What fluid for the rear end of an 01 GT?

Mike97gt · Mar 2, 2006

well according to the 99 service manual it's always been 75-140. for years now ford has used 75-140 on ALL traction lok equiped cars and trucks.

some people like to use the 80-90 because it's very cheap compared to the synth stuff.

i can not remember any ford recently that uses 80-90 with a trac lok rear. ford used to have a 80-90 synth fluid years ago but thats obsolete now. you can't use non synth 80-90. i do know what i am talking about. i rebuild these things by trade.

SigmaPride · Mar 3, 2006

I guess it is possible they mis-printed the 99' car manuals(or at least mine). Since it does say it never needs to be replaced I figured it was synthetic, but then the manual calls for 80-90. Never made sense to me really. Still doesn't....

Thanks for the info...though.

SigmaPride · Mar 3, 2006

Alright...it makes some sense now. I talked to a guy in Ford parts and apparantly 99' GT with original factory rear-ends can use 80-90 because of what the clutches(trac loc I guess) are made out of. However, sometime after that they upgraded the clutches to kevlar, which requires the 75-140 synthetic. So, my manual is correct in the 80-90, but I actually had rear-end work done and probably have the newer kevlar clutches, but I am not sure. He said if uncertain then definately go with 75-140 as it won't hurt anything. He said a 75-90 synthetic would also be fine...just make sure it is a GL-5 SYNTHETIC.

Mike97gt · Mar 3, 2006

your parts guy is right. the old traction-lok cars used 80-90 but i thought they switched over before 99.

i get my info out of the online ford service manuals. ford don't want us using the paper ones for this reason. when they update stuff like this the paper ones are wrong. sometimes they change stuff like this a lot.

so this is a perfect example of this. once they update our online books, i would have to go to my work and find the old paper book to see that.

yeah if you use non synth 80-90 on the kevlar clutches it tears them up. for this reason if i am not replacing the clutches on one of these rears i still use 75-140 how am i supposed to know if the clutches were replaced with the updated ones without taking the taction-lok apart.

SigmaPride · Mar 3, 2006

I see what you mean...I was just always confused by the paper manual I have. Now I see why.

Given what you say I presume I have 75-140 in there since they replaced some bearing that was making noise in my rear about 4 years ago. It made a constant grinding noise from the rear end...I want to say pilot bearing is what it was, but not sure. I haven't changed the fluid since then which has been about 60k I think, so I'm banking that its synthetic. My uncertainty was part of the reason I was going to change it out, but now I'm pretty sure its synthetic in there.

The parts store here wants $20 per qt of 75-140...damn that is high. You can get Royal Purple for $10 qt, but I'm not sure I want to go with anything different.

Mike97gt · Mar 3, 2006

sigma if you have the stock clutches you can use whatever your book says. BUT at your mileage you should be doing a t-lok build soon.

ultrashock2112 · Mar 5, 2006

Sorry if I'm flogging a dead horse here... I have a 2000 GT and my manual says to use 80-90... I don't recall seeing a tag on the diffential while I was changing it last time. Would it be a good idea for me to switch it to 75W-140? Would it be okay to use 75W-140 it even if I have one of the diffs that was 'designed' for 80-90? Thanks..

Mike97gt · Mar 5, 2006

yes it would be ok for you to use the 75-140. but if you know your car has never had the traction-lok discs repalced then you can use a good 80-90 too.

sgarlic · Mar 5, 2006

My maintenance guide for my '04 also says not to change rear end fluid unless submerged in water or have reasonable belief of contamination.

ultrashock2112 · Mar 5, 2006

svttech76 said:
yes it would be ok for you to use the 75-140. but if you know your car has never had the traction-lok discs repalced then you can use a good 80-90 too.

hmm... I don't think the traction-lok discs have been replaced. I changed the fluid a while ago with just regular 80-90 gear oil, I didn't add any sort of friction modifier or anything. I went by my car's manual and my Hayne's manual, neither said anything about it! I hope I haven't f**ked up my diff!! What do you think I should do?

SigmaPride · Mar 6, 2006

I just changed over to Royal Purple 75w140 in my '99 with 102k yesterday. I'm guessing that I had 80-90 non-synth in there because I have no tag saying otherwise. It was very black, but smelled just like the new royal purple. I wasn't 100% sure since I had some rear end work done, which is why I went with the RP.

If you put in the 80-90, then you need to add some friction modifier. The royal purple has it already in there. I switched to the synthetic bc I don't want to change it for a long time...hopefully it doesn't mess anything up.

Mike97gt · Mar 6, 2006

you will be fine

ultrashock2112 · Mar 6, 2006

svttech76 said:
you will be fine

Mike, what about me?

ultrashock2112 said:
hmm... I don't think the traction-lok discs have been replaced. I changed the fluid a while ago with just regular 80-90 gear oil, I didn't add any sort of friction modifier or anything. I went by my car's manual and my Hayne's manual, neither said anything about it! I hope I haven't f**ked up my diff!! What do you think I should do?

Mike97gt · Mar 7, 2006

ultrashock2112 said:
Mike, what about me?

if you turn a really tight turn at slow speeds does the rear end make any noise. does it feel like it's grabbing? like a 4x4 on dry pavement

ultrashock2112 · Mar 7, 2006

svttech76 said:
if you turn a really tight turn at slow speeds does the rear end make any noise. does it feel like it's grabbing? like a 4x4 on dry pavement

No noises at all... Not sure about the 4x4 feeling because I've never driven one... The only thing I notice is that if the pavement is wet and I'm taking a turn and accelerating that sometimes I can feel one wheel spinning (I think the one on the inside of the turn).

kstng50 · Mar 8, 2006

OK so I have a 2000 GT with a 5 speed. I dont think the rear was ever rebuilt. The car has 59k on it and im getting 4.10s installed on monday. I went to get the 75w-140 gear oil today but it was like $15 a bottle. My question is i can get the royal purple gear oil for $10 a bottle but all that i can find is 75w-90. what is the difference between the two? isnt royal purple better to use but why dont they sell the 75w-140 in it? would i be alright to use the royal purple even though it is not the 75-140? also is $15the average price for 75-140 for other brands besides royal purple?

Mike97gt · Mar 8, 2006

ultrashock2112 said:
No noises at all... Not sure about the 4x4 feeling because I've never driven one... The only thing I notice is that if the pavement is wet and I'm taking a turn and accelerating that sometimes I can feel one wheel spinning (I think the one on the inside of the turn).

your traction lok is blown. you need to have it rebuilt.

kstng50 said:
OK so I have a 2000 GT with a 5 speed. I dont think the rear was ever rebuilt. The car has 59k on it and im getting 4.10s installed on monday. I went to get the 75w-140 gear oil today but it was like $15 a bottle. My question is i can get the royal purple gear oil for $10 a bottle but all that i can find is 75w-90. what is the difference between the two? isnt royal purple better to use but why dont they sell the 75w-140 in it? would i be alright to use the royal purple even though it is not the 75-140? also is $15the average price for 75-140 for other brands besides royal purple?

they make 75-140 royal purple use that.

DerekStangGT · Mar 8, 2006

Mike, first of all, we really appreciate your expert knowledge. that being said, i have a question. i just ordered some 75w90 GL-5 royal purple w/ the friction modifier. will i be ok on my stock rear end? its a 2000 with 45k miles and my limited slip has been shot for quite some time. its so bad that somtimes it slips hard in first, is that possible? it acts just like my clutch did when it went out and was slipping. thanks for the help

ultrashock2112 · Mar 9, 2006

svttech76 said:
your traction lok is blown. you need to have it rebuilt.

Great... If I floor it I don't get the "one wheel peel", do you still think it's blown? Would there be any benefit in trying the 75-140 synthetic anyway?

tomustang · Mar 16, 2006

how much fluid does the rear take?

What fluid for the rear end of an 01 GT?

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