250!!!! I am unsure where to go from here. I am gonna change the oil and filter as I am unsure when it was done last. But in preparation for the worst can someone please give me a clue? thanx in advance Andie

[ianoz]

Just check you are getting full travel on the sticks to start with . Centre joint could be leaking/Bypassing . Or you have a sick drive motor .

[801_user]

Just check you are getting full travel on the sticks to start with . Centre joint could be leaking/Bypassing . Or you have a sick drive motor .

Hi Andy, I had the same problem with my 801.4 of a similar age. I thought my pump must have been goosed, although found a couple of things that were at fault. First as has already been suggested, check for full travel on the sticks. I found the cross shaft that both sticks run on was partially seized up.
Freeing this shaft off helped a great deal although it was still not quite right, the other things I found was that all 3 idlers on the track were either seized or the bearings had long gone creating a huge amount of drag. I used standard sealed bearings instead of the JCB ones as I am a tight git and standard ones are only a couple of quid each. The last thing was that the big sprocket was very hard to turn round, this was fixed by tapping in a grease nipple to the hub and lashing loads of grease into it. It tracks along lovely now

[801_user]

Hi Andy, I had the same problem with my 801.4 of a similar age. I thought my pump must have been goosed, although found a couple of things that were at fault. First as has already been suggested, check for full travel on the sticks. I found the cross shaft that both sticks run on was partially seized up.
Freeing this shaft off helped a great deal although it was still not quite right, the other things I found was that all 3 idlers on the track were either seized or the bearings had long gone creating a huge amount of drag. I used standard sealed bearings instead of the JCB ones as I am a tight git and standard ones are only a couple of quid each. The last thing was that the big sprocket was very hard to turn round, this was fixed by tapping in a grease nipple to the hub and lashing loads of grease into it. It tracks along lovely now

Oops sorry Andie, spelt your name wrong in the last post.

[kid_rock]

Thanx for the heads up. I'll give them all the once over and return some feedback. Don't worry about my name I work on sites, so answer to names that I don't think are in any baby naming books!!!!

Cheers again!

[Muz]

The last thing was that the big sprocket was very hard to turn round, this was fixed by tapping in a grease nipple to the hub and lashing loads of grease into it. It tracks along lovely now

I always wondered why JCB used a sprocket at each end ? no one else does to my knowledge ... anyway .. fitting a nipple for greasing works for a while but gets broken off after time IMHO

Sprockets at both ends make for a c**t of a job to get a track replaced .. plus they get damaged more easily when, and if it comes off


I guess I 'm asking a question ? And maybe we should have a thread on it elsewhere ? Sorry OP it gets bad when an admin hyjacks a thread ...

[kid_rock]

No worries Muz, I have an idler on one end and a sprocket on the other. I've tried the bottom rollers and they are all OK. Hopefully over the weekend I can get a look at the rest. I'll post up when I put the stethoscope away!

[Muz]

No worries Muz, I have an idler on one end and a sprocket on the other. I've tried the bottom rollers and they are all OK. Hopefully over the weekend I can get a look at the rest. I'll post up when I put the stethoscope away!

Personally , Ive not had sticky U/C parts causing the problem , its usually pressure related.

The big clue is ... Always, one section of the pump supplies that motor and something else, so if its down, so is another service, such as the slew or dipper. If everything else is fine, then the pressure is getting away somewhere else. The track drive is just a pump in reverse, it could be allowing oil bypass, but more often as ianoz mentioned its the orbital valve, or rotary distributer as the fitters like to call it. Theres a lot of seals in there, and its a common source of failure .

You need to get your pressure tester down at the motor .. or .. swap the feeds as they come off the valve and see if the problem is replicated on the other side ? .. that will give you your answer ... keep us posted

[801_user]

I hadn't considered the grease nipple getting bashed off, that's a good point. I did try and put it somewhere discreet, although maybe I will live to regret it! It would be interesting if anyone else has had the drag from seized items on the rollers causing a problem, certainly appeared to be for me. You are right though it certainly was a right c**t to get the tracks off as the adjusting bolt needed lots of heat and a 4 foot bar to shift the so and so.

Consulting the JCB handbook, the left track and dipper ram are on section 3 of the pump, so you would expect the dipper ram to be poor if pressure is an issue.

[Muz]

Consulting the JCB handbook, the left track and dipper ram are on section 3 of the pump, so you would expect the dipper ram to be poor if pressure is an issue.

Cool ... Thanks for posting that up .. that should help to either qualify or eliminate something

[801_user]

I should have said on the last post Muz, that I bow to your much greater excavator expertise. I would struggle to fill the back of a fag packet with my knowledge Although i was guessing that with quite small power output on these little machines compared with the big monsters that many here operate, that any drag on any of the running parts would add up to noticeably reduced track speed.

[Muz]

I should have said on the last post Muz, that I bow to your much greater excavator expertise. I would struggle to fill the back of a fag packet with my knowledge Although i was guessing that with quite small power output on these little machines compared with the big monsters that many here operate, that any drag on any of the running parts would add up to noticeably reduced track speed.

Well... the track motor is whats known as a power multiplier due to the way the gearing works. Its a method of getting a small input force to generate a massive output using gears

Essentially a small shaft rotates in the middle (sun gear) with three or more (planetary) gears around it... they in turn are connected to the outer ring or (annulus) .. the whole system is called an epicyclic reduction hub


http://en.wikipedia.org/wiki/Epicyclic_gearing

The outer ring is usually the casing that you look at from the outside when you look at your track motor.

Its a mechanically very efficient method of multiplying power ... the down side is that the gearbox is highly loaded and requires good oils and maintenance to keep it running smoothly to cope with the high surface loadings inside it.

You'd be surprised to see that the drive pinion on a 3 tonne digger for example will be no thicker than your pinky, but it delivers a tractive force through the sprocket that can be measured in tonnes

There you have it ... I got my fitter hat on for you tonight .. but its why the undercarriage wont be the problem. Yes it can cause drag, but not enough to stop that kind of tractive power

[801_user]

Well done Muz, I'm impressed, I shall go and stand in the corner wearing a pointy hat

[kid_rock]

Well it's been a while ile I I never came back with an answer! Let's just say I have continued to use the machine as it was until now. I'm gonna get the pressure gauges on it again and try and figure it out.

Thetrack is stoll slow and also the dipper and bucket are slow too. I have noticed that if I lift the dozer blade up it makes it slew faster though?!?