8HP90 Install help needed

[1moretoy]

Hey all, I'm installing my trans and having a slight issue. As I jack up the trans into the tunnel it pushes slightly to the pass side and starts to hit the brace. Does anyone have any suggestions on how to fix? Running RMS front K member 1" forward mounts. Using holley trans crossmember and 8HP90 adapter plate. Everything fits great except this issue. You can see in the photos that when lowered it is somewhat centered. Then when I jack it up it starts shifting to the pass side.

If anyone has some suggestions I'm willing to try. I knew everything was going to smooth to be true.

 

[scar426]

Hey all, I'm installing my trans and having a slight issue. As I jack up the trans into the tunnel it pushes slightly to the pass side and starts to hit the brace. Does anyone have any suggestions on how to fix? Running RMS front K member 1" forward mounts. Using holley trans crossmember and 8HP90 adapter plate. Everything fits great except this issue. You can see in the photos that when lowered it is somewhat centered. Then when I jack it up it starts shifting to the pass side.

If anyone has some suggestions I'm willing to try. I knew everything was going to smooth to be true.

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maybe could try loosening the motor mounts, then raise the transmission and see if it still pulls to the right. (might be bound up a bit) Also the transmission mount might help pull it back over to the left when installed, but again I would loosen the motor mounts first. Dos Centavos.

 

[pschlosser]

Will it move back to the left if you give it a good shove? Since you're jacking from the right side, I'm wondering if the jack is partially to blame for the pull to the right. Presuming the exhaust is not hooked up, and the engine pivots at just two points on the K-frame, I agree there is little reason or force for it to pull to the right. Does it still go to the right jacking up from the left side? Be observant, and look for any obvious physical obstructions.

 

[PLUM_72]

Did you trim away some of the tabs and bosses on the case that are known to interfere? I've seen plenty of pictures of the areas to trim on the 8HP70 (Attached), but not the HP90.

 

[1moretoy]

Thank you all for the prompt responses. I spoke with Bill this morning and as mentioned above he said to loosen the motor mount bols and install the trans mount. Then tighten everything together.

I did grind down the tabs towards the front of the trans and folded (hammered) the pinch weld down. I'll see how close the rear tabs are from hitting. I also noticed the vent tube is hitting the pinch weld where I folded it over. I need to figure out a solution for that as well.

 

[scar426]

Thank you all for the prompt responses. I spoke with Bill this morning and as mentioned above he said to loosen the motor mount bols and install the trans mount. Then tighten everything together.

I did grind down the tabs towards the front of the trans and folded (hammered) the pinch weld down. I'll see how close the rear tabs are from hitting. I also noticed the vent tube is hitting the pinch weld where I folded it over. I need to figure out a solution for that as well.

 

[scar426]

the solution I had to come up with, lol. not the best, but functional and did not have to cutout the entire tunnel

 

[1moretoy]

Ok, I may have found a solution. Loosening the motor mount bolts didn't really help much, but....

Gforce makes a short/low profile trans mount that will get me some added clearance. It measures 1-3/8 installed height where as the standard GM mount is 1-7/8. This will drop the tailshaft down enough to where is doesnt start shifting to the side while keeping the tailshaft at 3-3.5 degrees down.

I will have to clearance the cross member and support bracket slightly but shouldn't affect anything structural wise. I would just need to fishmouth the crossmember a little to clear the tailshaft bracket.

What are your thoughts?

 

[scar426]

Ok, I may have found a solution. Loosening the motor mount bolts didn't really help much, but....

Gforce makes a short/low profile trans mount that will get me some added clearance. It measures 1-3/8 installed height where as the standard GM mount is 1-7/8. This will drop the tailshaft down enough to where is doesnt start shifting to the side while keeping the tailshaft at 3-3.5 degrees down.

I will have to clearance the cross member and support bracket slightly but shouldn't affect anything structural wise. I would just need to fishmouth the crossmember a little to clear the tailshaft bracket.

What are your thoughts?

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yeah I'd say a little clearancing will be ok and so long as your pinon angle and Tali shaft angles still look good, go for it. but do keep in mind, the crossmember bracket is part of the torsion bar structural member, so don't clearance too much, as it could create a weak spot/flex point there.

 

[pschlosser]

I'll see how close the rear tabs are from hitting.

I concur. DO CONFIRM there is adequate clearance (1/4-inch) in all areas around the transmission and floor pan-hump, once the transmission cross member is bolted in place, and the engine mounts torqued to spec.

Otherwise, you're going to feel and hear road noise transmitted to the chassis.

 

[SFEbody]

3-3.5 degrees of slope to the trans will result in a less than acceptable pinion angle to the drive shaft. try and stay within 2.5 degrees. You may not like it but you are going to have to cut the crossmember out to get the front driveshaft ujoint to clear. It's not just the round monut on the 8HP90 that you have to worry about trustme on this one as I have been there.

 

[1moretoy]

3-3.5 degrees of slope to the trans will result in a less than acceptable pinion angle to the drive shaft. try and stay within 2.5 degrees. You may not like it but you are going to have to cut the crossmember out to get the front driveshaft ujoint to clear. It's not just the round monut on the 8HP90 that you have to worry about trustme on this one as I have been there.

What did you do to reinforce the crossmember after you cut the hoop out?

 

[SFEbody]

What did you do to reinforce the crossmember after you cut the hoop out

What did you do to reinforce the crossmember after you cut the hoop out?

Hooker makes an upper steel reinforcing loop that fits with the new crossmember. It is 5/16 steel and really strong. Hooker Headers BHS578 Hooker Blackheart Transmission Crossmember Hoops | Summit Racing

 

[1moretoy]

Hooker makes an upper steel reinforcing loop that fits with the new crossmember. It is 5/16 steel and really strong. Hooker Headers BHS578 Hooker Blackheart Transmission Crossmember Hoops | Summit Racing

I thought about that and purchased one for a B body since they don't make one for the E Body. Unfortunately the holes don't line up with the Crossmember. Did you have to drill new holes for that? I was thinking about doing that on the one I have.

 

[SFEbody]

I thought about that and purchased one for a B body since they don't make one for the E Body. Unfortunately the holes don't line up with the Crossmember. Did you have to drill new holes for that? I was thinking about doing that on the one I have.

I did modify the holes.. not a big job maybe 5 minutes

 

[TripleBlk70]

Regarding pinion angle: the key is making sure your angles are parallel, and if you do that 3-3.5 degrees should be fine (second image in the drawing below).

Based on what you're saying, I'd get the engine/trans mounted and set, then measure the angle and see how that compares to the rear axle side. If it doesn't match, you need to address it or you will have a driveline vibration.

If you have a standard leaf spring setup in back they make angled shims you can use to match the back side angle with the engine side.

I went through this process with my last build which happened to be a 55 chevy that had (old style) front motor mounts and bellhousing type trans mount. Starting from scratch to place the engine/trans mounts and getting the angle right was a little intimidating but I made it happen. The rear end had no spring perches, so I had to locate and weld those too. Happy to say I got the angles right and the car goes down the road @ 80mph with no vibrations.

 

[Buckminster]

Ok, I may have found a solution. Loosening the motor mount bolts didn't really help much, but....

Gforce makes a short/low profile trans mount that will get me some added clearance. It measures 1-3/8 installed height where as the standard GM mount is 1-7/8. This will drop the tailshaft down enough to where is doesnt start shifting to the side while keeping the tailshaft at 3-3.5 degrees down.

I will have to clearance the cross member and support bracket slightly but shouldn't affect anything structural wise. I would just need to fishmouth the crossmember a little to clear the tailshaft bracket.

What are your thoughts?

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Thanks for sharing this. I haven't dropped mine in the car yet, but I purchased the holley stock mount in anticipation of dropping it in when my car returns from the body shop.

 

[1moretoy]

Thanks for sharing this. I haven't dropped mine in the car yet, but I purchased the holley stock mount in anticipation of dropping it in when my car returns from the body shop.

You can see where I clearanced the crossmember and bracket that attaches to the trans. This and the shorter mount should work out perfectly. I also found a 1" mount I could use with shims if necessary. The 1-3/8 mount should be here tomorrow hopefully.

 

[1moretoy]

Ok, I received the short G Force trans mount today. The mount is wider than a stock GM style so I had to offset it a tad. I basically slotted the holes a little for added adjustment. Everything is bolted in with plenty of clearance. I have about 1/4" clearance on each side and plenty around the tunnel now.

The tailshaft is exactly 2.5 degrees down.

 

[ItsJustMe]

Ok, I received the short G Force trans mount today. The mount is wider than a stock GM style so I had to offset it a tad. I basically slotted the holes a little for added adjustment. Everything is bolted in with plenty of clearance. I have about 1/4" clearance on each side and plenty around the tunnel now.

The tailshaft is exactly 2.5 degrees down.

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Very nice! Do you have a link to the mount you used? The Gforce website isn’t very user friendly.