Hi From Canada

N

Neil Mac

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Apr 15, 2020
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Hi from up North,

My name is Neil and I live in Calgary Canada. Current circumstance on hand I'm going to have some time to start in on a front end rebuild on my 1973 GMC MH. I'm looking for a recommendation on ball joints and bushings for upper and lower control arms. Virtually impossible to get information or parts up here but here is what I see on the internet:

Upper Ball Joints - Moog K 5238 a good choice
Lower Ball Joints - Moog K 6215 a good choice - not sure on this one could it be Moog K 6312 and would appreciate some confirmation here?
Bushing kit - which is prefered OEM rubber or aftermarket Poly Urethane ? What about the offset or eccentric bushings I am reading about for upper control arms - good or bad idea?

Any clarifications on the appropriate part numbers or recommendations on ball joints and/or bushing gratefully accepted.

Thanks all,

Neil
 
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Ball Joints:
Upper: Moog K5238
Lower: Moog K6215

Bushings:
Upper: Moog K7006
Lower: Moog K5222

The offset bushings for the upper are Moog K7104


I left everything stock. As far as polyurethane...some people like them. I don't. I figure it the originals lasted 45 years, then replacement rubber will outlive me. I'd rather have a better ride than more precise handling.

Welcome to the Forum.
 
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Before you go replacing the lower ball joints, check the Manual. IIRC it allows for .120 movement before replacement is recommended. That is 1/8th inch. Seems like a lot but no need to replace if less than that. Also, IF you do replace the lower joints, the 5/16" bolts that come with the new ball joint are wrong for this application. You need to use 3/8 button bolts, and there is a very specific procedure that you should follow to install them. Research it on the other forum, in the GMCphoto site and the GMC Motorhome information site. Lots to learn about before you go doing this.

GMCforum: GMCnet

For enthusiast of the Classic GMC Motorhome built from 1973 to 1978. A web-based mirror of the GMCnet mailing list.
gmc.mybirdfeeder.net
JMHO
 
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Neil,

Looks like others have answered your question.
I'm not sure how long you have had your GMC but I'm assuming your a newbie, so just some more GMC info here. The GMC Registry shows shows 25 coaches in the Calgary area.

If you haven't already, download the Black List. Its a list of GMC owners who will help other GMCer's in case of break-downs or just passing through for a coffee. Local GMCer's tend to be guys that are willing to help others.


This site is a good starting point for links to other GMC motorhome sites and info.

http://www.bdub.net/GMCLinks.html
 
Neil,

Good to meet you and I am glad that you found your way here. Between this and the forum over at GMCnet, you have just acquired a couple of thousand new old friends.

Now, 73 was not a good year for lower control arms. There was a maintenance directive to reinforce them and even if it was done, it might not be sufficient. I do know that the documentation for this is available at the major GMC websites, but I cannot tell you how to find it. Some will say that '73 cannot be saved, but mine had the job done and one still did fail at 175K miles.

About bushings. I replaced my upper (with two rebuilt lowers - it didn't to do those) and it takes a serious press to do the job. If you do not have access to one. order up the urathane parts. They are much easier to do.

On the way to doing all of that, at GMCMI is a procedure to inspect the front end that is very complete. Do that first as you may not have as much trouble as you thing you do if the steering box is off center.

Matt
 
Gentlemen,

Thanks very much for your reply as you have indeed answered most of my questions. The part numbers look to line up with the info I have collected so far and thanks for the clarification on the lowers being K 6215. I have been unable to find much about the 3/8" button bolts for the lower ball joints on the other sites except for the following comment: "Do yourself a big favor and use 3/8 hardware and when you're finished, spot weld the bolts" so any further technical detail on this application so I can do it right would be good. I'm going to look around for this control arm directive to make this correct as well and a shove in the right direction would also be good. I will probably have to farm out pressing in the bushings as I do not have access to a proper press in my backyard garage but I'm leaning toward OEM for ride quality - any comments here? Overall many thanks for your help and I'm going to get working on all this stuff.

Neil Mac
 
If you have GMC Motorhome Maintenance Manual X-7725 and X-7525A, go to section 3A-16 for instructions on ball joint checks and removing of ball joints. If you don't have these manuals, you should get them. Invaluable information in these. If you still have the original ball joint, it can be identified by the two large rivets holding the ball joint in place. There is no updated information on proper installation of the joints. If your lower joint exceeds the .125 spec and replacement is necessary, Follow the removal instructions in the manual. Then to install, clean up the lower A frame in the area of the ball joint looking for stress cracks. I am not versed on the particulars of the early (73-74) lower control arms and their weak points so maybe someone else can pipe in here on what to look for. For installing the new joint, there are 3 bolts holding it in place. One main large bolt and two smaller bolts on the ears of the joint. The new joints come with 5/16 bolts for the ears and are not up to the task for the Motorhome application. You will need to get two button bolts. See attached picture. The button bolts are 3/8" X 1 1/4" grade 8. Matt..if you are reading this, please correct me if what I remember is not accurate. The button bolt is necessary for the thinner head. Standard grade 8 bolts have a thicker head on them and will act as a stop when turning the wheels lock to lock. The steering was not designed to be stopped at the far reach left or right at the lower A arm. The stop is built into the steering box. When it reaches its left or right limit, the box is designed to bleed off hydraulic pressure, keeping it from hitting the A arm. If you put in a normal 3/8" bolt, the bolt head becomes the stop and hydraulic pressure of the power steering wreaks havoc on all parts in the steering system, especially the lower control arm. Button bolt heads are thin enough to replicate the rivet that was originally in there. Again, Matt correct me if my understanding is wrong. So with this in mind, obviously the nut will go on the inside. So, start by placing the ball joint in the lower A arm and bolt in place with the one larger center nut. Do not torque down yet. Bring the ball joint ears up tight against the A arm matching ears. At this point , I use a couple of Vice Grips to pull the ball joint against the A-frame ears. Then one at a time using progressively larger drills or a ream, drill the ear holes only large enough for the 3/8 bolt to lightly friction fit into the hole. Put the nut on and tighten. Move to the other ear bolt and do same procedure on it. At this point, some would tighten and spot weld in place. I choose to put a drop of red lock tight on threads and tighten to whatever torque spec is spec'd for 3/8 grade 8. (Sorry, don't know that) I just pulled it down to what felt right to me. Now, drop of lock tight on the main center bolt and tighten.

The lock tight or tack weld is necessary. We had a work rally last summer where one of our goals was to bring everyones coach in the shop and check the ball joint bolts. Every single coach that came in had loose bolts. Most were the smaller 5/16" bolts. We advised those owners to go home and change them out to the 3/8 buttons. At one rally, a coach came in with the new right front tire almost worn to the steel belts. Looking closer at it we found both 5/16 bolts had dropped out and only a few threads on the center bolt holding the ball joint in place. A disaster averted.
Hope this helps. (HTH)

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Thanks Gents,

Great information to get me going. I'm working on the upper A Arms now and will be taking the lowers off shortly - as soon as the last of the ice and snow goes. It looks like I will have to do the reinforcement work to the lower A Arms as they appear to be stock. Anybody know if there are some templates or schematics available for the reinforcement parts to be welded on to the lower A Arms?

Thanks for all the help!

Neil Mac
 
Go to the GMC photo site and search "lower control arm" or other similar terms. Here are a couple of them.
www.gmcmhphotos.com

Front end rebuild

These are the a-arms from the 75 parts Transmode that were removed to be reworked to go in the 74 (updated factory reinforcing)
www.gmcmhphotos.com
www.gmcmhphotos.com

73 reinforced lower A arms

Per the discussion in the forum in early September 08, I am posting pictures of A arms from a meticulously maintained coach (not my fault, just luck)
www.gmcmhphotos.com
www.gmcmhphotos.com

IMG_2216

Reinforced Lower Control Arm as per the Steve Ferguson system!!!
www.gmcmhphotos.com

Also go to the GMCnet forum and search similar terms. Here's one

GMCforum: Search for lower control arm reinforced

For enthusiast of the Classic GMC Motorhome built from 1973 to 1978. A web-based mirror of the GMCnet mailing list.
gmc.mybirdfeeder.net

Lots of information on those sites. I've been using them for 17yrs.
 
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Looks like I have loose 5/16" bolts on the passenger side. I got about a turn and a half on the nut on the stud that sticks up vertically. Now I guess I'll drill out to 3/8" and look for some button head 3/8"-24 bolts.
Is there enough room to put a Nord-lock washer under the heads?
 
No, do not put a lock washer under the head of the button bolt. Put the lock washer under the nut on the inside of the A frame. The lock washer is thick enough that it will raise the head and become the lock to lock stop in the steering. See my post from April 16, 2020 about proper install procedure.
 
LarryW said:
No, do not put a lock washer under the head of the button bolt. Put the lock washer under the nut on the inside of the A frame. The lock washer is thick enough that it will raise the head and become the lock to lock stop in the steering. See my post from April 16, 2020 about proper install procedure.
Click to expand...
Thanks, that's what I was wondering. Now I hope the hole in the control arm isn't too enlarged so that the head will actually sit ok. If not, I guess dig out the MIG welder and make the hole smaller again.
 
Looks like I'll have to order those 3/8"-24 screws. Fastenal won't sell them to me without a business account.
I tried three other industrial suppliers locally, nobody would order them.
Ordered them here, along with Gr8 plated nylock nuts: https://www.rjm-fasteners.ca/collections/length_1-1-4/products/vpbf-03012

With minimum order and shipping I'm getting six for $30CAD, tired of running around town, I'll wait for UPS
 
Mike Perez said:
Ball Joints:
Upper: Moog K5238
Lower: Moog K6215

Bushings:
Upper: Moog K7006
Lower: Moog K5222

The offset bushings for the upper are Moog K7104


I left everything stock. As far as polyurethane...some people like them. I don't. I figure it the originals lasted 45 years, then replacement rubber will outlive me. I'd rather have a better ride than more precise handling.

Welcome to the Forum.
Click to expand...
I can't seem to access the parts interchange on GMCMI (site looks to be under attack by hackers)
are these the same (current) part numbers for the 78' Royale?
 
Scotty,
These parts are the same for all of TZE production.
The parts interchange is on B'dub's website. It seem the GMCMI site is down, but that just looks like the server is shut down for some reason. Hackers usually have to post a brag.
Matt
 
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I have ordered all the ball joints and bushings with the exception of the K6215
I am getting discontinued, unavailable, no longer available, notify me when.,...
suggestions?
 
GMCMI Spring 2026 Rally
Applied GMC

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