Hi all we had to remove the lefthand final drive to replace one of the brake separating plates due to some broken teeth causing the brake to drag. Anyway we put it all back together with new oil and fired it up but it won't move. When we shift it into gear the driveshaft stops stops turning but unit won't move. When we move steering tiller neither diff will move either. I suspect issue is with the brakes staying on. Prior to repair brake pressure was 425 psi with brakes off and pressure to 0 when you touch the brakes so all was working properly there. One guy said you need to bleed the brakes after repair so i removed plugs on both sides and a lot of oil is coming out the holes upon starting it. Not sure if bleeding is necessary or not but if so whats the procedure to do it without losing a lot of oil. Any advise is appreciated. TIA
There is no necessity to bleed the brakes after a repair such as the one you did. The brake piston seals leak slightly so any air would eventually be forced out. If you have oil coming out of the plugs (#30..?) then you have oil going to the brakes. If no pressure is being generated then IMHO you have an internal leak somewhere, possibly a cut seal from the repair.
Does the machine not move at all ..? Even at higher RPM, the right track (the other side, not the one you were working on), doesn't even tend to move? Since you say you have taken out the left final drive (which also includes the steering differential), did you also dismantle the diff. in the process? If the machine has a ripper, maybe it's worth suspending it on the blade & ripper, with both tracks clear off the ground, and see if the right track turns. True, most probably it's a leakage somewhere in the left brake circuit, but a D8N should have a lot of power... even with the left brake stuck ON, intuitively it would seem strange to me if the other (right) track had absolutely no tendency to move whatsoever...
Thanks guys for your responses. Heres an update When i suspend dozer with ripper and blade the tracks will turn but slow and brakes seem to drag. Dozer will move forward only when on the ground but engine must be wide open in 1st gear and only if i press on brake pedal about 1/4 of the way down. Sounds odd I know. It moves very slow and it will only move about 20 feet before tc temp reaches 250 ish and i stop to let it cool down. It will not move in reverse at all. Brakes are staying on to some extent it would appear. I did not do the disassembly and repair of the complete final drive assembly. I just removed it and took it to a mechanic who had experience with tearing it apart. I put it back into the dozer and put everything back together after he had replaced the broken plate so Im uncertain if he perhaps had a seal get buggered up upon reassembly.
It sounds as though you have a major leak somewhere in the brake pack. When you reinstalled the rebuilt final drive unit did you replace all the O-Ring seals between the chassis and the final drive with new..?
I belive the brake arr spring applied oil release with a common release pressure. When you push on the brake pedel u are stoping the oil flow and the spring starts to apply the brake. So if the brake you just had apart has a cut seal. Both brakes Will be applied... Please corect me if im in the wrong.
Yes, that is correct, and I was wrong on thinking the right track should turn in case of a problem with the left brake. I was very tired Friday evening when I posted about trying to suspend the machine, and I was under the recent impression from a D6R brake control valve which I just cleaned last week - which has separate circuits for each brake, even though they can't be independently applied. Sorry for (involuntarily) misleading you... I just checked now, and the brake control valve on the D8N has a single circuit / chamber which controls both brakes. So that means DARO is correct - if the left (recently worked-on) brake has a leak from a cut seal etc., it means BOTH brakes will be affected. I guess you'll probably have to take it off again and check...
Thanks a lot guys for the advise. Unfortunately it looks like I'm gonna pul her apart again
I would check the dump valve for the brakes. It's controlled by the lever you lift to lock the steering tiller. It dumps all brake pressure to 0 psi . Make sure it's connected properly