Tranny Swap HELP!

turbo_tom · 11-27-2007, 12:20 AM

Ok, I had originally decided that the first upgrade to my '69 for the spring would be suspension. Only problem is that I won't be going very far because my tranny is so wound out I can't do highway driving at all...

The guy I bought it from said the car has 355's with a TH350 3 speed. In 3rd at 70 mph the car is SCREAMING.

So here is what I would like:

* To be able to cruise at highway speeds (65-80) and keep the rpms < 2900.

* To still have enough low-end grunt to make up for the fact that the car only has a mild small block.

Suggestions?

superstreet · 11-27-2007, 08:29 AM

I just rebuilt all of my suspension trying to keep it "stock". I kept the original rear-end housing,but replaced the stock axles with Moser axles and the differential is now an Eaton posi. I wasn't too concerned about installing the 4:10 gears since I had a 700 R-4 with high performance parts in it,but a lower gear (numerically) would get you better gas milage and lower rpm's at cruising speeds. Over-drive in the 700 R-4 is .70 to 1 and first gear has a nice steep gear (3.06 to 1). I did put in a lock-up converter for better gas milage at highway speeds. I am not sure of what rpm's I am cruising at,but I would guess at 70 mph it would be about 2,400. Here's is a handy site for calculations: http://www.slowgt.com/Calc1.htm

There is a lock-up kit for the 700 R-4 for non-computer equipped cars.The lock-up converter usually locks up about 40-45 mph and when you touch the brakes it unlocks it.Just cruising around town I didn't want it locking up,because when it does lock up and you let off the accelerator the cars "bucks".To cure that,I installed a switch in the 12 volt line that locks up the converter.When I am on the highway and I want the converter to lock up I just flip the switch.

Here's another handy site for swaps. http://www.bowtieoverdrives.com/index.shtml

Another neat feature they have for the shifter is the shifter conversion kit.It looks stock,but it has the extra indentation for the extra gear plus it has the "OD" on the lens itself.

turbo_tom · 11-27-2007, 10:03 PM

So you're saying to go with a 700R-4...? Will 4.10's let me cruise at highway speeds ?

Your car looks slammed in your sig, what do you have for suspension? Mine sits like a 4x4 in the front...

superstreet · 11-27-2007, 11:16 PM

If you are wanting to cruise it on the highway and get better gas milage and are willing to spend the money for a rebuilt (or have an old one built) 700 R-4,I would seriously consider it. Look for a trans that is from 1984 and newer.It has the larger 30 spline input shaft. (Earlier ones from 1982-1984 have a 28 spline)

I actually put a 3,400 stall in too.

It is so easy to do a trans swap these days and most everything is bolt-on.You can use your old yolk from your 350 Turbo.They have the same number of splines.

With your set up you are probably running about 3,100-3,200 rpm's.With the same set up,but with the 700 R-4 you should be turning 2,100-2,200 rpm's.That is why I went with 4:10's because the overdrive helps a lot.I'm still only turing about 2,400.

I have lowered the front with Hotchkis lowering springs which should lower it 1-2 inches and then I cut 1/2 a coil off.It lowered it about 2 1/4".The back is lowered about 1 1/4" with aluminum lowering block I made at work.It has a slight rake to it now.

Here's a pic:

Please let me know if you have any more questions. It makes it SO much easier when someone else has already gone thru the problems and hassels to find out what works and what won't.