700r4 gave up the ghost!

[leftybass209]

Ever take your truck on a trip purposely to find some kinks and diagnose faults? I did, and found more than I expected!

I was trying to figure out why my trans was shifting 1-2 at 10mph, 2-3 at 20-22mph, and 3-4 at 30-32mph.

At around 45 mph I tried to test my 4-3 downshift and it started winding higher, like it was in neutral. I coasted around the corner and shut it down. Fired it back up and went through every gear.... nothing. Didn't try to move regardless of RPM.

Had it towed to my favorite trans shop and we did some diagnosing. We assumed torque converter snapped clean at it's cast hub, or the pump was toast. Looks like the pump failed.

I gave him the okay to do a full tear down and inspection, as I'm not sure the condition of the trans.

I'm considering my options now. Not sure if I want to go ahead with a rebuild of the 700r4, or swap to a TH350. My dilemma is, I have a 3.07 rear gear, which I know is not ideal, and needs to be changed. Based on the diagnosis, I'll see if the funds are available for a diff and 700r4 rebuild, or just swap to a TH350.

[Bigdav160]

Sounds like it was shifting early which could also result in low pressure (low TV pressure)

But it would be unusual to lose everything. A pump self destructing is easy enough to check; Does the fluid level go down when the truck is started?

[leftybass209]

Almost certainly the early shifts and pump pressure were related

The pump is confirmed to be the culprit.

I don't know the extent of the damage yet. There was no debris in the pan, nothing metallic at all. I'll find out on Monday if it was a sudden pump failure in which the clutches may still be good, or if it was ongoing and the clutches are toast.

Financially it doesn't bother me what's wrong with it, I just need the money spent to be worth the repair or replacement.

[72MARIO]

With a 307 gear i would rather have a 350 trans any day. No need for Overdrive imo

[leftybass209]

I agree about the rear gearing and the th350, and that's a major deciding factor. The problem is I'd like the rear gears to be lower so I can take advantage of the torque my small block makes, as it's not a high winding motor.

Decisions decisions

[Redline novdog]

Add in changing the length of the driveshaft ! If you go th350

[67ChevyRedneck]

This is quite easy... leave it in 3rd around town and any driving under 45mph. Just like a TH350 until you can afford to swap to a 3.73 or 4.11. Then, when you're over 45mph or out on the interstate, bump it up in D.

I have a Lokar floor shift and I've been bump shifting my 700R for the past 10+ years. I leave it in 3rd most of the time until I'm over 45/50mph. I think I have 45 or 50K on it now. My truck is a 350 w/ 3.73. Excellent combo for an old C10 with a 700R.

[leftybass209]

Originally Posted by Redline novdog

Add in changing the length of the driveshaft ! If you go th350

He has a 9 inch tailshaft for the th350 that would work with what I have. 67chevyredneck, I think you may have the answer.when the hard $ figures come in it'll be easier to decide. This was a great suggestion though.