Trans fluid/ shift kit

[GoToGuy]

An option code " MX1 " is a Turbo 400, 3 speed transmission.
An option code " MX0 " , ( zero, not oh!), Is a 700R4, 4 speed.

 

[Schurkey]

Hey all, I was wondering where in the world I could find me some dexron 2 fluid as specified in the book of my 1990 Chevy c1500. I also am wondering the capacity as I have no idea what it is… again not in book. And is they shift kits for these pickups I see first pop up worth it? Just looking to improve shift performance and quality of life on the trans. If it’s a performance upgrade I’d be ok with it as long as it doesn’t make it to where I need to rebuild my stock motor. Thanks!

Dexron 3 is backwards compatible.

No such thing any more...but "Dex/Merc" or "Merc/Dex" should be essentially the same stuff, without the Dexron trade name that GM doesn't license except for Dexron 6.

Last time I looked, they were asking over ten bucks a quart for Dex/Merc at NAPA and O'Reillys; I could get Amsoil synthetic delivered to my house for less than that.

A shift kit will improve the longevity of the trans. The quicker and firmer the shifts the less time the clutches have rubbing on each other

The firmer the shift, the less heat put into the clutches/bands. OTOH, it's harder on the metal parts--splined shafts, drums, geartrain, etc.

Given the problems with Sun Shells and planetary gears on the 700 family of transmissions, I'd be really careful about harsh shifts. The 400 seems to take harsh shifting better than the 700 family.

So does this one look good?

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I'm DONE with B&M "shift kits".

Transgo is my go-to now.

Ok, I’m thinking on doing a trans flux flush as well, do you know how much I should need?

A fluid flush needs the entire capacity of the trans, plus a few extra quarts.

The '700 4L60E on my Trailblazer needed 15 quarts altogether. I'd expect a 400 to need about the same. Buy extra, return the unopened quarts to the store? Buy extra, keep the unused fluid for "later"?

 

[someotherguy]

An option code " MX1 " is a Turbo 400, 3 speed transmission.
An option code " MX0 " , ( zero, not oh!), Is a 700R4, 4 speed.

You sure on those? I thought the MX codes were typically "merchandising" codes, whatever those are. From what I know, MD8 = 700R4, M40 = TH400. What makes it confusing is you will generally see the MX codes on the same SPID label. Let me shine a little more light on it to prove my point: a truck with a 4L80E, which is RPO code MT1, also has RPO code MX0. MX0 is simply "merchandised trans, auto provisions overdrive".. so seeing MX0 on this truck's SPID label absolutely does not mean 700R4.

This is a 1991 C2500 (8 lug):

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Regardless anything could have been swapped in over the years so I don't know if I would count solely on the RPO codes. Number of forward gears (3 or 4) would be helpful, but identifying by the pan shape and number of bolts would be very useful additional info.

Mostly square (kind of a stubby rectangle) pan with 16 bolts is 700R4 (also 4L60/4L60E)
"Kidney" shaped pan with 13 bolts is TH400
Square pan with one corner angled off and 13 bolts is TH350 (unlikely but possible someone swapped it in)

Richard

 

[Logan R]

Ok thanks for the info. I know for a fact that the previous owner spent the least amount of money they could on the truck, so I’m guessing it’s the 700 or 400. Hoping the 400, so that it would take a shift kit better. It is a 4 speed with overdrive Why no longer b and m?

 

[someotherguy]

TH400 is only 3 speeds sir. You need to correctly ID the transmission before buying anything for it though..

Richard

 

[Logan R]

Ok, that is the plan to confirm what I have. Is there any other recommendation for a different shift kit on the 700 then? Hoping not to have to put a new trans in right after putting a kit in

 

[Schurkey]

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