5R55S – Lost Reverse and Drive, 1-2-3 Still Work – Likey Not the Sprag

[metrolink]

Hey everyone, I need some advice.
I've got a 2006 Mustang GT 4.6 with the 5R55S auto trans. After accelerating to merge on the highway, I suddenly lost both Drive and Reverse — car felt like it slipped into neutral. No movement in D or R, just revs. I was able to drive it home using 1, 2, and 3, which still work fine.

At one point I played with the shifter and both gears came back briefly, but then it stopped again.
No warning lights or codes. Fluid looked clean, not burnt.

Quick backstory:
The car had been sitting since 2021. I bought it from the original owner's wife for $500 after he sadly passed. The odometer reads 290k miles, but I'm certain the drivetrain's been swapped at some point.
My uncle knew the owner and confirmed it was well-maintained (records back to 2008). No rust, newer motor was swapped in previously, clean body and underside. Everything is stock except the exhaust was modified.
I had $2K total, and needed a car fast for work (just graduated, job moved out of bus range). I replaced spark plugs, brakes, rotors, oil, and checked fluids — all looked decent. Car ran fine until this trans issue.

Here's what's been done:
- Paid $350 to have my mechanic buddy drop the trans and check the front — sprag and front components look fine
- He wants $120 more to open the rear section and inspect clutches, pistons, etc.
- He runs a shop, has some trans experience, and would offer a warranty if he fixes it himself.
If it's too far gone, he may send it to a 3rd party (more $$).
- He also mentioned a 75K-mile used 5R55S from someone he knows (no warranty, junkyard pull). Price pending.
Before this I called around for rebuild quotes:
- $3,000 for the cheapest rebuild
- $6,500 for a "replacement"
Trying to avoid that route if I can.

My Questions:
- If the sprag is good, what else could cause Drive and Reverse to fail while 1–2–3 still work?
- Would you take the risk and open the rear to try and repair, considering how clean the internals looked? Or skip it and go for the used/junkyard trans?
- Most importantly, is there anything I might've missed before moving forward?

My goal mainly is just to get the car running for a year or two while I save up. If it lasts, I'll decide whether to build it or move on. Just need it to be reliable for commuting (mostly highway miles).
Thanks in advance for any help or insight. Photos of the internals are posted below.

TL;DR:

2006 Mustang GT (5R55S auto) suddenly lost both Drive and Reverse after accelerating a bit hard. Car only moves in 1, 2, or 3 manually. No codes. Front half of the trans was opened — sprag and front components look good. Mechanic wants $120 to open the rear and check clutches. Trying to decide: open it and try to fix, or stop here swap in a 75k-mile used trans (no warranty). Just need the car to last a year or two for work — don't want to waste money. What would you do?








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[DieHarder]

Likely servo's; possibly band adjustment/valve body/service but w/300k clutches probably need replaced so you'll likely need a rebuild anyway.

For the servo's there's a replacement kit by AJ1E (~$250) that provides a permanent fix for the servo bores.

See video by Ford Tech Makuloco:

AJ1E Kit:

You can also try adjusting bands. Note: Whenever doing this never take the adjustment SCREWS off or the bands inside the transmission will fall apart, then all the work putting in the kit would be for nothing. Read instructions and watch video before attempting.

And lastly here's a vid of a trans with your symptoms describing areas to inspect if your buddy tears into the trans:

Understand above may not be your problem but these are the most common failures for the 5R55S/W transmissions. If your buddy is willing to work on it I'd let him. Have him look at the servo bores first (inexpensive to fix using the kit).

 

[Autokyrios]

TCI's overhaul kit and master rebuild kit are like $300 and $900 respectively. A new built 5R55s should be between 4 and 5K (Jegs has a TCI built 5R55S for 4.9k).

The fee to diagnose is pretty low, and may be needed either way, and even if it's good news inside. Might as well do it. What's the worst that happens? You have to rebuilt it or buy a new one? Already kinda there.

 

[metrolink]

Had my buddy open up the rear of the transmission to take a second look. The 4th and 5th clutch plates looked a bit brown from age but weren't burnt or damaged. Bands were intact, and the servos looked okay. The OD sprag did have a small crack in the cage, but it wasn't completely blown apart, so we weren't sure if that alone was causing the issue. Pictures attached.

After talking with a few other techs, he mentioned it could still be a TCM issue, even without any codes — apparently, they can sometimes fail silently.

At this point, we might just be overshooting by replacing parts and hoping for the best. I've already been quoted close to $3K for a full rebuild, so I'm now leaning toward either getting a remanufactured transmission while everything's out or trying to source a solid used one elsewhere. If anyone has recommendations for good places to get a reliable 5R55S (reman or used) at a fair price, I'd really appreciate it. Just trying to make the smartest move before locking anything in.

 

[07 Boss]

Well since you have it all apart you might as well rebuild it yourself. Just go to like level 10 and see how their tranny is upgraded and follow suit. Buying a used or rebuilt is a crap shoot. Buying a new built transmission is expensive and also may be a crap shoot. At least if someone local does it you have recourse to get it fixed a ton more easily.

My experience;
when I installed my blower I upgraded my tranny to a "bulletproof" one from Level 10. Was great for about 3 years and then.....
Had a local shop that works on race and monster trucks rebuild mine with kolene steel Alto Red Eagle clutches and bands. He guaranteed my transmission for 3 years knowing full well I was going to abuse it at the track. Haven't had any issues in many years.

 

[Juice]

I've been staying out of this thread because I don't know the clutch/band application to gear flow. But the description tells me you lost the common clutch for reverse and 4/5. Yet not one mention of air testing the transmission to confirm this.

Second on rebuild it AND air test the hydraulics before installing it. If it passes the air check, and still not fixed, you know it's electrical.

So who knew that Ford took a 4spd auto and turned it into a 5spd auto? You may find this useful/informative.

18 Troubleshooting Tips for 4R44E & 5R55E Transmissions | Sonnax

With the proper repair, these cores can be just like money in the bank. Set yourself up for a successful rebuild with these expert tips.

www.sonnax.com

 

[DieHarder]

Lucky you found that cage before it came apart. Losing Drive/Reverse is one of symptoms that point towards that item going bad. Another is the flow control valve in the pump. Like Boss said get a rebuild kit & I'd go for the AJ1E Servo kit; add a pump valve/valve body kit and bands as well. With that many miles on it definitely most things are worn. Watch the vids and take your time. If your friend knows his way around auto transmissions all the better. There are plenty of vids on rebuilding the 5R55S out there.

However, if you don't feel comfortable then a rebuilt or used unit is probably the way to go.

For a tear down and early warning signs/symptom overview see:

And a couple of do it your selfers...

Start at 10:40 on this vid:

 

[DieHarder]

Good rebuild video for the 5R55S if you can spare the time.