Allison transbrake

Jan 28, 2014
33
7
8
So I thought I would post on here...I don't get on here a lot not sure if I'm posting in the right thread or whatever. But I've been getting a lot of questions and interest in my transbrake. So I officially have it working after tons of trial and error. Still need to work on the bump so I can stage it more smoothly. First off I'd like to say this setup is definitely not for everyone since it only works well with 3rd gear start since I'm using c5 clutch pack to lock it in 3rd and reverse at the same time. C3 is used in reverse and 3rd so makes it way easier to just turn on c5 rather than 2 clutch packs which would be needed in 2nd gear start. I'm sure it is possible but I haven't looked into to much since my truck is light and 2wd it likes 3rd gear start better anyway.
So that being said I've found some very interesting things in my testing. So basically what I have done is isolated c5 from the valve body so I can manually control it with externally applying fluid pressure to c5. Now here is the head scratcher...so with the way I have it setup I figured I would have to hold the transbrake button to turn on c5 to use reverse. However that is not the case. Truck operates just like normal 1st gear and reverse (which use c5) work normal with no pressure going to c5. I'm very confused on how and why it works but it does...anyone have any ideas? To date I have 20ish passes on it zero issues or codes. Also side note...it now is the fastest 6speed allison on the planet to my knowledge went [email protected] with a 100% stock engine
 

Bbuchanan11

Member
Sep 9, 2011
177
19
18
Sarver, PA
Your truck must be the one I’ve been seeing on Instagram lately… never woulda guessed it had an Allison in it lol I want a trans brake now
 

Chevy1925

don't know sh!t about IFS
Staff member
Oct 21, 2009
19,366
1,920
113
Phoenix Az
considering the c3 is the weakest link clutch pack no matter how its addressed, i assume you have not torn down the trans yet to see how the clutches are coping? how many passes were on the trans before hand?
 
Jan 28, 2014
33
7
8
considering the c3 is the weakest link clutch pack no matter how its addressed, i assume you have not torn down the trans yet to see how the clutches are coping? how many passes were on the trans before hand?
I will be tearing it down shortly to see how it looks since the last 2 passes I made its starting to get lazy on shifts. Could very well be c3s but it's had prolly 70-80 6sec passes on it since it's been apart and lots of road hits also when I was testing it. My theory is since I'm only releasing c5 to launch it c3 is not releasing till the 3-4 shift c3 should not see any extra wear...at least in theory...
 

Chevy1925

don't know sh!t about IFS
Staff member
Oct 21, 2009
19,366
1,920
113
Phoenix Az
I will be tearing it down shortly to see how it looks since the last 2 passes I made its starting to get lazy on shifts. Could very well be c3s but it's had prolly 70-80 6sec passes on it since it's been apart and lots of road hits also when I was testing it. My theory is since I'm only releasing c5 to launch it c3 is not releasing till the 3-4 shift c3 should not see any extra wear...at least in theory...
id think so too but is be curious if they are holding and not slightly slipping at all.

are you hitting 5th through the 1/8 mile at all?
 
Jan 28, 2014
33
7
8
I think it is shifting into 5th I don't data log it normally but my shift points are at 4000rpm since it is a stock motor and according to my calculations it would be at over 5000rpm at 121mph in 4th but I'm honestly not quite sure mabe I should change my shift point for the 4-5 shift to like 5100 so it don't have to shift but once. But I'm little worried about floating valves at that rpm with stock valve springs
 
  • Like
Reactions: LBZ
Jan 28, 2014
33
7
8
Well here's the tear down...c1 and c3 opened up a good bit on clearance c3 was at .117 clutches look fine but steels got some hot spots. With the amount of abuse this trans took I don't think I can really blame any of this on the transbrake looks more like normal wear and tear for the abuse it's seen. C5s look mint so that's not a issue for sure! But c3s at .117 explains my lazy shift and the convertor seems to be hurt as well so tightening everything back up and getting the convertor fixed or replaced and we should be back to chasing that stock motor and allison record!!
 

Attachments

  • received_457226559738898.jpeg
    received_457226559738898.jpeg
    281.2 KB · Views: 25
  • Like
Reactions: LBZ and juddski88