"New" transmission - WOW

[Lobo'74]

I've had trouble with my stock clutch and stock 3 speed for the last couple of years. Sometimes it won't go into reverse, sometimes it will get stuck in first, sometimes it engages with a loud, metalic, "Thunk" that reverberates through the bed. Feels loose and sloppy. It turns out 3 or 4 fingers on the stock pressure plate were bent. My shop said they didn't even know how it was shifting at all in that condition.

Replaced the clutch with a Centerforce II and a new Centerforce II pressure plate. Found a racing shop up in Wisconsin that makes Saginaw trannys for street and circle track applications. Got a "one line" Saginaw 4 speed for street use from them. The "lines" refers to lines cut around the 10 spline input shaft for identification of the various ratios available. The "one line" ratios are: 2.54/1.80/1.44/1.00. They called it a close ratio, I have seen it described as a "wide ratio" in another site online. I know that Chevrolet put them in Camaros, Chevelles, and even in some Corvettes, It was the factory close ratio 4 speed unless the old "rock crusher" type Muncie was ordered. (according to various internet research sites).

My local mechanic said this one was stronger than a Muncie (I have some trouble having absolute confidence in that assesment) and the Tranny shop said the "one line" was as strong as a Muncie. I just know that a salvage Muncie runs $900 - $1000 and up around here (central VA), if you can find one, then you need to get it rebuilt. This rebuilt Saginaw transmission was $545. Put Royal Purple 75W90 fluid in it and got it and the new clutch installed.

Put in a new Hurst shifter. I picked the one that was closest to the hole in the floor for the existing Fenton (an OLD Hot Rod name) 3 speed shifter. Turned out the shifter for the '67-'68 Camaro was it. Shifter sits more towards center of the tranny tunnel than the old one, but not out of reach.

WOW. What a difference in driving. I just took it out on the highway for the first time (completed install two days ago, completed floor redo yesterday). Smooth, crisp operation of the clutch and the tranny. Drops a very consistant 1000 rpm each gear (may be a little off from 1000 exactly, but close enough for me). Exactly the operation I wanted. On top of that, much lower RPM in 4th than the old one in 3rd. Both were 1.00 to 1 final drive ratio, so it should be the same. Old 3 speed was 3000 - 3200 rpm at 70. "New" 4 speed is 2600 - 2700 at 70. Shoot, at 55 in 4th I'm under 2000 rpm. I figure the old clutch was so bad that the slipage there was a problem, and the solid grip of the Centerforce II delivers more power to the transmission, so lower RPMs at the same final drive ratio. This is with a 4.10 (or 4.11, not positive which) rear end, and 31" tires. My reasoning may be off, but thats my best explanation for the drop in RPM.

Can't wait to get the 450 - 500 miles Centerforce requires for break in before going full throttle. THAT shoud be a rush . . .

[Sinister]

Very cool, enjoy it...

[stllookn]

Nice job on the research to get what you wanted and it looks to be a great price on the tranny as well!

[airdale94]

I had a Saginaw 4-speed in a 2nd gen T/A that came out of a chevy something. It had 2 narrow (close together) and 1 wide (seperated from the other 2) parting lines. Was told it was a close ratio. Went on internet and it said the 1 line was the close.

The "close" means the 4 gear ratios are closer numerically. Less difference between gears.

And the "wide" have a greater difference numerically.

The close ratio Muncie with the 26 spline input shaft and large output shaft (same as the TH-400) is known as the "rock crusher", the Saginaw's don't even come close to it. The B/W "Super" T-10 that came in 75-79 T/A's and Z-28's is the closest you'll get. And they're bringing $500-$600.

[67_C-30]

They are pretty good trannys, and will last quite a while in a street vehicle. The However, they are no where near as strong as the Muncie. A 300+ HP engine on slicks will break them early and often!! The WOW factor over the 3 speed definitely malkes the swap worthwhile! Good job!

[Boog]

I replaced the broken 3 speed in my 78 stepside with a close ratio Muncie 4 speed I had been saving. It was an absolute bolt in. All splines were the same, same mount. All I had to do was cut the hole in the floor. It was in and out of the shop in under 3 hours. Sure made the little 305 more fun to drive. I would like to have tried a wide ratio in the same truck to see the difference. It might get a heavier vehicle moving easier. Glad your swap worked well for you.

[67_C-30]

Originally Posted by Boog

I replaced the broken 3 speed in my 78 stepside with a close ratio Muncie 4 speed I had been saving. It was an absolute bolt in. All splines were the same, same mount. All I had to do was cut the hole in the floor. It was in and out of the shop in under 3 hours. Sure made the little 305 more fun to drive. I would like to have tried a wide ratio in the same truck to see the difference. It might get a heavier vehicle moving easier. Glad your swap worked well for you.

The wide ratios get out the hole better, but kinda lay on their head between 2nd and 3rd. It's a tradeoff to which you prefer and how an engine is built. If you have a long duration cam that operates best at high PRM, a wide ratio with make it a slug in the midrange. A stock or mild cammed engine works pretty good with the wide ratio because the operating range is broader, even though they don't make peak power at very high RPM. Most of the late 60's -early 70's GTO's with 400's and 455's were faster with the wide ratio Muncies because they have gobs of low end torque, and the 2 - 3 shift didn't effect them like they did the solid cam 396's and 427's in Chevelles.

[BCOWANWHEELS]

if both trannys are 1 to 1 in high gear speed and rpm,s will be same in both trannys. only way to drop rpm,s is to have O.D

[Jim_PA]

Originally Posted by BCOWANWHEELS

if both trannys are 1 to 1 in high gear speed and rpm,s will be same in both trannys. only way to drop rpm,s is to have O.D

Exactly - I'm guessing his speedo is way off.

With 3.73's and a 1:1 4-speed, I'm turning 3,000 RPM's at 65mph with 295/50/15's (about 28" diameter). And my speedo is within 1 or 2 mph.

Glad you stuck with a manual trans though... way too many slush boxes out there

[Lobo'74]

I thought about the spedo gear being off, but in a 65 mph speed zone and my spedometer showing 65 I was staying up with the traffic around me.

The clutch/pressure plate I took out of it was slipping badly under acceleration - enough that it was very noticable. If it was bad under acceleration I figure it must have been slipping under load, and our trucks at 65 and above have an awful lot of frontal drag . . .

I am planning on checking out the spedometer in the next couple of days to take that out of the equation, but its a mystery to me. Like I said in my post, same final drive ratio SHOULD mean same rpm/speed regardless of 3 or 4 speed. Why the rpm drop when it initially appears my new spedo gear is correct is a mystery to me.

[Lobo'74]

Just got back from checking my speedometer. Checked against a new Audi (neighbor's) at 25, 35, 45, 55, 60, 65, and 70. Speedometer was right on the money at each speed. In 4th, 55 is 2200 rpm, and it goes up 200 rpm per 5 mph, up to 2800 at 70. Again, 31" tires, 4.10 (or so) rear end. Speedometer gear the shop put into the tranny was based on telling those figures to the transmission shop.

Althought it is a mystery to me, the three speed was 3000 to 3200 at 70. Only theory I have is: Since the rpm is read off the distributer and the mph is read off the transmission, a badly slipping clutch would mean higher rpm's to get the transmission turning at the "correct" speed for the mph. New, tight, high performance clutch with centrifugal weights on the fingers with NO slip turns the transmission at the correct speed without working the engine faster to get there through the slippage. Kinda like tires spinning on a slick road showing you are at 20 mph when you're not even moving...

Only explanation I have unless someone else has a better one.

I'm just happy with the smooth, positive shifts and more useful gearing. Much more fun to drive.

[Lobo'74]

Unless my tach is out to lunch with the rpm readings . . . Always a possibility I suppose.

[airdale94]

Here's a link I saw in the classifieds about Saginaw trans. Scroll down to the bottom. It looks like none were close or wide. Just different ratios.

http://www.dandltransmission.com/saginaw.html