Tech article by Aaron Modlin (BUCKETOBOLTS)

I snapped a few PICs as I’ve been working on my C4 rebuild and thought I’d share how I modified my transmission. Most early Bronco and truck application transmissions are already well equipped. The input shafts are usually hardened. They have the “H” servo and five forward clutches. They are also all the pan fill case design, which is referred to as the stronger casting. The Bronco version also had a deeper sump pan.

I’ll start with the cooler circuit. I drilled the aluminum ball plug out of the stator to remove the 2 check balls and spring. Then tapped the hole 1/8″ pipe and plugged. This allows full volume to the cooler. Then I reamed the 5/32” cooler return at the rear of the case to 3/16″ to get rid of the restriction there.

I then drilled the #9 thrust bearing lube circuit. The 1/8″ hole intersects the cooler return I just reamed. This allows for a pressurized lube for the bearing which is prone to shearing the ears off and spinning in the case. This circuit may already be drilled on later model transmissions.

I bought Alto Red Eagle clutches and Kolene coated steels. I’ve had very good service from these in my Mustangs. My transmission already had 5 disks in the forward pack, so I just set the clutch pack clearance at .025″. The high/reverse on the other hand only had 4. I added one friction and one steel by machining the pressure plate

to allow for the five total disks. I set this clearance at .025″ also. I relieved the high/reverse drum by drilling 5/16” holes around the band area. This allows the clutches to displace the oil faster and help release the band quicker for a good 2-3 shift.

My kit also came with a Kevlar intermediate band. These bands will last much longer and stand up to more abuse than stock replacement bands. The intermediate servo is used to apply the band. Most early Bronco C4’s have the “H” servo. It has a large 2.960” surface area on the apply side. This servo does well and doesn’t usually need any type of modification with a stock valve body. A manual valve body will have specific directions on how to modify the servo to work with the valve body.

To firm up the shifts I did a few simple tricks to the valve body per the BURLY4×4.com website. First I disabled the intermediate servo accumulator valve by switching the position of the valve and spring. This valve acts as a cushion for the 1-2 shift. I then drilled the two holes in the spacer plate to 3/16”. Whe

n I reassembled the body, I only used two check balls. One in each oblong passage in each half of the body.

I replaced my factory deep sump pan with a BTE racing cast aluminum pan. This pan holds approximately two more quarts of fluid. It also came with a matching deep pickup and a drain plug in the bottom of the pan. Because of its cast design it adds extra rigidity and strength to the case.

Tech article by Aaron Modlin (BUCKETOBOLTS)

Related posts:

1. 4R70W 4 speed automatic with overdrive Tech article by Tim Bowsher (Broncobowsher) Selecting a new transmission....
2. AOD 3 speed automatic – Transmission Guide Tech article by Jon Hanna (Admin) Automatic Trans Intro •...
3. C4 3 speed automatic – Transmission Guide Tech article by Jon Hanna (Admin) Automatic Trans Intro •...
4. 700R4 4 speed automatic – Transmission Guide Tech article by Jon Hanna (Admin) Automatic Trans Intro • Gear...
5. AODE & 4R70W 3 speed automatic – Transmission Guide Tech article by Jon Hanna (Admin) Automatic Trans Intro •...

This entry was posted on Wednesday, January 14th, 2009 at 9:03 am and is filed under - Automatic, Transmission. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.