# Automatic Transmission Rebuild - D21 Hardbody



## MarkWalker (Mar 29, 2019)

So the tranny failed on my recently acquired 1991 D21 pickup (automatic). Here are the symptoms: As I was driving, a whirring/wheezing/grinding noise gradually crept up in tandem with the RPMs of the engine. About a minute later, the truck gradually slipped out of gear and just coasted as if in neutral. I pulled over, let it sit there while I checked the fluid - then on a whim, I started it up and tried to go again, put it in gear and I'll be damned if it didn't lock into gear and drive. However that only lasted about a block or two, then it slipped out of gear again. I did this process over & over until I got the truck home. It only took about 30 seconds of waiting each time before starting up again.

The day I took it to a local tranny repair shop up here, it wouldn't engage in either fwd or reverse, and wouldn't engage for the guys at the shop either. Based on their topline basic inspection, they say it could be a pressure issue, (won't build pressure) or a problem with the torque converter, or a bad pump. They said the fluid looked fine, but smelled burned. They also want about $2200 to fix it. Way out of my price range, but the truck is solid on all other points and I'd like to fix it, so I'm just now researching the whole DIY rebuild process. Any sage insight into this area would be greatly helpful! 

The last kicker: After I had the truck towed back home, I started it up and successfully put it in gear again - actually drove it a little in fwd and reverse just to prove that it worked again, then quickly shut it off so's not to F anything up & possibly do more damage. So, it's an intermittent problem? WTF?

Thanks!


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## jp2code (Jun 2, 2011)

I'd say get a used transmission to swap in.


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## rogoman (Dec 16, 2004)

I would agree with JP2CODE. If the ATF is dark, burnt smelling, and you see little flakes or speck in it, the tranny possibly has hard part damage. You can buy used tranny's on Ebay for around $700 - $900; rebuilt units go for around $1200 and up.


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## smj999smj (Jan 1, 2006)

As someone who was a Nissan tech that used to rebuild Nissan transmissions, I wouldn't recommend rebuilding it yourself if you have no experience in doing so. For starters, you are going to need some special tools to get the clutch pack assemblies apart and back together. Secondly, it is not an easy valve body to take apart and service; it is very easy to lose check balls and not get the thing back together correctly. Third, you need equipment to thoroughly clean out any clutch lining debris and/or metal shavings from the case and other parts of the transmission; if you don't, the debris will clog the screen and restrict the flow to the pump, eventually causing low pressure and slipping (don't ask me how I know!). Fourth, it can get expensive! At the very least, you will need an overhaul kit (seals, gaskets, friction plates and/or steel plates) and probably a torque converter, which isn't cheap. Add to that any potential hard parts you may need once you get it apart, such as planetaries, one-way clutch, bearings...possibly even a control valve body); hard parts are not cheap! Fifth, if you don't get it right the first time, you'll have to take the transmission out of the vehicle, again, and tear it apart as many times until you get it right! A reman transmission would be the best way to go, but they are pricey! I would price compare getting a used trans with at least a 30-day warranty and an estimate from a reputable transmission shop to rebuild it.


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