Allison 6sp: LMM Trans cooler lines

m&mjenna

New member
Mar 6, 2017
16
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Alright guys I have a question about these transmission lines. My LMM has 230K+ on the transmission lines that are there don't look original but they are factory lines not hydraulic or anything. I have no idea how ling they have been on there but its at least been 40k miles. They are leaking and I have found that its a common issue and a lot of guys go to Hydraulic lines. I have no problem with getting the Hydraulic lines but the factory lines are $100 less a little tough for me to swallow especially since I think GM is good about updating parts. So my question is how long do the factory lines? last part numbers are 20835125, 20835123, and 20835127 or just get the hydraulic lines. Also only 2 of my lines are leaking the 2 that come off the radiator could a problem in the radiator cause them to leak I can't really find any support in that department. Thanks for the input if you have any!:thumb:
 

Ne-max

I like turtles
Nov 15, 2011
3,361
64
48
Lincoln, Ne
The last 3 sets of OEM lines we installed fit like ass. Especially the two that do up to radiator. Like to kink.
 

m&mjenna

New member
Mar 6, 2017
16
0
0
3 Times all on the same truck? Im trying to I wanna find out about how long i can expect the OEM lines to last or if i should just bite the bullet and order the Hydraulic lines.
 

Ron Nielson

Active member
Oct 11, 2009
760
141
43
Berryton, KS
The most current GM parts seem to work just fine. Mine were installed 5/13 and no leaks. I understand that the trans line pressure is highest when temps are cold, and even higher when engine is revved just after startup. Best to let it warm up just a minute or so before higher revs to get the fluid moving thru the system
 

Ne-max

I like turtles
Nov 15, 2011
3,361
64
48
Lincoln, Ne
3 Times all on the same truck? Im trying to I wanna find out about how long i can expect the OEM lines to last or if i should just bite the bullet and order the Hydraulic lines.

Different trucks. It's like the solid aluminum piece is 2 inches to long.
 

ikeG

Oughta Know Better
Apr 19, 2011
2,462
146
63
Western PA
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I have used many Merchant auto lines with success. They can be spliced in while leaving the ends attached to cooler & trans.
The Fleece lines are what I would recommend if you want to remove the o.e. lines completely.

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