TH350 trans - can they cut the Mustard ? - Team Camaro Tech
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post #1 of 16 (permalink) Old Oct 6th, 02, 06:07 AM Thread Starter
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Eric
 
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Guys I finally got my car to the track yesterday for the GM M7 event. The engine ran great considering I did not have a chance to dial it in at all. BUT 3rd gear in my TH350 trans went out during a run in the quarterfinals causing me to loose by .0012 seconds following an awesome holeshot .

My goal is to run mid to high 11's with my 383 small block, 3000 stall and 3.55 gear. Last year I broke some teeth off one of the drums and had to replace the drum and the input shaft, I also broke the 1-2 servo spring. So I rebuilt the trans using the B&M transkit last winter following directions to a Tee. Now it looks like I blew an oil seal, lost pressure, and burned up the direct drive clutch plates.

I don't think I will be rebuilding the trans again myself. I'm debating whether to buy another TH350 already built and ready to go (B&M, TCI or Hughes) or buy a TH400 and convert over.

What do you think?
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post #2 of 16 (permalink) Old Oct 6th, 02, 06:27 AM
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Damn dude, if it wasn't for bad luck you would have no luck at all huh? A built TH350 will hold it just fine...there are many 11 second big block chevelles using them, but as you know for outright durability a TH400 can't hardly be beat. With a shift kit and a good cooler they just seem to last forever...even in 1 ton trucks. I have heard from several people that swapped from a 350 to a 400 that they only lost less than .1 second et, so it shouldn't affect your times much at all. I think a 2.75 low gear TH400 would work beautifully with your 3.55's and big cam, but they are quite pricey.
If you are going to stay with a TH350, I have heard nothing but good things about the TCI streetfighter tranny's...I can't say that about any of the other big names out there.

Just curious...how difficult was the B&M transpak to install? Was any special tools or machining required?
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post #3 of 16 (permalink) Old Oct 6th, 02, 12:06 PM Thread Starter
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The B&M kit was a PITA but I wouldn't blame that on B&M. I suppose rebuilding an automatic transmission will always be a PITA.

My drums were already cut down (to make room for extra clutches) so I didn't have to do that. the directions are great and give specs for cutting down the drums, so you could easily drop them off at the local machine shop and have them milled down for a few bucks if you had to. I don't think you could get them flat enough even with a good mill file.

The only special tools I needed I made myself - there is a compressor that you need to get the very back piston and clutches out of the tranny. I used a long nut & bolt then bent a U shape into a piece of bar stock.

You also have to get your own bushings and press them in if you really want to do a complete rebuild. That cost me an extra $60 to buy the bushings and have the ones I couldn't get in/out done at the machine shop.

I don't think I would do the kit again - by the time you get all the little extras it doesn't cost much more to buy one already done. Maybe I would do the kit if were just freshening one up.
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post #4 of 16 (permalink) Old Oct 6th, 02, 01:04 PM
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Eric, you might want to get ahold of Bruce at Performance Transmissions 916-739-0510. When I destroyed my trnsmission (he did not build the one I destroyed)I went to see him. He stripped it down right in front of me and showed me the problems, also explained how it could have been built differently to avoid what happened and make it live in my car. I am 100% happy with the trans he built me. He really knows his stuff and I am pretty sure he ships transmissions too. He stops by this page every once in a while, but I would just give him a call. When mine went I managed to ruin the case too. Our cars run similar numbers and I haven't had a single problem out of the turbo 350 Bruce built for me (it's been in the car for about 1 1/2 years now). Even if you don't go with him, he might be able to offer some advice.

Royce
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post #5 of 16 (permalink) Old Oct 6th, 02, 02:54 PM
 
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Bruce goes by WE4 here and I think Team Chevelle if you want to search for him to come up to speed.. Good stuff.

Off the subject, but I kept pulling up the long thread on the 700- trans
rebuild/re-engineering story, "Gonna make this sucker live if it kills us" type name and probably need to bring it up from the dead to check the latest progress!! pdq67



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post #6 of 16 (permalink) Old Oct 7th, 02, 09:26 AM Thread Starter
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Eric
 
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Thanks guys.

So far my options:

1) Bruce built TH350 Cost ?
2) TCI built TH350 $700
3) TCI TH400 plus swap parts $900

I might have to go with the TCI TH350 or TH400 - shipping from CA would be killer. I still need to give him a call to find out.
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post #7 of 16 (permalink) Old Oct 7th, 02, 11:32 AM Thread Starter
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Update: Talked to Bruce at performance transmission. Nice guy. He put me in touch with a guy in Akron OH (on my side of the world LOL) Vince Janus, Janus Transmission. 330-753-6609.

Vince seemed to think that TH350 transmissions have weak cases and running 11's is pushing the envelope a little bit. He thinks I might have cracked my case and that's where my fluid leak and 3rd gear prob came from.

Sooooo, it looks like a swap to a TH400 might be the way to go.
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post #8 of 16 (permalink) Old Oct 7th, 02, 11:54 AM
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What about a turbo splined glide?
Then you'd have to see some 4.11 gears though, i think.
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post #9 of 16 (permalink) Old Oct 8th, 02, 02:01 AM
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It has been my experience with TH350 to break second gear (intermediate sprag) 5 times in two years.

I pulled it out, went to the shed, dusted off the P/glide, 1.82 ratio, replaced the input shaft for a Turbo-splined shaft, to use the same convertor, installed P/G, and went racing. Same ET & mph, 11.90 @ 115 w/4.11.

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post #10 of 16 (permalink) Old Oct 8th, 02, 11:02 AM Thread Starter
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Eric
 
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I got rid of my old powerglide, hated that thing LOL.

I'm seriously considering the swap to a TH400. So far I know that I need a new crossmember, new driveshaft yoke with conversion U-joint, and the switch for the downshift function. Driveshaft length should be OK, right?

What do you guys know about TH400 with the 2.75 1st gear? I wonder if that would make up for the extra HP needed to turn the trans.

I was also thinking if I go to a TH400 a Gear Vendors OD would be a nice addition a few years down the line.
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post #11 of 16 (permalink) Old Oct 8th, 02, 11:39 AM
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Your present driveshaft will probably be about 1" or so too long. The big block, 400 turbo combination sits about 1" further forward in the frame than a small block. So, if you use a small block with a 400TH on stock small block frame mounts, the engine/trans combo will be 1" further back in the subframe. You'll have to cut the mounting bracket off of the new cross member, and move it back and to the center of the car. I just went through this with my race car project, and ended up having a new driveshaft made with greaseless Spicer U-joints. I had forgotten about the driveshaft being shorter, and purchased a conversion joint for the original only to find that it was too long.
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post #12 of 16 (permalink) Old Dec 10th, 02, 01:08 PM Thread Starter
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UPDATE

Well I rebuilt the TH350 again myself. It was not that bad. Coan sells a rebuild kit with all the seals and Raybestos clutches in it for only $120. What a steal.

The oil pump was the main problem. I had it resurfaced when I rebuilt it the first time and the finish was not smooth enough to get a good seal between the plates. I also learned that the iuse of alignment pins when reassembling the two halves is important. I bought a new pump this time.

Clutch plates were fine except the low/reverse set. The direct drive plates were a little burned but not enough to cause a problem. On the low reverse set the inside teeth (the ones with the friction material) on one plate had half the teeth bent outward and had slipped on the drum. Bizarre. All of them were pretty black.

I got it all back together today and went for a quick ride. It shifts good and does not leak anymore. We'll see how it holds up next season.
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post #13 of 16 (permalink) Old Dec 11th, 02, 05:44 AM
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Glad to see you're on the road.

The best tool I found in the garage to align the pump halves is the worm gear clamps used in household duct work, at any Lowes, Home Depot, etc., and the right length or circumference.

The teeth bent back means that particular plate was not aligned with the rest of them when assembled.

Did you use synthetic fluid? Or, since you changed plates and steels, did you changeover to Type F fluid?

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post #14 of 16 (permalink) Old Dec 11th, 02, 06:27 AM Thread Starter
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I wonder if the teeth bent back problem resulted from me jacking around with the pump so much the first build. Input shaft end play was a real PITA to set up right, maybe one of the low/rev plates (this WAS the rearmost plate) "fell out" of position during one of the many de-install / reinstalls I did with the direct and intermediate clutch drums.

I use B&M Trick Shift for tranny fluid. Did not switch over to Type F. As I understand it, Type F has 2 main additives and Dextron has 3. The missing 3rd additive with the type F I've heard can cause varnish to build up and other probs. But that's just what I've heard.
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post #15 of 16 (permalink) Old Mar 25th, 10, 10:07 PM
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Re: TH350 trans - can they cut the Mustard ?

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Originally Posted by Eric68 View Post
Thanks guys.

So far my options:

1) Bruce built TH350 Cost ?
2) TCI built TH350 $700
3) TCI TH400 plus swap parts $900

I might have to go with the TCI TH350 or TH400 - shipping from CA would be killer. I still need to give him a call to find out.
Get the super street fighter 31005 or go with huges performance 35-1 they are big name companies that do more than just break down a transmissions and show you internal gear, they replace the parts with performance parts and they use kevlar. Id get a tranny from a reptuable place and get a cooler for the tranny as well... im not convinced with a 400 i just dont see it at all a TH-350 is a great tranny, i have invested in a 12 bolt rear end, correct ring and pinion i know my gear ratio etc and its really about getting the horses from the engine to the ground.

I have seen many use all sorts of trannys from a power glide, to a 350 to a 400 or even the 700r thus id stick with TCI or even Hughes, the regualr street figheter is less but truthfully id go with the super street figheter compare the parts they use to rebuild those cores.. what i like about hughes performance is out the gate.

Either way both are well known in the hobby and i wouldnt wantto pay 700-1k just to someyone that takes a core from their back junk yard and rebuilds them etc.. go with the repuatbel company they will cost maybe 300-400 more butthey are worth it.

it about helping others
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