Saginaw Tranny?

I have a '67 GTO rolling project that I believe was used for racing at one time, so the original engine and tranny were probably blown up long ago. It has a '69 400 block with #45 (8.6:1) heads, a 2.73 (!) open diff., and a Saginaw 4-speed with a 3.42 1st gear. With headers and an 800 cfm QJet, it is probably putting out barely 300 hp. My question is, until I decide what upgrades to do on the drivetrain (a 3.55 posi and M-20 at least), how much abuse can the Saginaw handle? It was professionaly rebuilt.  

I know you posted this several months back but wanted to give you my input.

I have a saginaw 4-speed that was rebuilt. I have been pretty rough on it at times but then again I do have a 3.55 open differential(wish I could afford to change that right now).

MySetup
'69 400- YS block if I remember right
62 heads
Performer RPM intake
Hooker Comp headers
HEI ignition
292 CompCam

Not sure of the exact hp or torque of this motor but I know it has good numbers factory. Anybody on here want to give me an estimate?

Everybody says it will not hold up, but it has so far. I don't drive it constantly though.

Nick  
400 YS, 62 Heads, 292 CompCam, Hooker Headers, HEI, PerformerRPM Intake

Thanks for your info. I know the Saginaw was generally used in lighter vehicles. I don't thrash mine too often, and it was rebuilt by a racing house in WI, so who knows. The one thing I like about it is that I've never had the shifter get jammed like the Muncie I had in my '68 LeMans used to do.  

'67 project,

I've struggled with the manual power question for years, and i think i've recently handcuffed myself to the muncie with a composite driveshaft that cannot be shortened.  it would be nice to have a piece-of-mind-number for your 4-speed, like tremec affords when it says it's box, so to speak, is rated to 650 torque, but i don't think you or I will ever get a solid answer for the muncie and saginaw.  i've decided to give up pursueing a number.  my recommendation is to look at the engines that were matched to the saginaw -- the more power your car makes, the more potential for the saginaw to break.  if you're not loading up the transmission with drag launches on that 2.73, the saginaw may handle torque for years.  not the answer you're looking for, i know.  regarding it being "professionally rebuilt"... have you ever taken a part your saginaw?  how could you put it together better than previously?  a typical manual rebuild kit comes with new wear components - minus gears, so i wouldn't consider your saginaw any stronger than stock because it was rebuilt.  If a transmission builder can weigh-in and tell me how to build stronger muncie's -- please do!  sorry for the vague answers, this is where i've arrived on this topic after 15 years of asking similar questions.

While this reply is here, can I piggyback a question about the linkage lockup?  I have had this problem on M21s and M20's, with old muncie's with broken in parts and with freshly rebuilt muncie's with new sleeves/forks/gears.  It seems this occurs most easily when trying to shift quickly, and is related to how fast one is on fully disengaging the clutch.  the linkage will pull to neutral with the slider still locked over the gear.  anyone know a fix to this?  

With new sliders and hubs I hope the springs and dawgs were replaced also, if not it's not really rebuilt completely and can hang up easy. Most of them that I have worked on did fine when the shift tower was clean and lightly lubed. A real important part that a lot people over look is the shifter bushings. New metal ones should always be installed at the first hint of a hang shift. These things need adjustment now and then too. To make them shift (Muncies) better we used to mix our own fluid. This was per synthic, which may not work?? We'd mixed 90 weight and automatic fluid 1 to 1 and added a pint of STP. Worked well for us. Saginaws are fine for daily driving but if you start yanking on them they won't last long. They put all the gears including reverse in the main case, less room for the bigger forward gears and the cases weren't as strong as Muncies. Maybe it's because of their iron case that won't flex as much as aluminum???? One thing I learned a long time ago is that brake shoes are a lot cheaper than sycros and clutches, don't down shift any of 'em except under mild conditions.  

Thanks Hammertime;

Something I just recalled on the Muncie lockup issue... A couple of years ago I was looking at an M21 after blowing up a Saginaw. It did not have a shifter mounted on it, and the guy was going to show me that the levers shifted in and out of gear, and guess what? One locked up. So I believe, as indicated by 65pmdgto1, that it is not a shifter issue, but an internal thing. This was a used M21 that had a mounting ear broken off and welded back on, so who knows what the internal condition was.

I don't thrash mine too badly. I THOROUGLY enjoy running it through the gears briskly but not harshly and listening to the beautimous sound of 400 cubes through 2-1/2 inch Flowmaster American Thunder duals, and open 2-1/4 inch Qjet secondaries.

YEAH, BABY!!  

Hammertime is right about the HP Muncie Vs. Saginaw. The general saw fit to install Muncies on anything over 250 HP. That's brake HP not net.  

If you drive it sanely you will be fine, but my buddy and I went through 3 of them in one summer in a relatively stock camaro. We were in high school back then and ran the *** out of that poor camaro. The good O'l days.  

i CAN ANSWER THAT QUESTION FROM FIRST HAND EXPERIENCe! One half ass burn out in my 68 firebird at a high school dance. When I bought the car it was pretty nasty and had a muncie m-21 in it . Well, the first day I drove it to school and did a burn out in the school parking lot ,all the teeth except 2 got ripped off first gear.Oh yeh, when i pulled the trans , it was full of saw dust' the bastard!)  I looked and looked for a muncie and it was summer time and everybody was cruising the hiway in their rods and I was clattering around in my 74 vega hatchback that topped out at 55mph. ( thats no B.S.)I couldn't find a muncie and the summer was passing me by and it was killing me. So , I found a saginaw and against some pretty wise advise I got it anyway. I babied it for about amonth and would slowly get into it and all was fine. But, the first time i dumped the clutch, Bam! It was ripped to shreads. Then i heard my favorite words from my dad, "I told you so"! I would wait, but that's just me. I would find a muncie or super t-10. You will not like having to replace the trans if something happens. You will be really bummed out. It would probably be fine depending on how you drive. But, if you romp and stomp occassionally I doubt it will hold up. It's ahard decision because I know you want to get out there in it. Good Luck,Dave