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Broken 26 splines input shaft (with pictures)

5K views 5 replies 3 participants last post by  BlueScreen 
#1 ·
My days of shifting my old T-45 are now gone. I was road racing the car, coming out of a corner in 2nd gear gradually stepping on the loud pedal, then I heard A LOT of noise and squealing, the car would not accelerate anymore. I had to tow it home, and after a couple of nights of work, this is what I got.









This transmission was completely built with cryo / REM polished gears, hardened 26 spline input shaft, everything. So I won't waste my time and money putting another one back in there, and swap to an 4R70W. I know next to nothing on automatics so I will have quite a few questions in the next few days.
 
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#3 ·
At first I wanted to upgrade to a T-56 Magnum, then I realized that this transmission has the exact same input shaft I just broke. So I have the choice of doing the same thing again and hoping it would not break soon, or swap an automatic. I choose the automatic.
 
#4 · (Edited)
Ouch knock on wood mine has held, but the stickest tire I've ran a 315 MT DR and I make less tq with my Vortech. I'm running the 26 spline on a T56.
 
#5 ·
You should be fine. I'm pretty sure those 5500 rpm clutch drop on slicks without any wheelspin hurted the input shaft, and it ended up snaping later while road racing.
 
#6 ·
It's been a while since I updated this thread. Here's a resume of the last few weeks.

Got a used 134 000 miles 4R75W out of a 2004 Mustang GT


Bought a driveshaft out of an automatic Mustang.


The shafts are the exact same length, only the yoke is different so I swapped the yoke over my aluminium driveshaft and called it done


Custom made tool to remove the snap-rings in the valve body area. The idea come from the YouTube channel Transmission Bench =>
I used their video for the whole disassembly and reassembly of the transmission.


The internals have all been removed and are sitting here


The tailshaft has been modified to get more oil to the bushing. Simple mod with brake lines, 1/8 NPT fittings. The bushing was drilled 0.050" for the oil passage


Custom made press to remove the snap-rings in the drums. The idea also come from Transmission Bench


Here's the important part. I bought a Sonnax Forward Drum to replace my OEM Forward Drum. I wanted to put 6 frictions disk in it. I took the measurement and had the piston machined 0.030 to get my clearance. When the piston came back, here's what happened when I installed the first steel plate =>
This happened because the teeths in Sonnax drum don't go as far on the bottom as the OEM one.

OEM


Sonnax


This forced me to use the thicker inplate as shown in the video, and that threw off my measurement and I had to get back to the machine shop tho have the piston machined again.

I got some urethane bushing to the 4R70W from SummitRacing. It align perfectly with my crossmember to nothing have to be fabricated to fit the transmission under the car. That's the crossmember and mount in the picture. The holes line up perfectly


Thoses are the internal ready to return inside the case


Empty case


Direct drum and ring gear installed


Comparaison of the 300M Stub Shaft on the left vs the OEM shaft on the right


Sun gear shell and forward hub


Forward drum and reverse drum getting installed. This was a pain to align the friction disk with the hub. Took a lot of patience


Intermediate clutch pack. Ready to close the transmission


After closing the transmission I had a problem. No input shaft end play at all, and it was hard to turn. I removed the pump and remeasured everything. I had 1.528" to the reverse drum bearing, so needed to install the #3 natural thrust washer. It's that one that came inside the transmission so I re-used that one. That was wrong. The OEM one was 0.010" thicker than the one I had with the rebuild kit. Installed the new one and now I have some end-play and the shaft turns easier.

That's the overdrive piston that come with Sonnax SureCure Kit. It has groove to prevent oil leak and loss of pressure. When I disassembled the transmission the overdrive band was showing some sign of slippage, and sure enough, the piston was not very tight in the bore. This Sonnax piston correct this problem


Here's the separator plate with the hole marked for drilling. That's part of the J-Mod


Now the transmission is re-assembled. I should take delivery of my CircleD 4C torque converter this week. Meanwhile I will try to get the B&M Hammer Shifter installed, or the USShift Controller.

Questions, comments and suggestions are always welcome
 
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