Rebuilding a TH2004R. Is it possible....?

McHaggis

Member
Joined
Nov 25, 2009
The information on this site about rebuilding TH2004R's is both extensive and contradictory. How anyone can reliably rebuild one with confidence is remarkable. Just trying to understand what parts are sensibly required for a given power level is a mission in itself!

My question is simply this: Can I, with my mechanic and engineering background, who has build and modified a few TH400’s, TH350’s, etc, confidently rebuild a TH2004R to perform as expected and last the distance?

Here are some concepts I’m less than sure of:

Can any available TH2004R be modified to perform as expected or do you HAVE to have the GN or SS cores? Keeping in mind I’d use an ’86 or later core.

Are the VB’s so different that an unknown VB can’t be modified give the same level of performance as a performance one?

What VB’s modification need to be done to give moderate up shifts at part throttle but good aggressive shifts at WOT? Some on here say you don’t need to do much, others suggest getting a SS or GN VB. I also see special separator plates that “fix” some issues. Hence my confusion.

Are these transmissions difficult to get “right”? I see on here so many of “us” with TH2004R issues that I’m sure they must be.



CK Performance has a TH2004R that is exactly what I need but the cost to have one shipped to me here in New Zealand makes it beyond my reach. At US$1500 it sounds great but by the time I get it landed here it’s going to cost something like NZ$3700! They also sell a parts kit (I’m hoping it contain everything that goes into their “Street Strip” unit) that they put into this trans for $949. This option is affordable for me.

So, I need to make sure that if I get this “kit”, freight it to NZ, buy a local core and rebuild it as per Chris’s book, can I end up with a great trans or will I be posting on this forum with issues forever? LOL


Simple really…..or is it????
 
I've re-built several 200r4's, I always use Chris's book for reference,always. I've done mild builds, less than 300 horse, up to 500 horse. Depending on how much power your going to run thru it, will depend on what you'll need for hard parts. There are alot of good trans builders out there,but, as with anything, you can ask ten guys the same question and get ten different answers.I would figure out your power level goal and build accordingly.Chris's kits and hard parts are great. Customer service is great also. You get the trans and parts, fly me out,I'll build it!!!:D Good luck. Phil.
 
2004r is a great performance trans if built right. You dont need a GN or SS core. The only diff inthose units is servo and VB calibration. If you use good quality SK and either sonnax or superior servo( 11% larger than 87 servo) you will be changing calibration so it doesnt matter. Only thing to watch for is year model. Only 83-up units will work in our cars cause of the use of ECM controlled lock up. These units do not have convertor clutch valves in VB 82 and earlier will have these valves. Seperator plate also diff for 81-82 units
 
2004r is a great performance trans if built right. You dont need a GN or SS core. The only diff inthose units is servo and VB calibration. If you use good quality SK and either sonnax or superior servo( 11% larger than 87 servo) you will be changing calibration so it doesnt matter. Only thing to watch for is year model. Only 83-up units will work in our cars cause of the use of ECM controlled lock up. These units do not have convertor clutch valves in VB 82 and earlier will have these valves. Seperator plate also diff for 81-82 units


The car it's going into has no ECU so this isn't an issue. Right?
As for VB calibration. Surely this can be changed to suit any application with the use of "shift kit" so in theory any VB can be used as long as it's been modified. Up grading the servo is a given.

I have found a total of 4 cores here in New Zealand. The years of these are: 82, 84, 86 and 90? Although the 90 trans has some weird numbers on it. It also looks to have been wet at some stage as the input shaft and stator support are very rusty. The 86 is out of an unknown but this is the one I'm considering. The stator support is stripped which is OK as I'm replacing it anyway but would this have casued any internal damange I need to be aware of?

Is CK Performance’s TH2004R book a good read? Does anyone have a spare copy? Chris has none.
 
If you want lock up to work properly with no ECM you will have to use the 82 core or run toggle switch on later ECM trans
 
my understanding

It is my understanding as in all things Turbo Buick you must employ a witch doctor for all reliable mechanical upgrades. Just my understanding.
 
Any late unit can lock up w/out a computer.Just use a normally open 4th gear pressure switch in the 4th pressure port in the v body connected to solonoid ground and 12 volts to trans case to the solenoid hot.Now you have 4th gear lockup.As soon as you hit the gas a 3/4 kdown unlocks converter.There are several switches that ground only at low pressureses,ie below 150 psi but wont allow lock up @heavy throttle if you want to get fancy.
 
mis matched parts

It is my understanding that the reason for prefering the SS or TR VB is because they are calibrated for more than 1 reason but the main reason is they are for 3.42 gear ratio.
 
mis matched parts

It is my understanding that the reason for prefering the SS or TR VB is because they are calibrated for more than 1 reason but the main reason is they are for 3.42 gear ratio. This could turn into a nightmare--I understand your options are very limited. Jusy saying.
 
It is my understanding as in all things Turbo Buick you must employ a witch doctor for all reliable mechanical upgrades. Just my understanding.

LOL! That's my understanding too. That's why I started this thread. Lets hope the witch doctor fronts up!

I've had a PM from a member (thank you again) and he's saying that the info on here is confusing when in fact rebuilding one of these is quite simple.
 
It is my understanding that the reason for prefering the SS or TR VB is because they are calibrated for more than 1 reason but the main reason is they are for 3.42 gear ratio. This could turn into a nightmare--I understand your options are very limited. Just saying.

So you're saying they work well if running a 3.42 diff as the VB and governor are calibrated for this gearing? Surely this can be modified with "shift kits" etc to suit other applications.
 
Any late unit can lock up w/out a computer.Just use a normally open 4th gear pressure switch in the 4th pressure port in the v body connected to solonoid ground and 12 volts to trans case to the solenoid hot.Now you have 4th gear lockup.As soon as you hit the gas a 3/4 kdown unlocks converter.There are several switches that ground only at low pressureses,ie below 150 psi but wont allow lock up @heavy throttle if you want to get fancy.

I've seen a bit on here about doing this. My limited understanding it that all you need to do is to supply 12v to the trans through some switches and the 4th gear switch will go to ground when it's in 4th. You can get fancy I guess and wire it through the brake light switch circuit and maybe a vacuum switch so it unlocks at 1/2 throttle etc. Add a timer and you could get auto lockup at steady part throttle.
 
It is my understanding that the reason for prefering the SS or TR VB is because they are calibrated for more than 1 reason but the main reason is they are for 3.42 gear ratio. This could turn into a nightmare--I understand your options are very limited. Jusy saying.

It was my understanding that most Monte SSs had 3:73 gears . . .

Is there a source for this book that was mentioned? Automatic trannies seem like black magic to me, just trying to absorb as much info as I can.
 
true

It was my understanding that most Monte SSs had 3:73 gears . . .

Is there a source for this book that was mentioned? Automatic trannies seem like black magic to me, just trying to absorb as much info as I can.

Monte also have a different governor--point being that both are close enough to work without all the headaches.

CK has a book--very helpful.
 
Yes, the SS-Monte's with 2004R trans came with 3.73 gears. The Olds H/O-442 did as well.
2004R Trans codes>> THM 200-4R Information

Chris's manual>> www.CKPerformance.com may be out of them as said above.
The GM (Hydramatic)2004R Principles of Operation manual is helpful and an ATSG 2004R manual. Both can be found on Ebay etc..

A few 2004R Build articles:
http://www.turbobuick.com/forums/tr...ttention-new-version-strengthening-2004r.html
Answer Question
200R4 Rebuild
THM 200-4R
http://www.jakesperformance.com/200-4R_Rebuild_Tech.html Pics take time to load.
TH200-4R Rebuild - Dynotech Performance - GM High-Tech Performance Magazine
Olds FAQ -- TH-200-4R Trans Detail

Several Lockup Wiring diagrams>> Lockup TCC Wiring
 
Yes, the SS-Monte's with 2004R trans came with 3.73 gears. The Olds H/O-442 did as well.
2004R Trans codes>> THM 200-4R Information

Chris's manual>> www.CKPerformance.com may be out of them as said above.
The GM (Hydramatic)2004R Principles of Operation manual is helpful and an ATSG 2004R manual. Both can be found on Ebay etc..

A few 2004R Build articles:
http://www.turbobuick.com/forums/tr...ttention-new-version-strengthening-2004r.html
Answer Question
200R4 Rebuild
THM 200-4R
http://www.jakesperformance.com/200-4R_Rebuild_Tech.html Pics take time to load.
TH200-4R Rebuild - Dynotech Performance - GM High-Tech Performance Magazine
Olds FAQ -- TH-200-4R Trans Detail

Several Lockup Wiring diagrams>> Lockup TCC Wiring

There's excellent info in the links you've listed. Thanks.
Looks like buying a local core and shipping parts over in small shipments could be the way to go.

Still not sure about the VB calibration/modifications as there are a lot of different ideas out about this out there.
Am I right in saying that any VB can be modified to work the required way if it's been set-up correctly?
 
There's excellent info in the links you've listed. Thanks.
Looks like buying a local core and shipping parts over in small shipments could be the way to go.

Still not sure about the VB calibration/modifications as there are a lot of different ideas out about this out there.
Am I right in saying that any VB can be modified to work the required way if it's been set-up correctly?

Yes, your correct. Chris sells a VB calibration kit.
 
Yes, your correct. Chris sells a VB calibration kit.

There looks to be a huge range out there from "shift kits" to complete new VB's! :eek:

I've had a few PM's from members and an offer of help so I'm looking to get a core here and then start collecting hard parts.
 
Two things I never attempted are setting gear lash and automatic transmissions. That said, a retired teacher who ran a vocational transmission shop took apart/reassembled a BQ core I bought "rebuilt" guy honestly claimed he never could get it to "shift right"

Point is WITH the correct tools it's not that much worse than a manual trans. No feeler gauges, pretty much the torque wrench suffices. True we started with a clean trans with all new clutches, etc. nothing visably worn. Much of the upgrades mentioned on this board are available from mainstream suppliers like Dacco. Some specialized tools are MANDATORY, second pair of hands help. You might be able to do it to stand up behind moderate power.

What did he find wrong? The spring on the governor was missing. I'm putting it behind a strictly street engine, front wheels only coming off the ground over a jack.

Good luck, YMMV
 
Get the video! I read Chris's book cover to cover,it all made sense to me after watching the vid. I haven't broken mine yet,never had a problem at all.
Mind you I had never even seen the inside of any kind of trans before I did this.
Mart
 
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