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During some "spirited" driving with a 71 big block, the front bracket where the differential ( snubber ) mounts to the frame separated.
I have a new bracket on order.
My question is regarding placement of the new bracket on to the frame.
With the front diff bracket removed, does the diff sit passively in place or is it tilted upward a bit?
My plan is to remove the old bracket, bolt the diff bracket to the diff, and then bolt the new frame bracket to the diff's snubber bushing.
I could then tack weld the bracket in place, remove the snubber bushing and then complete the weld.
Does this sound correct or does anybody have a better way of doing it?
Thanks
Can you see up where the diff cover bolts to the cross member , Is there any sign of distortion on the crossmember ?
Interestingly ,I just read a procedure for changing the pinion seal in a c3 that willcox wrote , he says to chock the front of the diff to prevent it going up when you remove the front bushing brace .
The welding procedure you mention is probably the only way to do it . Obviously you would put a straight edge across the bottom of the old one and measure distances up to the glass in a few places. It looks kind of pitted on the frame area inside the mount as well . Hope the steel can handle being welded
When I installed aluminum Dana 44 in my '73 I made a biscuit out of aluminum as shown below to locate the differential more precisely than using the rubber bushing. You might want to do the same.
You'll be doing just the opposite of what I did. I used the frame bracket to locate the differential. You will use the differential to locate the frame bracket.
Can you see up where the diff cover bolts to the cross member , Is there any sign of distortion on the crossmember ?
Interestingly ,I just read a procedure for changing the pinion seal in a c3 that willcox wrote , he says to chock the front of the diff to prevent it going up when you remove the front bushing brace .
The welding procedure you mention is probably the only way to do it . Obviously you would put a straight edge across the bottom of the old one and measure distances up to the glass in a few places. It looks kind of pitted on the frame area inside the mount as well . Hope the steel can handle being welded
That's one thing that worries me....how will I know how much to chock the front of the diff to get it in the right place?
Originally Posted by Kid Vette
When I installed aluminum Dana 44 in my '73 I made a biscuit out of aluminum as shown below to locate the differential more precisely than using the rubber bushing. You might want to do the same.
You'll be doing just the opposite of what I did. I used the frame bracket to locate the differential. You will use the differential to locate the frame bracket.
Any chance you still have that biscuit and want to lend it out?
I am not an engineer or such ,
if it was mine ,for peace of mind I would take the broken piece out of the rubber snubber unit and try and fit it back in the hole and see just how much it distorted before it popped out. It looks a clean break so I wouldn't worry too much about the rest of the mount being out at all .
Then do the measurement thing and maybe wait until you get the new one in your hand and compare them with a ruler so if there's any difference you can take that into account before you remove the original .
But somewhere along the way you would have to get the diff back UP to where it was .
Actually thanks for posting this , I will be doing more reinforcement on mine now
You may be over thinking the repair/replacement of the bracket. Your bracket separated from what appears to be rust compromised condition. It would appear all you need to do is, after clearing parts from around the bracket, cut it out with a cutoff wheel on a 4.5 inch angle grinder and then smooth the remaining welds on the cross member with a grinder.
Place the new bracket in the same place on the cross member as the old one removed and weld in place. With this done, the original parts with fit the same as from the factory. Forget trying to repair the separated metal, it is all thin metal and will burn through on welding. Once the new bracket is welded in place, you can experiment with a solid mount, but you can always go back to the rubber cushion. That is how I would do the repair, just hope the cross member is as solid as the new bracket.
The damage I see in the picture is usually related to someone having a poly or solid mounting bushing between the diff and the bracket. This is the main reason I do not support the poly rear snubber cushions.
When you repair this the main thing you need to be aware of... The positive and negative angel of the drive shaft. The rear negative should match the front positive.
Installing the bracket is not all that hard, you can use these pictures for locating the position. The top side pretty much is flush with the crossmember on the frame. If you need me to take some measurements, post back. I can't do that until Monday but I'd gladly do this if you need it.
Willcox
Last edited by Willcox Corvette; Jul 29, 2017 at 12:21 PM.
The damage I see in the picture is usually related to someone having a poly or solid mounting bushing between the diff and the bracket. This is the main reason I do not support the poly rear snubber cushions.
When you repair this the main thing you need to be aware of... The positive and negative angel of the drive shaft. The rear negative should match the front positive.
Installing the bracket is not all that hard, you can use these pictures for locating the position. The top side pretty much is flush with the crossmember on the frame. If you need me to take some measurements, post back. I can't do that until Monday but I'd gladly do this if you need it.
Willcox
To get the angles right I assume you do it by eye?
As long as it's close I think I should be OK
The snubber was rubber, not poly, but the bracket was thinned out due to rust
To get the angles right I assume you do it by eye?
As long as it's close I think I should be OK
The snubber was rubber, not poly, but the bracket was thinned out due to rust
To check the angel, you'll need a protractor... Measure the angel on top of the drive shaft at the yoke, measure it on the bottom at the diff yoke... they should be the same. I think if you just use the pictures I sent you as a guide you'll be fine. The top of the bracket pretty much defines where the bracket goes.
Not to highjack the thread but why would a poly bushing fail and pull thru before a rubber bushing?
Would it make sense to add a 1/8" plate to either the bottom or the top of the new bracket to prevent pull thru?
If you have the means as in a welder and some fab equipment I would build the bracket out of 3/16" CRS with bigger flanges to really burn some welds into the cross member.
Not to highjack the thread but why would a poly bushing fail and pull thru before a rubber bushing?
Would it make sense to add a 1/8" plate to either the bottom or the top of the new bracket to prevent pull thru?
If you have the means as in a welder and some fab equipment I would build the bracket out of 3/16" CRS with bigger flanges to really burn some welds into the cross member.
Just my .02.
The rear cushion is supposed to have give and flex, it's an inherit design of the car.
When you replace the rubber cushion with a poly you will lose the give and something has to make up for it.
I've posted pictures on this forum over the years of cars where the rear snubber cushion bracket has been torn away from the cross member due to these poly bushings.
Willcox.
Last edited by Willcox Corvette; Aug 1, 2017 at 01:02 PM.
Differential To Frame Bracket
