transmission swaps

[20387774]

Have any of you CMP owners tried to swap your transmissions for one with synchromesh, like the GM SM420 transmission? How easy was your conversion? Were you happy with it?

John

[jim sewell]

Hi John
Yes the later chev truck trans can be fitted.
you would require the later bell housing to suit preferrably the one with the horizontal engine mounts .
Starter , flywheel , handbrake and clutch are ok.
The later trans may butt against the rear of engine crossmember so this will require altering ( bending or cutting )
The trans is also longer so on 4wd this will require a back to back uni joint and on 2wd a shortened tailshaft.
There does not appear to be any problems with this conversion as the SM 420 is a very robust simple trans.
Regards
Jim S.

[Lionelgee]

Originally Posted by 20387774

Have any of you CMP owners tried to swap your transmissions for one with synchromesh, like the GM SM420 transmission? How easy was your conversion? Were you happy with it?

John

G'day John,

I found this website about the SM420: http://www.novak-adapt.com/knowledge/sm420.htm

Also suggest you go to stovebolt.com which is one of the best Chevrolet restoration websites and go to their Tech Tips.

Kind Regards
Lionel

[Bob Carriere]

HI John

The tranny swap can be done.... the big problem is that the 420 is much longer and you will have to spend $$$ to get a custom made very short drive shaft to link up to the Transfer case..... or move the engine forward or move the T-case and cross member backward. The original CMP 4 speed is incredibly short by todays standards.

Some additional problems maybe encountered when you install the emergency brake lever... it will probably bolt right on but be in a different location that will not match the floor opening.

Which CMP model are you working on..... C15a would be easier than the C60 because of the different system for engaging the front axle which bolts on the tranny for the C60....

Bottom line anything can be made to fit if greased with enough $$$$$

I had original plans to install the 4 speed that came with my 261...fully synchro.... would have been a dream...... gave up and went back to the CMP tranny to avoid all the headaches...

Boob

[cletrac (RIP)]

I don't see why anybody would want to change them over. There's something neat about driving one of those old gear crunchers with their telltale noise and all.

[Yeo.NT]

I'd say if you are going to the trouble of changing the transmission go with a possibly easy route. Change everything (ie Engine, Transmission and Transfer case) I know of a 30cwt that runs a chevy 350 with a TH400.

[Matt Baker]

Gday,

I have a CCKW five speed gearbox fitted to my C15 radio van and it works great + it gives me a higher cruising speed which i haven't worked out yet due to no speedo drive, mind you it keeps up with jeeps ok.

[Phil Waterman]

This topic comes up from time to time, but one thing I always wonder about is the matching the ratios of the transmission and axles to the peak torque of the engine.

While lowering the engine RPM in 4th gear over the road for the original 216 engine is kinder to the engine, without and increase in power don't really think any of the bigger CMPs are going to travel faster.

Has anybody matched up the ratios of the different synchronize candidates?

I saved the transmissions and bell housings from the 235 and 261 cubic inch Chevy engines I have. Both are synchronized transmissions 4 speeds.

Briefly considered going the full engine and transmission transplants into the C60L and C60S but the list of modifications concerned me as some of them require modifications to the trucks which I didn't want to make.

As mentioned the bell housings for the synchronized is different, engine mounts different, clutch fork location different, and of course the short shaft would get even shorter.

Matt with the CCKW in your C15 Radio Van which engine are you running? I didn't think the CCKW transmissions were synchronize so the advantage in that swap is the 5th gear?

Cheers Phil

[cletrac (RIP)]

Any of those older trannys will be 1 to 1 ratio in high gear. You have to get well into the 1970s to get a five over. Ratios in the lower gears wouldn't make much difference with everything that slow speed. If you use a non Canadian military bell housing the clutch fork sticks out on the wrong side so clutch linkage would be a nightmare. Those old straight cut trannys will last forever so I can't see any reason to make the swap.

[Matt Baker]

Gday Phil,

As far as i know my engine is a standard 216 but i was told a while back that it could be a splash 235 because it has a TR engine number but i am not too sure of this?

Cheers Matt

[Phil Waterman]

David

I have had good luck in converting standard Chevy left hand bell housing to CMP right hand clutch fork. With extra CMP bell housings being scarce I needed to convert a US Chevy NOS housing to accept the right hand clutch fork location. While the conversion is not as easy as converting an original CMP bell housing to left hand, the original Chevy bell housing were cast for either side and only the machining determined which side.

To convert a bell housing for the other side it is just a matter of carefully drilling and tapping for the clutch fork ball stud and cutting out the side opening for the fork arm. Alignment of the ball stud is rather simple with a couple of center bolts and compass the location can be copied from a CMP housing. In my case I used the very tired and very cracked housing from my C60L. Cutting out the rectangle for the fork arm is done by carefully drilling each of the corners then cutting between the drill holes, careful cutting don’t go past your pilot hole to prevent a cracking point. So as to take up the strain of the ball stud I made a tapered washer so that the lip of the ball was flatly grounded all the around.

If anybody needs more details I’ll post better pictures.

[Phil Waterman]

More pictures

[hrpearce]

Or if you don't have the tools for a conversion leave the fork where it is and use hydraulics.

[Phil Waterman]

Hi All

Robert's point is a very valid option Hydraulic slave cylinder will work. And if a different engine and bell housing may be the only practical solution.

I would love to see how they handled the widespread conversion of Chevys to Ford engines in North Africa that is mentioned in one of Bill Greggs book.

Now back to Chevys bell housing conversion time involved is at most 4-6 hours will be one of the major savings over conversion to hydraulic. The tools necessary to covert a Chevy bell housing from right side to left side are relatively simple and are as follows and.

Tools
1. Measurement bolts with heads cut off and spun in lathe or drill press to mark the center of the bolt end these are then threaded through the mounting holes on the bell housing measure with a compass to transfer the location to the new housing.
2. Drill hand or drill press
3. Drill Tap of the correct size and thread for the ball stud
4. 3” masking tape to locate the left side fork port and mirror to the right side confirm corners by basic measurements.
5. Air cut off saw to cut between the holes of the lever port – alternate to drill series of small holes to insert saw blade (slower but works)

One other point if at all possible replace the clip spring in the fork that hold it on the ball stud, these are available from many antique Chevy parts houses. These springs get tired after 60 years. When the springs are tired they tend to allow the fork to pop of the ball stud, particularly while you are adjusting the linkage.


Cheers Phil

[Tony Smith]

Originally Posted by Phil Waterman

Hi All

Robert's point is a very valid option Hydraulic slave cylinder will work. And if a different engine and bell housing may be the only practical solution.

I would love to see how they handled the widespread conversion of Chevys to Ford engines in North Africa that is mentioned in one of Bill Greggs book.

Cheers Phil

Believe it or not, Ford actually distributed a conversion kit! It involved a stamped steel front mounting that replicated the Chev mount, and an adapter on the Ford integral bellhousing that mated to the chev gearbox, eliminating the Chev bellhousing and clutch arrangement. The early ones were cast steel (rarities these days), but were later popularly copied in alloy by Offenhauser, Cragar and others. I think more people should put Ford Flatheads in Chevs, it would make the world a nicer sounding place. Unfortunately, the trend these days is to replace the Ol' Flatmotor with crate GM 350, for which adapters are widely available.

[Lynn Eades]

Does this prove the Ford is better?
Mostly I wondered if the Bedford bellhousing is the same as the Chev one. Has anyone been down that track?

[Yeo.NT]

This should be posted with the Funnies but I'll make the stab at the Ford boys here

Q. What goes on pages 4-5 of the Ford's user's manual?
A. The train & bus schedule.

Q. What do you call a Ford at the top of a Hill?
A. A Miracle.

Q. What do you call two Fords at the top of a hill?
A. A mirage.

FORD ACCRONYMS

First On Rubbish Dump

Fix Or Repair Daily

Fixed On Race Day

Factory Ordered Road Disasters

Found On Roadside Dead

Flip Over Read Directions

Ford Owners Recommend Daywoo

Fast Only Rolling Downhill

Ford Owner Really Dumb

For Only Retarded Drivers

Freaking Only Runs Downhill

Failure On Research & Development

Found On Road Deserted

Forget Out Running Danie

F.cked On Race Day

Four Old Rusted Doors

Freaking Old Rusted Datsin

"Backwards" - Don't Ride Over Fifty

"Backwards" - Driver Returns On Foot

"Backwards" - Dumb Retards Own Fords

"Backwards" - Dorks Ride On Fords

[maple_leaf_eh]

Originally Posted by Matt Baker

Gday,

I have a CCKW five speed gearbox fitted to my C15 radio van and it works great + it gives me a higher cruising speed which i haven't worked out yet due to no speedo drive, mind you it keeps up with jeeps ok.

My sweetie gave me a dashboard mounted GPS reciever for Christmas. It gives a speed across the ground, which shows that my car speedometer is underreporting by a few km at 110kph.

[Lynn Eades]

I drive two Toyotas (not at the same time) and a Holden. All read faster than the gps.