700R4 trans install

[XQIZT]

Running the financial numbers, and it just makes good sense to get the old tranny out and install a 700R4 so we have an overdrive gear. 30-40% increase in MPG is huge and will pay for itself.

I see some places have all up kits and all that needs to be completed is the drive shaft shortening and the moving of a cross member.

I know cutting and welding is involved in the drive shaft modification, but what about the cross member? Is that a bolt on situation?

Thanks!

[6880 Mike]

Use the 82 crossmember; it's bolt in.

[rtj]

I've had a bunch of driveshafts shortened and balanced at Advanced Driveline here in Orlando. If you need driveshaft work you might consider them.

[tektrans]

I have a Bowtie Overdrives 700R4 crossmember for sale, if you are interested PM me.

,Mark

[XQIZT]

pm sent.

[KacyC3]

Bowtie overdrives is the place my crossmember came from and i also recommend their tv cable linkage kit. It gives you a cam that allows how aggressive the transmission shits.

[XQIZT]

I also like that they provide a new shift detent and indicator window that truly shows OD, D, 2, 1

[KacyC3]

Originally Posted by XQIZT

I also like that they provide a new shift detent and indicator window that truly shows OD, D, 2, 1

Mine has a B&M ratchet shifter, so I don't have any info on that.

[gkull]

You don't magically get increased MPG with a reduction of rpm with an OD tranny.

a 3.55 or lower number rearend can attain 20+ mpg with an efficient motor and a th350

a 700R4 is a serious power user compared to well built th350

The 200r4 is a more bolt in tranny with better gear spacing and not as power robbing as a 700

[XQIZT]

Originally Posted by gkull

You don't magically get increased MPG with a reduction of rpm with an OD tranny.

a 3.55 or lower number rearend can attain 20+ mpg with an efficient motor and a th350

a 700R4 is a serious power user compared to well built th350

The 200r4 is a more bolt in tranny with better gear spacing and not as power robbing as a 700

Explain this please. Are you saying that running 55mph at 3000rpm vs. 55mph at 1700rpm will no show a MPG difference?

[gkull]

Originally Posted by XQIZT

Explain this please. Are you saying that running 55mph at 3000rpm vs. 55mph at 1700rpm will no show a MPG difference?

What kind of a rearend do you have that causes 3000 rpm at 55?

years ago i built a 7000 rpm 355 ci and routinely got over 20 mpg on trips with a built th350 and 3.55 gears driving 75-85 all the time. I would drive 500 miles on my 25 gallon tank.

Then i installed a 700R4 and my mileage went down because rpm dropped to the point where it was below the cam efficency range. so i installed a 4.11 rear to bring the rpm somewhat up and the MPG was still less than before and I lost a couple of 1/10ths at the drag strip.

The problem is a 700r4 even built up looses about 25 RWHP compared to a built TH350. It is a power robbing tranny just like the TH400.

MPG is dependant on running the engine in an efficient rpm. Dropping below like 1700 rpm would require more gas to maintain a highway speed because the motor is near lugging. I had a modded 98 C-5 vette and it ran better in 5th than 6th gear. I installed a 4.10 rear end in it and then it could actually use the 6th gear.

[XQIZT]

I was just tossing out those numbers...

But all else being equal, and no other changes, every person that has swapped in a tranny with an OD has seen increased MPG.

[gkull]

Originally Posted by XQIZT

I was just tossing out those numbers...

But all else being equal, and no other changes, every person that has swapped in a tranny with an OD has seen increased MPG.

Not everyone (Me)! the 700R4 is a worst case. The 200R4 is much more efficient. I ran my 700's in my Vette for 18 years and finally got smart and installed a TKO 600 and then I saw an instant increase in highway mileage. My 434 ci exceeds 18 on long trips Like when i drove 1200 miles to southern Cal for a Vette get together.

[garys 68]

Real world experience. My 89 camaro got about 10% better milage with the 700R4 in OD (0.7) vs 1:1 drive.
A 30% reduction in rpm does not equal a 30% increase in milage.

[shakedown067]

What cross-member do you have to remove? Why not just buy a used auto driveshaft and C-beam? They are relatively cheap. Or did those only change for the ZF6? Good luck on the swap.