If you are looking for an Allison 1000 transmission for sale, you probably drive a GM heavy-duty pickup with a Duramax, and something has gone wrong behind the engine. Slipping, flare between gears, limp mode, burnt fluid. The Allison has a reputation as one of the toughest automatics ever put in a pickup, but tough is not the same as indestructible, especially after years of towing and maybe a tune.
Need one now? Our Allison 1000 transmission for sale is in the shop with price and details, and we ship worldwide.
This guide covers the specs, the trucks that use it, five-speed versus six-speed, the details that must match, common problems, rebuild versus replace, costs, and how to fit a used one so it lasts.
Table of Contents
Why an Allison 1000 Transmission for Sale Is Worth Buying Used
GM paired the Allison 1000 with the Duramax diesel from 2001, and the combination became the benchmark for heavy-duty pickups. The Allison was built for work: big clutch packs, a strong case, a lock-up torque converter and electronic control that shifts smoothly under heavy loads. Many owners chose a Silverado or Sierra HD specifically because of it.
Because GM used it for nearly two decades, there are a lot of these transmissions around. That makes a good used Allison 1000 transmission for sale far easier to find, and far cheaper, than a new or fully rebuilt unit. For a truck that is otherwise sound, a used Allison is often the smartest repair.
Allison 1000 Specifications
| Specification | Allison 1000 Series |
|---|---|
| GM name | LCT1000 |
| Type | Electronically controlled automatic, rear-wheel-drive layout |
| Speeds | 5-speed (early) or 6-speed (from about the 2006 model year) |
| 6-speed ratios | 3.10, 1.81, 1.41, 1.00, 0.71, 0.61, reverse 4.49 |
| 5-speed ratios | 3.10, 1.81, 1.41, 1.00, 0.71, reverse 4.49 |
| Converter | Lock-up torque converter |
| PTO | PTO provision on many versions |
| Main engines | Duramax 6.6 V8 turbo diesel, Vortec 8.1 V8 petrol |
| Years in GM HD pickups | 2001 to 2019 |
The Allison 1000 page has more on its history and versions. The short version: two overdrive gears on the six-speed make later trucks quieter and more economical at highway speed.
Which Trucks Use the Allison 1000?
- Chevrolet Silverado 2500HD and 3500HD with the Duramax (LB7, LLY, LBZ, LMM, LML and early L5P)
- GMC Sierra 2500HD and 3500HD with the Duramax
- Silverado and Sierra HD trucks with the Vortec 8.1 petrol V8
- Chevrolet Kodiak and GMC TopKick medium-duty trucks
- A range of other medium-duty trucks, buses and motorhomes
From the 2020 model year, GM moved its Duramax pickups to a ten-speed automatic. If your HD truck is a 2019 or earlier with a Duramax, an Allison 1000 transmission for sale is very likely what you need. Knowing your Duramax generation helps, because GM updated the transmission alongside the engine.
Five-Speed or Six-Speed?
Trucks up to around the 2005 or 2006 model year have the five-speed. Later trucks have the six-speed. The cases look alike, but the internals, wiring and software differ. A six-speed can be put into an earlier truck, but it needs the right control module and wiring work. For a straight replacement, buy the same type your truck came with. It is the simplest and cheapest way to do the job.
Other Details That Must Match
Five or six speeds is only the start. Before you pay for any Allison 1000 transmission for sale, check these:
- Two-wheel drive or four-wheel drive. The tail housing and output shaft are different. A 4WD transmission needs the adapter for the transfer case.
- Diesel or petrol. The bellhousing and torque converter differ between Duramax and 8.1 petrol trucks.
- PTO provision. If your truck runs a PTO for a dump bed, a winch or a hydraulic pump, you need a transmission with the PTO opening.
- Control module and software. The TCM must suit the transmission and the engine. Some years combine engine and transmission control.
Your VIN answers most of this. That is why we ask for it before selling any Allison 1000 transmission for sale.
7 Checks Before You Buy an Allison 1000 Transmission for Sale
1. Confirm the type
Five or six speed, 2WD or 4WD, diesel or petrol.
2. Ask about the donor truck
Year, model, mileage and how it was used. A truck that towed a heavy trailer every weekend is different from one that drove empty to work.
3. Look at the fluid
Clean, red-to-light-brown fluid is good. Black, burnt-smelling fluid with metal in it is not.
4. Check the pan and filter
A little fine material in the pan is normal. Chunks or lots of clutch material are a warning.
5. Ask about tuning
Big tunes on a Duramax put huge stress on the converter and clutch packs. A transmission out of a stock truck is the safer buy.
6. Ask whether the converter is included
And what condition it is in. A failed converter can send debris through a fresh transmission.
7. Read the warranty and return terms
Ask what cover comes with the transmission, in writing, before you order. Our used engine warranty guide explains what fair terms look like, and most of it applies to transmissions too.
Common Allison 1000 Problems
The Allison is strong, but there are patterns any honest seller of an Allison 1000 transmission for sale should tell you about.
Heat. Overheating is the biggest killer of automatic transmissions. Heavy towing in hot weather, a blocked cooler or a slipping converter all push fluid temperatures up and cook the clutches.
Converter shudder and wear. A shudder when the converter locks up, especially at light throttle, is a common complaint. Old fluid and tuned engines make it worse.
Slipping in higher gears on early five-speeds. Some early transmissions developed slips under heavy load in the upper gears, especially behind tuned engines.
Electrical faults. Shift solenoids, speed sensors, wiring and connectors can cause harsh shifts or limp mode that look like mechanical failure. Always scan for codes first.
Cooler line leaks. Old cooler lines and fittings leak. Low fluid leads to slipping and heat.
We look at these points on every Allison 1000 transmission for sale we ship. Our guide to tested used engines explains the thinking behind inspections, and most of it applies to transmissions as well.
Signs Your Allison Is on the Way Out
- Slipping or flaring between gears, especially under load
- Harsh or delayed shifts that do not improve after a fluid change
- Burnt-smelling, dark fluid with debris in the pan
- The truck going into limp mode and holding one gear
- Shudder when the converter locks
- Fluid overheating warnings when towing loads it used to handle easily
Have a mechanic read the codes and check the fluid before you buy an Allison 1000 transmission for sale. Sometimes a solenoid or wiring fault is the real problem.
Rebuild or Replace?
A good rebuild with upgraded parts can make an Allison stronger than new, which is why heavily tuned trucks often go that way. But a rebuild takes time and the price can grow as the shop finds more worn parts. A used Allison 1000 transmission for sale has a fixed price and can be fitted quickly. For a stock or mildly tuned truck that needs to get back to work, used is usually the sensible choice.
Get a rebuild price and a price for an Allison 1000 transmission for sale, think about how long you can be without the truck, and decide from there.
Towing, Cooling and Tuned Trucks
If your truck tows heavy, the best thing you can do for any transmission is keep it cool. A bigger auxiliary cooler, clean cooler lines and fresh fluid make a real difference. Watch the transmission temperature on long climbs and back off if it climbs high.
If your Duramax is tuned, be honest with yourself about how much power the transmission is seeing. A stock Allison handles mild tunes well. Big power needs upgraded clutches and a stronger torque converter. Putting a stock used transmission behind a big tune is a quick way to need another one.
Two Typical Allison Jobs We See
The fifth-wheel tower. A 2011 Sierra 3500HD Duramax pulls a big fifth-wheel camper across the mountains every summer. One trip, the transmission temperature climbs, then the truck starts flaring between fourth and fifth. The fluid is dark and smells burnt. The owner buys a used Allison 1000 transmission for sale matched to his VIN, his mechanic replaces the cooler and lines, and he adds a larger auxiliary cooler. Next summer, same trip, temperatures stay in check.
The tuned work truck. A contractor runs a tuned LBZ Duramax to tow equipment. After a few years of hard pulls, the converter starts shuddering and the truck slips in higher gears. He has two choices: a stock used unit and turning the tune down, or a built transmission for the power he wants. He chooses a used Allison 1000 transmission for sale and a milder tune, because the truck is for work, not racing, and he needs it back fast.
Both stories have the same message: find out why the last transmission failed and change that, or the next one will go the same way.
Allison 1000 in Medium-Duty Trucks and Motorhomes
Pickups get most of the attention, but the Allison 1000 family also went into medium-duty trucks like the Chevrolet Kodiak and GMC TopKick, and into a range of motorhomes, buses and specialist vehicles. These versions can have different housings, PTO setups and control programming from the pickup units.
If you need an Allison 1000 transmission for sale for a medium-duty truck or a motorhome, send us the identification tag details from your current transmission as well as the vehicle VIN. That tag tells us the exact model and build, which matters more on these vehicles than on pickups.
How to Check Allison Fluid Properly
A lot of transmission problems start with the wrong fluid level, and a lot of wrong fluid levels come from checking it the wrong way. On these trucks, the level should be checked with the transmission at operating temperature, the truck on level ground and the engine idling, following the procedure in your owner’s manual. Checking cold gives a misleading reading.
Overfilling is as bad as underfilling. Too much fluid gets churned into foam, which overheats and causes slipping. Too little starves the pump and clutches. Get it right after fitting any Allison 1000 transmission for sale, and check it again after the first few drives.
Questions to Ask Any Seller
- Five-speed or six-speed?
- Two-wheel drive or four-wheel drive?
- Out of a diesel or petrol truck, and what year and model?
- What was the mileage, and how was the truck used?
- Was the engine tuned?
- Is the torque converter included, and what condition is it in?
- Does it have the PTO opening?
- What warranty or return terms come with it?
We answer every one of these for each Allison 1000 transmission for sale we list. A seller who cannot is guessing.
A Short History of the Allison 1000
Allison Transmission is best known for heavy commercial and military transmissions. When GM wanted a gearbox that could handle the new Duramax diesel in 2001, it turned to Allison, and the 1000 Series was born. The original five-speed was soon followed by a six-speed with a second overdrive gear, which arrived around the 2006 model year. Over the years, the internals and software were updated to cope with each new Duramax generation and its extra torque.
By the time GM switched its Duramax pickups to a ten-speed for 2020, the Allison 1000 had been behind millions of heavy-duty trucks. That huge installed base is exactly why a good used Allison 1000 transmission for sale is still easy to find today.
What an Allison 1000 Transmission for Sale Costs
Our fairly used Allison 1000 transmission for sale is listed in the shop with its current price. That covers the transmission. You will also need fitting, fluid, a new filter, possibly cooler lines or a new cooler, and any parts that differ between your old unit and the replacement. Shipping is set out in our shipping policy, and import charges depend on your country.
A new transmission from a dealer costs several times more, and a fully built performance transmission even more. For most owners, a good used unit is the best value.
What Comes With Our Transmission
- Complete transmission with gear sets and clutch packs
- Torque converter, condition noted on your quote
- Valve body and internal solenoids
- Bellhousing and tail housing to suit the version
- Packing on a pallet with every opening sealed
The transfer case, control module, cooler lines and shifter are not included unless agreed in writing.
Installing a Used Allison 1000
- Confirm the match. Five or six speed, 2WD or 4WD, diesel or petrol, PTO if needed.
- Flush or replace the cooler. Debris from the old transmission sitting in the cooler can destroy the new one in hours.
- Seat the converter properly. It must engage fully before the transmission bolts to the engine.
- Fill with the correct approved fluid and check the level hot with the engine running.
- Check the control module setup and let it relearn shift points.
- Road test, scan for codes and check for leaks after the first drive.
What Your Mechanic Should Check on Delivery Day
- Look at the case, bellhousing and tail housing for cracks or damage.
- Turn the input and output shafts by hand to check they turn freely.
- Check the electrical connector and pins for damage or corrosion.
- Compare the unit side by side with the old one, especially the tail housing and PTO cover.
- Photograph the identification tag and all sides for your records.
If anything looks wrong, call the seller before fitting your Allison 1000 transmission for sale.
Notes for Four-Wheel-Drive Trucks
On 4WD trucks, the transmission bolts to the transfer case, and the two have to match. The 4WD Allison has a short tail housing and an output designed for the transfer case. A 2WD unit has a long tail housing and a yoke for the driveshaft. You cannot just swap one for the other without changing housings and shafts.
While the transmission is out, check the transfer case too. Look for leaks, check the fluid, and make sure the input seal is in good shape. A leaking transfer case input seal can let fluid migrate between the two units, which confuses fluid level checks. It is a cheap seal to change when everything is apart, and it protects your new Allison 1000 transmission for sale.
Small Jobs to Do While It Is Out
- Replace the cooler lines if they are original or show any rust or weeping.
- Check the engine rear main seal for leaks, since it is easy to reach now.
- Inspect the flexplate for cracks around the bolt holes.
- Check the transmission mount and replace it if it is cracked or soft.
- Look at the wiring harness and connectors for damage or corrosion.
Each of these is quick and cheap while the transmission is on the floor, and each one can cause trouble later if it is ignored. A good mechanic will do most of them as a matter of habit when fitting an Allison 1000 transmission for sale.
Looking After It Afterwards
Change the fluid and filters on the severe-service schedule if you tow or haul. Keep an eye on transmission temperature. Fix cooler leaks as soon as you see them. Use only approved fluid. Most Allison failures we hear about come down to heat and old fluid, and both are easy to prevent.
Buying an Allison 1000 Transmission for Sale From Abroad
We ship transmissions worldwide. The unit travels drained, sealed and strapped to a pallet, with tracking. Ask your customs broker what paperwork they need for a used transmission, and budget for import duty and local taxes. When it arrives, check the crate before signing and report any damage the same day.
How to Order
- Send us your VIN through our contact page, or go to the Allison 1000 product page.
- We confirm the match, what is included and the price.
- You pay by bank transfer and get an invoice.
- We ship it and send you tracking.
New to buying heavy parts online? Our guide on how to buy used engine online covers the same questions you should ask about a transmission. Our refund and returns and terms and services pages explain the rules.
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See everything we stock in the shop.
Frequently Asked Questions
Will it fit my 2008 Silverado 2500HD Duramax?
A 2008 Duramax HD has the six-speed Allison 1000. Send the VIN and we will confirm 2WD or 4WD and the other details.
Does the Allison 1000 transmission for sale include the converter?
Normally yes. We note its condition on your quote.
Can I put a six-speed in my five-speed truck?
It can be done, but it needs the right control module and wiring. A like-for-like swap is simpler.
Can it handle my tuned Duramax?
Mild tunes, usually yes. Big power needs upgraded internals and a stronger converter.
Do you ship worldwide?
Yes.
How do I pay?
By bank transfer. You get an invoice and order confirmation by email.
Get Your Truck Pulling Again
A good Allison 1000 transmission for sale is often the quickest way to get a heavy-duty GM truck back to work. Match it to your VIN, flush the cooler, use the right fluid and keep it cool, and it should give you a long life of hard work. When you are ready, visit the Allison 1000 transmission for sale page or send us your VIN.