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tremec t5 resonance

sloopy

sloopy

2-digit whp
Joined
May 25, 2020
Location
North Texas
I'm making this thread because I think this is a little different than the issue in the other thread (https://turbobricks.com/index.php?threads/b230-t5-3k-rpm-shake.352028/)

I recently did a t5 swap on my b230f powered 240. Incredible transmission. I'm loving the close gear ratios (2.95 first and 0.73 fifth) and I'm loving how fast I can shift this thing. I have noticed in lower gears that I have the infamous decel gear rattle around 2500-3000 rpms, but its not bad and doesn't bug me much because it's just a funny transmission noise.

What gets me is that there is an incredible resonance inside the car specifically in 4th and 5th gear. I need to drive the car again to really narrow down the rpm window, but I know that at 3000 rpms in 4th and 5th gear, the body of the car resonates and creates an awesome noise in the interior. I say awesome because it sounds really cool, but it's a very boomy and overwhelming noise which is not so nice to live with.

I'm using the stock 2-piece driveshaft modified to take the regular slip yoke. I used a yoshifab crossmember with a stock 5.0 mount and yoshifab engine mounts. I swapped the yoshifab engine mounts for some volvo 164 engine mounts which helped with vibrations at idle, but it didn't seem to do much if anything about the resonance. The next thing I was going to try was modifying an oem crossmember to mount the t5 since the oem crossmember has isolation where it mounts to the frame.

Has anyone dealt with this and solved it? Does anyone just not have this problem?
 
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i didn't want to just reply with "my car ain't do dat" but
Does anyone just not have this problem?
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I can't say that I do. Mine absolutely has the decel gear rattle from 3000-2500 rpm but otherwise it has no perceptible external-to-trans buzzing, resonances, or vibrations.
 
I have a sound like that on my cd009. kind of annoying, but it seemed to go away. I have a yoshifab driveshaft, but its not balanced to the other shaft.
 
When I had my T5, I made some rubber isolators out of 1/4" thick 50-60 durometer rubber, 2 layers thick that went between the body and the transmission crossmenber. I just remembered this, it was 2015 or so when installed it. Weed can be fun but it sure makes your forget stuff. The holes in the rubber were big enough for stacked large flat washers that helped locate the big holes in the crossmember. I wish I had a picture. Anyway it made that crazy noise go away.
 
esmth said:
i didn't want to just reply with "my car ain't do dat" but

I can't say that I do. Mine absolutely has the decel gear rattle from 3000-2500 rpm but otherwise it has no perceptible external-to-trans buzzing, resonances, or vibrations.
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What's your engine mount, trans mount, and trans crossmember setup like? Which slip yoke? It's good to know if other people are not having this issue.
 
VB242 said:
When I had my T5, I made some rubber isolators out of 1/4" thick 50-60 durometer rubber, 2 layers thick that went between the body and the transmission crossmenber. I just remembered this, it was 2015 or so when installed it. Weed can be fun but it sure makes your forget stuff. The holes in the rubber were big enough for stacked large flat washers that helped locate the big holes in the crossmember. I wish I had a picture. Anyway it made that crazy noise go away.
Click to expand...
So you had this resonance and it went away when you isolated the crossmember? I'm trying this asap.
 
It can be a good idea to isolate the cross member, but it depends on how the other components want to react. How does your cross member attach to the car? The cars I’ve been riding in that have very little transmission noise use a bushed tube and solid-ish poly trans mount, and hd motor mounts, along with a torque mount, so rotating flex is super limited and fore-aft is super limited via staggering chassis connections by 4-5”. In these cases they’re also not hanging the tail section out behind the trans-chassis connection. That ends up causing lots of tuning fork like things.
 
sloopy said:
What's your engine mount, trans mount, and trans crossmember setup like? Which slip yoke? It's good to know if other people are not having this issue.
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I have classicswede black poly engine mounts, a generic GM-style t5 poly trans mount I redrilled the tailhousing to accept. The STS t5/t56 crossmember, Spicer 2-3-8251X yoke, single piece coleman aluminum driveshaft, old style torque rods with poly, bne spherical tab, stock rubber front trailing arm bushing, stock shifter base. STS flat fw and non ic turbo clutch. I think that's it that matters.

I also want to clarify the car does make noises/rattles and isn't quiet nvh-wise like stock but nothing that I believe was created or exasperated by the trans swap. the 0.80 5th gear set whines when i give it the beans in 5th as the guy i bought it from said it would, the poly engine mounts rattle something deep in the dash at idle etc. but no booming or unbearable tuning fork resonations i guess.
 
also relating to the crossmember, i did notice the STS one is very bouncy while driving. I had originally thought it was the mounts flexing, but the shifter bounces up and down because the crossmember itself flexes... maybe that is absorbing some vibes? I have it bolted straight to the frame rails with new class 10 flange bolts.
 
cwdodson88 said:
It can be a good idea to isolate the cross member, but it depends on how the other components want to react. How does your cross member attach to the car? The cars I’ve been riding in that have very little transmission noise use a bushed tube and solid-ish poly trans mount, and hd motor mounts, along with a torque mount, so rotating flex is super limited and fore-aft is super limited via staggering chassis connections by 4-5”. In these cases they’re also not hanging the tail section out behind the trans-chassis connection. That ends up causing lots of tuning fork like things.
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My crossmember is bolted directly to the frame rails with no isolation. I wouldn't call it a transmission noise. More like the engine is resonating through the transmission and through the crossmember into the frame. What kind of torque mount setups have you seen? I know of the old ratchet strap and the sts machining torque mount. What's this about limiting fore-aft movement by staggering the chassis connections? I don't understand that or the last point about hanging the tail section out behind the trans-chassis connection.
 
esmth said:
I have classicswede black poly engine mounts, a generic GM-style t5 poly trans mount I redrilled the tailhousing to accept. The STS t5/t56 crossmember, Spicer 2-3-8251X yoke, single piece coleman aluminum driveshaft, old style torque rods with poly, bne spherical tab, stock rubber front trailing arm bushing, stock shifter base. STS flat fw and non ic turbo clutch. I think that's it that matters.

I also want to clarify the car does make noises/rattles and isn't quiet nvh-wise like stock but nothing that I believe was created or exasperated by the trans swap. the 0.80 5th gear set whines when i give it the beans in 5th as the guy i bought it from said it would, the poly engine mounts rattle something deep in the dash at idle etc. but no booming or unbearable tuning fork resonations i guess.
Click to expand...
esmth said:
also relating to the crossmember, i did notice the STS one is very bouncy while driving. I had originally thought it was the mounts flexing, but the shifter bounces up and down because the crossmember itself flexes... maybe that is absorbing some vibes? I have it bolted straight to the frame rails with new class 10 flange bolts.
Click to expand...
I would think that the flex in the crossmember and having it bolted directly to the chassis would be a recipe for resonance in the car. Besides the rattles and stuff, does the engine seem to resonate inside the car?
 
sloopy said:
My crossmember is bolted directly to the frame rails with no isolation. I wouldn't call it a transmission noise. More like the engine is resonating through the transmission and through the crossmember into the frame. What kind of torque mount setups have you seen? I know of the old ratchet strap and the sts machining torque mount. What's this about limiting fore-aft movement by staggering the chassis connections? I don't understand that or the last point about hanging the tail section out behind the trans-chassis connection.
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The torque mounts have been fabricated units that run from the head to a chassis point, strut tower or other position that gives the engine a 3rd point of contact. Spreading the vibration and another frequency to the chassis.

The trans crossmember being in front of the transmission output can create a tuning fork like point of resonance aft of the crossmember, so by taking say the driver side of the cross member and moving it’s attachment point to the chassis towards the rear of the car, the frequency of one leg of the tuning fork (chassis rail) differs from the other changing the resonance. What I have seen is the cross member is attached to the chassis rail on one side perpendicular to the rail at the point of the trans mount, then the other side goes aft about 4-5” and then makes a perpendicular connection to the chassis rail. By staggering the points of contact, it creates a polygon of mounting between the engine, transmission, and chassis of unequal distances, this does a couple things, it changes the limits of the amount of fore and aft movement, and changes the nvh frequency running through the chassis rails.
 
I would be inclined to measure the driveshaft/u-joint angles and pinion angle at ride height. could be the cause of drivetrain vibration.
 
CaseyHooligan said:
I would be inclined to measure the driveshaft/u-joint angles and pinion angle at ride height. could be the cause of drivetrain vibration.
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Yeah I just drove the car for the first time in a while and I'm sure it's driveshaft related. The noise really picks up around 40 mph, peaks around 50-55 with an unbearable ultra-bass resonance that rattles the loose bits in the car, then past 65 it turns into a really awesome sounding noise that isn't so intensely attacking my skull. The noise is not related to gear at all and is directly related to speed and persists with the clutch in or in neutral. 4th and 5th gears add something to the noise, but it seems unrelated. I'm going to check driveline angles and I'm sure I'm going to find that it's not good.
 
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