Missing Trans Crossmember?

[KEH]

Am I missing a transmission crossmember? I used to have a 250/3-speed and now have 350/4-speed. It looks like there should be a crossmember, but there is not one in my parts pile and can't remember taking one off. My floor shifter rattles, maybe this is why?

[cableguy0]

u saying theres no cross member at all under the transmission? if there isnt your asking for major trouble like the motor mounts breaking and the engine falling back not to mention bad driveline angles that will cause broken parts.

[CHEVYE]

yeah that could=kaboom time in the future. you can make a mount for these old trucks if you have to.

[KEH]

Ouch, that's what I thought. Is there a universal mount, or do I need to look for one specific to the 4-speed?

[mindhive]

You should have a one x-member under the oil pan that the engine and front suspension mount to and another under the bellhousing supporting the rear of the engine and the transmission behind it. On a factory truck you wont have one under the tailshaft like on an automatic. If your shifter is moving excesively your motor/trans mounts may be shot or maybe you just removed the trans mounts and not put them back in during the swap. They look like the pic below. Just my $.02.

Tim

[Brainchild]

You should have a crossmember like this one with a 4 gear in it.




Hope this helps

[KEH]

OK, I do have the bellhousing crossmember in Brainchild's photo, and of course the engine mounts. Thanks for replys. So there is not a crossmember that attaches only to the transmission?

[Brainchild]

Nope just the one that bolts the bellhousing in.

[Russell]

Shouldn't there be a crossmember near the end of the tranny, near the output shaft?

[kingsolver72]

This is exactly why I love this board.There is a vast amount knowledge and willingness to help.

[KEH]

Russell, that is my question. It just looks like there should be. There are a couple of bolt holes on the underside of the tailhousing.

kingsolver72, you are right, this board rocks! I would have never done as well on my truck without the guidance and inspiration that I received on this board.

[Brainchild]

No,just the one crossmember.The tranny is a newer model.The one in the wrecker has the rear crossmember,it's a 76,and has a huge PTO hanging on it.My 71,and 67,and even the 49 all have 4 speeds,and just the one crossmember bolted to the bellhousing.

[stickshift_or_walk]

KEH,

The factory solution for your '70 truck was the bellhousing crossmember pictured here,



or one very similar. The bellhousing crossmembers came on 3 speed and 4 speed trucks, and were slightly different depending on engine config - V8 or I6. Yes, it looks a little strange, but the tranny just hangs out the back.

So as mindhive and brainchild told you, you have all the parts that would have originally come on your truck, with no support at the rear of the tranny. Your vibration problem could be in bad motor/tranny mount pads, or a vibration from the other end. Since your driveshaft was probably modified during the swap from I6/3spd to V8/4spd, it could be out of balance, have a phasing problem (u-joints not mounted parallel at opposite ends), bad u-joints, or even a carrier bearing that's going out or gone.

Another possible source of the rattle is the lever itself - they have a tendency to break where the hardened tong is attached to the lever itself - it stays together, but will wiggle a lot more.

I've swapped 4spds into both 3spd and auto trucks, and preferred to use the auto tranny crossmember (mounts at the rear of the tranny) in both setups. I removed the bellhousing crossmember from the I6/3spd truck. You're right about the holes in the rear of the 4spd, they do work with the auto crossmember and the tranny mount pad.

FYI, later model trucks all came with the transmission crossmember at the rear, no bellhousing crossmembers.

SSOW

[sweet n rare67]

Correct, Your truck should only have and need the bellhousing cross member. However as i have found out, i you put in a car 4 speed or an M21 in my case an auto x-member can be used for support in the rear of the tranny. However this will not work with a truck 4 speed.

[KEH]

Stickshift, I will check your suggestions for the source of vibration. Thanks for the ideas. It has to be one of them. I do have a car 4-speed saginaw, and would think that a crossmember would help too.

[69_hafton]

Originally Posted by sweet n rare67

Correct, Your truck should only have and need the bellhousing cross member. However as i have found out, i you put in a car 4 speed or an M21 in my case an auto x-member can be used for support in the rear of the tranny. However this will not work with a truck 4 speed.

I'm planning on using a later model overdrive truck tranny - NP-A833 with the auto rear cross member and removing the cross member that supports the bell housing on my current 4 speed (granny gear).

sweet n rare67, I hope you were refering to the auto cross member not working with the original sm465(?) transmission?

[69ChevyLB]

Not trying to hijack the thread but do I need to modify my driveshaft when changing from a 3 speed Saginaw to an M21 Muncie 4speed?

[crazy longhorn]

Originally Posted by 69ChevyLB

Not trying to hijack the thread but do I need to modify my driveshaft when changing from a 3 speed Saginaw to an M21 Muncie 4speed?

Nope, your saginaw is the same lenght as the old M 20/21/22 Muncies. depending on what trans you get, you may have a clutch change(some were 1 1/8 X 26 spline input shaft), & your truck is 1 1/8 X 10 spline. the M 22 also used a different slipypolk (same as the 400 turbo). On your bellhousing. be aware that the centerhole is larger on the 68 & later trucks than it is on the cars.....you can opt for the 67 or early truck bell, or have a ring made to press over the front bearing retainer to get you proper the "center" on the trans. best of luck,crazyL

[69ChevyLB]

Thanks. Don't suppose I could just swap bearing retainers.

[KEH]

No, you cannot swap the retainers. I can't remember for sure why, but they look alike on the outside but there is something different inside. I tried that and also spent some time looking to have a ring made. End the end I just bolted up the bellhousing like it was and have not hade any problems.

[Willy Prost]

KEH, if you were able to locate the transmission with a 4.684 outside bearing retainer diameter with a 68-72 chevy truck bellhousing with 5.124in diameter retainer hole and you still got the tramsmission located to the engine crankshaft within 0.05in runout, you are one really lucky son-of-a-gun.

Everyone else will eiher need a pressed on spacer to make up the difference, or another bellhousing with the smaller bearing retainer diameter hole. This is necessary for the long term health and longetivity of your clutch, throwout bearing, throwout bearing retainer, transmission input shaft, input shaft bearings, etc.etc.


If you change bellhousings, you will then need to locate the new bellhousing to the crankshaft centerline to make sure the new bellhousing retainer hole is concentric with the engine crankshaft centerline.
_______________
Oh yeah, back to your original question. You could also use both the bellhousing crossmember and add a truck auto transmission crossmember to go under the rear of the car Muncie transmission.

Early Classic Industries make a truck auto transmission crossmember if you can't find an original one easily.