MH Cabover frame rail

[snowman_w900]

Good evening guys,

 

I'm wanting to put air ride suspension and update my 1989 MH cabover. I found a very clean 2006 Mack CXN with CRDPC92/93 rears, 3:86 gears on Mack air ride. Cab is trashed, but the rest of the truck is great shape. 

Issue I'm having is frame rail height.  Has anyone ever added a newer Mack cutoff to an older Mack truck like im wanting to do?

I came up with this:

MH frame rail height 9.5" outside to outside

2006 CXN frame rail height is about 10.5" outside to outside

I'm trying to decide on how I need to do this other than buy new rails and drilling them. I'd like to use what I have.

 

I'm looking for opinions and ideas.

Edited June 17, 2020 by snowman_w900

[Maxidyne]

IIRC, the '06 uses a Volvo frame that's metric and a bit different in many dimensions, the MH frame, at least the back of it, is built to the old SAE dimensions. Probably be easier to bolt the rear assembly onto the MH frame rather than trying to weld on the CX cutoff.

[AZB755V8]

Sure, cut the old rails behind the cab after the fish belly about 3-4 feet past. Cut the new rails to slip over the old, splice should be about 3-4 feet. New rail should go right against the widening fishbelly. Top of new frame will be about 5/16 higher than before. Have enough room to bolt a crossmember at each end of the splice. Weld the end of each frame together. Have photos of this if you need, was done to my 88 Superliner. Old rails 9.5 new rear 10.5 high and can hardly tell it was spliced. Plus the wheel base was extended to 245" 

[snowman_w900]

9 hours ago, AZB755V8 said:

Sure, cut the old rails behind the cab after the fish belly about 3-4 feet past. Cut the new rails to slip over the old, splice should be about 3-4 feet. New rail should go right against the widening fishbelly. Top of new frame will be about 5/16 higher than before. Have enough room to bolt a crossmember at each end of the splice. Weld the end of each frame together. Have photos of this if you need, was done to my 88 Superliner. Old rails 9.5 new rear 10.5 high and can hardly tell it was spliced. Plus the wheel base was extended to 245" 

I really like this idea and I was wondering about where it widened towards the front if I could make it work....wow what a great idea you posted.

Would you mind posting as many pics of this as you can.  You can text them if that works better.

I really appreciate it @AZB755V8 !

[kscarbel2]

Actually, the cutting edge all-new chassis used first with the MH Ultra-Liner and later the RWI second generation Super-Liner was our first "metric" frame design. Naturally we used metric fasteners including "body bound" bolts as well.

https://www.bigmacktrucks.com/topic/42109-mack-frames-1989/

 

[Maxidyne]

Thanks for correcting me on that and posting the link, looks like even the back of the frame was a few hundredths narrower than the old 34" SAE standard.

[Ditchdiggerjcf]

On 6/17/2020 at 7:49 AM, kscarbel2 said:

Actually, the cutting edge all-new chassis used first with the MH Ultra-Liner and later the RWI second generation Super-Liner was our first "metric" frame design. Naturally we used metric fasteners including "body bound" bolts as well.

https://www.bigmacktrucks.com/topic/42109-mack-frames-1989/

About what year was that?

[kscarbel2]

4 hours ago, Ditchdiggerjcf said:

About what year was that?

The MH entered limited production in 1984. and the RWI arrived in 1985.

[Ditchdiggerjcf]

So my 86 RS will have the metric frame? How do I tell?

[kscarbel2]

27 minutes ago, Ditchdiggerjcf said:

So my 86 RS will have the metric frame? How do I tell?

No. You have an RS Value-Liner with an SAE frame, not an RWI Super-Liner with a metric frame.

[IH Farms 2]

Superliner frame to newer CH frame unknown year about 3 ft of double frame works great no issues after 3 yrs 

[Ditchdiggerjcf]

Wow, no glove or diamond shaped gussets? You are a brave man.

[terry]

1 hour ago, Ditchdiggerjcf said:

Wow, no glove or diamond shaped gussets? You are a brave man.

Looks like to me he slid the rails from one set of frames inside the other set of rails, then overlapped them, I have seen that done many times.    terry

[snowman_w900]

Definitely some good info here. I appreciate you guys posting this stuff. Sure does help on projects like this!

[AZB755V8]

This is how the frame splice turned out for my RW. It was done about 15 years ago and going strong.

Outside of frame front weld just ahead or rear fuel tank mount see crossmember just behind. Total double frame splice is 4 feet.

Rear of splice ends at rear edge of back crossmember and welded

 

Mid splice with frame bolts. There are a total of 12 bolts per side, 4 in each crossmember front and rear, 4 bolts mid-span per rail.

Front crossmember behind fuel tank.

This is where the splice would be on a MH about 4 foot in length.

Happy Splicing 

[Vladislav]

On 6/17/2020 at 7:49 AM, kscarbel2 said:

Actually, the cutting edge all-new chassis used first with the MH Ultra-Liner and later the RWI second generation Super-Liner was our first "metric" frame design. Naturally we used metric fasteners including "body bound" bolts as well.

https://www.bigmacktrucks.com/topic/42109-mack-frames-1989/

So far it seemed to me like not all the hardware used in MH frame was metric. Wonder which style of threads was used to attach Camelback stand or Neway brackets if airride was used. Neway was a vendor so the brackets could be pre-drilled SAE. 3/4 is equal to 19 mm but you have 18 mm or 20 mm of metric hardware.

[kscarbel2]

On 6/20/2020 at 4:04 PM, Vladislav said:

So far it seemed to me like not all the hardware used in MH frame was metric. Wonder which style of threads was used to attach Camelback stand or Neway brackets if airride was used. Neway was a vendor so the brackets could be pre-drilled SAE. 3/4 is equal to 19 mm but you have 18 mm or 20 mm of metric hardware.

Trust me......the MH chassis was 100 percent metric. This is the chassis that introduced the "AM" part numbers for metric fasteners. Previously, most fasteners had "AX" part numbers.

[ws721]

On 6/17/2020 at 7:58 PM, kscarbel2 said:

The MH entered limited production in 1984. and the RWI arrived in 1985.

Thought the MH came out in 81 at the end of the F models? 

[kscarbel2]

44 minutes ago, ws721 said:

Thought the MH came out in 81 at the end of the F models? 

No, after Macungie Cruise-Liner production ended. We had a partial first year of MH production in 1984. 
The initial production parts ramp up didn’t go well. Incompetence reared it’s ugly head.

[ws721]

47 minutes ago, kscarbel2 said:

No, after Macungie Cruise-Liner production ended. We had a partial first year of MH production in 1984. 
The initial production parts ramp up didn’t go well. Incompetence reared it’s ugly head.

Very interesting. Thank you

[snowman_w900]

On 6/18/2020 at 6:23 PM, IH Farms 2 said:

Superliner frame to newer CH frame unknown year about 3 ft of double frame works great no issues after 3 yrs 

I've been really thinking bout this idea. I've got the newer cut off. I'm preparing it now to get it ready to go onto the old MH rails.

Did you weld it on the ends or basically just bolt and cross member it? 

[IH Farms 2]

On 7/9/2020 at 11:32 AM, snowman_w900 said:

I've been really thinking bout this idea. I've got the newer cut off. I'm preparing it now to get it ready to go onto the old MH rails.

Did you weld it on the ends or basically just bolt and cross member it? 

I welded the ends but not the flange part plus bolted every thing 

[IH Farms 2]

You can see what I did in this picture 

[mrsmackpaul]

I have managed to miss this thread somehow

Whilst reading thru it I was "what dogs breakfast this will be"

I was pleasantly surprised at how neat the splice of different size rails was 

And I have no doubt after seeing the photos thats the way to go 

 

Paul