How To Rebuild A Transmission? Easy Guide

Transmissions are one of the most complex components in vehicles, responsible for smoothly shifting gears to transfer power from the engine to the wheels. Over time, transmission parts like gears and shafts endure immense stresses, eventually wearing down and requiring major repair. When transmission problems emerge, drivers often ask: How difficult is it to rebuild a transmission?

Rebuilding a transmission is an involved but cost-effective process compared to replacement, which any DIY mechanic can complete with the right tools, workspace, and patience to follow crucial steps. This comprehensive DIY guide covers when you need a rebuild, what’s entailed, step-by-step instructions, tips to avoid mistakes, costs, swap considerations, and expert answers to frequently asked questions.

We’ll specifically break down:

Symptoms that indicate your transmission needs a rebuild
Pros and cons of rebuilding vs replacing your transmission
Must-have parts, tools, and safety equipment

Work area preparation for a smooth DIY rebuild
The complete step-by-step transmission rebuild process from A to Z
Estimated costs and options for saving money

Helpful troubleshooting tips from transmission rebuild experts
FAQs on common transmission rebuild questions

Equipped with these details, you can decide if tackling a transmission rebuild is right for your skills and budget, then fully prepare for this extensive project if you choose to forge ahead.

When Do You Need a Transmission Rebuild?

Determining if your transmission truly requires a rebuild versus minor repair involves detecting certain telling symptoms. Here are the top signs a rebuild is imminent:

Slipping gears – Your RPMs surge but speed fails to increase as gears slip. This commonly happens when shifting into higher gears at higher speeds.
Leaking fluid – Trans fluid puddles under your vehicle indicate seals & gaskets need replacement.

Burning smell – The transmission overheating from slipping gears or lack of lubrication produces a distinctive burning odor.
Delayed engagement – You push the gas but experience a long lag before acceleration.
Check engine light – Error codes confirm mechanical issues like solenoid failures.

Loud noises – Clunking, humming or whining noises point to internal damage.
Failed component – Your mechanic diagnoses a specific damaged part in need of rebuild.

Rebuilding or replacing a severely damaged transmission is unavoidable. But is it better to rebuild or replace? Here are the key differences in the rebuild vs replace decision:

Transmission Rebuild vs Replacement Comparison

The pros of opting for a rebuild include:

Cost savings – Reusing components cuts parts expense by 50% or more

Familiarity – Knowing your transmission’s service history if you rebuild
Environmental benefit – Less waste from reusing components

Cons associated with transmission rebuilds involve:

Variability – Durability of reused parts is uncertain
Complexity – Far more labor-intensive process than a swap
Shop skill needed – Precise expertise required to rebuild internal components

After weighing the rebuild route based on your budget, skills and transmission repair history, the next key steps are preparation and understanding the full rebuild procedure before getting your hands dirty.

Preparing for a Transmission Rebuild

To set yourself up for rebuild success, gather the necessary equipment, choose an appropriate workspace, and implement safety precautions.

Parts & Tools Needed

At minimum, acquire the following transmission rebuild parts and supplies:

Gasket kit – Includes all seals, o-rings and gaskets
Filter kit – All new filters for removing debris
Fluid – New transmission oil meeting OEM specifications

Friction discs & plates – New clutch discs if worn
Solenoids – Replacements if faulty
Misc. small parts – Bushings, bearings, springs, fasteners

You’ll also need an extensive assortment of mechanic’s tools:

Socket sets – Various 3/8″ and 1/2″ drive metric and standard sockets with ratchets
Wrenches – Standard and metric combination wrenches

Screwdrivers – Phillips and flat head varieties
Pliers – Standard, needle nose, and lock ring pliers
Pullers & hooks – For removing gears and bearings

Inspection mirror – For viewing internal transmission components
Magnets – Retrieving dropped hardware
Measuring tools – Micrometers, calipers, feeler gauges

Work Area, Lift & Fluids

All rebuild work should take place in a clean, dry, and temperate garage or workshop area. You’ll need ample lighting, outlets for power tools, sturdy work benches, and plenty of space. Since the average transmission weighs between 150-250 lbs, floor jacks and jack stands are instrumental for safely raising and supporting your transmission at a comfortable working height. Also designate catch pans for collected transmission fluid and organized parts storage.

Safety Precautions

To prevent injury and contact with harmful fluids, be sure to wear:

Protective gloves

Safety goggles
Closed toe shoes
Ear protection when using power tools

Dust mask if blowing components off with compressed air

Step-by-Step Transmission Rebuild Process

Completing an entire transmission rebuild has roughly 12 major steps that tear down, thoroughly clean and inspect, reassemble, and reinstall your transmission with all new gaskets, seals, filters, fluids, and worn hard parts. Here is the full sequence:

1. Remove Transmission

Disconnect negative battery terminal

Jack up vehicle securely on stands
Label and disconnect any electrical connectors, lines, linkage
Unbolt transmission housing and detach driveshaft

Carefully separate transmission from engine and lower it
Secure to transmission jack or rests on ground

2. Complete Tear Down

The meticulous teardown process separates all individual components for thorough cleaning and inspection. This crucial step sets the foundation for a smooth-shifting rebuilt transmission.

Methodically tag and bag each part grouping with labels
Document part order and orientation with photos
Carefully disassemblebell housing, torque converter, valve body, gears

Use proper tools to contain exploding clutch springs

3. Wash & Dry Components

Transmission components must be pristine to operate properly when rebuilt.

Wash in solvent tank or with spray cleaner and stiff brushes

Use compressor to blow out fluid passages
Allow parts to fully dry to prevent corrosion

4. In-Depth Inspection

A thorough inspection after cleansing Parts reveals the full scope of needed replacements. Closely check:

Gears for abnormal wear, pitting, cracking, distortions
Sealing surfaces for grooving and irregularities
Bearings and bushings for play or roughness

Shafts for straightness and journal imperfections
Friction discs for adequate thickness
End play specifications with dial indicators

Electronic sensors resistance levels & solenoids

5. Order Replacement Parts

After identifying faulty components, purchase quality replacement parts like bearings, bushings, solenoids gears, hard parts, and all new soft parts in the gasket/seal kit. Using high-grade new components vastly improves potential transmission longevity versus only reusing worn parts.

6. Correct Irregularities

Before reassembly, resurface and smooth anysmall defects found on reused parts:

Dress bearing surfaces with fine grit stones
Hone bushings to precise fit if ovalized
Polish scratched sealing surfaces with emery cloth

Trim gears to correct end play spacing

7. Reassemble Internals

Rebuild experts recommend completing all intricate internal reassemblybefore integrating the transmission case. Key pointers:

Closely follow part order notations

Check end play with dial indicators
Stake caps and fasteners with punch
Install new seals, gaskets, o-rings, and friction discs

8. Bolt Case Halves

The transmission case encloses all cleaned and rebuilt internals:

Inspect case sealing surface for flatness
Apply liquid gasket sealant or silicone

Torque case bolts to exact specs

9. Refill Fluids

Replenish fresh transmission fluid to provide vital cooling and lubrication:

Pour OEM-approved oil through dipstick tube

Cycle gears while adding to spread throughout
Check plugs and lines for any leaks

10. Reinstall Transmission

With rebuilt transmission reconnected to engine, complete reinstallation under the vehicle:

Secure on jack to align with engine
Attach mount hardware and driveshaft
Connect shifter linkages, lines, wiring

Refill with more fluid as needed

11. Road Test

The all-important road test checks operation and adjusts if needed:

Drive through all gears

Verify smooth shifting engagement
Correct leaks and adjust bands for firm shifts
Road test a second time before considering complete

12. Final Inspection

Check fluid color for contamination
Top off levels after test drive
Inspect for leaks underneath

Reset any engine codes

And with that, your transmission is rebuilt! While this comprehensive process is complex for a first-timer, taking it slow and methodical with organization and photos guarantees a reliable outcome.

Doing a Transmission Swap vs Rebuild

Some situations better warrant doing a transmission swap using a used/remanufactured unit instead up a rebuild. Consider a swap if:

Certain internal parts are unavailable for your model
Overhaul costs exceed replacement transmission cost
You lack rebuild equipment, skill and workshop space

Pros of opting for a swap include:

Simplicity – Bolts in easier than meticulous rebuild
Saving labor – Swap done in under 5 hours typically

Warranties – Certified reman units have 12-24 month warranties

The cons of transmission swaps involve:

Programming – Replacement transmission must sync with vehicle computer

Compatibility – Getting identical transmission or using adapters
Defects – Risk of undiagnosed problems in used transmissions

If the swap route makes more sense, take care in sourcing a suitable used/remanufactured transmission from a reputable seller that stands by their products. They should also handle any computer reprogramming to sync the new transmission if required.

Here is a quick rundown of the simpler swap process:

Procure transmission with matching specs
Disconnect and remove old transmission

Disconnect wires, sensors, mechanical linkages from replacement
Secure new transmission to engine
Reconnect all attachments

Refill transmission fluid as needed
Road test thoroughly after install

Cost to Rebuild a Transmission

Transmission rebuilds have significant parts expenses paired with extensive labor times that add up. Expect to budget:

$800-$1,200 in parts – Gasket sets, filters, fluids, small components
$700-$2,300 for labor – Based on mechanics’ hourly shop rates and hours needed. Rebuilds demand 15-25 hours so costs add up quick. Doing it yourself drastically cuts this labor expense down to $0 if you have the skill.

Additional incidentals like:

Transmission jack rental
Used parts if available
Replacement transmission cost if opting to swap instead

Programming expenses if doing a computer-controlled transmission swap

Factors that increase transmission rebuild costs include:

Vehicle make and model – Luxury and European cars have pricier parts

Greater component damage – Requiring more new parts
Advanced transmission types – Manual versus automatic/CVTs add complexity
Shop location – Urban shops have higher overheads and labor rates

Getting quotes from several transmission shops ensures fair pricing, and doing the rebuild yourself has the highest potential for major savings.

Transmission Rebuild Tips

These key troubleshooting tips help avoid headaches for first-time rebuilders:

Invest in a factory service manual with torque specs and procedures

Take abundant photos during teardown for reference
Closely follow suggested factory rebuild sequences
Check end play and tolerances frequently during rebuild

Road test repeatedly until smooth operation results

Here are quick pitfalls to avoid:

Mixing up reinstallation order of components

Forgetting thrust washers causing gear or case damage
Botching prescribed torque procedures damaging fasteners or parts
Allowing dust or debris into seals and bearings
Overfilling transmission fluid leading to leaks

While transmission rebuilds seem intimidating to DIYers, methodically following OEM procedures, investing time and patience pays off for thousands saved over shop quotes.

Frequently Asked Questions

What transmission tools do I need?

Specialized tools like bearing pullers and installers, snap ring pliers, small parts grabs, seal installers and custom wrenches for transmission fasteners are extremely helpful. Manuals detail special tools needed for your transmission model.

Can I rebuild a transmission myself?

With study of repair manuals, ample tools and workspace, patience and mechanical skill, an intermediate to advanced DIYer can successfully rebuild most rear-wheel drive domestic transmissions in their own garage. Electronic and front-wheel drive transmissions add more complexity.

Is it hard to rebuild an automatic transmission?

Yes, automatic transmission rebuilds are far more intricate than standard transmissions due to greater part complexity, precise rebuild procedures and tight tolerances inside for smooth shifting operation.

How long do rebuilt transmissions last?

When all wear items are replaced and rebuild done properly, a rebuilt transmission can easily deliver 60,000 to over 100,000 additional miles of reliable service. Using a reputable shop and adding a short warranty ensures longevity.

What causes a rebuilt transmission to fail again?

Common causes of premature rebuilt transmission failures include: incompetent rebuilds missing damage, improper assembly, use of low quality parts, and inadequate road testing afterwards. Doing your homework picking a shop or DIYing helps avoid these pitfalls.

Conclusion

When faced with major transmission repair, rebuilding yourself or via a trusted transmission specialist presents a far more budget-friendly and sustainable option than costly replacements. Equipped with this A-to-Z transmission rebuild guide’s key steps, critical tips and answers to the most frequently asked DIY questions, you can make an informed decision if tackling one suits your skill level.

While immersed in oil pans and baskets of parts seems intimidating initially, methodically working through proper procedures as outlined leads to an immense sense of DIY accomplishment. Gradually enjoying those smooth, solid shifts over hundreds of thousands of miles in your rebuilt transmission makes all the effort more than worthwhile.

How to Rebuild a Transmission? Easy Guide

When Do You Need a Transmission Rebuild?

Transmission Rebuild vs Replacement Comparison