996 clutch overhaul questions

Posted by torquilmackenzie on 2017-07-04 15:12:00 

Hi all.
I've split my 1976 996 Q cab to replace the clutch as the PTO clutch had packed up and started interfering with the transmission clutch.
It transpires that the PTO release mechanism had started to come detached from the fork due to a failed/missing split pin, and I have also discovered the transmission release bearing and bearing inside the flywheel (spigot bearing?) are both very rough.
I will replace all the clutch parts, but need a bit of help if possible:
- how do I remove the transmission bearing - should it just pull/lever off ?
- how do I remove the flywheel spigot bearing - do I just remove the 4 tab locked bolts and cover to lift it out ?
- looks like my PTO fork was secured with 2 Belleville washers, and the manual suggests I should replace the pin and use 6 - is that right ?
- although I didn't suffer excessive oil leakage from the engine/transmission, I'm considering replacement of seals if it's relatively easy ?
- Any known source vfor a clutch plate pilot/guide for a sensible price ?
- when I split the tractor I didn't install "retaining staples over each PTO release lever", could that be a problem?
Any and all help much appreciated, Tog.
Posted by: ollek on 2017-07-04 17:18:00 
The transmission bearings are inside the gear box and not in the clutch compartment. Both the transmission clutch drive shaft (hollow shaft) and the pto drive shaft bearings (in the fly wheel) are removed in the normal way using inside or outside bearing pullers. This is a normal workshop practice. The retaining staples are used to prevent the clutch levers from rising up and make it difficult to remove the clutch cover and to get it back on as the bolts will be too short, when the pressure plate is pushed away from the clutch cover by the springs, when you remove the bolts. There is no need to change the engine crankshaft rear end seal if there is no obvious oil leak. The rope seal used will never completely stop the oil leak. A small leak is a feature, not a fault. The following is a link to the pto clutch release bearing and fork arrangement. http://partstore.caseih.com/us/parts-se ... 9ar1277555 The bellewille washers are acting as a spring and will give some load to the friction washer. The bellewille washers do not secure the pto fork. The following is a link to a drawing that shows the transmission clutch drive shaft and the bearings on that shaft. http://partstore.caseih.com/us/parts-se ... 9ar1276079 The bearing ref 31 and seal ref 34 are inside the gear box. These parts can not be changed unless the gear box top and the gear box are removed. The bearing ref 23 is supporting the front end of the transmission clutch drive shaft and sits in the clutch housing.
Posted by: torquilmackenzie on 2017-07-04 17:43:00 
Ok thanks Ollek.
The release bearing for the transmission does seem to slide when pulled by hand away from the fork but not all the way off. I'll try that with pullers.
Do I need to remove the flywheel to pull out the spigot/pilot bearing that the end of the shaft sits in ?
Thanks for the invaluable advice, Tog.
Posted by: ollek on 2017-07-04 17:58:00 
The following is a drawing of the release bearing for the transmission clutch. The picture shows you how the parts are fitted http://partstore.caseih.com/us/parts-se ... 9ar1278937 You do not have to remove the flywheel in order to get to the pto shaft support bearing.
Posted by: torquilmackenzie on 2017-07-06 12:19:00 
Thanks again Ollek.
Unfortunately after looking more closely I see that the failure of the split pin in the right hand trunnion of the PTO bearing carrier has caused it to rest on the transmission bearing carrier and support snout and has worn right through them!
I haven't yet removed the PTO unit from the rear axle or the cardan shaft, and as it's a Q cab nor have I removed the clutch cover as access is limited.
From studying the manual and parts diagrams, I'm guessing I'll need to remove all of the above and wondering if this is possible with the cab in place (I've read about 990's having the clutch cover bolted to the gearbox cover that requires taper wedges installing when reassembling) ?
As the split tractor is in a shed with limited height my options seem to be reducing.
I will also price up all parts to see if it's worth the increasing effort.
Thanks once again, Tog.
Posted by: ollek on 2017-07-06 13:37:00 
You MUST split the tractor to get to the clutch. Do NOT start to remove the cab, clutch cover, gear box cover and pto unite, it will not help you at all. The transmission clutch drive shaft (hollow shaft) can not be removed from the top even if you remove the clutch cover and the gear box covver. Both clutch shafts (transmission and pto) will be separated from the clutch plates when you split the tractor. If you are not able to split the tractor where it stands at the moment, then you will HAVE to move the tractor to a location where the splitting is possible. If you do not know how to split a David Brown for a clutch repair, ask someone with the knowledge to help you out.
Posted by: torquilmackenzie on 2017-07-06 13:50:00 
Ollek,
I've split the tractor and found the clutch release mechanisms damaged.
Basically I'm wondering if I can realistically replace the transmission thrust bearing carrier and snout without removing the cab which will then allow me to remove the clutch cover ?
Posted by: ollek on 2017-07-06 14:04:00 
To change the snout you will need to remove the clutch cover and the gear box cover. You then remove the snout bolts and turn the snout 180 degrees and lift and support the front of the gear box a few millimetres. This will make it possible to pull the snout to the front. I have never tried to do this without removing the cab.
Posted by: torquilmackenzie on 2017-07-06 15:58:00 
Thought that might be the case.
Guess I'll see what the cost is of all the parts, then work out what might be involved in jacking up the Qcab to create enough room to remove the clutch/gearbox cover, but first impressions tell me there'd be a load of dismantling to do all that and not sure it's worth the effort on this tractor.
Possibly put it back together and it can see out it's days as a loader tractor with no PTO.
Thanks for your help Ollek.
Posted by: jamba on 2017-08-07 19:27:00 
ollek wrote: ↑
Tue Jul 04, 2017 5:58 pm
The following is a drawing of the release bearing for the transmission clutch. The picture shows you how the parts are fitted http://partstore.caseih.com/us/parts-se ... 9ar1278937 You do not have to remove the flywheel in order to get to the pto shaft support bearing.
I'm doing clutch repair... I have splitted tractor. How do remove clutch release thrust bearing (number 18 in picture)? Do i have to remove transmission fork (14) to get off bearing carrier (17)?
Posted by: jamba on 2017-08-08 17:53:00 
Yep.
http://partstore.caseih.com/us/parts-se ... 9ar1277555
First i took of bolt 21 and nut 20, then circlip 14. Then bolt 16. Then pulled axle 11 to left side of tractor.
http://partstore.caseih.com/us/parts-se ... 9ar1278937
Took of left adjusting cotter pin 15, pulled of stubshaft and lever 7. This allowed me to turn axle so that i could remove bearing carrier 17.
Ok. now to press bearing off!