Need Help w/ Engine/Transmission Replacement

[Austin S]

I have a 1994 GMC Sierra (SLT) with a 5.7L engine. It has 290k miles and very recently started knocking which I lay the blame on Seafoam, which a mechanic put in my engine during a tune-up session without my knowledge until he had already put it in :angry:. The transmission has hit hard since I bought it at 267k miles, and there’s a few second delay when putting it in gear (assumption that the transmission is the cause of this, however I have no solid evidence that this is the culprit).

So with that being said, I’m thinking about just replacing the entire engine,transmission, and anything related that may cause any premature wear (dirty fluid systems i.e.). However, I don’t really know what I’m looking for as far as parts go. It was my first truck and I don’t ever intend on selling it or getting rid of it so I want to make sure I have a solid idea of what needs to be done as far as replacing the engine/transmission instead of jumping in blindly and getting incompatible parts.

I was thinking GM OE parts would be the best option. However, I only found a shortblock engine on their website, and I don’t really know the difference between shortblock and longblock. I read that the difference had to do with how far the engine was built. For example, you have to install your own heads into the shortblock correct? Are rebuilt engines and transmissions worth the cost and time?

Does anybody have suggestions about where to start? How to find the right parts that I need?

Any help would be much appreciated.

Topic

[redfury]

You should be able to buy a full ‘crate” motor from an engine rebuilder, and some auto parts stores can get it for you. It’s all going to depend on how much you love that truck and how much you want to spend on it.

A short block is the engine block without the heads or intake manifold. A long block is the engine block, and heads. If you are looking for parts compatibility, then it’s a matter of finding out what vehicles used the same engine and transmission in your truck. 1994 was pretty much the end of the TBI motors. The transmission is the 700R4, and that can be found in any large V8 powered GM, though you have to be careful on some differences, most notably if you have 4wd, you can’t use a transmission out of a 2wd vehicle.

In regards to rebuilding what you have, it’s a matter of finding a reputable builder near you. I found a guy on Craigslist that rebuilt my transmission and reinstalled it for under 1300 and he gave me a 3 year warranty, plus upgraded some internal parts. Been rock solid for me for the last 5 years. He was terrible to work with, but his work speaks for itself. Do a little research before jumping in if you aren’t well versed automotively speaking.

Engine rebuilders, you can spend big bucks and go with a Jasper remanufactured engine and transmission. They have a network of shops that will do your installs for you and back up their product very well..but you pay a little more for the peace of mind. Jasper Engine/transmission rebuilding website

I had a bad experience with an engine rebuilder…they rebuilt the engine fine, but the rear main seal started leaking shortly after the second round with them, and the second round with them was because the block was cracked on both sides and leaked coolant…. They took care of me with no extra charges, but took forever and my stereo system got stolen while in their possession the second time….sigh. Oh, and they installed a clamp wrong which took out my fan belt, which wrapped around my transmission cooler lines and left me stranded in a different state. So, no matter what, you will always want to double check the work of anything that happens this major….even the great transmission experience I had, they didn’t tighten up the rear transmission mounting bolts all the way.

Boy, I’m making this sound complicated…but it’s not…this kind of thing happens every day and we are all human.

The best tool you have in your arsenal is your brain, and access to information. Gather up as much as you can before making a decision on which direction to go.

As far as other things to consider when replacing the engine/transmission? I’d put in a new radiator and hoses for sure, and motor mounts…take care of any of those pesky things that are easy to replace now that the engine is out. Put new U joints in the driveshaft and maybe consider having the rear end gone through and get your end play figured out…at the very least, pull the differential cover of and replace the fluid..look at those spider gears and think about replacing them if they show any wear ( super easy to replace…just watch a video and pretty cheap in comparison to replacing a blown out rear end ).

I’d buy new ground straps as well, since bad grounds will have you hunting demons if it doesn’t fire up and run great. Also consider replacing the fuel pump if it’s an original ( and use a Delphi or GM brand…you’ll thank me later ).

[Austin S]

I’d like to get a brand new transmission, not even rebuilt. From what I know, transmissions are pretty complicated and because of that, I doubt I would trust a rebuilt transmission. I would be okay with a rebuilt engine if it came from a creditable place like Jaspers. I was thinking I would do the installations myself (with research of course) and save money for the reasons you mentioned below. I’ve had nothing but bad experiences with every mechanic I’ve been to. The last one seemed fine until he put seafoam in my engine without my acknowledgement. I don’t want any foreign fluids/objects in my truck, period.

I’m willing to spend a lot of money to “restore” the truck. One day I want to possibly get a supercharger or a turbo for the hell of it. Would I need a higher performance parts to handle the extra power?

As I mentioned before, I have close to 300k miles on this engine. Would it be worth rebuilding this engine or to just buy a new one? Which would get me a better mileage to cost ratio? Current engine burns lots of oil, and just very recently started the knocking (and as much as I hate to admit it, I ran completely out of oil when it started which in my defense the oil consumption had gotten higher too). I think it may still be good but something needs to be done to it and I’m not sure what. I don’t know if it’s still lacking oil from a worn oil pump and that’s what’s causing it, or if it’s damaged from where the brief time that it went dry.

[Gary]

I’d go with a crate longblock from Chevy. That way you get the cylinder heads and don’t have to worry about doing a mill and valve job on the old ones.
As for transmission, get a reman 700R4 from Jasper.
For Jaspers warranty, I believe they have to do the install.

[redfury]

Transmission and engine rebuilds are always going to be subject to inspection of the core parts. If the transmission case is junk, then you are looking at a replacement, most likely a remanufactured unit. I’d doubt there is much demand for brand new off the shelf 700R4s, though I could be mistaken. The 4L60 replaced the 700R4.

If you are thinking of doing some supercharging in the future, and plan to keep this truck for life, then you’d want to look at a performance rebuilders crate motor. You could start by looking at Summit racing, though there are a lot of really good engine builders out there that aren’t the name brands you might be familiar with.
These guys offer a 30 month, 50k warranty for example

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