GM Synchromesh transmission fluid question (Page 2/4)
Vintage-Nut DEC 24, 10:32 AM

quote
Rsvl-Rider:
GM Synchromesh fluid, as is highly recommended by so many on the forum. / Different labels, but both labels have the same part number "10-4006" / Did I get the right stuff???



To answer your question, yes!

I believe There are 2 types of GM Synchromesh fluids; Standard and Friction Modified

You brought ACDelco 10-4006 which is 'Standard'

The bottle also has (GM) 88900333 on the label which is a SAE 75W-80 Synchromesh Transmission Fluid.

BTW - Some members also suggest adding a 4 oz. bottle of ACDelco 10-4003 / GM 88900330 which is a "Limited Slip Axle Lubricant Additive" to the GM Standard Fluid if your Getrag/Muncie which has the ‘rattle’ of the unengaged gears.

{EDIT}

quote
82-T/A:
what does the LSD additive do?



I learn that the additive is also known as Friction Modifiers to reduce unwanted noise and wear.

The other GM Fluid is Synchromesh - Friction Modified which is part number 88900399 or ACDelco 10-4014.

I found a thread on 'Bob Is The Oil Guy' forum that discusses the difference between standard GM Synchromesh and Synchromesh Friction Modified which have the same viscosity. According to the forum, both fluids are 'Friction Modified', however the Friction-Modified version dosage has 5% more and has a friction additive for LSD clutch packs that require a GL4 fluid. The standard fluid lacks the friction additive.

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Original Owner of a Silver '88 GT
Under 'Production Refurbishment' @ 136k Miles

[This message has been edited by Vintage-Nut (edited 12-31-2023).]

82-T/A [At Work] DEC 24, 01:48 PM

quote
Originally posted by Vintage-Nut:

To answer your question, yes!

I believe there are 2 types of GM Synchromesh fluids, and you want ACDelco 10-4006

The bottle also has (GM) 88900333 on the label which is a SAE 75W-80 Synchromesh Transmission Fluid.

BTW - Some members also suggest adding a 4 oz. bottle of ACDelco 10-4003 / GM 88900330 which is a "Limited Slip Axle Lubricant Additive".





Vintage nut... what does the LSD additive do? I'm assuming the 5-Speed Getrag does not actually have a limited slip differential in it, right?

Also... would you say the GM Synchromesh fluid would ALSO be good for my daughter's 5-Speed Isuzu in your 4-cyl?


Thanks!
PhatMax DEC 25, 10:21 AM
Pennzoil Syncromesh all the way.. no need to to put LSD additive in….in fact I’ve never heard of that used in a manual. It for the clutch packs in a posi diff.
FormulaGT DEC 25, 12:36 PM
The '88 service manual for Getrag 5 speed specifies part number 12345349 or equivalent. I used Valvoline synchromesh which cross references that GM number on the bottle.
Vintage-Nut DEC 25, 04:27 PM
Firstly, I’m not an expert and merely searched the forum like Rsvl-Rider did…….

My research found that GM / Pontiac changed the manual gearbox fluid in 1988.
{Technical Service Bulletin 88-7-17 titled “Proper Service Fluid For Manual”}

The TSB and countless PFF threads highly recommend GM Synchromesh Fluid intended to deal with shifting difficulty when the gearbox is cold and the biggest differences will be felt in the Getrag/Muncie.

And no, I haven't been able to locate an actual copy of TSB 88-7-17
{See this thread “4 spd manual transmission fluid? by Madess started on Oct-18-2005}
https://www.fiero.nl/forum/...060811-2-067743.html

Since many manuals have similar construction, I imagine GM Synchromesh Fluid (which is compatible with non-ferrous metals) would also be applied to other gearboxes’ that the original fluid recommended 5W30 oil.

GM changed synchromesh part numbers over the years;
The 'Newest' GM number is 88900333 for 'Standard' Synchromesh in the USA, which formerly was 12345349
{EDIT - Canada GM / ACDelco number is 89021808 for standard synchromesh}

And yes, many members like other brands of synchromesh 'better', however my research says that GM isn't the 'same' ......

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As a side note, some members commented that synchromesh helped for smoother shifting, but the fluid didn’t help the Getrag/Muncie ‘rattle’ (vibrations) of the unengaged gears.

I found a ‘recipe’ which says it will ‘tame’ or cure the noise but never tried it….
“Getrag Rattle Tamed Redline MT90 by Larryinkc”
https://www.fiero.nl/forum/Forum2/HTML/136966.html

[This message has been edited by Vintage-Nut (edited 12-31-2023).]

cyrus88 DEC 25, 05:48 PM
Both GM and Valvoline Synchromesh did not tame the Getrag/Muncie "rattle" for me. I also tried Amsoil but with no success.

However, Royal Purple Synchromax got rid of the "rattle." I've been very happy with it.

[This message has been edited by cyrus88 (edited 12-25-2023).]

Patrick DEC 25, 05:57 PM

quote
Originally posted by cyrus88:

However, Royal Purple Synchromax got rid of the "rattle."



Is it thicker than the others?
cyrus88 DEC 26, 09:11 PM
I don't know for sure , but it did not appear to be thicker.
Patrick DEC 26, 10:29 PM

I've been tolerating the Getrag rattle for years in my Formula (although I hate the racket). I forget what oil I have in the transmission, although I believe it's synthetic 10w30.

From my January 2016 YouTube description...


quote

I wanted to get a video of the sound of the 2.8L engine in my '88 Fiero with the newly installed CompCam 1.6 roller-tip rockers, but it's difficult to hear much of anything else over the clatter of the transmission! The notorious Getrag rattle... ugh. For anyone not familiar with this rattle, it's "normal" with this 5-spd tranny, and the sound disappears when the clutch is depressed.
fierogt28 DEC 26, 11:19 PM


This is the correct oil as pictured.

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fierogt28

88 GT, Loaded, 5-speed.
88 GT, 5-speed. Beechwood interior, All original.