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700r4 rebuild advice

garonsmoak

garonsmoak

Registered Member
Joined
Dec 10, 2022
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Location
Savannah, Ga
Hello All,

I've been lurking here for a a while but I finally acquired myself a 1990 Blazer. I bought it knowing the tranny is going out and I'm planning on taking it somewhere to have it rebuilt but pondered doing the rebuild myself. I've helped rebuild more than a couple and I've never done one on my own but I'm thinking I can figure it out. It's currently sitting on 35s and I plan on using it for trails, trips to the beaches near me where I'll be driving on sand, and towing my boat to the ramp. So a little bit of some mix usage. Nothing too crazy. I also plan on beefing up the powerplant to the 400 hp area. So...on one hand, what rebuild kit/parts should I be looking for to accommodate my wants if I decide to rebuild it? On the other hand (since I do realize that this is an incredibly skilled task and dont want to risk completely ****ing it up) what should I ask for in a rebuild if I take it somewhere and what would the costs look like? I'm currently in the Norfolk, Ne area for work and will be in this area for a while if anyone has any transmission shop recommendations.
 
First off, does it have 4.56 or lower axle gears? Secondly, it’s just a box of parts. No magic happens in there. It’s just a bunch of fluid moving. A solid repair manual and a clean bench is a good start.
Lastly, a 4l80 is probably a better use of your money and time.
 
obijuank5 said:
First off, does it have 4.56 or lower axle gears? Secondly, it’s just a box of parts. No magic happens in there. It’s just a bunch of fluid moving. A solid repair manual and a clean bench is a good start.
Lastly, a 4l80 is probably a better use of your money and time.
Click to expand...
The last owner told me he had 3.55 gears installed.
Why would you recommend the 4l80 over the 700r4?
 
high HP = death to a NON built 700r4 not done right .

gears are your friend with over drive trans = less work and less heat that kills trans .

and 3.55 gears in gm truck axles = smells real funny and why 3.55 for all the work of the swap ..... ? :doah:
 
I always say that an automatic transmission is a machine designed by men and built by men, so if you assemble it as designed, it will work as designed. So, you do you have about 200 chances to get something wrong, but just like every boy who built a jump to sky his bike over a creek...it could end up glorious! If you do it yourself, organization and cleanliness are paramount. Lots of help to be had from people on this site as well if you're good with pictures and showing the details.

There are many good upgrades for the 700, but a 1990 unit will have most of the real ones already incorporated. It's easy to go off the rails and waste money with aftermarket parts and "MAW" mentality, but the real useful durability upgrades are just a few key things.

3.55 is a dubious claim, but the actual gear ratio is important and once somebody is proven to give misinformation on one item, why believe anything else? GM offered 3.08, 3.42, 3.73, 4.10, etc, so why would anybody pay for a weird aftermarket-only ratio like 3.55?. Search for how to determine gear ratio by turning the driveshaft by hand or pop a diff cover to find the stamped numbers. The transmission really cares more about torque than HP. Unless you tell us what you're really doing to the engine, HP ratings are meaningless - they're kind of like MPG claims - mostly fiction.

Also important to transmission life is cooling and proper lockup operation (can you verify?)
 
sweetk30 said:
high HP = death to a NON built 700r4 not done right .

gears are your friend with over drive trans = less work and less heat that kills trans .

and 3.55 gears in gm truck axles = smells real funny and why 3.55 for all the work of the swap ..... ? :doah:
Click to expand...
Definitely feels like I'm going with the 4l80e then. Yeah I thought so too since its not original gears. When I get a chance this week, I'll roll it and see what the ratio is
 
3.73 to 1, is a very common ratio, more than likely, the actual ratio will be stamped on the side of the ring gear, somewhere.
Inquiring minds are now interested. Let us know...
 
Blue85 said:
I always say that an automatic transmission is a machine designed by men and built by men, so if you assemble it as designed, it will work as designed. So, you do you have about 200 chances to get something wrong, but just like every boy who built a jump to sky his bike over a creek...it could end up glorious! If you do it yourself, organization and cleanliness are paramount. Lots of help to be had from people on this site as well if you're good with pictures and showing the details.

There are many good upgrades for the 700, but a 1990 unit will have most of the real ones already incorporated. It's easy to go off the rails and waste money with aftermarket parts and "MAW" mentality, but the real useful durability upgrades are just a few key things.

3.55 is a dubious claim, but the actual gear ratio is important and once somebody is proven to give misinformation on one item, why believe anything else? GM offered 3.08, 3.42, 3.73, 4.10, etc, so why would anybody pay for a weird aftermarket-only ratio like 3.55?. Search for how to determine gear ratio by turning the driveshaft by hand or pop a diff cover to find the stamped numbers. The transmission really cares more about torque than HP. Unless you tell us what you're really doing to the engine, HP ratings are meaningless - they're kind of like MPG claims - mostly fiction.

Also important to transmission life is cooling and proper lockup operation (can you verify?)
Click to expand...
Yeah I found it strange about gear ratio as well but when I get a chance this week, I'll turn the driveshaft and get the ratio. Just messaged the last owner again and he said he'll ask his mechanic to make sure on the gears which makes me doubt he knew what he wasn't talking about. I'll check on transmission lockup.
 
Ok, last owner got back to me again and he said that they are they are the 3.73 gears, not 3.55. I'm still gonna pull the cover to check and make sure everything looks good. Also, I'm going to start looking for a 4l80e.
 
What's your plan for getting 400 HP? If newer engine swap I would plan it all at once. The 700r4 is definitely not the best choice but a newer 4L60e behind an LS is not a bad choice.
 
A 700/4L60 has better gearing than the 4L80, so that might change which differential gears you want long term. Also, 4L80's tend to come with loose torque converters that are better suited for big cam engines, not low-end grunt motors, so you might want to change that as well.

And I agree, if an engine swap is in the future, get that all sorted before you change anything else in the driveline.
 
Blue85 said:
A 700/4L60 has better gearing than the 4L80, so that might change which differential gears you want long term. Also, 4L80's tend to come with loose torque converters that are better suited for big cam engines, not low-end grunt motors, so you might want to change that as well.

And I agree, if an engine swap is in the future, get that all sorted before you change anything else in the driveline.
Click to expand...
Hmmm valid points. Thanks for your input. Sounds like I have a lot more info I need to research.
 
Chickntrk said:
Because the 700R4 is a pile
Click to expand...
So much hatred!!!
:D

I have had a 700R4 behind a big block in my '70 K10 for almost 50K miles. Yes it has a upgraded input drum and a Transgo shift kit, Corvette servo and a few other things. It works very well for me. I do have 4:56 gears, and had 33's for about 40K miles, now it's on 35s.
My '72 C10 has had a 700 in it for years as well. It has a small roller cam in a 406 small block with 3:73 gears.
Both transmissions have been great for me, I just need to get my governor setup a little better in the C10 to get the full throttle shifts down a couple hundred rpm when in drive.

I see no problem running 400 hp through one if you don't want to change the transfer case input gear and adapter to run the 4L80E. You will also have to decide how you want to control the 4L80E, and this can also come into play with what you decide on for induction on the new engine.

Yes, a better axle ratio will be beneficial no matter what way you go.

I put a looser convertor in my '01 2500HD with a 6.0. Got it from @Greg Ducato
He did a very nice job with all 3 convertors that we have purchased from him.
 
garonsmoak said:
Hello All,

I've been lurking here for a a while but I finally acquired myself a 1990 Blazer. I bought it knowing the tranny is going out and I'm planning on taking it somewhere to have it rebuilt but pondered doing the rebuild myself. I've helped rebuild more than a couple and I've never done one on my own but I'm thinking I can figure it out. It's currently sitting on 35s and I plan on using it for trails, trips to the beaches near me where I'll be driving on sand, and towing my boat to the ramp. So a little bit of some mix usage. Nothing too crazy. I also plan on beefing up the powerplant to the 400 hp area. So...on one hand, what rebuild kit/parts should I be looking for to accommodate my wants if I decide to rebuild it? On the other hand (since I do realize that this is an incredibly skilled task and dont want to risk completely ****ing it up) what should I ask for in a rebuild if I take it somewhere and what would the costs look like? I'm currently in the Norfolk, Ne area for work and will be in this area for a while if anyone has any transmission shop recommendations.
Click to expand...
I have same, but a 90 Jimmy, stock axle ratio according to build sticker is 3.42. According to specs some had 3.90 or 3.91, and there were a lot of 3.23. I have the HD Trans with code MD8 with MX0 overdrive, which means a Auto 4 spd, HMD, 470E Super Duty. Sent tranny & transfer case to reputable shop for upgrade to kevlar bands etc. and non-lockup, which required a different torque converter. Rebuild cost for trans & transfer case about $2500. I am doing an engine swap to a 383 strocker with al heads, roller cam, and Holley Sniper system, expect close to 500 hp. Also, lifted 2.5" which required changing rear drive shaft, & steering pitman arm replacement, plus a few other mods.
 
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