What do the overrun clutches do ?

[nightdiver]

I needed some space in the garage and i had to through away some things.
I found my first tranny that had the overrun clutches burned and in one piece with the steel plates.
Whats their job in there ? and how come they got burned ?

 

[skata]

over-run clutches provide the engine braking effect when the trans is in D or 2 or 1.
they are not applied in over-drive (OD).
they also help hold 3rd gear better when in drive(D).
was that the only thing that failed in the trans?
what do you mean by "burned and in one piece with the steel plates"?
yasou

 

[nightdiver]

How come you choose this name :wink:
This was the only failure...well the 3-4 cluches were a little bit more brown than they had to.
The overrun had almost no clutch material on them and they become one thing (melted) with the plates

 

[skata]

one possibility is that your forward sprag was slipping, which would put a lot of force on those clutches and they would slip.
another possibility is maybe a bad seal on the piston that pushes those clutches.
or maybe one of the teflon seals on the input shaft was leaking.
or maybe low line pressure.

lympic:

 

[jwaller]

the ovr run's are applied only when you have D selected. it you select OD they will not engauge. it just 2 extra clutchs to help out the forwards. in 1,2,3 when D is selected. it's very common for the alum pistons in the inout drum to break cauing this problem.

 

[JustBeachin]

I lost all engine braking about 2-3 years ago. I was told it was my overrun clutches. I can be driving 80 or so, and drop it in d, 2, or 1, and it just coasts........

I was told, just wait till it goes, then get it fixed. So far we're ticking along at 106k miles.

How hard would it be to fix, and would it be worth it to pull it just to fix this?

 

[nightdiver]

Some clutch pieces will go and stay on the piston sealing lip (any) and this will cause fluid pressure drop when it has to work. Then an other set of clutches will burn

 

[Matthew Little]

overrun

overrun

Mine didn't work when I got my truck a year and a half ago, and I also have a nice under load tranny line leak.