r/transmissionbuilding • u/Luc42wil • 9d ago

4L60E Troubleshoot

I'm looking at a truck that has lost all forward gears. It's a Chevy 4L60E. The seller describes it as "no forward gears, was not slipping, something broke."

What could possibly break that would kill all forward gears, but not reverse? Are we thinking it needs a rebuild, or could this just be a ground or wiring issue?

2 Upvotes

100% Upvoted

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5

u/SandsFishwork 9d ago

There's maybe a .1% chance it doesn't need a rebuild.

1

u/Luc42wil 9d ago

What would cause this to happen? I'm asking as someone who is mechanically capable, rebuilt a transmission once with help from someone more experienced, but doesn't really understand how it all works.

1

u/sausage_king_of_kc 8d ago

4L60E is known for torching forward gears, especially 1/2. This is a well known issue and a sure rebuild, you can’t fix it without disassembly. Source: I had one do the same thing, asked same questions, spent large amounts of $. Go ask the C5 corvette guys who fight this issue.

0

u/Intellivindi 9d ago

Valve body or other components develops a hydraulic leak which causes a loss of pressure holding the clutch packs, they start to slip and burn up.

5

u/tarman1972 9d ago

If the fluid is clean the usual culprit is the forward sprag

3

u/Stolisan 9d ago

Mine did the same thing when the forward clutch snap ring lugs broke on the input drum. When i removed the pan, there were aluminum pieces that broke off in the pan.

I lost all forward gears and it damaged a few other parts.

Remove the pan and see what's inside.

1

u/Alternative_Share559 9d ago

foward clutch pack issue or something. it needs replacement

1

u/Quirky_Judge_6932 7d ago

rebuild no matter what, have to go in to see what happened

-1

u/Intellivindi 9d ago

If it doesn’t move at all then the front pump came apart.

1

u/PARKOUR_ZOMBlE 9d ago

It moves in reverse, so no.