Torque for '69 Differential Bracket?

[Bob B.]

Hi all,

Attached is a pic of my 1969 differential bracket. It is a Grade 8 bolt and the AIM specifies a torque of 55-75. I was shooting for 60, but I'm just not sure about that much torque on bushings as opposed to steel plate. Both upper and lower bushings are starting to smash down and I'm not even at 60, so I'm wondering if what torque I should really use??

Thanks,

Bob

[Joe L.]

Re: Torque for '69 Differential Bracket?

Hi all,

Attached is a pic of my 1969 differential bracket. It is a Grade 8 bolt and the AIM specifies a torque of 55-75. I was shooting for 60, but I'm just not sure about that much torque on bushings as opposed to steel plate. Both upper and lower bushings are starting to smash down and I'm not even at 60, so I'm wondering if what torque I should really use??

Thanks,

Bob

Bob-------


The bushings will compress. You are using stock-type rubber bushings and not urethane, aren't you? I'd go with 60-65 ft/lb.

[Bob B.]

Re: Torque for '69 Differential Bracket?

Joe,

These are poly. After seeing what 46 years did to the rubber, I didn't want a repeat.

Thanks,

Bob

[Steve G.]

Re: Torque for '69 Differential Bracket?

If I'm not mistaken, there is a steel bushing in the centre of the rubbers. The rubbers will only compress until the bushing is contacting the top and bottom washers and the torque is against the bushing.

You are right. If there is no bushing 70 ft lbs will just keeping tightening until the rubbers split.
Steve

[Joe L.]

Re: Torque for '69 Differential Bracket?

Joe,

These are poly. After seeing what 46 years did to the rubber, I didn't want a repeat.

Thanks,

Bob

Bob------


Personally, I would not even consider using polyurethane. The rubber will probably last you a lot longer than you're ever going to need it to.

[Joe L.]

Re: Torque for '69 Differential Bracket?

If I'm not mistaken, there is a steel bushing in the centre of the rubbers. The rubbers will only compress until the bushing is contacting the top and bottom washers and the torque is against the bushing.

You are right. If there is no bushing 70 ft lbs will just keeping tightening until the rubbers split.
Steve

Steve-----


Yes, there is a steel sleeve in one of the cushions. Both cushions have steel backing plates. The rubber compresses until the steel sleeve contacts the backing plate in the opposing cushion.

[Bob B.]

Re: Torque for '69 Differential Bracket?

Joe,

I have heard others who preferred rubber to poly also. What is the benefit of rubber and downside to poly?

Thanks,

Bob

[Joe L.]

Re: Torque for '69 Differential Bracket?

Joe,

I have heard others who preferred rubber to poly also. What is the benefit of rubber and downside to poly?

Thanks,

Bob

Bob------


The rubber used in these bushings has the correct durometer per the design specifications of the guys that designed the the car's chassis. Deviating from that, deviates from the design. The design of the polyurethane bushings is also usually different than the original bushings. The polyurethane bushings also cause more squeaks than rubber. As I mentioned, the rubber bushings are going to last a lot longer than you're ever likely to need them. So, why deviate from stock?

By the way, polyurethane has been around for a long time now. However, GM still uses mostly rubber in the suspensions of brand new Corvettes. If polyurethane is better, why don't they design that in to the suspensions of new Corvettes?

[Steve G.]

Re: Torque for '69 Differential Bracket?

Poly bushings are much stiffer than rubber which means they don't absorb as much of the vibration and noise as rubber, which is the whole purpose in using a rubber isolator.

Racing applications like them because they keep the geometry closer to the nominal values. Of no value in a street cruiser and even the racers are questioning the benefit.

I'd rather replace the diff isolators every 20 years than live with the added noise and vibration for even longer live span.
Steve

[Gary R.]

Re: Torque for '69 Differential Bracket?

We found some of the poly were made wrong and were too thick. Some of the rubber ones on the market didn't have the steel sleeve in them too. I run the correct rubber bushings in my street cars, for the track car we run solid mounts since the poly and rubber both failed.