The importance of measuring bell housing runout.
The topic of bell housing runout has gained a lot of attention the last few years with the rise in popularity of the aftermarket overdrive manual transmission kits.
Years ago, I never heard of it, never heard of anyone even talking of it. I’d hear guys talk of clutch chatter, the transmission popping out of gear, hard shifting, noise and stuff but did not ever hear that any of those issues being blamed on the runout.
For those that haven’t heard, I’m referring to the relationship between the centerline of the crankshaft and the centerline of the transmission input shaft. When our engines and manual transmissions were first mated together, the story is that the factory put the bell on the engine and line bored the bell housing to the centerline of the crank. Any mis-alignment that may have existed was now corrected and would be eliminated….until you tried using a different bell housing.
I don’t have a lot of experience with Mopar manual transmissions but the ones I’ve had didn’t have any problems despite parts swapping without any regard for runout.
Now though, the companies offering these Tremec and other kits require proof of the measured runout to validate the warranty.
How close do you have to be?
Can you believe no more than .005” off center total.
Whuuut?
I’m a Carpenter…. All my life I dealt with framing houses and schools where if we were within 1/8 of an inch, we were good. (Kidding)
.005 now?? A human hair is wider than that, isn’t it?
I know a guy that didn’t measure his runout at all and his Tremec was fine. He beat on that car then sold it because he wanted to build a house and move out of the teepee he was in.
Yeah…..a teepee.
Back on point:
What is it about these new transmissions that the vendors require such precise alignment?
.005 is the limit for the SST kit. If you’re at .006 they won’t honor the warranty??
I did the dial indicator measuring of the runout twice in my car…. The first time WAS my first time ever. The second time was after I pulled and rebuilt the engine. It was a LOT easier with the engine out of the car.
Now I’m helping a FBBO member with his car and the initial number we got is over .080. That is.040 off center, more than a standard spark plug gap.
Correcting that could be difficult.
There are companies that make offset dowels to shift the bell housing around to align the bell to the crank but the available sizes are limited. Nobody makes a .040 dowel from what I’ve seen. SST suggests scraping any and all paint and crud from the mating surfaces of the engine block and bell. I’d be surprised to learn that it helps but it is a fast and no cost effort to try.
In the meantime….I’d be interested in opinions and comments on those that have dealt with unanswered transmission issues that may have been related to a misalignment.
Finally… how is it that automatics don’t have this issue?
Maybe they do.
It could explain cracked flex plates or leaky input seals?
The topic of bell housing runout has gained a lot of attention the last few years with the rise in popularity of the aftermarket overdrive manual transmission kits.
Years ago, I never heard of it, never heard of anyone even talking of it. I’d hear guys talk of clutch chatter, the transmission popping out of gear, hard shifting, noise and stuff but did not ever hear that any of those issues being blamed on the runout.
For those that haven’t heard, I’m referring to the relationship between the centerline of the crankshaft and the centerline of the transmission input shaft. When our engines and manual transmissions were first mated together, the story is that the factory put the bell on the engine and line bored the bell housing to the centerline of the crank. Any mis-alignment that may have existed was now corrected and would be eliminated….until you tried using a different bell housing.
I don’t have a lot of experience with Mopar manual transmissions but the ones I’ve had didn’t have any problems despite parts swapping without any regard for runout.
Now though, the companies offering these Tremec and other kits require proof of the measured runout to validate the warranty.
How close do you have to be?
Can you believe no more than .005” off center total.
Whuuut?
I’m a Carpenter…. All my life I dealt with framing houses and schools where if we were within 1/8 of an inch, we were good. (Kidding)
.005 now?? A human hair is wider than that, isn’t it?
I know a guy that didn’t measure his runout at all and his Tremec was fine. He beat on that car then sold it because he wanted to build a house and move out of the teepee he was in.
Yeah…..a teepee.
Back on point:
What is it about these new transmissions that the vendors require such precise alignment?
.005 is the limit for the SST kit. If you’re at .006 they won’t honor the warranty??
I did the dial indicator measuring of the runout twice in my car…. The first time WAS my first time ever. The second time was after I pulled and rebuilt the engine. It was a LOT easier with the engine out of the car.
Now I’m helping a FBBO member with his car and the initial number we got is over .080. That is.040 off center, more than a standard spark plug gap.
Correcting that could be difficult.
There are companies that make offset dowels to shift the bell housing around to align the bell to the crank but the available sizes are limited. Nobody makes a .040 dowel from what I’ve seen. SST suggests scraping any and all paint and crud from the mating surfaces of the engine block and bell. I’d be surprised to learn that it helps but it is a fast and no cost effort to try.
In the meantime….I’d be interested in opinions and comments on those that have dealt with unanswered transmission issues that may have been related to a misalignment.
Finally… how is it that automatics don’t have this issue?
Maybe they do.
It could explain cracked flex plates or leaky input seals?