My 700r4 is dying - what are my options?

[Mattchu60]

Eariler this week the trans in my 87' V10 starting to slip in 2nd gear rarely. I drove it tonight and its slipping in 1st, 2nd and 3rd gear if you push into the gas a little bit. If I am cruising at road speed its fine (so far).

Anyways, its going to be dead sooner or later.

What are my options here> A rebuilt 700r4 is around $1k, a local shop will rebuild it and do the removal/install for $1,500.

I'm considering going to a TH350 to save money and avoid having another burned up trans, also I don't really use the O/D anyways due to low rear end gears and the 33" tires, it drives much better in Drive.

I have done some searching on the site, seems like there is a adapter kit for a TH350 which allows it to drop into the 700r4 spot.

What am I missing or not thinking of? I hate surprises when installing stuff.

Any other options to consider?

 

[HotRodPC]

I think you're right. I'd do the Th350 too. I have done this to my 85 K10. I only miss the OD when on the freeway doing 75. But I've only got 31in tires. 3.73 and 33in tires at 70 would not be bad.

You're right about the 700r4 not going to last long either. We've got guys on here that get a 700r4 rebuilt about every year. Th350 and be done.

 

[Mattchu60]

Would it be better (easier) to find a combo TH350 and transfer case or just get a TH350?

What about speedometers and cables? What are the small things (issues) that I would run into?

What I am trying to find out is - if I want to go with a TH350, what is going to be the most bolt in method to replace the 700r4 and its transfer case?

Will I need to worry about driveshaft lengths?

 

[HotRodPC]

That's the purpose of using the spacer and the the modified 2wd shaft. You're making the Th350 the same exact length as the 700r4, therefore, EVERYTHING stays in it's original location. The driveshafts stay the same lengths so no mods needed, the crossmember lands in the same spot so no holes to drill or mount to modify. Cooling lines and shift linkage will all be in the same spot. Only thing you'd have to do different is run a Vac Line to the Vac modulator since the 700r4 does NOT use a vac modulator but the Th350 does.

The Th350 will need to be built with the modified output shaft installed.

http://news.compperformance.com/Instructions/329900.pdf

 

[HotRodPC]

Here is my 700r4 to Th350 Conversion for 4x4 with NP208 or NP241C thread.

http://www.gmsquarebody.com/forum/showthread.php?t=1181

You'll see I cut down my own 2wd output shaft to make the modified length 4x4 output shaft. All I really had the spacer I got for the junk yard. The rest of the kit I made mods to make it work.

Here is just the Adapter For $100 but no shaft included by Advance Apapters who is expensive as hell.
http://www.summitracing.com/parts/add-7q-35a

May as well do the TCI complete kit with cover, shaft and all for $185.
http://www.summitracing.com/parts/TCI-329900/?rtype=10

 

[Mattchu60]

Thanks for the information.

The instructions say that they may be modifications needed for the cat. Any idea what those are?

Also - what about my speedometer, will I run into any issues there?

Sounds like this is the best route.

 

[HotRodPC]

Thanks for the information.

The instructions say that they may be modifications needed for the cat. Any idea what those are?

Also - what about my speedometer, will I run into any issues there?

Sounds like this is the best route.

Hmmm, mods needed to the Cat? As in Cat Converter? I wonder if a Cat Bracket bolts to the back of the Trans or something? None of my trucks have Cats. I can only imagine it would be an OEM bracket or clamp that must bolt to the back of the trans or Tcase.

Speedo is no issue at all either. It will be the same hook up in the same Tcase, in the same exact position.

It appears you'd want to get the $185 Kit from Summit then have your trans builder use the that output shaft.

I wish to hell I could find someone to make me those spacers because the rest of the kit it easily made. You can use all thread cut down to make your own studs, and I have plenty of 2wd Th350's to cut shafts out of.

You'll also need to decide if you want to use a Th350 or Th350C. That won't matter on the kit. But be sure you know which one you're getting before you get a torque converter. They ARE NOT compatible with each other. Th350C is the Converter Clutch model, aka Lock Up Converter. The Lock Up units are just a little weaker in the pump area, but if your just the average driver and not extremely abusive, the Th350C is fine and will still last much better than the 700r4. The Lock Up will save you 200-300 rpm on the highway and will also have the trans running much cooler which means the trans is likely to last longer. So if you're not a heavy duty 4x4'er, then I'd probably go for the lock up model. You're 700r4 has provisions for Lock Up already, so that should not be that hard to adapt to the Th350.

Then again, the standard Th350 is plenty strong and will last a good long time too. So which ever one you choose is fine. I guess that will matter on which core you find cheap.

 

[philjafo]

Just a thought but have you serviced the transmission? I've had good luck with the following as long as its done as soon as the slipping starts. Change the fluid and the filter, and add a quart of Lucas trans fix in a bottle. It won't rebuild a shot transmission, but it will add a lot of miles to it. Give you time to put together what you need for the turbo 350 swap.