The VIN decoder says my truck has a 4L70 transmission, that's not right is it?

[351FUN]

It's a 1992 blazer Silverado, I know it's a 4 speed auto and that's about it. I'd never even heard of the 4L70, and I'm not sure if I'm reading this right or if it's saying that was an option on diesels (which this one isn't). Quick Google search says the transmission started in 1992 in some GM suv's, but I've always heard I had a 60

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[GoToGuy]

What does your glove box RPO label have for codes, I'd trust the factory label first.

 

[351FUN]

I'll check it soon, actually about to go pick the truck up from the shop.

 

[Schurkey]

www.700r4transmissionhq.com/gm-automatic-transmissions/4l70e/

All about the 4L70E | Drivetrain Resource

Everything you'd want to know about the 4L70E transmission. This includes identification, specs, history, and compatibility.

www.700r4transmissionhq.com

The '70E started in '92, but I have the impression from your VIN search that it was only available with Diesel engines.

Look at the connector color to see for sure.

 

[someotherguy]

RPO MD8 is right there on the list, as is G80, so to that point - RPO codes get "recycled" over the years to mean different things. G80 is a great example.. in the GMT400 trucks, G80 means you have the Eaton Gov-Loc. In other vehicles like the B-body Impala SS, it means you got an Auburn limited slip.

In this case a 1992 GMT400 with RPO code MD8 has a 4L60 (aka 700R4)
Any year GMT400 with RPO code G80 has an Eaton Gov-Loc locking rear differential (not a posi or limited slip)

The VIN decoder program you're using is simply wrong in its description for the MD8 code. It's also wrong with the G80 description.

Richard

 

[df2x4]

^ This is one of the reasons I prefer compnine.com to other VIN decoders. It costs money but their RPO descriptions are pretty much always accurate to the specific vehicle in question, at least in my experience.

 

[someotherguy]

The "RPO Master List" that has been circulating for many years now says RPO MT8 is an 18 speed manual transmission. Nevermind that it's also the RPO code for the early version of the NV4500 in a GMT400..

Yeah baby! 18 speed manual in my '93 C3500 dually!

Richard

 

[351FUN]

Yeah I was 99% sure already that it was the 700r4/4l60, but I figured I'd check just because I know blazers are different than pickups (4wal in a 92 for example)

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And just for confirmation here's the sticker.

Just so I don't make another thread for a simple question, @Schurkey I know you hate the trailing drums on the JB5, why is that? I've got a blown wheel cylinder and need to replace it asap but I was wondering if I should stop here and upgrade first.

 

[Schurkey]

@Schurkey I know you hate the trailing drums on the JB5, why is that?

1. 10" drums are weak. Also, have little mass, get hot, fade.
2. The front shoe on each side wears faster than the rear shoe. Front shoe does almost all the "work" of braking.
3. The self-adjuster doesn't work unless you use the park brake frequently. The rear brakes are therefore almost always out-of-adjustment because nobody uses the park brake.

I've got a blown wheel cylinder and need to replace it asap but I was wondering if I should stop here and upgrade first.

Ideally, you'd upgrade. The 254mm (10") leading-trailing drums aren't worth putting money into.

Problem is, backing plates to put bigger brakes on the 10-bolt axle are tough to come by. Essentially, you'd need to swap the entire axle for a 14-bolt semi-float 9.5" ring-gear axle assembly, which also gets you the wonderful 11.x Duo-Servo drums.

The JB5 booster/master, and front rotors/calipers, combined with the 11.x rear brakes, is essentially JB6-equivalent.

 

[351FUN]

Gotcha. The good news is I do use the parking brake regularly at least. So it sounds like I'll just replace what's bad for now and start getting things together for a full upgrade in the future.