Mating a Cadillac 390 and a 700R4 transmissionHere are the parts and web sites used to mate the 390 to 700R4
The Hydramatic was leaking from a number of places, and the labor to R&R was the same as upgrading to the 700R4. So we bit the bullet and told Pruitt to forge ahead. He recommended the Bendtsen adapter because it is made of ¾ inch STEEL plate. I had looked at Wilcap adapters, but they are aluminum. In addition, Pruitt had seen one used locally on a 1962 Sedan that, after installation, cruised to California and back!!
Fuzzy pic of the adapter sitting between the block and the trans
The kit includes a Mopar mini starter that requires a bit of rewiring
if you plan to keep the points-type ignition. The Cadillac starter has both
an “S” terminal (for starting) and an “R” terminal (for running). The MOPAR
starter only has the R terminal. Some ingenuity will be required. However,
we had converted to a Pertronix ignition system, so 12V is used everywhere,
and the ignition resistor had been deleted.
The other problem with the starter was the stacking of tolerances concerning ring gear engagement. As initially installed, the starter teeth did not engage deep enough into the ring gear teeth; .030 clearance is ideal. Unfortunately, the gap was larger than this. In order to adjust the clearance, the starter was shimmed. A call to Bendsten by Pruitt was initially met with skepticism. When they realized they were dealing with a professional shop that had done this before, they listened. Bendsten made a new adapter end that slid the end of the starter closer to the flexplate teeth.
The Kugel arm has to be bent in order to correctly align with the column arm and the trans shifter shaft.
The 700R4 was built using Corvette clutches, new hard parts, and non-electronic overdrive engagement. It shifts into o-drive at about 50MPH. No shift kit was used.
A wide selection of driving and driven speedometer cable gears is available from Chevrolet to calibrate the output. Tire diameter and rear axle ratio will determine the appropriate gear set for the 700R4 and your car.
A driveshaft was built using a new trans yoke (700R4), new original-type u-joints, and a new Center Support Bearing. The old shaft had a weird double-tube section in the rear, where a smaller tube was inside a larger tube and the 2 pressed (??) together. This rear section had somehow twisted itself so that the u-joints were no longer “in phase”. So…. A new driveshaft emerged from the machine shop:
I can’t get the pic to fit properly here…use your imagination, or email me for the details.
A trans mounting plate, welded to the original crossmember, was made to allow the use of a stock 700R4 rubber transmission mount.
Someone asked about the shift quadrant on the dash. Well, She Who Must Be Obeyed had decreed that the interior be left stock. So, as of now, the quadrant still reads : PND1D2LR. Pruitt was able to align the “D” of the 700R4 with the first D of the quadrant. So, if someone tries to steal the car and has to backup, they won’t find Reverse where they think it is!
We’re still using the original cooler lines and the radiator-based cooling loop. Long range plans call for moving the radiator in front of the crossmember and adding a B&M Supercooler.
Ok, so how does it work. Well, it works great! The car has A LOT more initial acceleration from a dead stop, shifts better, and doesn’t leak.
Gary and Helen Mulholland