best rear gears for 700r4

[squarebodyScotty]

I have a 84 k10 with a newly swapped sbc350 paired with a 700r4 and it tends to slide in and out of OD at 65mph (ish) and wont hold speed. If I drop it in to 3rd gear it drives great at 2k rpms without issue. Could the rear gears be wrong for 700r4 if it has the original axel set up for the 305 and 3 speed it came with? What would be the ideal gears for a 700r4?
Thanks first time square body guy 715 551 5282 wisconsin

 

[mibars]

Do you know your current ratios? What does your glove box sticker say about your axles? (via RPO codes).
Ideal gear will depend on your wheel size. Your assumption of wrong gears is quite possible, if your rpm is about 2000 in 1:1 ratio and now in D it would be close to 1400 in OD, provided that your converter is locked. The old 3 speeds had no TCC so they probably spun the engine extra 200-300 rpm. Or if you are saying that you have 2000 rpm in 3rd gear with converter unlocked then the transmission will sure struggle in OD slipping a converter a lot.

I had an issue with transmission falling out of OD, but it was caused by low ATF - It seeped from gearbox to transfer case with no evident leak.

Speaking of 700R4 and swapped motors are you 1000% sure that TV cable geometry is correct? Geometry of that link is critical, it's not a kickdown cable, but controls everything, shift points, line pressure, kickdown, feel of transmission, you get it wrong and the transmission won't live too long. Worst case with TV cable disconnected it won't survive a test drive around the block. If your transmission wants to downshift early then the TV cable is possibly on a tight side. TV cable geometry would be the very 1st thing that I'd check. And don't loosen it more than a click or two after you are sure that the bracketry and cable stroke is correct.

Do you have a setup to lock the converter? AFAIR 700R4 does not like to be driven with the converter unlocked and no additional cooling.

 

[NickTransmissions]

I have a 84 k10 with a newly swapped sbc350 paired with a 700r4 and it tends to slide in and out of OD at 65mph (ish) and wont hold speed. If I drop it in to 3rd gear it drives great at 2k rpms without issue. Could the rear gears be wrong for 700r4 if it has the original axel set up for the 305 and 3 speed it came with? What would be the ideal gears for a 700r4?
Thanks first time square body guy 715 551 5282 wisconsin

3.23 to 3.73.m with stock diameter tires.

What's your current ratio?

Had a customer with 2.73s in a vette where we did a 700r4 swap from a th350 and he would slip/fall out of OD when trying to accelerate while in 4th. Upgraded to 3.42 and problems went away.

How many miles on the trans?

What year 700r4 trans?

What kit are you using to lock up the TC?

Check TV geometry and cable adjustment - verify with a transmission pressure gauge at idle and at 1000 rpms. You should have 55-70 psi in P, N, D at idle and appx 100-130 psi at 1000rpms.

If that checks out, check 4th apply servo piston sealing rings for wear by dropping plan and doing air check using shop air and rubber tip nozzle - there's a small hole on the case pan rail right below the servo - that's the 4 gear exhaust.

Another possibility is worn 2-4 band or 3-4 clutch pack.

 

[Trucksareforwork]

I just went back to stock tire size on my truck rusty (only about 2.5% reduction in tire diameter from 265/70-15 to 235/75) which has a 305, 700r4 and 2.73 gears. Experience driving in OD is already way better even with that slight change in tire “gearing.”

I wouldn’t mind having shorter gears in the back, for sure, but am not likely to spend the $$$ on it. It’s one reason I went down in tire size. I don’t like it hunting in the 45-65 mph range.

That said, truck drives sweet at 70 on the highway.

 

[PrairieDrifter]

I would go with 3.73's if I were gonna spend the money on it. On smaller diameter tires. That seems to be the best factory setup, that I've seen the most of, lots of 3.73 axles.

 

[82sbshortbed]

I have 3.73 rear end and 275/60/r15 on mine with 700r4. 2200 tc

Good setup for me. Runs about 2,200 rpm at 65mph in od.