Post by joe11 on Jan 13, 2017 23:08:25 GMT
Hi all, I have bought a 1275 engine and box which from the outside looked like it suffered a gearbox failure as torque convertor was missing, Transfer gear case, oil pump missing, Ive pulled the forward clutch out, to find its the 3 type clutch assembly, that someone has recently changed the top pressure plate due to the previous one breaking into a dozen pieces, and i wonder if any one knows why this has happened as it seems a common thing.
The bottom Forward clutch pressure plate on its underside had toggle wear marks in a circle like the bottom plate had been spinning at some point, yet it cannot as its locked by its outer spurs to the inside of the forward clutch housing ? Is this another sign of a previous top pressure plate failure? or worn clutches and over operating piston ? Ive seen this before as well in a 998 box. Does the alloy piston spin when clutches are worn causing this circular wear ?
Why do the Top pressure plates break ? inferior material may be, or fatigue, may be centre web bearings have too much play ? or something else ?
I stripped the gear train out, The Top/Reverse , top pressure plate had now broken into about 11 pieces as well as the forward clutch one, The clutch face of it was not burned at all and the red coloured top clutch friction plate had worn out but not to bare metal, (well one small part to bare metal) but the top plate had not over heated or discoloured and gone brittle. Do these top plates flex during use and finally break when they get old or is it for some other reason ? It looks bad manufacturing practice that these cast pressure plates are all sharp edged as cracks can form from these.
Ive not seen a top/reverse top plate break before, Looking at the engine bore wear the motor has done at a guess 75k "ish"
To my surprise the bands were covered in writing on material surface: Sonnax, Du Pont, Hand Made in USA, Kevlar and were a pale green in colour.
I noticed two bands, where the ends meet at the hook end, one end of each band had 1.5 inches of worn down lining almost to the metal backing of the band ring.
This is a common thing to see. With gear train out, i operated the servo arms by hand while watching the bands meet together at hook ends and two bands dont join flush but go together slightly staggered, causing the 1.5 inches of lining to wear near right through to metal. I dont fancy getting bands like this remanufactured as they will likely do the same again and i think they may not flex enough to grip the gear train drum well if they are out of shape like this and may take a long time to bed in by which time they are worn out on that high spot at the hook end. Do AP2 bands flex enough to cope with this discrepancy or do they just grip the gear train drum less ?
Joe Knight
11/02/2017 Since the above was written, from 3 separate gearboxes ive found top pressure plates professionally de-edged using a soft, spinning, wire wheel, and i guess the plate clamped and spun slowly in something like a lathe chuck, to round off the raised inner/outer sharp edges left by manufacture, This could also be done in similar fashion by the home repairer to try to prolong the life of 1275 pressure plates which i think are the prone ones to break. All you need is a drill and a soft wire wheel and some care and thought as to what to de-edge. (And you dont need to put much of a de-edge radius on their just a small/fine one).
Ive also fitted 2 bands that were slightly out of shape to a clutch drum on a work bench, they do effectively flex well and wrap around the drum, some look like they loose 1.5 inches of visual clamp area (if the fault is one clamp end thats very slightly curved inwards/distorted at clamp end), and at a guess, unless it has a well modded engine used with the gearbox it will not really matter.
What might matter is if you have a slightly distorted band and you adjust it up a little too much as it might drag lightly on the drum and over considerate time create a little more wear to both components possibly.
I rang Sonnax, they used to sell Generic kevlar material to other companies years ago hence why i found Kevlar lined bands in an old box in UK that had been repaired years ago by someone.
The circular wear marks on underside of forward clutch plate: Im guessing again here, it might be the small coil springs have lost some tension over time, and under some conditions may not hold the alloy piston well enough while its turning with the drum, if the drum suddenly changes rotation or speed, the alloy piston might spin at a guess. I checked this theory by manually turning the alloy piston with a large flat screwdriver in an assembled forward clutch drum on a work bench in my shed.
I also found some advice from someone who said watch out just giving a faulty gearbox a refresh without properly diagnosing the fault, as faults can cause a knock on effect in a automatic gearbox and when you find broken things by stripping the box you may have to look back to see why it happened, If you dont and just replace broken or worn parts and renew seals, bands and clutches, You might be just putting the box back to the condition it was in when it developed the fault, and in time it will likely fail again. But i guess this does largely depend on what type of fault it is. As an example, I checked the above gearbox for center web bearing play and a number of other things that i thought might cause the pressure plates to brake in the clutch drums and i found nothing wrong with the rest off the box that might cause it, My conclusion after some research is metal fatigue, and raised sharp stress edges left by manufacturer where a crack can form on a material that is flexing in use. Though its also easy to guess why something has failed but it not be the answer !
The bottom Forward clutch pressure plate on its underside had toggle wear marks in a circle like the bottom plate had been spinning at some point, yet it cannot as its locked by its outer spurs to the inside of the forward clutch housing ? Is this another sign of a previous top pressure plate failure? or worn clutches and over operating piston ? Ive seen this before as well in a 998 box. Does the alloy piston spin when clutches are worn causing this circular wear ?
Why do the Top pressure plates break ? inferior material may be, or fatigue, may be centre web bearings have too much play ? or something else ?
I stripped the gear train out, The Top/Reverse , top pressure plate had now broken into about 11 pieces as well as the forward clutch one, The clutch face of it was not burned at all and the red coloured top clutch friction plate had worn out but not to bare metal, (well one small part to bare metal) but the top plate had not over heated or discoloured and gone brittle. Do these top plates flex during use and finally break when they get old or is it for some other reason ? It looks bad manufacturing practice that these cast pressure plates are all sharp edged as cracks can form from these.
Ive not seen a top/reverse top plate break before, Looking at the engine bore wear the motor has done at a guess 75k "ish"
To my surprise the bands were covered in writing on material surface: Sonnax, Du Pont, Hand Made in USA, Kevlar and were a pale green in colour.
I noticed two bands, where the ends meet at the hook end, one end of each band had 1.5 inches of worn down lining almost to the metal backing of the band ring.
This is a common thing to see. With gear train out, i operated the servo arms by hand while watching the bands meet together at hook ends and two bands dont join flush but go together slightly staggered, causing the 1.5 inches of lining to wear near right through to metal. I dont fancy getting bands like this remanufactured as they will likely do the same again and i think they may not flex enough to grip the gear train drum well if they are out of shape like this and may take a long time to bed in by which time they are worn out on that high spot at the hook end. Do AP2 bands flex enough to cope with this discrepancy or do they just grip the gear train drum less ?
Joe Knight
11/02/2017 Since the above was written, from 3 separate gearboxes ive found top pressure plates professionally de-edged using a soft, spinning, wire wheel, and i guess the plate clamped and spun slowly in something like a lathe chuck, to round off the raised inner/outer sharp edges left by manufacture, This could also be done in similar fashion by the home repairer to try to prolong the life of 1275 pressure plates which i think are the prone ones to break. All you need is a drill and a soft wire wheel and some care and thought as to what to de-edge. (And you dont need to put much of a de-edge radius on their just a small/fine one).
Ive also fitted 2 bands that were slightly out of shape to a clutch drum on a work bench, they do effectively flex well and wrap around the drum, some look like they loose 1.5 inches of visual clamp area (if the fault is one clamp end thats very slightly curved inwards/distorted at clamp end), and at a guess, unless it has a well modded engine used with the gearbox it will not really matter.
What might matter is if you have a slightly distorted band and you adjust it up a little too much as it might drag lightly on the drum and over considerate time create a little more wear to both components possibly.
I rang Sonnax, they used to sell Generic kevlar material to other companies years ago hence why i found Kevlar lined bands in an old box in UK that had been repaired years ago by someone.
The circular wear marks on underside of forward clutch plate: Im guessing again here, it might be the small coil springs have lost some tension over time, and under some conditions may not hold the alloy piston well enough while its turning with the drum, if the drum suddenly changes rotation or speed, the alloy piston might spin at a guess. I checked this theory by manually turning the alloy piston with a large flat screwdriver in an assembled forward clutch drum on a work bench in my shed.
I also found some advice from someone who said watch out just giving a faulty gearbox a refresh without properly diagnosing the fault, as faults can cause a knock on effect in a automatic gearbox and when you find broken things by stripping the box you may have to look back to see why it happened, If you dont and just replace broken or worn parts and renew seals, bands and clutches, You might be just putting the box back to the condition it was in when it developed the fault, and in time it will likely fail again. But i guess this does largely depend on what type of fault it is. As an example, I checked the above gearbox for center web bearing play and a number of other things that i thought might cause the pressure plates to brake in the clutch drums and i found nothing wrong with the rest off the box that might cause it, My conclusion after some research is metal fatigue, and raised sharp stress edges left by manufacturer where a crack can form on a material that is flexing in use. Though its also easy to guess why something has failed but it not be the answer !
