The Stovebolt Site Forums The Shop Area The HiPo Shop Rear engine mount for 235 w/SM420 transmission

Hello Stovebolt Family,

Finally getting to continue my 1951 chevy project. I will soon be installing a 235 engine with an SM 420 4 speed trasmission from a 1957 chevy pickup.

I do have the bell housing which has the mount locations but I'm trying to find the correct rubber mounts and if there are mount brackets or a crossmember that works to support the back end.

If no such hardware exists, can someone recommend what mounts match up to the housing and then I will fabricate my own custom brackets.

Thanks for the help.

Scott M.

My 54 Canadian gmc has the 235 with the 420 tranny it uses these mounts .

The picture did not work ,but they are a horseshoe looking mount that goes under the bell housing on both sides and hugs the crossmember there is a bolt that goes through it and another rubber piece that goes on the underside of the crossmember with a locking plate..The bolt screws into the bellhousing from the underside of the crossmember.

Scott 4 Chevy,

Do you have and are you planning on using the original 1951 bell housing???

If you are intending to use the 1957 bell housing that came with your 1957 235 and SM420, the mounts on that bell housing will not be a bolt in to the 1951 frame.

According to this page Parts Group 0.683 Housing, Clutch and Flywheel in the 1929-1957 Chevrolet Master Parts and Accessories Catalog, the bell housing for 1948-1954 do not interchange with 1955-1957. The mounting flanges and mounts themselves are different.

Others will most likely chime in here with additional information and suggestions.

Hope this is of some help.

You need to show us what is under truck now and where the bell housing mounts land in that space. Then we will find you the correct method/parts. The mounts Kevin speaks of are available if that turns out to be what you need. If your crossmember is not in the right place for the bell hsg mounts, there are several options. But first things first....... Pics pics pics....mock up mock up mock up!!!!!!!! Hang with cherry picker or block/jack stand the motor in there. Front clip off is best. See what's cookin' and sit back and think and wait for our suggestions.

Make sure pics area at correct distance to show everything clearly and well lit.

Example. Newer top. Older bottom.

If you get the casting number off the bellhousing, you can use the parts page Gdads51 provided to confirm what you are starting with.

Thanks guys for the information and I will try and send some pictures soon. Truck is outside waiting to come back in my garage to continue working. I was getting ready to order some parts and thought maybe to order mounts if I can get the right setup.

I have only the engine with the 57 bell housing and SM tranny and no other mounting hardware because the engine was pulled from another truck for an engine swap.

I did confirm I have the correct bell housing for the mounts to attach, I just don't know the part numbers or if any of it will align with the 1951 frame crossmember. If it does where do I get those attaching brackets.

Scott here,
Looking at the images Buoymaker sent above, I have the newer housing which makes sense and just need those U shaped rubber mounts and the attaching bolts provided it all lines up to the crossmember.

I thought I recall in reading various posts that this engine and transmission combination can be used in the earlier years like my 51.

Thanks again for the help and looking forward to your responses.

Scott

Your bellhousing in not correct for mounting to a 51 chevy truck. Here is a [LINK] for the rear engine mount and pictures of what the bellhousing should look like. The mount bolts to the side of the bellhousing shown in the second and third picture. Two bolts to the bellhousing and one bolt up under the crossmount.

Hi Phak1,

I agree I don't have the original configuration and that is why I'm asking if there is a way to make what I have work.

I don't want to go changing the bell housing, I would much rather make a custom bracket if necessary to tie in to the crossmember and use a rubber mount pad.

The way it appears at the end of the day is you need about a 1 inch thick rubber mount and a way to go from the crossmember to the housing.

If that already exists and I can just buy some parts great, if not I have access to a machine shop and can make whatever I need.

Thanks for the feedback.

Scott

Scott, please excuse my very crude cut-n-paste picture.
I think, and may be wrong, that your idea would raise the back of your engine by the thickness of your proposed rubber mount.
For sake of simplicity, most folks use the bell housing that fits the crossmember properly.

Agree to use a bell housing that fits the cross member.

If you were installing a V8, you could buy a new cross member.

I have a 1962 235 engine and a 1967 sm420. The bellhousing is the original 1954 one that came with the truck. Originally the truck was 6 volts, so the flywheel, starter and clutch are 1954. I'm not sure that a newer flywheel and clutch would fit my bellhousing. My point is that it all has to work together so choose carefully.

What happened to the original 1951 bellhousing? Your engine and transmission should work with it.

If you want to go the hybrid route, like modify existing cross member, swap in a newer cross member or fab a cross member.....maybe these parts will help with the brainstorming.

https://www.classicindustries.com/product/1956/chevrolet/belair/parts/tf800005.html

https://www.classicindustries.com/product/1956/chevrolet/belair/parts/tf800215b.html

https://www.amazon.com/MOUNTING-BRACKETS-CYLINDER-TRANSMISSIONS-BELLHOUSING/dp/B01MT5P40Q

https://www.ebay.com/itm/2312377636...foZY-dJq3QbhOYGjFRcLtSICFHhoCk5QQAvD_BwE

https://www.classicindustries.com/product/1959/chevrolet/truck/parts/14501.html

I know that you have your mind set on adapting what you already have, but there are plenty of correct bellhousing out there especially if you look at all of the SBC and LS swaps that have been done. Have you thought about the clutch linkage? What about the foot starter. If you are keeping that, you’ll have to adapt that too.

IMHO, post an ad in the “Truck Parts Wanted” forum for the correct bellhousing. I found a replacement for a cracked one on my ‘52 that way, shipped to my house.

If your still intent on adapting it, what Bartamos posted should point you in the right direction. Good Luck!

I forgot to mention that this original crossmember is also part of the structural integrity of the complete frame. Any alteration or removal needs careful consideration. It is riveted to the frame and adds solid support as the frame flexes. Also, if rivets are to be removed and replaced with bolts, there is a proper way to do this and it is described here on Stovebolt.

Thanks for all the responses.

I think my best option is to see exactly where the bellhousing aligns to my current crossmember.

If they align with one another, it would appear that the issue will be the need for a custom angled block to make the two mount surfaces parallel and the allow for a space for a rubber bushing.

If this doesn't align or appear to be more work, I guess I can always fall back to getting the original housing, assuming that the SM420 transmission will bolt up to it.

As mentioned one other hurdle will be to figure out the shift linkages.

I have taken many pictures over the last couple years of other trucks so I have some idea of whats needed. Plus I do have the assembly manual.

I'm hoping to have the engine installed by the new year. I have to paint the interior of the doors first and I just ordered a lower access panel I needed.

Wish everyone a Safe and Happy Holiday.

A SM420 4 speed will bolt up with a '47.2-'53 bellhousing. (The bellhousing style in your picture began in 1954.)
What shift linkages are you referring to? Isn't it a 4 on the floor?

I believe the cross members are in the same place, right at the back of the bell housing. Adding custom mount wedges and the rubber mounts will raise the back of the trans to where it might be into the floor.



Your SM-420 doesn't have any shift linkages...it's a floor shift.

Mike B

Phil said clutch linkage, poster said "shift". Could be talking about the same thing.

Scott has access to a fab shop, understands the situation and has taken the advice to mock it up to design what it takes. Unless he sells the BH he has and buys the BH he needs.

My mistake on the linkages, what I meant to say is the clutch components. I don't think I got a portion of those components when I purchased the truck.

The truck was in somewhat of kit form, only partially assembled and so not all components were installed and the engine and transmission was from another truck.

I guess I will see if the clearance to the floor becomes an issue when I do the installation.

Is your '51 a 3100 pickup or something else?

Are you using the original rear?

Mike B

Are we talking open or closed driveshaft?

The rear I'm installing is out of a 2012 Ford mustang because it has limited slip and disk brakes and was the correct width.

I also grabbed the driveshaft from the mustang in case I can make it work or I will get one made custom.

Pretty warm today in CT so maybe I'll crawl under the truck and do a quick check with the bellhousing.

Have a good day everyone.

Yes my truck is the 5 window 3100.

I'm leaving the outside original patina look and the engine bay, interior, and chassis fully restored.

Bart, Scott's post says," 235 engine with an SM 420 4 speed transmission from a 1957 chevy pickup". That would be open driveshaft.

I was able to crawl under the truck and put the bellhousing sitting on the crossmember. I took a measurement from the top of the transmission mount diameter opening to the floor and it is 3 inches. I then measured the transmission and I have about 4 inches to the top surface (not including the shifter area which sticks up higher).

In looking at the pictures from the earlier post it doesn't look like even changing the bell housing is going to get me any more clearance at the top. Both appear to line up in the same place just have different points they rest on. Even with my crossed configuration you are pretty much in the same spot.

I think this is partially a result of the original floor not being in place in that area and a flat steel plate sits in the center section of the floor.

Based on what I'm seeing, I have two options, I can cut an opening in the floor large enough to let the transmission have the clearance it needs (I was planning to have some center console anyway) or I can modify the crossmember and weld in some mount pieces so the bellhousing sits lower in the crossmember. There is sufficient clearance in the center to lower it the extra inch.

I have time to think about it and see what others say in their comments. Then once I get it back in the garage I will mock it up again and make a final decision what to do.


Just so everybody is clear on the origins of my truck and engine.

The truck was pulled out of a barn by the person I bought it from but the original engine and transmission were not useable. He had a friend with an original 235 with a SM420 in a 1957 that he was pulling to change for a small block and automatic transmission. That is how I ended up with the combination.

So far the project has been very enjoyable but mostly doing the grunt work of cleaning, fabricating, and painting. Now I'm at the stage where I need to make all the pieces come together and work.

I'm so thankful for all the expertise on this forum because I'm not sure I would be able to complete it all without the help.

Looking forward to your comments.
Scott

Reproduction transmission cover (picture). Notice the clearance for the shifter.

A 1950 216 and bell housing was originally bolted on the crossmember of your truck.
A 1957 235 will fit a/the 1950 bell housing.
A 1957 SM420 and 1950 SM420 are the same, except closed and open drive shaft connections and a few minor things.
If your 1950 was originally a 3 speed column shift transmission then you have to change the transmission cover when going to the 4 speed.

You need the 235 engine to be in the same position as the 216. Fan to radiator. Engine front mount. Carburetor fuel bowl float position.

If you modify the original crossmember you pass the point of no return in my opinion.

Originally Posted by buoymaker
Bart, Scott's post says," 235 engine with an SM 420 4 speed transmission from a 1957 chevy pickup". That would be open driveshaft.

Yes, I know. After reading this, my way of reminding him if his diff was older. Looks like that wasn't necessary.

"I thought I recall in reading various posts that this engine and transmission combination can be used in the earlier years like my 51."

Hi Buoymaker,

I do agree with you that I don't really want to hack up the current crossmember.

The other option I thought about is to just move the crossmember further rearward and re-attach it to the frame rails.

Then I can put a 1/4 thick flat steel crossmember under the bellhousing with a rubber cushion and make the correct angled mounts to bolt to my current housing. This will give me the ability to control the location height wise of the transmission so I can clear the floor and will give me a another crossmember making the frame even stronger.

I think this solves all my issues and will be the easiest to fabricate.

I can hold the new crossmember in with bolts and also weld in place.

ISTM that there is not a lot of space between the crossmember and the transmission. If the crossmember is moved rearward, you might not be able to slide the transmission in all the way up to the bellhousing. Too dark and cold for me to go out to the garage and check the clearance for you at the moment.

I guess if clearance is an issue with transmission installation, I can always just make the original cross member that I move rearward a bolt in crossmember.

This way if you ever need to pull the tranny you can just take the crossmember out.

The SM420 is very deep. The crossmember must be right under the bell housing. If it was moved rearward, it would interfere with the transmission.

You don't want or need to weld these cross members. They should be removable. There is no special procedure for bolting them on. Just drill and bolt. Gr 5 hardware. Obviously if the cross member already has holes, you use them to mark frame.
It seems the discussion is mostly premature to mock up. It will all be evident then as to what is best. Leave all things as they are until motor and trans are slung into approx location for the first time. You will take out and install several times. Your ideas are good.

I'm bowing out on this one. Good luck.

Thank you everyone for the responses. I think ultimately because of all the variables I'm dealing with I'm going to end up with a non-traditional installation.

The good news is my friend owns a machine shop and I can custom fabricate whatever I need to make it work for free.

I guess will see when I install the motor and bellhousing and just go from there.

Thanks again and hope everyone has a safe and happy holiday.

Scott

Scott -- As the owner and overall administrative head of this site and forum, all I can offer at this point is to kindly and gently point out that the gang has been sincerely trying to help you and save you frustration, effort and expense -- and quite possibly (we've seen it before over the last 27 years of running this site) project failure.

May I gently ask that you pause once last time to consider the advice given above (essentially just to find the correct bellhousing and use it) before you do anything you can't undo?

I do not have the experience that the guys above have, but I *have* done more than one restoration on these trucks. PLEASE listen to these guys -- they KNOW what they are talking about. If you still want to do what you seem intent on doing, we will still support you as best we can. But neither we as individuals nor Stovebolt.com will accept *any* responsibility for what happens -- if you go that route, you do so against our advice. We MUCH prefer to see you complete your project successfully and happily

Thanks,
John

Since this thread has crossed over to the HiPo Forum, I have moved it there.

Hello John,

I greatly appreciate the advice everyone has provided and I know there are many far more experienced people on this site than myself.

But I too have done a lot through my life and worked on cars/ trucks for many years seeing I'm now 53.

The main issue driving much of this is my current floor configuration is not all original. The floor had rotted out years ago and the original owner put a piece of steel plate across and welded it in place. The floor is nice and solid and I don't really want to start cutting that all up to put back to original.

That being said, the original bellhousing doesn't solve my problem. The floor will still cause interference with the top of the SM420 transmission and in fact I think would be worse with the old housing because it appears to sit up even higher on the crossmember. That would then require me to cut a hole in the floor for the needed clearance and would make the top of the transmission sit 1-2 inches above the floor in the cab. Maybe thats fine and I will go that route but I won't really know until after I have put the engine back in with the bellhousing attached.

I truly am very sincere when I say I'm thankful for everyone's help and I know I will have many more questions as I now get into reassembly. I also know that I will not be able to complete my project without the continued assistance from this great site and membership.

Have a safe and Happy Holiday John and members.