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Removing rear engine crossmember
#1349111 Sat Mar 07 2020 04:58 AM
Joined: Sep 2019
Posts: 150
R
Shop Shark
Is there any danger of the frame "shifting" on my '50 3100 if I temporarily remove the back engine crossmember? It won't allow the space for installing an LT1 with a 4L60E tranny without modifications. Once I have the combo where I want it, I will reinstall it with the necessary modifications completed. I won't remove any other factory crossmembers.

Re: Removing rear engine crossmember
Rocket man #1349114 Sat Mar 07 2020 05:30 AM
Joined: Feb 2004
Posts: 20,351
H
Boltergeist
Just make sure the frame is well supported on jack stands and level when you remove the crossmember, and when reinstalling the modified part. You'll also need to fabricate mounting points for the mid-engine mounts and a crossmember for the transmission tail shaft, so the only purpose for the dropped crossmember at the bellhousing area is to prevent frame flexing at the spring mounts. If you're doing a butcher job on the frame to install independent front suspension, the frame is probably going to get distorted anyway, no matter how many precautions you attempt.
Jerry


The murder victim was drowned in a bathtub full of Rice Krispies and milk.
The coroner blamed the crime on a cereal killer!

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
Re: Removing rear engine crossmember
Hotrod Lincoln #1349138 Sat Mar 07 2020 02:34 PM
Joined: Mar 2004
Posts: 192
F
Shop Shark
Rocketman: removing and then modifying and then reinstalling that crossmember is certainly doable, however, I’ve attached photos of how I addressed that roadblock. I cut out the center of that crossmember and then fabricated a removable tie-plate of 1/8” steel to straddle that opening. Those are 1/2 inch grade 5 bolts (4 on each side) bolted into 1/2” coupler nuts bolted onto the flange at the bottom of that crossmember. That flange is plenty wide to accommodate the bolts. You can then also adjust the position of the tie-plate as needed to get clearance for the transmission oil pan. Good Luck, Dave

Attached Files
110A6F1F-F2E3-453E-8A8F-EC300A342E75.jpeg (179.04 KB, 276 downloads)
58F0A88A-56B6-4CCC-B6E2-B15DA03D4901.jpeg (178.98 KB, 281 downloads)
D138757C-D193-48A1-958F-D324D340340E.jpeg (166.67 KB, 263 downloads)

1948 5-window 3100 Chevy
327 V-8 TBI 700R4 Posi 3.73
"Old Blue"
In the Stovebolt Gallery
More pix on Flickr
Re: Removing rear engine crossmember
Rocket man #1349152 Sat Mar 07 2020 04:56 PM
Joined: Mar 2010
Posts: 9,223
5
Master Gabster
I'm not a mechanical engineer, but that crossmember connector design does not look to have the kind of support required along the lateral plane.
I am envisioning the bolt heads eventually shearing the metal of the stub end of what is left of the crossmember.
Your 1/8" plate steel should be able to withstand the shear forces inherent to this design, but the original crossmember steel is not as durable as plate steel.
There is a lot of support needed in this area because the spring perches are located in that vicinity.
Personally, I am not so sure that your design will provide that support.

Re: Removing rear engine crossmember
Rocket man #1349156 Sat Mar 07 2020 06:01 PM
Joined: Mar 2004
Posts: 192
F
Shop Shark
52Carl: I appreciate your comments, and granted, my modification is a compromise and not as preferable as the original design, but it has held up for the past 5 years and 5000 miles (I baby my truck). Plus, as you can imagine, removing the transmission is fairly easy (I switched out the 400 Turbo I originally installed in favor of a 4L60). If and when my arrangement fails, I guess I’ll consider further modifications. I just wanted to give Rocketman some ideas. What did you do? Regards, Dave


1948 5-window 3100 Chevy
327 V-8 TBI 700R4 Posi 3.73
"Old Blue"
In the Stovebolt Gallery
More pix on Flickr
Re: Removing rear engine crossmember
Rocket man #1349192 Sun Mar 08 2020 12:18 AM
Joined: Feb 2004
Posts: 20,351
H
Boltergeist
I would have put a couple of 45 degree bends in that plate with some gussets added, or made the stiffener out of 1 1/2" square tubing instead of creating all the stress risers with the bolts and spacers. Of course, I'm accustomed to building frames that survive dirt track racing conditions, where the rule of thumb is "Build it three times a strong as you think it needs to be, and don't be too surprised when it breaks"!
Jerry


The murder victim was drowned in a bathtub full of Rice Krispies and milk.
The coroner blamed the crime on a cereal killer!

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
Re: Removing rear engine crossmember
Flatblu4748 #1349215 Sun Mar 08 2020 02:34 AM
Joined: Mar 2010
Posts: 9,223
5
Master Gabster
Originally Posted by Flatblu4748
52Carl: I appreciate your comments, and granted, my modification is a compromise and not as preferable as the original design, but it has held up for the past 5 years and 5000 miles (I baby my truck). Plus, as you can imagine, removing the transmission is fairly easy (I switched out the 400 Turbo I originally installed in favor of a 4L60). If and when my arrangement fails, I guess I’ll consider further modifications. I just wanted to give Rocketman some ideas. What did you do? Regards, Dave

I was searching far and wide for the pics of what I did but could not find them. I am pretty sure that I posted them on this site.
Basically what I did was made my cuts in the same place that you did, but I cut them perpendicular to the ground. I welded plate steel drop plates to crosmember stub ends as well as to the ends of the cut out section of the crossmember.
I then drilled two holes in the drop plates for 1/2" bolts for easy installation and removal of center section.
This ended up giving me a 2" drop to clear the transmission. I can drop the oil pan on the transmission without removing the center section and it looks somewhat more like a stock setup and is very rigid.
As long as you continue to baby your truck and keep an eye on where your bolts go through your plate steel and the crossmember stub ends for failure, you should be alright.
Carl

Re: Removing rear engine crossmember
Rocket man #1349255 Sun Mar 08 2020 02:37 PM
Joined: Aug 2018
Posts: 33
1
Wrench Fetcher
I just had a buddy help me out with this. Added (4) 3/8" steel plates with heavy gauge hardware. Allows to slide the engine / trans in easy and simply bolt it back in. Pic attached.

Attached Files
rear bracket mod.jpg (245.07 KB, 164 downloads)

Mike

1952 -3100 with '54 235 Iowa farm truck "Cecil"
Re: Removing rear engine crossmember
1952Cecil #1349262 Sun Mar 08 2020 04:47 PM
Joined: Mar 2004
Posts: 192
F
Shop Shark
52Carl: I was able to find your picture that you referenced in your above explanation. I wanted the other Bolters to appreciate your effort....”a picture is worth a thousand words”. Carl, like you, “I’m not an engineer”, either, and everybody’s got an opinion....I’ll just leave it at that...

Attached Files

1948 5-window 3100 Chevy
327 V-8 TBI 700R4 Posi 3.73
"Old Blue"
In the Stovebolt Gallery
More pix on Flickr
Re: Removing rear engine crossmember
Rocket man #1349277 Sun Mar 08 2020 08:22 PM
Joined: May 2015
Posts: 2,367
K
Housekeeping (Moderator) Making a Stovebolt Bed & Paint and Body Shop Forums
I am a mechanical engineer, for what that's worth. wink
I like Mike's (1952Cecil) solution. Nice and stiff. Although it's not dropped that much.
Carl's has a couple of hinge points that would work better if stiffened up a bit. A couple of gussets from the frame side of the plate up to the original crossmember would help immensely.

Last edited by klhansen; Sun Mar 08 2020 08:23 PM.

Kevin
First car '29 Ford Special Coupe
#2 - '29 Ford pickup restored from the ground up.
Newest Project - 51 Chevy 3100 work truck. Photos [flickr.com]
Busting rust since the mid-60's
Re: Removing rear engine crossmember
Rocket man #1349284 Sun Mar 08 2020 11:00 PM
Joined: May 2005
Posts: 7,165
B
General Purpose
To your original question:
If I read this right. Truck has no motor or trans. You want to mock up a new motor and trans. If you intend to cherry pick sling/jack stand and block the new stuff in there to design the motor and trans mounts, you can remove the crossmember without any worries. You can design, build and tack weld (and maybe finish weld) the various mounts while motor and trans are mocked in place, if you wish as long as new motor/trans are not "loaded" onto the frame per se. You will want to measure the exact dimension between frame rails before removing the crossmember to observe any slight change afterwards. (probably none)

To the "new" crossmember phase:
I hope you are looking at those universal tubular motor and trans mount crossmembers. I like to use those.
Example1
Example2
Example3

Your idea of modifying the existing crossmember may need some engineering thought/advise. Not sure if you mean for the tranny or the motor. Modifying/dropping existing crossmember may not be advisable strength wise. Probably best to derivet the crossmember and use above linked or equivalent. I have used them several times on 55-59. 350's, 454's and TH350. If there is some special reason they won't work on AD, learn me. I have also used an existing crossmember with mods. I am a Mechanical Design Engineer FWIW, like Kevin. I would also probably go with Mike's deal. It has a lot of bolts and hard to design. If you want to hear why my linked crossmembers are cheaper, better, easier, faster, better looking and more accurate. Let me know. If you wish to do a modification to the existing, maybe I and others can help but would have to see pics/drawing of the idea. All of us are just giving you input. Only opinions.


I'm away on an ego trip. Will be back on Feb 30.
I'm not an Auto Mechanic, but I play one on TV.
I charge $0.02 for every opinion and I take Paypal.
Plan B is always better than plan A, by definition.


Re: Removing rear engine crossmember
Rocket man #1349386 Mon Mar 09 2020 07:39 PM
Joined: May 2005
Posts: 7,165
B
General Purpose
I see all these efforts for crossmember modifications. I read that the poster wants to make a temporary one to support the frame from "shifting". Not having a good look at the AD frame in person or what different motor/trans combos are contemplated, I am giving a general engineering opinion mixed with my crossmember experience.

It seems the issues folks are solving are:

1. Removal of original motor crossmember to allow a new motor/trans clearance. The removed member is near the rear hanger of the front leaf spring. Which, when removed, some believe would causes the frame to deform during operation and cause something to happen.
2. Adding/designing/fabing a (dropped for clearance) replacement for this crossmember to clear a new V8 and auto trans on their way back to a new support member.
3. Adding/designing/fabing a crossmember and support for a new transmision which is located at X distance rearward of the original.
4. Adding/designing/fabing a new motor mount for the V8 Mouse or Rat.

So the challenge is presented. Many ideas. Many designs. Many theories. Here's another batch of those from little ol' timid me.

1. The tubular crossmembers that are available are cheap, already fabricated to the approximate desired shape. Dropped. Universal. Few pieces. Boltable. Strong. Elegant. Adjustable. Not much fab work. No welding unless desired. They are crossmembers! Tubes are used all over hot rod suspension, roll bars, supports. Provides a strong one piece custom shape.

2. Some folks abandon the original crossmember and do not replace it. A "C" shaped channel frame is pretty strong. The side loads from a leaf spring hanger are not huge. If the new crossmember is strong and not too far away from the old crossmember, my engineering gut tells me everything will be fine. Some of the designs I have seen are not doing much. My first reaction was the same as Hot Rod Jerry's. No gussets. True, they have been used for years and no issues. That could be because they are just extra weight metal and have no function. I won't judge because I don't know for sure. The one's that are not carrying a motor or trans load, are not hurting anything.

3. If you want to replace the original because you feel it is necessary. That's fine. Derivet the entire old member and install a universal tubular crossmember. Either one for a transmission or one for a motor. Whatever has the best shape. Bolt it on. If the adjustable flange ends of those tubular crossmembers can be welded to the tube and the whole thing can still be removed, that's the best method. Maybe it would never have to be removed depending on the other clearances. I know it can be extreme pain to derivet the old crossmember. But schlepping onto the cut off part is not the right thing to do. Takes a lot of time and effort. Can't stick it up there, mark and mount it like you can a Universal Tubular. You have to measure, design, cardboard it, and keep testing, cut some pieces, tack it, clamp it up there, then final drilling and welding.

4. Use two more of those universal tubular crossmembers for the motor and trans.

5. Some builders are also changing to IFS. The leaf spring side load support issue goes away. If there is a IFS frame boxing requirement that interferes with a universal motor crossmember, work it out/mock it up.... or use a different motor-mount-to-frame part/design.

Contrary to popular belief, I am not a Cross Member.


I'm away on an ego trip. Will be back on Feb 30.
I'm not an Auto Mechanic, but I play one on TV.
I charge $0.02 for every opinion and I take Paypal.
Plan B is always better than plan A, by definition.


Re: Removing rear engine crossmember
Flatblu4748 #1350074 Sun Mar 15 2020 01:14 PM
Joined: Jan 2010
Posts: 109
J
Shop Shark
Originally Posted by Flatblu4748
52Carl: I was able to find your picture that you referenced in your above explanation. I wanted the other Bolters to appreciate your effort....”a picture is worth a thousand words”. Carl, like you, “I’m not an engineer”, either, and everybody’s got an opinion....I’ll just leave it at that...


That idea looks doable but I would've made my cuts at 90 degrees to the ground. Looks like these ar 90 degrees to the area cut.

If you cut 90 degrees to the ground and welded flat plate to each side of the cut, you would basically be able to move it up and down easily.

This is basically how the bigger trucks are set up.


1955 GMC 150, 1980 Chevy C10, 2011 Sierra 3500 HD SLT Duramax Dually Crewcab, 1960 Chevy BelAir 2dr sedan, 1978 Pontiac Trans-Am
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