Re building a th350
August 31st, 2013, 06:35 PM
#1
Re building a th350
Ok fellow members. Im venturing off into the wild and rebuilding my own th350 trans. I have been doing alot of reading studying the chiltons trans manual over and over and watching multiple videos on youtube and im even buying the tools needed. I have 3 good cores ranging from ok to previously rebuilt in the past with not many miles and one with an unknown past. My plan is to rebuild the best core which was the rebuilt unit and doing a practice one to disassemble and re assemble with a junker unit. If anyone has any technical advice to contrubite to this project jump on board. Im buying a rebuild kit from phoenix transmissions in fl. it has the hardened sprag and roller unit in the kit and raybestos redline clutches all new steels etc. etc. and a transgo 1-2 kit to reprogram to full manual control with the drive function still. Is there anything anyone would suggest.
August 31st, 2013, 06:44 PM
#2
Registered User
Join Date: Jun 2010
Location: Rogues Island, USA
Posts: 3,613
I rebuilt my TH400 with a B&M kit. It's just a matter of taking your time and doing it right. I did mine with simple hands tools but I won't lie that some parts were challenging. Keep things clean and make sure the sprag goes in with the wishbones tilted in the proper direction. On the front pump do this when you're ready to re-install it. Take the two halves and put them in upside down in the core and bolt them together. Then take it out and re-install it when you get to that point. What you're doing is aligning the halves so it doesn't bind in it's bore. Your kit may explain all this but just incase.
Although at first it may be daunting it all makes sense soon enough. If your overwhelmed take pics before you proceed and use them for reference.
Although at first it may be daunting it all makes sense soon enough. If your overwhelmed take pics before you proceed and use them for reference.
August 31st, 2013, 06:57 PM
#3
Im stocking up on small boxes, ziplocks, and parts tags. Im actually feeling pretty confident about this whole deal the last 2 weeks all I have been doing is research. I always have my phone handy to take pics. The manual I have is actually very detailed and explains in picture by picture frames and articles on individual components. very easy to follow which is a plus since repair manuals sometimes can be confusing. I will also be doing my th400 when the time comes.
August 31st, 2013, 07:10 PM
#5
You bring up a good point. The manual states to dip the clutches as you build but others have stated what you are talking about. I guess I"ll use a bunch of old tuppeware so I don't get confused on whats what to keep things separated and organized. I will be doing my trans in my basement .
August 31st, 2013, 07:21 PM
#7
The reason for me bagging and tagging as I go is because the manual explains the complete teardown from front pump to reverse piston assembly and tearing down all the parts individually as you work your way down. I plan on doing the same as I have been really studying this book and it make sense. My friend told me the same thing as you as far as disassembly and assembly that makes sense to me too but im a little hyperactive so I kinda need something to follow so to speak so I don't go nuts trying to figure out what I forgot .
August 31st, 2013, 07:25 PM
#8
Justin
Join Date: Mar 2012
Location: utah
Posts: 3,448
Yeah I understand I had my gm buddy rebuild my th400 I didn't want to chance anything right now to me it made since to pay him for his time and thirty years of transmissions plus he only charged me a bottle of JD
August 31st, 2013, 07:29 PM
#9
Those are the kind of friends I need lol. Most guys who do it from their own garage have quoted me between 200 and 250 and the rebuild kit cost me that so 250 and 250 is 500. The local trans shop who is well established was chaging me 650 and I get a warranty. I guess there is no better time to learn to build a trans than now lol.
August 31st, 2013, 07:37 PM
#10
Justin
Join Date: Mar 2012
Location: utah
Posts: 3,448
Yeah my truck I ended up buying a rebuilt from a shop cause it was 50 less after replacing everything in mine and it was done but I don't like the way it shifts I am sure it is cheap clutches
Oh yeah his other payment is he wants do test drive I once installed . Good thing thats at least a year out he had a 69 cutlass and said it was fun to drive he isn't a car guy tho he loves his bikes
Oh yeah his other payment is he wants do test drive I once installed . Good thing thats at least a year out he had a 69 cutlass and said it was fun to drive he isn't a car guy tho he loves his bikes
September 1st, 2013, 05:11 AM
#11
Registered User
Join Date: Jan 2010
Location: central Indiana
Posts: 5,342
Machine the direct clutch piston the equivalent of one friction and steel plate. I prefer not to use the wave plate in the the direct clutch. For that matter,does your core trans have 5 forward frictions, and 5 low and reverse? The pistons can be machined if not.
September 1st, 2013, 05:30 AM
#12
Matt olds since this will be my first rebuild Im not going to do a whole lot of modifications. Machining might be a little be too much for me at the moment. Im going to venture to say a steel and friction is about .030 to .040 ? I also have 3 cores . Is there anything I should look for maybe to pick the best core for high perf.
September 1st, 2013, 11:29 AM
#13
hey copper I hear you about this project but, I would save cost somewhere else in your project. I do not do trannys either I had mine done elsewhere. I would check with king transmissions in Bensenville on grand but do the homework first. kings used to do a lot of performance work back in the day but things can change buddy, by the way upgrade for strength it really pays off. I also do not now check back until next Saturday. good luck.
September 1st, 2013, 11:45 AM
#14
Im not worried if it fails. I want to learn how to do this. Just like my engines little by little I have learned what works what dosent what will live and how long based on what I did. I don't mind learning at my expense. I'm not gonna lie I am cheap but if I learn and it means I have to do it twice so be it . You gotta crawl before you walk.
September 1st, 2013, 07:09 PM
#15
Registered User
Join Date: Jan 2010
Location: central Indiana
Posts: 5,342
Its really simple to machine the pistons, I have a buddy that runs a automotive repair shop and use his brake lathe. I use a junk cutting tool, set the machine to the high speed and let it go. The surface cut and exact measurement isn't critical, shoot for .010 per clutch plate clearance. If you don't have one already get Ron Sessions book on modifying the TH350 trans. Its the best 20 bucks you will spend on the transmission. It has lots of rebuild tips, instructions on how to make the tools to teardown and rebuild the trans plus parts interchange info. If your tearing apart 3 different trans to build a good one the book is very important, there are a few part production changes you need to be aware of. Ive built quite a few of these trans, they are pretty easy to do.
September 2nd, 2013, 04:50 PM
#19
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Join Date: Mar 2010
Location: South-central Pa.
Posts: 1,309
September 3rd, 2013, 08:17 PM
#21
Im really torn about what I should be doing. I think the b&m transpack is a very complete kit and it comes with instructions. Maybe I should keep modifications to a minimum until im more comfortable with the trans rebuilding. My 355 is in the 400 hp range I would say give or take. Will the b&m kit work for my application. What are the limitations of a moderately built th350. Im also afraid to overdo it in case I mess something up. Should I just do a stock style rebuild with a shift kit ?
Jeremy you going to Byron on sunday ?
Jeremy you going to Byron on sunday ?
September 4th, 2013, 07:27 AM
#22
Registered User
Join Date: Jan 2010
Location: central Indiana
Posts: 5,342
I have built many TH350 that live comfortably in the mid 11sec range with a stock type rebuild kit, my own shift kit and upgraded sprag race. Don't waste your money on the "high performance" blue clutches that come in the upgraded kits. Go to any trans shop, order a rebuild kit and ask them to order a extra clutch plate and steel. If you haven't ordered a Trans-Go or B&M shift kit save your money, its easy enough to make your own shift kit.
September 4th, 2013, 10:22 AM
#23
I have the mondello book where it explains what to do. I want to just get the b&m rebuild kit with the shift kit because it's actually the best bang for the buck. Do you think I can do with out the sprag for my power level.
September 4th, 2013, 05:57 PM
#24
Registered User
Join Date: Jan 2010
Location: central Indiana
Posts: 5,342
Read this for rebuild tips, it explains the dual feed modifications and valve body tips.www.nastyz28.com/forum/showthread.php?t=53671
Unless you have a newer edition Mondello tech book that cover TH350 trans the only tech tips applies to the TH400 trans. By the way, I'm guessing Joe was typing that info as it was given to him over the phone! It really isn't very clear and hard to understand what is being described.
If you have the trans out of the car and on the bench I think the dual feed modification is best done internally. All TH350 shifts kits accomplish the dual feed modification the same way with the block-off plate, transfer plate, and sandwiching those parts under the factory steel plate. If you have a trans in good condition and don't want to remove it then a shift kit is a good upgrade.
I have asked several professional trans builders and many of the instructors that taught transmission classes at the GM training center why GM decided to split the direct drum into 2 separate chambers (one for high gear, one for reverse) and nobody has any clue. The TH350, TH400 and 2004R trans all do this, meaning people in the aftermarket have had to figure out ways to fix it. On all 3 trans, its a simple matter of removing a seal, and installing a set-screw, freeze plug or different style bolt to prevent 3rd gear oil from back feeding and applying reverse gear.
For a 400hp engine I would think a stock outer sprag race would be fine. If you decide to upgrade the race make sure you get a quality part from a reputable source. Some of the races you get on ebay or similar places are junk! They are much weaker than stock and shatter.
Unless you have a newer edition Mondello tech book that cover TH350 trans the only tech tips applies to the TH400 trans. By the way, I'm guessing Joe was typing that info as it was given to him over the phone! It really isn't very clear and hard to understand what is being described.
If you have the trans out of the car and on the bench I think the dual feed modification is best done internally. All TH350 shifts kits accomplish the dual feed modification the same way with the block-off plate, transfer plate, and sandwiching those parts under the factory steel plate. If you have a trans in good condition and don't want to remove it then a shift kit is a good upgrade.
I have asked several professional trans builders and many of the instructors that taught transmission classes at the GM training center why GM decided to split the direct drum into 2 separate chambers (one for high gear, one for reverse) and nobody has any clue. The TH350, TH400 and 2004R trans all do this, meaning people in the aftermarket have had to figure out ways to fix it. On all 3 trans, its a simple matter of removing a seal, and installing a set-screw, freeze plug or different style bolt to prevent 3rd gear oil from back feeding and applying reverse gear.
For a 400hp engine I would think a stock outer sprag race would be fine. If you decide to upgrade the race make sure you get a quality part from a reputable source. Some of the races you get on ebay or similar places are junk! They are much weaker than stock and shatter.
September 4th, 2013, 06:31 PM
#25
Thanks matt69olds for all your help. Im going to go with the b&m kit get the ron sessions book and give it hell. Well atleast not for a few weeks until I have the money lol.
September 16th, 2013, 06:24 PM
#26
Just an update guys. I ordered the b&m kit and the ron sessions book. I also ordered the reverse piston compressor tool and some new snap ring pilers last week. I plan on probably tearing down the trans this weekend. Then im going to send the case to get cleaned up at my dad's shop to get it degreased and look like new.
September 18th, 2013, 06:25 PM
#27
Matt69olds I can use a regular lathe for machining the parts correct. I got the book and I think the b&m kit supplied the max amount of clutches and steels . So I figured why not. My friend does have a lathe so I have access to it. I do have a small back ground in machining My only issue is which surfaces I cut the blueprints are kinda vague.
September 21st, 2013, 06:15 PM
#28
Alright guys I started teardown and inspection today. I picked my best core and it looks to have been rebuild . The clutches where in good shape and all the bushings looked great I'm going to check em with a micrometer to make certainn I don't have to replace them. A few thins I found is there was no spring on the modulator valve and there was no shim on the thrust bearing on the pump. I'm going to call the local trans guy and see how much he would charge to machine the parts to hold the max amount of clutches . All in all I was kind of dreading the tear down but it went smooth over all I'm happy I started with my best core I think that made it a bit easier. I will add pics soon.
September 22nd, 2013, 09:15 AM
#32
Ok guys I have a few questions I hope you can help me out. As you can see in the first pic the stator shaft has had some wear with some heat build up. that surface is there the converter slides into. I looks like it had some fine splines which are now almost gone. I think whatever flake was in the pan was from here. I mic'd out the clutch frictions and they where all over .090 so they are almost like new and all the bushings are in great shape no scoring on any bearing or bushing surface. My question is do I need a new pump I have 2 more cores so I guess I should probably go ahead and do that but what would cause failure in that area of the stator shaft. I got everything ready for re assembly im tempted to re use the original clutches and just add the shift kit and keep the clutches for another core. The ron sessions book says .090 is minimum for re use.
September 22nd, 2013, 12:09 PM
#35
Registered User
Join Date: Jan 2010
Location: central Indiana
Posts: 5,342
The blue spots on the stator support tube is from the heat treat process, pretty sure you will see something similar on all the pumps. and the small grooves I don't think is anything to worry about, I don't think anything rides there to cause those marks. It might be something left over from the manufacturing process.
The finish on the clutch pistons wont matter, they will sit against a steel plate in the clutch pack. as long as its reasonably smooth but needs to be flat and square you will be fine.
The finish on the clutch pistons wont matter, they will sit against a steel plate in the clutch pack. as long as its reasonably smooth but needs to be flat and square you will be fine.
September 22nd, 2013, 01:01 PM
#37
Thanks for the input and advice. I like the bucket idea. I will do that for re assembly. What do you think about re using the cluthes most are above. .095 on second imspection. I'm starting to think maybe I'll re use what's there clean everything up do the shif kit and go from there. I want to make sure if something fails I atleast reused what I could and I don't mind doing the work. I guess I just want to do it in baby steps
September 22nd, 2013, 01:15 PM
#39
Justin
Join Date: Mar 2012
Location: utah
Posts: 3,448
I know. Under gm warranty if they measured hood you reused all parts I know two gm trans builders one does a side builds and I know he saves all good parts and builds trans to help keep cost down in the rebuilds proble more hard parts then clutches
September 22nd, 2013, 01:42 PM
#40
Proffessur to put it in prespective the new cltches avg at .098 the old clutches range between .094-.097. This is why it would make sense to re use them since this is my first rebuild . I will still have my new raysbestos cltches ready to go if something goes wrong.
