Hard Downshifts Allison 1000

gjpowell14

New member
Nov 14, 2020
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I have a 2017 L5P and rebuilt the transmission with a stage 3 suncoast kit this summer. Haven’t had any issues for 6k miles and all of the sudden I’m getting hard downshifts from 4-3-2-1 and my 5-4 downshift has produced a howl. None of this is consistent though. Changed the spin on filter to see if maybe I had any metal on the magnet but just some break in material. So from there I drained my trans (oil was still very clean and not burnt, no metal material in pan) and threw in a new internal filter in hopes of getting rid of the issue and just to appease myself but the issue persists. No codes or anything so I’m just curious to hear if any of you Allison gurus have some insight and guidance on where to start or what to look for.
 
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gjpowell14

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Nov 14, 2020
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Get rid of it.
Ok. Any reason why all of the sudden it’s starting to do that? I did a proper relearn when I tuned it and everything has been good for the last 6k miles. Just strange that all the sudden it’s acting up.
 

gjpowell14

New member
Nov 14, 2020
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Oh
Get rid of it.
So threw a p0700 code this morning. Came to a stop and trans was stuck in 6th gear. Shut the truck off and started it again and it was stuck in 6th still. Finally got it to 1st but it won’t move and makes a strange grinding noise in reverse. If I give it throttle it wraps out and hits the rev limiter and then dies off to an idle
 

gjpowell14

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Nov 14, 2020
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Who built it? Was pressure raised in the trans tune? Was my Ratio Tek kit used during build?
It’s a suncoast kit but built it myself and yes a ratio tek kit was used and ppei said there was no pressure added in the tuning
 

gjpowell14

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Nov 14, 2020
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Why not see what suncoast has to say?
Super bad experience with them and their customer service to say the least. I’ve heard nothing but great things about Mike and his knowledge on Allison’s. Suncoast is the last place I’d call for help.
 

PureHybrid

Isuzu Shakes IT
Feb 15, 2012
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Super bad experience with them and their customer service to say the least. I’ve heard nothing but great things about Mike and his knowledge on Allison’s. Suncoast is the last place I’d call for help.
I'm in no way saying Mike is incompetent, he's more capable than anyone. But why install a Suncoast kit when you've had no luck with their customer service?
 

TheBac

Why do I keep doing this?
Staff member
Apr 19, 2008
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Mid Michigan
This whole thing reads like the "trans tuning" was creating a hard parts issue, and the problem finally reared its head.

I will never understand this continuing fascination with "tuning" the transmission.
 
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Ne-max

I like turtles
Nov 15, 2011
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Lincoln, Ne
This whole thing reads like the "trans tuning" was creating a hard parts issue, and the problem finally reared its head.

I will never understand this continuing fascination with "tuning" the transmission.
Problem is everyone thinks they have a race truck and listen to idiots on Facebook groups that never had anything fast. In some applications trans tuning is a must. We had to do a lot with the 6 speed tcm. But agreed that 98% don't need it.
 

DAVe3283

Heavy & Slow
Sep 3, 2009
3,387
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Boise, ID, USA
Problem is everyone thinks they have a race truck and listen to idiots on Facebook groups that never had anything fast. In some applications trans tuning is a must. We had to do a lot with the 6 speed tcm. But agreed that 98% don't need it.
With my built motor's cam+converter+lowered compression combo, trans tuning was a must before it would get out of its own way. I dialed that in back in 2013 and some 40,000 miles later everything works perfect. Though I had tweaked the shift points even with the stock motor, and that trans lasted almost 300,000 miles before I smoked 5th.

So I guess my question is, are the old TCMs just way more forgiving (or more locked down so you can't shoot your foot off)? Or do people mess with things they don't understand / need to, and break things that way?

I get that if you up line pressure (on one of the new ones that let you) and then do the same thing with hard parts, you are in for a bad time. Or is even changing shift points / TCC behavior risky on the newer ones?
 

Ne-max

I like turtles
Nov 15, 2011
3,312
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Lincoln, Ne
The newer the tcm the smarter it is. We fought that with the a40 tcm. It plans its shifts way to early in a high hp application. It will defuel until it sees what it wants to make the shift. More power you put to it the longer the defuel is. Also there's tables in the 6 speed tcm that efi does not give us access to. You can kill the defuel on ecm/tcm and it will still defuel.

5 speeds don't care. They do what they're told. This is why you can here them click off the shifts so much faster. Was my biggest mistake building a lbz instead of a lly.

Unsure on the newer 6 speeds.
 

gjpowell14

New member
Nov 14, 2020
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I'm in no way saying Mike is incompetent, he's more capable than anyone. But why install a Suncoast kit when you've had no luck with their customer service?
Because the transmission was 75% built when I ran into the first problem and the customer service got worse with the next 2 problems I had with their kit so it’s not like I had a bad experience with them before and decided to use them again. I guess I was too far along to decide to send everything back and go with someone else’s kit.
 

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