700R4 Trans Install and 4.56 gears


The car came with a Powerglide.  When it failed several years ago I put in a Turbo 350 which was a direct swap. For this rebuild I wanted an overdrive trans.  Since I have changed the rear end to 3.73 gears, the overdrive is better for highway driving.  The 700r4 trans that I used is not a bolt in swap.  The following are the changes I made.

Got a junkyard trans for $400 and decided to put a B&M performance rebuild kit in it ($200).  This turned out to be an enormous amount of work and although successful, probably not worth the effort.  Should have purchased one already built.

Failed after 10,000 miles see below

Trans Mount - I cut the back of the mount off and made an extension of 1/8" steel. I MIG welded it on. IMGP0260-600.JPG (65026 bytes)
Shorten the Drive shaft - With the car assembled, insert the output yoke and measure the distance from the centerline of the yoke universal to the centerline of the rear universal.  A local drive shaft shop shortened it.  The shaft had to be shortened at both ends.  Cutting it at only one end would have put the weld at a point where the shaft was changing diameter.  
Shift Linkage - (replaced see below) The 700 R4 is set up for a cable linkage and the 69 Impala uses a rod type linkage.  I had to make a new rod linkage to attach to the existing column shifter.  I used 1/2" fine threaded rod and shaped it to fit using the old one as a model. The actuator lever arm was held in place temporarily with hex nuts.

The differences were in how the rod connects to the transmission gear selector and the length of the rotating arm that is moved by the column shifter.  With the new transmission, more rotation is needed to get to low gear.  This required a shorter arm on the linkage.  Once all the lengths and angles were right, I welded it up with the hex nuts in place.

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Carb Throttle Valve Linkage - The Holly does not have the correct rotation at the throttle shaft to correctly move the trans link cable correctly.  I added an adapter made by http://www.transmissioncenter.net  

(replaced see below)

Transmission torque converter lockup control - The 700 R4 transmission has a lock-up converter and the car does not have a computer to control it. I purchased a B&M lockup controller.

This consists of a speed sensor that goes in-line with the speedometer cable, a control box where the speed is controlled and a wire to the transmission connector for triggering the lockup.

I wanted the control within  reach of the driver for setting, but invisible.  I placed it in the front ash tray which required modification. I cut off the two cigarette holders inside, wired the ball bearing slider to the rear (to avoid interference with the control knob), spread the ash-tray holder slightly to make it  easier to slide without the bearings, bent the spring retainer flat to give more clearance for the control knob, put a 7/16" hole in the rear with a rubber grommet to feed the wires through.

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Shift indicator - Conversion shift indicator plates are not available so I set the alignment for neutral.  Park and Drive are then reasonably close.  
Trans kick-down cable - The 700R4 is not normally set-up for a carb.  An adaptor is needed to correct the motion of the throttle shaft linkage for the trans. Adaptor available from http://www.transmissioncenter.net/highperf700r4.htm

(replaced adaptor with adjustable type, see below)

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Post Restoration changes

The  transmission described above failed after about 10,000 miles.  From the start, there was excessive slippage during hard throttle up-shifts.  This gradually got worse until 3dr and 4th gears failed entirely.   

Purchased a modified 700r4 trans from Bowtie Overdrives http://www.700r4.com/sitemap.html

I got their level 2 trans.  It has quicker up-shifts, the governor is set for higher rpm full throttle up-shifts and is good for 450 hp

I also got their adjustable carb linkage adapter for the TV cable on a Holly.

It gives the proper amount of travel for the cable and allows adjustment of the rate that the cable advances

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I needed to add a Trans cooler.  and a temperature sensor in the trans oil pan. I installed a Flex-a-lite 4120 that is rated for a 20,000 lb GVW.  This gives an oil temperature of 115 deg measured with an infrared sensor on the outside of the pan.  The cooler dimensions are 7.5 x 20 x 3/4"

A Kugal steering column linkage was purchased from Bowtie Overdrives that is fully adjustable on the travel. The letter spacing is still off but the travel is close  
High speed Governor - I replaced the V8 governor that came with the Bowtie trans with a V8 governor. This effects only the full throttle shift points and raises them to about 5000 rpm with the 4.56 gears that were installed (see below).  


Rear Axle and Differential

Since the overdrive trans gave a a 30% drop in RPM on the highway, I decided to go to 4.56 gears in the 12 bolt rear end. This is a 3 series gear set, the biggest ration available for the 3 series. I got them from Strange Engineering. This is 15% over the 3.73 gears I had before. One side effect is that It was no longer possible to get the speedometer reading correct using just the internal gears. I purchased an external gear reducer from Performance Automotive and Transmission Center to fix the problem. 

The following are not complete instructions on the process, just some usefull notes on things that were not written in the instructions that I had.

When removing the axle retaining pin on a chevy 12 bolt, you need to be careful not to loose the spring steel washers that go on the pin, just inside of the center section case. On a new unit, these are snug and should not fall out. If there is any wear, they can slide out and you may not notice them. What I do is to loosen the center pin retaining bolt, rotate the pin to vertical, as the pin is slid down, insert a piece of wire into the hole to keep the washer from sliding around. Then rotate the center section to allow the pin to be removed out the bottom, pull it out and insert a wire for the bottom one.

The axles and center section can then be removed.

Pinion removal- disconnect the drive shaft and hammer the pinion out. If you plan to save the old pinion, use a brass drift pin to keep from mushrooming the end of the pinion (or use a soft mallet)  

The pinion must be located a specific distance from the center of the ring gear. This should be written on the pinion when you get it. I made a straight edge from a piece of aluminum angle. I flattened it with sandpaper on a flat surface. I then used calipers to measure the distance from where the center section bolts in to the top of the pinion (- the thickness of the aluminum). This got me within 0.010 in the first try.

Tightening Pinion Bolt and Crush Sleeve - It takes about 180 lb-ft to tighten the pinion bolt and crush the sleeve. In the end there should be about 10 lb-in of turning resistance on the pinion. To hold it in place I made the tool at right. It is made of 1/8" x 2" steel stock. I drilled 3 holes to match the pinion yoke and cut a clearance hole for the impact socket. If you use all 4 holes there is not enough width to cut the clea5rance hole. The other end of the bar rests on the floor and prevents rotation. My Husky "500 ft-lb" impact wrench had just enough power to turn the nut slowly. You need to pay careful attention as you tighten it. Tighten it until the play just goes away. You then have to take the retaining bar off and check how tight it is. Repeat the process until you get the specified resistance. I tightened mine to 25 in-lb my mistake. Hopefully this should be ok, otherwise I will need a new pinion bearing set later.
The center section needs to be shimmed to give 0.080 of rotational play at the ring gear. The shims need to be tight enough that they need to be gently hammered in with a soft mallet.  

Rear Axles and Bearings - When pulling the axles for the gear change I notices they were worn at the bearing contact area. I got new Yukon axles and bearings from Randy's Ring and Pinion.

To remove the wheel bearings I cut a piece of 1/" inch steel just smaller than the wheel bearings and used a slap hammer to pull the bearings. This was just strong enough to do the job. The steel was bent when I was done.